services: Introduce extensible services.

This patch rewrites GuixSD services to make them extensible.

* gnu-system.am (GNU_SYSTEM_MODULES): Add gnu/services/dbus.scm.
* gnu/services.scm (<service>): Replace with new record type.
  (<service-extension>, <service-type>): New record types.
  (write-service-type, compute-boot-script, second-argument): New
  procedures.
  (%boot-service, boot-service-type): New variables.
  (file-union, directory-union, modprobe-wrapper,
  activation-service->script, activation-script,
  gexps->activation-gexp): New procedures.
  (activation-service-type, %activation-service): New variables.
  (etc-directory, files->etc-directory, etc-service): New procedures.
  (etc-service-type, setuid-program-service, firmware-service-type): New
  variables.
  (firmware->activation-gexp): New procedure.
  (&service-error, &missing-target-service-error,
  &ambiguous-target-service-error): New condition types.
  (service-back-edges, fold-services): New procedures.
* gnu/services/avahi.scm (<avahi-configuration>): New record type.
  (configuration-file): Replace keyword parameters with a single
  'config' parameter.
  (%avahi-accounts, %avahi-activation, avahi-service-type): New
  variables.
  (avahi-dmd-service): New procedure.
  (avahi-service): Rewrite using 'service' and 'avahi-configuration'.
* gnu/services/base.scm (%root-file-system-dmd-service,
  root-file-system-service-type): New variables.
  (root-file-system-service): Use them.
  (file-system->dmd-service-name): New procedure.
  (file-system-service-type): New variable.
  (file-system-service): Use it.  Replace keyword parameters with a
  single 'file-system' object.
  (user-unmount-service-type): New variable.
  (user-unmount-service): Use it.
  (user-processes-service-type): New variable.
  (user-processes-service): Use it.
  (host-name-service-type): New variable.
  (host-name-service): Use it.
  (console-keymap-service-type): New variable.
  (console-keymap-service): Use it.
  (console-font-service-type): New variable.
  (console-font-service): Use it.
  (mingetty-pam-service, mingetty-dmd-service): New procedures.
  (mingetty-service-type): New variable.
  (mingetty-service): Use it.
  (nscd-dmd-service): New procedure.
  (nscd-activation, nscd-service-type): New variables.
  (nscd-service): Use the latter.
  (syslog-service-type): New variable.
  (syslog-service): Use it.
  (<guix-configuration>): New record type.
  (%default-guix-configuration): New variable.
  (guix-dmd-service, guix-accounts, guix-activation): New procedures.
  (guix-service-type): New variable.
  (guix-service): Replace list of keyword parameters with a single
  'config' parameter.  Rewrite using 'service'.
  (<udev-configuration>): New record type.
  (udev-dmd-service): New procedure.
  (udev-service-type): New variable.
  (udev-service): Use it.
  (device-mapping-service-type): New variable.
  (device-mapping-service): Use it.
  (swap-service-type): New variable.
  (swap-service): Use it.
* gnu/services/databases.scm (<postgresql-configuration>): New record
  type.
  (%postgresql-accounts, postgresql-activation): New variables.
  (postgresql-dmd-service): New procedure.
  (postgresql-service): Rewrite using 'service' and
  'postgresql-configuration'.
* gnu/services/dbus.scm: New file.
* gnu/services/desktop.scm (dbus-configuration-directory, dbus-service):
  Remove.
  (wrapped-dbus-service): New procedure.
  (<upower-configuration>): New record type.
  (upower-configuration-file): Replace keyword parameters with single
  <upower-configuration> parameter.
  (%upower-accounts, %upower-activation): New variables.
  (upower-dbus-service, upower-dmd-service): New procedures.
  (upower-service-type): New variable.
  (upower-service): Rewrite using 'service' and 'upower-configuration'.
  (%colord-activation, %colord-accounts): New variables.
  (colord-dmd-service): New procedure.
  (colord-service-type): New variable.
  (colord-service): Rewrite using 'service'.
  (<geoclue-configuration>): New record type.
  (geoclue-configuration-file): Replace keyword parameters with a single
  'config' parameter.
  (geoclue-dbus-service, geoclue-dmd-service): New procedures.
  (%geoclue-accounts, geoclue-service-type): New variables.
  (geoclue-service): Rewrite using 'service' and
  'geoclue-configuration'.
  (%polkit-accounts, %polkit-pam-services, polkit-service-type): New
  variables.
  (polkit-dmd-service): New procedure.
  (polkit-service): Rewrite using 'service'.
  (<elogind-configuration>)[elogind]: New field.
  (elogind-dmd-service): New procedure.
  (elogind-service-type): New variable.
  (elogind-service): Rewrite using 'service'.
  (%desktop-services): Remove argument to 'dbus-service'.  Remove 'map'
  over %BASE-SERVICES.
* gnu/services/dmd.scm (dmd-boot-gexp): New procedure.
  (dmd-root-service-type, %dmd-root-service): New variables.
  (dmd-service-type): New macro.
  (<dmd-service>): New record type.
* gnu/services/lirc.scm (<lirc-configuration>): New record type.
  (%lirc-activation): New variable.
  (lirc-dmd-service): New procedure.
  (lirc-service-type): New variable.
  (lirc-service): Rewrite using 'service' and 'lirc-configuration'.
* gnu/services/networking.scm (<static-networking>): New record type.
  (static-networking-service-type): New variable.
  (static-networking-service): Rewrite using 'service' and
  'static-networking'.
  (dhcp-client-service-type): New variable.
  (dhcp-client-service): Rewrite using 'service'.
  (<ntp-configuration>): New record type.
  (ntp-dmd-service): New procedure.
  (ntp-service-type): New variable.
  (ntp-service): New procedure.
  (%tor-accounts, tor-service-type): New variable.
  (tor-dmd-service): New procedure.
  (tor-service): Rewrite using 'service'.
  (<bitlbee-configuration>): New record type.
  (bitlbee-dmd-service): New procedure.
  (%bitlbee-accounts, %bitlbee-activation, bitlbee-service-type): New
  variables.
  (bitlbee-service): Rewrite using 'service'.
  (%wicd-activation): New variable.
  (wicd-dmd-service): New procedure.
  (wicd-service-type): New variable.
  (wicd-service): Rewrite using 'service'.
* gnu/services/ssh.scm (<lsh-configuration>): New record type.
  (activation): Rename to...
  (lsh-initialization): ... this.
  (lsh-activation, lsh-dmd-service, lsh-pam-services): New procedures.
  (lsh-service-type): New variable.
  (lsh-service): Rewrite using 'service' and 'lsh-configuration'.
* gnu/services/web.scm (<nginx-configuration>): New record type.
  (%nginx-accounts): New variable.
  (nginx-activation, nginx-dmd-service): New procedures.
  (nginx-service-type): New variable.
  (nginx-service): Rewrite using 'service' and 'nginx-configuration'.
* gnu/services/xorg.scm (<slim-configuration>): New record type.
  (slim-pam-service, slim-dmd-service): New procedures.
  (slim-service-type): New variable.
  (slim-service): Rewrite using 'service' and 'slim-configuration'.
* gnu/system.scm (file-union): Remove.
  (other-file-system-services): Adjust to new 'file-system-service'
  signature.
  (essential-services): Add #:container? parameter.  Add
  %DMD-ROOT-SERVICE, %ACTIVATION-SERVICE, and calls to
  'pam-root-service', 'account-service', 'operating-system-etc-service',
  and a SETUID-PROGRAM-SERVICE instance.
  (operating-system-services): Pass #:container? to 'essential-services.
  (etc-directory): Remove.
  (operating-system-etc-service): New procedure.  Rewrite as a call to
  'etc-service'.
  (operating-system-accounts): Change to not return accounts required by
  services.
  (operating-system-etc-directory): Rewrite as a call to 'fold-services'
  and 'etc-directory'.
  (user-group->gexp, user-account->gexp, modprobe-wrapper): Remove.
  (operating-system-activation-script): Rewrite as a call to
  'fold-services' and 'activation-service->script'.
  (operating-system-boot-script): Likewise.
  (operating-system-derivation): Add call to 'lower-object'.
  (emacs-site-file, emacs-site-directory, shells-file): Change to use
  'computed-file' and 'scheme-file' instead of the monadic procedures.
* gnu/system/install.scm (cow-store-service-type): New variable.
  (cow-store-service): Rewrite using 'service'.
  (/etc/configuration-files): New procedure.
  (configuration-template-service-type,
  %configuration-template-service): New variables.
  (configuration-template-service): Remove.
  (installation-services): Adjust accordingly.  Adjust argument to
  'guix-service'.
* gnu/system/linux.scm (/etc-entry, pam-root-service): New procedures.
  (pam-root-service-type): New variable.
* gnu/system/shadow.scm (user-group->gexp, user-account->gexp,
  account-activation, etc-skel, account-service): New procedures.
  (account-service-type): New variable.
* tests/services.scm: New file.
* doc/guix.texi (Base Services, Desktop Services): Adjust accordingly.
  (Defining Services): Rewrite.
* doc/images/service-graph.dot: New file.
* doc.am (DOT_FILES): Add it.
* po/guix/POTFILES.in: Add gnu/services.scm.

24 files changed, 3328 insertions, 1689 deletions

diff --git a/.gitignore b/.gitignore
index a363c074ca7..e3f2ac2c21d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -129,3 +129,6 @@ GTAGS
 /doc/images/coreutils-bag-graph.png
 /doc/images/coreutils-graph.png
 /doc/images/coreutils-size-map.eps
+/doc/images/service-graph.png
+/doc/images/service-graph.eps
+/doc/images/service-graph.pdf
diff --git a/Makefile.am b/Makefile.am
index a8dab5d3261..18fbd9d5786 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -219,6 +219,7 @@ SCM_TESTS =					\
   tests/size.scm                                \
   tests/graph.scm                               \
   tests/file-systems.scm                        \
+  tests/services.scm                            \
   tests/containers.scm
 
 if HAVE_GUILE_JSON
diff --git a/doc.am b/doc.am
index 9c1dc83e88b..71a65ba0c47 100644
--- a/doc.am
+++ b/doc.am
@@ -22,7 +22,8 @@ info_TEXINFOS = doc/guix.texi
 DOT_FILES =                                     \
   doc/images/bootstrap-graph.dot                \
   doc/images/coreutils-graph.dot                \
-  doc/images/coreutils-bag-graph.dot
+  doc/images/coreutils-bag-graph.dot            \
+  doc/images/service-graph.dot
 
 DOT_VECTOR_GRAPHICS =                           \
   $(DOT_FILES:%.dot=%.eps)                      \
diff --git a/doc/guix.texi b/doc/guix.texi
index 1b25bd938fb..a3fa989d48b 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -182,6 +182,13 @@ Services
 * Web Services::                Web servers.
 * Various Services::            Other services.
 
+Defining Services
+
+* Service Composition::         The model for composing services.
+* Service Types and Services::  Types and services.
+* Service Reference::           API reference.
+* dmd Services::                A particular type of service.
+
 Packaging Guidelines
 
 * Software Freedom::            What may go into the distribution.
@@ -5899,23 +5906,41 @@ Return a service that runs @code{syslogd}.  If configuration file name
 settings.
 @end deffn
 
-@deffn {Scheme Procedure} guix-service [#:guix guix] @
-       [#:builder-group "guixbuild"] [#:build-accounts 10] @
-       [#:authorize-hydra-key? #t] [#:use-substitutes? #t] @
-       [#:extra-options '()]
-Return a service that runs the build daemon from @var{guix}, and has
-@var{build-accounts} user accounts available under @var{builder-group}.
+@anchor{guix-configuration-type}
+@deftp {Data Type} guix-configuration
+This data type represents the configuration of the Guix build daemon.
+@xref{Invoking guix-daemon}, for more information.
+
+@table @asis
+@item @code{guix} (default: @var{guix})
+The Guix package to use.
 
-When @var{authorize-hydra-key?} is true, the @code{hydra.gnu.org} public key
-provided by @var{guix} is authorized upon activation, meaning that substitutes
-from @code{hydra.gnu.org} are used by default.
+@item @code{build-group} (default: @code{"guixbuild"})
+Name of the group for build user accounts.
 
-If @var{use-substitutes?} is false, the daemon is run with
-@option{--no-substitutes} (@pxref{Invoking guix-daemon,
-@option{--no-substitutes}}).
+@item @code{build-accounts} (default: @code{10})
+Number of build user accounts to create.
 
-Finally, @var{extra-options} is a list of additional command-line options
-passed to @command{guix-daemon}.
+@item @code{authorize-key?} (default: @code{#t})
+Whether to authorize the substitute key for @code{hydra.gnu.org}
+(@pxref{Substitutes}).
+
+@item @code{use-substitutes?} (default: @code{#t})
+Whether to use substitutes.
+
+@item @code{extra-options} (default: @code{'()})
+List of extra command-line options for @command{guix-daemon}.
+
+@item @code{lsof} (default: @var{lsof})
+@itemx @code{lsh} (default: @var{lsh})
+The lsof and lsh packages to use.
+
+@end table
+@end deftp
+
+@deffn {Scheme Procedure} guix-service @var{config}
+Return a service that runs the Guix build daemon according to
+@var{config}.
 @end deffn
 
 @deffn {Scheme Procedure} udev-service [#:udev udev]
@@ -6179,11 +6204,10 @@ The @var{%desktop-services} variable can be used as the @code{services}
 field of an @code{operating-system} declaration (@pxref{operating-system
 Reference, @code{services}}).
 
-The actual service definitions provided by @code{(gnu services desktop)}
-are described below.
+The actual service definitions provided by @code{(gnu services dbus)}
+and @code{(gnu services desktop)} are described below.
 
-@deffn {Scheme Procedure} dbus-service @var{services} @
-                         [#:dbus @var{dbus}]
+@deffn {Scheme Procedure} dbus-service [#:dbus @var{dbus}] [#:services '()]
 Return a service that runs the ``system bus'', using @var{dbus}, with
 support for @var{services}.
 
@@ -6197,8 +6221,7 @@ and policy files.  For example, to allow avahi-daemon to use the system bus,
 @var{services} must be equal to @code{(list avahi)}.
 @end deffn
 
-@deffn {Scheme Procedure} elogind-service @
-                         [#:elogind @var{elogind}] [#:config @var{config}]
+@deffn {Scheme Procedure} elogind-service [#:config @var{config}]
 Return a service that runs the @code{elogind} login and
 seat management daemon.  @uref{https://github.com/andywingo/elogind,
 Elogind} exposes a D-Bus interface that can be used to know which users
@@ -6957,54 +6980,378 @@ build users.
 @node Defining Services
 @subsection Defining Services
 
-The @code{(gnu services @dots{})} modules define several procedures that allow
-users to declare the operating system's services (@pxref{Using the
-Configuration System}).  These procedures are @emph{monadic
-procedures}---i.e., procedures that return a monadic value in the store
-monad (@pxref{The Store Monad}).  For examples of such procedures,
-@xref{Services}.
-
-@cindex service definition
-The monadic value returned by those procedures is a @dfn{service
-definition}---a structure as returned by the @code{service} form.
-Service definitions specifies the inputs the service depends on, and an
-expression to start and stop the service.  Behind the scenes, service
-definitions are ``translated'' into the form suitable for the
-configuration file of dmd, the init system (@pxref{Services,,, dmd, GNU
-dmd Manual}).
-
-As an example, here is what the @code{nscd-service} procedure looks
-like:
+The previous sections how the available services and how one can combine
+them in an @code{operating-system} declaration.  But how do we define
+them in the first place?  And what is a service anyway?
 
-@lisp
-(define (nscd-service)
-  (with-monad %store-monad
-    (return (service
-             (documentation "Run libc's name service cache daemon.")
-             (provision '(nscd))
-             (activate #~(begin
-                           (use-modules (guix build utils))
-                           (mkdir-p "/var/run/nscd")))
-             (start #~(make-forkexec-constructor
-                       (string-append #$glibc "/sbin/nscd")
-                       "-f" "/dev/null" "--foreground"))
-             (stop #~(make-kill-destructor))
-             (respawn? #f)))))
-@end lisp
+@menu
+* Service Composition::         The model for composing services.
+* Service Types and Services::  Types and services.
+* Service Reference::           API reference.
+* dmd Services::                A particular type of service.
+@end menu
+
+@node Service Composition
+@subsubsection Service Composition
+
+@cindex services
+@cindex daemons
+Here we define a @dfn{service} as, broadly, something that extends the
+operating system's functionality.  Often a service is a process---a
+@dfn{daemon}---started when the system boots: a secure shell server, a
+Web server, the Guix build daemon, etc.  Sometimes a service is a daemon
+whose execution can be triggered by another daemon---e.g., an FTP server
+started by @command{inetd} or a D-Bus service activated by
+@command{dbus-daemon}.  Occasionally, a service does not map to a
+daemon.  For instance, the ``account'' service collects user accounts
+and makes sure they exist when the system runs; the ``udev'' service
+collects device management rules and makes them available to the eudev
+daemon; the @file{/etc} service populates the system's @file{/etc}
+directory.
+
+GuixSD services are connected by @dfn{extensions}.  For instance, the
+secure shell service @emph{extends} dmd---GuixSD's initialization system,
+running as PID@tie{}1---by giving it the command lines to start and stop
+the secure shell daemon (@pxref{Networking Services,
+@code{lsh-service}}); the UPower service extends the D-Bus service by
+passing it its @file{.service} specification, and extends the udev
+service by passing it device management rules (@pxref{Desktop Services,
+@code{upower-service}}); the Guix daemon service extends dmd by passing
+it the command lines to start and stop the daemon, and extends the
+account service by passing it a list of required build user accounts
+(@pxref{Base Services}).
+
+All in all, services and their ``extends'' relations form a directed
+acyclic graph (DAG).  If we represent services as boxes and extensions
+as arrows, a typical system might provide something like this:
+
+@image{images/service-graph,,5in,Typical service extension graph.}
+
+At the bottom, we see the @dfn{boot service}, which produces the boot
+script that is executed at boot time from the initial RAM disk.
+
+@cindex service types
+Technically, developers can define @dfn{service types} to express these
+relations.  There can be any number of services of a given type on the
+system---for instance, a system running two instances of the GNU secure
+shell server (lsh) has two instances of @var{lsh-service-type}, with
+different parameters.
+
+The following section describes the programming interface for service
+types and services.
+
+@node Service Types and Services
+@subsubsection Service Types and Services
+
+A @dfn{service type} is a node in the DAG described above.  Let us start
+with a simple example, the service type for the Guix build daemon
+(@pxref{Invoking guix-daemon}):
+
+@example
+(define guix-service-type
+  (service-type
+   (name 'guix)
+   (extensions
+    (list (service-extension dmd-root-service-type guix-dmd-service)
+          (service-extension account-service-type guix-accounts)
+          (service-extension activation-service-type guix-activation)))))
+@end example
 
 @noindent
-The @code{activate}, @code{start}, and @code{stop} fields are G-expressions
-(@pxref{G-Expressions}).  The @code{activate} field contains a script to
-run at ``activation'' time; it makes sure that the @file{/var/run/nscd}
-directory exists before @command{nscd} is started.
+It defines a two things:
+
+@enumerate
+@item
+A name, whose sole purpose is to make inspection and debugging easier.
+
+@item
+A list of @dfn{service extensions}, where each extension designates the
+target service type and a procedure that, given the service's
+parameters, returns a list of object to extend the service of that type.
+
+Every service type has at least one service extension.  The only
+exception is the @dfn{boot service type}, which is the ultimate service.
+@end enumerate
+
+In this example, @var{guix-service-type} extends three services:
+
+@table @var
+@item dmd-root-service-type
+The @var{guix-dmd-service} procedure defines how the dmd service is
+extended.  Namely, it returns a @code{<dmd-service>} object that defines
+how @command{guix-daemon} is started and stopped (@pxref{dmd Services}).
+
+@item account-service-type
+This extension for this service is computed by @var{guix-accounts},
+which returns a list of @code{user-group} and @code{user-account}
+objects representing the build user accounts (@pxref{Invoking
+guix-daemon}).
+
+@item activation-service-type
+Here @var{guix-activation} is a procedure that returns a gexp, which is
+a code snippet to run at ``activation time''---e.g., when the service is
+booted.
+@end table
+
+A service of this type is instantiated like this:
+
+@example
+(service guix-service-type
+         (guix-configuration
+           (build-accounts 5)
+           (use-substitutes? #f)))
+@end example
+
+The second argument to the @code{service} form is a value representing
+the parameters of this specific service instance.
+@xref{guix-configuration-type, @code{guix-configuration}}, for
+information about the @code{guix-configuration} data type.
+
+@var{guix-service-type} is quite simple because it extends other
+services but is not extensible itself.
+
+@c @subsubsubsection Extensible Service Types
+
+The service type for an @emph{extensible} service looks like this:
+
+@example
+(define udev-service-type
+  (service-type (name 'udev)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          udev-dmd-service)))
+
+                (compose concatenate)       ;concatenate the list of rules
+                (extend (lambda (config rules)
+                          (match config
+                            (($ <udev-configuration> udev initial-rules)
+                             (udev-configuration
+                              (udev udev)   ;the udev package to use
+                              (rules (append initial-rules rules)))))))))
+@end example
+
+This is the service type for the
+@uref{https://wiki.gentoo.org/wiki/Project:Eudev, eudev device
+management daemon}.  Compared to the previous example, in addition to an
+extension of @var{dmd-root-service-type}, we see two new fields:
+
+@table @code
+@item compose
+This is the procedure to @dfn{compose} the list of extensions to
+services of this type.
+
+Services can extend the udev service by passing it lists of rules; we
+compose those extensions simply by concatenating them.
+
+@item extend
+This procedure defines how the service's value is @dfn{extended} with
+the composition of the extensions.
+
+Udev extensions are composed into a list of rules, but the udev service
+value is itself a @code{<udev-configuration>} record.  So here, we
+extend that record by appending the list of rules is contains to the
+list of contributed rules.
+@end table
+
+There can be only one instance of an extensible service type such as
+@var{udev-service-type}.  If there were more, the
+@code{service-extension} specifications would be ambiguous.
+
+Still here?  The next section provides a reference of the programming
+interface for services.
+
+@node Service Reference
+@subsubsection Service Reference
+
+We have seen an overview of service types (@pxref{Service Types and
+Services}).  This section provides a reference on how to manipulate
+services and service types.  This interface is provided by the
+@code{(gnu services)} module.
+
+@deffn {Scheme Procedure} service @var{type} @var{value}
+Return a new service of @var{type}, a @code{<service-type>} object (see
+below.)  @var{value} can be any object; it represents the parameters of
+this particular service instance.
+@end deffn
+
+@deffn {Scheme Procedure} service? @var{obj}
+Return true if @var{obj} is a service.
+@end deffn
+
+@deffn {Scheme Procedure} service-kind @var{service}
+Return the type of @var{service}---i.e., a @code{<service-type>} object.
+@end deffn
+
+@deffn {Scheme Procedure} service-parameters @var{service}
+Return the value associated with @var{service}.  It represents its
+parameters.
+@end deffn
+
+Here is an example of how a service is created and manipulated:
+
+@example
+(define s
+  (service nginx-service-type
+           (nginx-configuration
+            (nginx nginx)
+            (log-directory log-directory)
+            (run-directory run-directory)
+            (file config-file))))
+
+(service? s)
+@result{} #t
+
+(eq? (service-kind s) nginx-service-type)
+@result{} #t
+@end example
+
+@deftp {Data Type} service-type
+@cindex service type
+This is the representation of a @dfn{service type} (@pxref{Service Types
+and Services}).
+
+@table @asis
+@item @code{name}
+This is a symbol, used only to simplify inspection and debugging.
+
+@item @code{extensions}
+A non-empty list of @code{<service-extension>} objects (see below.)
+
+@item @code{compose} (default: @code{#f})
+If this is @code{#f}, then the service type denotes services that cannot
+be extended---i.e., services that do not receive ``values'' from other
+services.
+
+Otherwise, it must be a one-argument procedure.  The procedure is called
+by @code{fold-services} and is passed a list of values collected from
+extensions.  It must return a value that is a valid parameter value for
+the service instance.
+
+@item @code{extend} (default: @code{#f})
+If this is @code{#f}, services of this type cannot be extended.
+
+Otherwise, it must be a two-argument procedure: @code{fold-services}
+calls it, passing it the service's initial value as the first argument
+and the result of applying @code{compose} to the extension values as the
+second argument.
+@end table
+
+@xref{Service Types and Services}, for examples.
+@end deftp
+
+@deffn {Scheme Procedure} service-extension @var{target-type} @
+                              @var{compute}
+Return a new extension for services of type @var{target-type}.
+@var{compute} must be a one-argument procedure: @code{fold-services}
+calls it, passing it the value associated with the service that provides
+the extension; it must return a valid value for the target service.
+@end deffn
+
+@deffn {Scheme Procedure} service-extension? @var{obj}
+Return true if @var{obj} is a service extension.
+@end deffn
+
+At the core of the service abstraction lies the @code{fold-services}
+procedure, which is responsible for ``compiling'' a list of services
+down to a single boot script.  In essence, it propagates service
+extensions down the service graph, updating each node parameters on the
+way, until it reaches the root node.
+
+@deffn {Scheme Procedure} fold-services @var{services} @
+                            [#:target-type @var{boot-service-type}]
+Fold @var{services} by propagating their extensions down to the root of
+type @var{target-type}; return the root service adjusted accordingly.
+@end deffn
+
+Lastly, the @code{(gnu services)} module also defines several essential
+service types, some of which are listed below.
+
+@defvr {Scheme Variable} boot-service-type
+The type of the ``boot service'', which is the root of the service
+graph.
+@end defvr
+
+@defvr {Scheme Variable} etc-service-type
+The type of the @file{/etc} service.  This service can be extended by
+passing it name/file tuples such as:
+
+@example
+(list `("issue" ,(plain-file "issue" "Welcome!\n")))
+@end example
+
+In this example, the effect would be to add an @file{/etc/issue} file
+pointing to the given file.
+@end defvr
+
+@defvr {Scheme Variable} setuid-program-service-type
+Type for the ``setuid-program service''.  This service collects lists of
+executable file names, passed as gexps, and adds them to the set of
+setuid-root programs on the system (@pxref{Setuid Programs}).
+@end defvr
+
+
+@node dmd Services
+@subsubsection dmd Services
+
+@cindex PID 1
+@cindex init system
+The @code{(gnu services dmd)} provides a way to define services managed
+by GNU@tie{}dmd, which is GuixSD initialization system---the first
+process that is started when the system boots, aka. PID@tie{}1
+(@pxref{Introduction,,, dmd, GNU dmd Manual}).  The
+@var{%dmd-root-service} represents PID@tie{}1, of type
+@var{dmd-root-service-type}; it can be extended by passing it lists of
+@code{<dmd-service>} objects.
+
+@deftp {Data Type} dmd-service
+The data type representing a service managed by dmd.
+
+@table @asis
+@item @code{provision}
+This is a list of symbols denoting what the service provides.
 
+These are the names that may be passed to @command{deco start},
+@command{deco status}, and similar commands (@pxref{Invoking deco,,,
+dmd, GNU dmd Manual}).  @xref{Slots of services, the @code{provides}
+slot,, dmd, GNU dmd Manual}, for details.
+
+@item @code{requirements} (default: @code{'()})
+List of symbols denoting the dmd services this one depends on.
+
+@item @code{respawn?} (default: @code{#t})
+Whether to restart the service when it stops, for instance when the
+underlying process dies.
+
+@item @code{start}
+@itemx @code{stop} (default: @code{#~(const #f)})
 The @code{start} and @code{stop} fields refer to dmd's facilities to
 start and stop processes (@pxref{Service De- and Constructors,,, dmd,
-GNU dmd Manual}).  The @code{provision} field specifies the name under
-which this service is known to dmd, and @code{documentation} specifies
-on-line documentation.  Thus, the commands @command{deco start ncsd},
-@command{deco stop nscd}, and @command{deco doc nscd} will do what you
-would expect (@pxref{Invoking deco,,, dmd, GNU dmd Manual}).
+GNU dmd Manual}).  They are given as G-expressions that get expanded in
+the dmd configuration file (@pxref{G-Expressions}).
+
+@item @code{documentation}
+A documentation string, as shown when running:
+
+@example
+deco doc @var{service-name}
+@end example
+
+where @var{service-name} is one of the symbols in @var{provision}
+(@pxref{Invoking deco,,, dmd, GNU dmd Manual}).
+@end table
+@end deftp
+
+@defvr {Scheme Variable} dmd-root-service-type
+The service type for the dmd ``root service''---i.e., PID@tie{}1.
+
+This is the service type that extensions target when they want to create
+dmd services (@pxref{Service Types and Services}, for an example).  Each
+extension must pass a list of @code{<dmd-service>}.
+@end defvr
+
+@defvr {Scheme Variable} %dmd-root-service
+This service represents PID@tie{}1.
+@end defvr
 
 
 @node Installing Debugging Files
diff --git a/doc/images/service-graph.dot b/doc/images/service-graph.dot
new file mode 100644
index 00000000000..3397b878e96
--- /dev/null
+++ b/doc/images/service-graph.dot
@@ -0,0 +1,35 @@
+digraph "Service Type Dependencies" {
+  dmd [shape = box, fontname = Helvetica];
+  pam [shape = box, fontname = Helvetica];
+  etc [shape = box, fontname = Helvetica];
+  accounts [shape = box, fontname = Helvetica];
+  activation [shape = box, fontname = Helvetica];
+  boot [shape = house, fontname = Helvetica];
+  lshd -> dmd;
+  lshd -> pam;
+  udev -> dmd;
+  nscd -> dmd [label = "extends"];
+  "nss-mdns" -> nscd;
+  "kvm-rules" -> udev;
+  colord -> udev;
+  dbus -> dmd;
+  colord -> dbus;
+  upower -> udev;
+  upower -> dbus;
+  polkit -> dbus;
+  polkit -> pam;
+  elogind -> dbus;
+  elogind -> udev;
+  elogind -> polkit [label = "extends"];
+  dmd -> boot;
+  colord -> accounts;
+  accounts -> activation;
+  accounts -> etc;
+  etc -> activation;
+  activation -> boot;
+  pam -> etc;
+  elogind -> pam;
+  guix -> dmd;
+  guix -> activation;
+  guix -> accounts;
+}
diff --git a/gnu-system.am b/gnu-system.am
index c2dc323a617..64260dd3000 100644
--- a/gnu-system.am
+++ b/gnu-system.am
@@ -348,6 +348,7 @@ GNU_SYSTEM_MODULES =				\
   gnu/services/avahi.scm                        \
   gnu/services/base.scm                         \
   gnu/services/databases.scm                    \
+  gnu/services/dbus.scm                         \
   gnu/services/desktop.scm                      \
   gnu/services/dmd.scm                          \
   gnu/services/lirc.scm                         \
diff --git a/gnu/services.scm b/gnu/services.scm
index 43e51b998c9..fdfa569b239 100644
--- a/gnu/services.scm
+++ b/gnu/services.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -18,49 +18,428 @@
 
 (define-module (gnu services)
   #:use-module (guix gexp)
+  #:use-module (guix monads)
+  #:use-module (guix store)
   #:use-module (guix records)
-  #:export (service?
+  #:use-module (guix sets)
+  #:use-module (guix ui)
+  #:use-module (gnu packages base)
+  #:use-module (gnu packages bash)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (srfi srfi-9 gnu)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
+  #:use-module (ice-9 vlist)
+  #:use-module (ice-9 match)
+  #:export (service-extension
+            service-extension?
+
+            service-type
+            service-type?
+
             service
-            service-documentation
-            service-provision
-            service-requirement
-            service-respawn?
-            service-start
-            service-stop
-            service-auto-start?
-            service-activate
-            service-user-accounts
-            service-user-groups
-            service-pam-services))
-
-;;; Commentary:
+            service?
+            service-kind
+            service-parameters
+
+            fold-services
+
+            service-error?
+            missing-target-service-error?
+            missing-target-service-error-service
+            missing-target-service-error-target-type
+            ambiguous-target-service-error?
+            ambiguous-target-service-error-service
+            ambiguous-target-service-error-target-type
+
+            boot-service-type
+            activation-service-type
+            activation-service->script
+            etc-service-type
+            etc-directory
+            setuid-program-service-type
+            firmware-service-type
+
+            %boot-service
+            %activation-service
+            etc-service
+
+            file-union))                      ;XXX: for lack of a better place
+
+;;; Comment:
+;;;
+;;; This module defines a broad notion of "service types" and "services."
 ;;;
-;;; System services as cajoled by dmd.
+;;; A service type describe how its instances extend instances of other
+;;; service types.  For instance, some services extend the instance of
+;;; ACCOUNT-SERVICE-TYPE by providing it with accounts and groups to create;
+;;; others extend DMD-ROOT-SERVICE-TYPE by passing it instances of
+;;; <dmd-service>.
+;;;
+;;; When applicable, the service type defines how it can itself be extended,
+;;; by providing one procedure to compose extensions, and one procedure to
+;;; extend itself.
+;;;
+;;; A notable service type is BOOT-SERVICE-TYPE, which has a single instance,
+;;; %BOOT-SERVICE.  %BOOT-SERVICE constitutes the root of the service DAG.  It
+;;; produces the boot script that the initrd loads.
+;;;
+;;; The 'fold-services' procedure can be passed a list of procedures, which it
+;;; "folds" by propagating extensions down the graph; it returns the root
+;;; service after the applying all its extensions.
 ;;;
 ;;; Code:
 
-(define-record-type* <service>
-  service make-service
+(define-record-type <service-extension>
+  (service-extension target compute)
+  service-extension?
+  (target  service-extension-target)              ;<service-type>
+  (compute service-extension-compute))            ;params -> params
+
+(define-record-type* <service-type> service-type make-service-type
+  service-type?
+  (name       service-type-name)                  ;symbol (for debugging)
+
+  ;; Things extended by services of this type.
+  (extensions service-type-extensions)            ;list of <service-extensions>
+
+  ;; Given a list of extensions, "compose" them.
+  (compose    service-type-compose                ;list of Any -> Any
+              (default #f))
+
+  ;; Extend the services' own parameters with the extension composition.
+  (extend     service-type-extend                 ;list of Any -> parameters
+              (default #f)))
+
+(define (write-service-type type port)
+  (format port "#<service-type ~a ~a>"
+          (service-type-name type)
+          (number->string (object-address type) 16)))
+
+(set-record-type-printer! <service-type> write-service-type)
+
+;; Services of a given type.
+(define-record-type <service>
+  (service type parameters)
   service?
-  (documentation service-documentation            ; string
-                 (default "[No documentation.]"))
-  (provision     service-provision)               ; list of symbols
-  (requirement   service-requirement              ; list of symbols
-                 (default '()))
-  (respawn?      service-respawn?                 ; Boolean
-                 (default #t))
-  (start         service-start)                   ; g-expression (procedure)
-  (stop          service-stop                     ; g-expression (procedure)
-                 (default #~(const #f)))
-  (auto-start?   service-auto-start?              ; Boolean
-                 (default #t))
-  (user-accounts service-user-accounts            ; list of <user-account>
-                 (default '()))
-  (user-groups   service-user-groups              ; list of <user-groups>
-                 (default '()))
-  (pam-services  service-pam-services             ; list of <pam-service>
-                 (default '()))
-  (activate      service-activate                 ; gexp
-                 (default #f)))
+  (type       service-kind)
+  (parameters service-parameters))
+
+
+
+
+;;;
+;;; Core services.
+;;;
+
+(define (compute-boot-script mexps)
+  (mlet %store-monad ((gexps (sequence %store-monad mexps)))
+    (gexp->file "boot"
+                #~(begin
+                    (use-modules (guix build utils))
+
+                    ;; Clean out /tmp and /var/run.
+                    ;;
+                    ;; XXX This needs to happen before service activations, so
+                    ;; it has to be here, but this also implicitly assumes
+                    ;; that /tmp and /var/run are on the root partition.
+                    (false-if-exception (delete-file-recursively "/tmp"))
+                    (false-if-exception (delete-file-recursively "/var/run"))
+                    (false-if-exception (mkdir "/tmp"))
+                    (false-if-exception (chmod "/tmp" #o1777))
+                    (false-if-exception (mkdir "/var/run"))
+                    (false-if-exception (chmod "/var/run" #o755))
+
+                    ;; Activate the system and spawn dmd.
+                    #$@gexps))))
+
+(define (second-argument a b) b)
+
+(define boot-service-type
+  ;; The service of this type is extended by being passed gexps as monadic
+  ;; values.  It aggregates them in a single script, as a monadic value, which
+  ;; becomes its 'parameters'.  It is the only service that extends nothing.
+  (service-type (name 'boot)
+                (extensions '())
+                (compose compute-boot-script)
+                (extend second-argument)))
+
+(define %boot-service
+  ;; This is the ultimate service, the root of the service DAG.
+  (service boot-service-type #t))
+
+(define* (file-union name files)                  ;FIXME: Factorize.
+  "Return a <computed-file> that builds a directory containing all of FILES.
+Each item in FILES must be a list where the first element is the file name to
+use in the new directory, and the second element is a gexp denoting the target
+file."
+  (computed-file name
+                 #~(begin
+                     (mkdir #$output)
+                     (chdir #$output)
+                     #$@(map (match-lambda
+                               ((target source)
+                                #~(symlink #$source #$target)))
+                             files))))
+
+(define (directory-union name things)
+  "Return a directory that is the union of THINGS."
+  (match things
+    ((one)
+     ;; Only one thing; return it.
+     one)
+    (_
+     (computed-file name
+                    #~(begin
+                        (use-modules (guix build union))
+                        (union-build #$output '#$things))
+                    #:modules '((guix build union))))))
+
+(define (modprobe-wrapper)
+  "Return a wrapper for the 'modprobe' command that knows where modules live.
+
+This wrapper is typically invoked by the Linux kernel ('call_modprobe', in
+kernel/kmod.c), a situation where the 'LINUX_MODULE_DIRECTORY' environment
+variable is not set---hence the need for this wrapper."
+  (let ((modprobe "/run/current-system/profile/bin/modprobe"))
+    (gexp->script "modprobe"
+                  #~(begin
+                      (setenv "LINUX_MODULE_DIRECTORY"
+                              "/run/booted-system/kernel/lib/modules")
+                      (apply execl #$modprobe
+                             (cons #$modprobe (cdr (command-line))))))))
+
+(define* (activation-service->script service)
+  "Return as a monadic value the activation script for SERVICE, a service of
+ACTIVATION-SCRIPT-TYPE."
+  (activation-script (service-parameters service)))
+
+(define (activation-script gexps)
+  "Return the system's activation script, which evaluates GEXPS."
+  (define %modules
+    '((gnu build activation)
+      (gnu build linux-boot)
+      (gnu build linux-modules)
+      (gnu build file-systems)
+      (guix build utils)
+      (guix build syscalls)
+      (guix elf)))
+
+  (define (service-activations)
+    ;; Return the activation scripts for SERVICES.
+    (mapm %store-monad
+          (cut gexp->file "activate-service" <>)
+          gexps))
+
+  (mlet* %store-monad ((actions  (service-activations))
+                       (modules  (imported-modules %modules))
+                       (compiled (compiled-modules %modules))
+                       (modprobe (modprobe-wrapper)))
+    (gexp->file "activate"
+                #~(begin
+                    (eval-when (expand load eval)
+                      ;; Make sure 'use-modules' below succeeds.
+                      (set! %load-path (cons #$modules %load-path))
+                      (set! %load-compiled-path
+                        (cons #$compiled %load-compiled-path)))
+
+                    (use-modules (gnu build activation))
+
+                    ;; Make sure /bin/sh is valid and current.
+                    (activate-/bin/sh
+                     (string-append #$(canonical-package bash) "/bin/sh"))
+
+                    ;; Tell the kernel to use our 'modprobe' command.
+                    (activate-modprobe #$modprobe)
+
+                    ;; Let users debug their own processes!
+                    (activate-ptrace-attach)
+
+                    ;; Run the services' activation snippets.
+                    ;; TODO: Use 'load-compiled'.
+                    (for-each primitive-load '#$actions)
+
+                    ;; Set up /run/current-system.
+                    (activate-current-system)))))
+
+(define (gexps->activation-gexp gexps)
+  "Return a gexp that runs the activation script containing GEXPS."
+  (mlet %store-monad ((script (activation-script gexps)))
+    (return #~(primitive-load #$script))))
+
+(define activation-service-type
+  (service-type (name 'activate)
+                (extensions
+                 (list (service-extension boot-service-type
+                                          gexps->activation-gexp)))
+                (compose append)
+                (extend second-argument)))
+
+(define %activation-service
+  ;; The activation service produces the activation script from the gexps it
+  ;; receives.
+  (service activation-service-type #t))
+
+(define (etc-directory service)
+  "Return the directory for SERVICE, a service of type ETC-SERVICE-TYPE."
+  (files->etc-directory (service-parameters service)))
+
+(define (files->etc-directory files)
+  (file-union "etc" files))
+
+(define etc-service-type
+  (service-type (name 'etc)
+                (extensions
+                 (list
+                  (service-extension activation-service-type
+                                     (lambda (files)
+                                       (let ((etc
+                                              (files->etc-directory files)))
+                                         #~(activate-etc #$etc))))))
+                (compose concatenate)
+                (extend append)))
+
+(define (etc-service files)
+  "Return a new service of ETC-SERVICE-TYPE that populates /etc with FILES.
+FILES must be a list of name/file-like object pairs."
+  (service etc-service-type files))
+
+(define setuid-program-service-type
+  (service-type (name 'setuid-program)
+                (extensions
+                 (list (service-extension activation-service-type
+                                          (lambda (programs)
+                                            #~(activate-setuid-programs
+                                               (list #$@programs))))))
+                (compose concatenate)
+                (extend append)))
+
+(define (firmware->activation-gexp firmware)
+  "Return a gexp to make the packages listed in FIRMWARE loadable by the
+kernel."
+  (let ((directory (directory-union "firmware" firmware)))
+    ;; Tell the kernel where firmware is.
+    #~(activate-firmware (string-append #$directory "/lib/firmware"))))
+
+(define firmware-service-type
+  ;; The service that collects firmware.
+  (service-type (name 'firmware)
+                (extensions
+                 (list (service-extension activation-service-type
+                                          firmware->activation-gexp)))
+                (compose concatenate)
+                (extend append)))
+
+
+;;;
+;;; Service folding.
+;;;
+
+(define-condition-type &service-error &error
+  service-error?)
+
+(define-condition-type &missing-target-service-error &service-error
+  missing-target-service-error?
+  (service      missing-target-service-error-service)
+  (target-type  missing-target-service-error-target-type))
+
+(define-condition-type &ambiguous-target-service-error &service-error
+  ambiguous-target-service-error?
+  (service      ambiguous-target-service-error-service)
+  (target-type  ambiguous-target-service-error-target-type))
+
+(define (service-back-edges services)
+  "Return a procedure that, when passed a <service>, returns the list of
+<service> objects that depend on it."
+  (define (add-edges service edges)
+    (define (add-edge extension edges)
+      (let ((target-type (service-extension-target extension)))
+        (match (filter (lambda (service)
+                         (eq? (service-kind service) target-type))
+                       services)
+          ((target)
+           (vhash-consq target service edges))
+          (()
+           (raise
+            (condition (&missing-target-service-error
+                        (service service)
+                        (target-type target-type))
+                       (&message
+                        (message
+                         (format #f (_ "no target of type '~a' for service ~s")
+                                 (service-type-name target-type)
+                                 service))))))
+          (x
+           (raise
+            (condition (&ambiguous-target-service-error
+                        (service service)
+                        (target-type target-type))
+                       (&message
+                        (message
+                         (format #f
+                                 (_ "more than one target service of type '~a'")
+                                 (service-type-name target-type))))))))))
+
+    (fold add-edge edges (service-type-extensions (service-kind service))))
+
+  (let ((edges (fold add-edges vlist-null services)))
+    (lambda (node)
+      (reverse (vhash-foldq* cons '() node edges)))))
+
+(define* (fold-services services #:key (target-type boot-service-type))
+  "Fold SERVICES by propagating their extensions down to the root of type
+TARGET-TYPE; return the root service adjusted accordingly."
+  (define dependents
+    (service-back-edges services))
+
+  (define (matching-extension target)
+    (let ((target (service-kind target)))
+      (match-lambda
+        (($ <service-extension> type)
+         (eq? type target)))))
+
+  (define (apply-extension target)
+    (lambda (service)
+      (match (find (matching-extension target)
+                   (service-type-extensions (service-kind service)))
+        (($ <service-extension> _ compute)
+         (compute (service-parameters service))))))
+
+  (match (filter (lambda (service)
+                   (eq? (service-kind service) target-type))
+                 services)
+    ((sink)
+     (let loop ((sink sink))
+       (let* ((dependents (map loop (dependents sink)))
+              (extensions (map (apply-extension sink) dependents))
+              (extend     (service-type-extend (service-kind sink)))
+              (compose    (service-type-compose (service-kind sink)))
+              (params     (service-parameters sink)))
+         ;; We distinguish COMPOSE and EXTEND because PARAMS typically has a
+         ;; different type than the elements of EXTENSIONS.
+         (if extend
+             (service (service-kind sink)
+                      (extend params (compose extensions)))
+             sink))))
+    (()
+     (raise
+      (condition (&missing-target-service-error
+                  (service #f)
+                  (target-type target-type))
+                 (&message
+                  (message (format #f (_ "service of type '~a' not found")
+                                   (service-type-name target-type)))))))
+    (x
+     (raise
+      (condition (&ambiguous-target-service-error
+                  (service #f)
+                  (target-type target-type))
+                 (&message
+                  (message
+                   (format #f
+                           (_ "more than one target service of type '~a'")
+                           (service-type-name target-type)))))))))
 
 ;;; services.scm ends here.
diff --git a/gnu/services/avahi.scm b/gnu/services/avahi.scm
index 929ac2fbb62..b576c395ffd 100644
--- a/gnu/services/avahi.scm
+++ b/gnu/services/avahi.scm
@@ -18,10 +18,13 @@
 
 (define-module (gnu services avahi)
   #:use-module (gnu services)
+  #:use-module (gnu services base)
+  #:use-module (gnu services dmd)
+  #:use-module (gnu services dbus)
   #:use-module (gnu system shadow)
   #:use-module (gnu packages avahi)
   #:use-module (gnu packages admin)
-  #:use-module (guix store)
+  #:use-module (guix records)
   #:use-module (guix gexp)
   #:export (avahi-service))
 
@@ -32,12 +35,27 @@
 ;;;
 ;;; Code:
 
-(define* (configuration-file #:key host-name publish?
-                             ipv4? ipv6? wide-area? domains-to-browse)
-  "Return an avahi-daemon configuration file."
+  ;; TODO: Export.
+(define-record-type* <avahi-configuration>
+  avahi-configuration make-avahi-configuration
+  avahi-configuration?
+  (avahi             avahi-configuration-avahi    ;<package>
+                     (default avahi))
+  (host-name         avahi-configuration-host-name) ;string
+  (publish?          avahi-configuration-publish?)  ;Boolean
+  (ipv4?             avahi-configuration-ipv4?)     ;Boolean
+  (ipv6?             avahi-configuration-ipv6?)     ;Boolean
+  (wide-area?        avahi-configuration-wide-area?) ;Boolean
+  (domains-to-browse avahi-configuration-domains-to-browse)) ;list of strings
+
+(define* (configuration-file config)
+  "Return an avahi-daemon configuration file based on CONFIG, an
+<avahi-configuration>."
   (define (bool value)
     (if value "yes\n" "no\n"))
 
+  (define host-name (avahi-configuration-host-name config))
+
   (plain-file "avahi-daemon.conf"
               (string-append
                "[server]\n"
@@ -45,14 +63,63 @@
                    (string-append "host-name=" host-name "\n")
                    "")
 
-               "browse-domains=" (string-join domains-to-browse)
+               "browse-domains=" (string-join
+                                  (avahi-configuration-domains-to-browse
+                                   config))
                "\n"
-               "use-ipv4=" (bool ipv4?)
-               "use-ipv6=" (bool ipv6?)
+               "use-ipv4=" (bool (avahi-configuration-ipv4? config))
+               "use-ipv6=" (bool (avahi-configuration-ipv6? config))
                "[wide-area]\n"
-               "enable-wide-area=" (bool wide-area?)
+               "enable-wide-area=" (bool (avahi-configuration-wide-area? config))
                "[publish]\n"
-               "disable-publishing=" (bool (not publish?)))))
+               "disable-publishing="
+               (bool (not (avahi-configuration-publish? config))))))
+
+(define %avahi-accounts
+  ;; Account and group for the Avahi daemon.
+  (list (user-group (name "avahi") (system? #t))
+        (user-account
+         (name "avahi")
+         (group "avahi")
+         (system? #t)
+         (comment "Avahi daemon user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define %avahi-activation
+  ;; Activation gexp.
+  #~(begin
+      (use-modules (guix build utils))
+      (mkdir-p "/var/run/avahi-daemon")))
+
+(define (avahi-dmd-service config)
+  "Return a list of <dmd-service> for CONFIG."
+  (let ((config (configuration-file config))
+        (avahi  (avahi-configuration-avahi config)))
+    (list (dmd-service
+           (documentation "Run the Avahi mDNS/DNS-SD responder.")
+           (provision '(avahi-daemon))
+           (requirement '(dbus-system networking))
+
+           (start #~(make-forkexec-constructor
+                     (list (string-append #$avahi "/sbin/avahi-daemon")
+                           "--syslog" "-f" #$config)))
+           (stop #~(make-kill-destructor))))))
+
+(define avahi-service-type
+  (service-type (name 'avahi)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          avahi-dmd-service)
+                       (service-extension dbus-root-service-type
+                                          (compose list
+                                                   avahi-configuration-avahi))
+                       (service-extension account-service-type
+                                          (const %avahi-accounts))
+                       (service-extension activation-service-type
+                                          (const %avahi-activation))
+                       (service-extension nscd-service-type
+                                          (const (list nss-mdns)))))))
 
 (define* (avahi-service #:key (avahi avahi)
                         host-name
@@ -75,36 +142,11 @@ When @var{wide-area?} is true, DNS-SD over unicast DNS is enabled.
 
 Boolean values @var{ipv4?} and @var{ipv6?} determine whether to use IPv4/IPv6
 sockets."
-  (let ((config (configuration-file #:host-name host-name
-                                    #:publish? publish?
-                                    #:ipv4? ipv4?
-                                    #:ipv6? ipv6?
-                                    #:wide-area? wide-area?
-                                    #:domains-to-browse
-                                    domains-to-browse)))
-    (service
-     (documentation "Run the Avahi mDNS/DNS-SD responder.")
-     (provision '(avahi-daemon))
-     (requirement '(dbus-system networking))
-
-     (start #~(make-forkexec-constructor
-               (list (string-append #$avahi "/sbin/avahi-daemon")
-                     "--syslog" "-f" #$config)))
-     (stop #~(make-kill-destructor))
-     (activate #~(begin
-                   (use-modules (guix build utils))
-                   (mkdir-p "/var/run/avahi-daemon")))
-
-     (user-groups (list (user-group
-                         (name "avahi")
-                         (system? #t))))
-     (user-accounts (list (user-account
-                           (name "avahi")
-                           (group "avahi")
-                           (system? #t)
-                           (comment "Avahi daemon user")
-                           (home-directory "/var/empty")
-                           (shell
-                            #~(string-append #$shadow "/sbin/nologin"))))))))
+  (service avahi-service-type
+           (avahi-configuration
+            (avahi avahi) (host-name host-name)
+            (publish? publish?) (ipv4? ipv4?) (ipv6? ipv6?)
+            (wide-area? wide-area?)
+            (domains-to-browse domains-to-browse))))
 
 ;;; avahi.scm ends here
diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index d9d73b45973..adafe1b55ea 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -21,9 +21,11 @@
 (define-module (gnu services base)
   #:use-module (guix store)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu services networking)
   #:use-module (gnu system shadow)                ; 'user-account', etc.
   #:use-module (gnu system linux)                 ; 'pam-service', etc.
+  #:use-module (gnu system file-systems)          ; 'file-system', etc.
   #:use-module (gnu packages admin)
   #:use-module ((gnu packages linux)
                 #:select (eudev kbd e2fsprogs lvm2 fuse alsa-utils crda))
@@ -49,6 +51,7 @@
             host-name-service
             console-keymap-service
             console-font-service
+            udev-service-type
             udev-service
 
             mingetty-configuration
@@ -64,9 +67,14 @@
             nscd-cache
             nscd-cache?
 
+            nscd-service-type
             nscd-service
             syslog-service
+
+            guix-configuration
+            guix-configuration?
             guix-service
+
             %base-services))
 
 ;;; Commentary:
@@ -76,13 +84,13 @@
 ;;;
 ;;; Code:
 
-(define (root-file-system-service)
-  "Return a service whose sole purpose is to re-mount read-only the root file
-system upon shutdown (aka. cleanly \"umounting\" root.)
+
+;;;
+;;; File systems.
+;;;
 
-This service must be the root of the service dependency graph so that its
-'stop' action is invoked when dmd is the only process left."
-  (service
+(define %root-file-system-dmd-service
+  (dmd-service
    (documentation "Take care of the root file system.")
    (provision '(root-file-system))
    (start #~(const #t))
@@ -116,181 +124,230 @@ This service must be the root of the service dependency graph so that its
                   #f)))))
    (respawn? #f)))
 
-(define* (file-system-service device target type
-                              #:key (flags '()) (check? #t)
-                              create-mount-point? options (title 'any)
-                              (requirements '()))
-  "Return a service that mounts DEVICE on TARGET as a file system TYPE with
-OPTIONS.  TITLE is a symbol specifying what kind of name DEVICE is: 'label for
-a partition label, 'device for a device file name, or 'any.  When CHECK? is
-true, check the file system before mounting it.  When CREATE-MOUNT-POINT? is
-true, create TARGET if it does not exist yet.  FLAGS is a list of symbols,
-such as 'read-only' etc.  Optionally, REQUIREMENTS may be a list of service
-names such as device-mapping services."
-  (service
-   (provision (list (symbol-append 'file-system- (string->symbol target))))
-   (requirement `(root-file-system ,@requirements))
-   (documentation "Check, mount, and unmount the given file system.")
-   (start #~(lambda args
-              ;; FIXME: Use or factorize with 'mount-file-system'.
-              (let ((device (canonicalize-device-spec #$device '#$title))
-                    (flags  #$(mount-flags->bit-mask flags)))
-                #$(if create-mount-point?
-                      #~(mkdir-p #$target)
-                      #~#t)
-                #$(if check?
-                      #~(begin
-                          ;; Make sure fsck.ext2 & co. can be found.
-                          (setenv "PATH"
-                                  (string-append
-                                   #$e2fsprogs "/sbin:"
-                                   "/run/current-system/profile/sbin:"
-                                   (getenv "PATH")))
-                          (check-file-system device #$type))
-                      #~#t)
-
-                (mount device #$target #$type flags #$options)
-
-                ;; For read-only bind mounts, an extra remount is needed,
-                ;; as per <http://lwn.net/Articles/281157/>, which still
-                ;; applies to Linux 4.0.
-                (when (and (= MS_BIND (logand flags MS_BIND))
-                           (= MS_RDONLY (logand flags MS_RDONLY)))
-                  (mount device #$target #$type
-                         (logior MS_BIND MS_REMOUNT MS_RDONLY))))
-              #t))
-   (stop #~(lambda args
-             ;; Normally there are no processes left at this point, so
-             ;; TARGET can be safely unmounted.
-
-             ;; Make sure PID 1 doesn't keep TARGET busy.
-             (chdir "/")
-
-             (umount #$target)
-             #f))))
+(define root-file-system-service-type
+  (dmd-service-type (const %root-file-system-dmd-service)))
+
+(define (root-file-system-service)
+  "Return a service whose sole purpose is to re-mount read-only the root file
+system upon shutdown (aka. cleanly \"umounting\" root.)
+
+This service must be the root of the service dependency graph so that its
+'stop' action is invoked when dmd is the only process left."
+  (service root-file-system-service-type #f))
+
+(define (file-system->dmd-service-name file-system)
+  "Return the symbol that denotes the service mounting and unmounting
+FILE-SYSTEM."
+  (symbol-append 'file-system-
+                 (string->symbol (file-system-mount-point file-system))))
+
+(define file-system-service-type
+  ;; TODO(?): Make this an extensible service that takes <file-system> objects
+  ;; and returns a list of <dmd-service>.
+  (dmd-service-type
+   (lambda (file-system)
+     (let ((target  (file-system-mount-point file-system))
+           (device  (file-system-device file-system))
+           (type    (file-system-type file-system))
+           (title   (file-system-title file-system))
+           (check?  (file-system-check? file-system))
+           (create? (file-system-create-mount-point? file-system))
+           (dependencies (file-system-dependencies file-system)))
+       (dmd-service
+        (provision (list (file-system->dmd-service-name file-system)))
+        (requirement `(root-file-system
+                       ,@(map file-system->dmd-service-name dependencies)))
+        (documentation "Check, mount, and unmount the given file system.")
+        (start #~(lambda args
+                   ;; FIXME: Use or factorize with 'mount-file-system'.
+                   (let ((device (canonicalize-device-spec #$device '#$title))
+                         (flags  #$(mount-flags->bit-mask
+                                    (file-system-flags file-system))))
+                     #$(if create?
+                           #~(mkdir-p #$target)
+                           #~#t)
+                     #$(if check?
+                           #~(begin
+                               ;; Make sure fsck.ext2 & co. can be found.
+                               (setenv "PATH"
+                                       (string-append
+                                        #$e2fsprogs "/sbin:"
+                                        "/run/current-system/profile/sbin:"
+                                        (getenv "PATH")))
+                               (check-file-system device #$type))
+                           #~#t)
+
+                     (mount device #$target #$type flags
+                            #$(file-system-options file-system))
+
+                     ;; For read-only bind mounts, an extra remount is needed,
+                     ;; as per <http://lwn.net/Articles/281157/>, which still
+                     ;; applies to Linux 4.0.
+                     (when (and (= MS_BIND (logand flags MS_BIND))
+                                (= MS_RDONLY (logand flags MS_RDONLY)))
+                       (mount device #$target #$type
+                              (logior MS_BIND MS_REMOUNT MS_RDONLY))))
+                   #t))
+        (stop #~(lambda args
+                  ;; Normally there are no processes left at this point, so
+                  ;; TARGET can be safely unmounted.
+
+                  ;; Make sure PID 1 doesn't keep TARGET busy.
+                  (chdir "/")
+
+                  (umount #$target)
+                  #f)))))))
+
+(define* (file-system-service file-system)
+  "Return a service that mounts @var{file-system}, a @code{<file-system>}
+object."
+  (service file-system-service-type file-system))
+
+(define user-unmount-service-type
+  (dmd-service-type
+   (lambda (known-mount-points)
+     (dmd-service
+      (documentation "Unmount manually-mounted file systems.")
+      (provision '(user-unmount))
+      (start #~(const #t))
+      (stop #~(lambda args
+                (define (known? mount-point)
+                  (member mount-point
+                          (cons* "/proc" "/sys" '#$known-mount-points)))
+
+                ;; Make sure we don't keep the user's mount points busy.
+                (chdir "/")
+
+                (for-each (lambda (mount-point)
+                            (format #t "unmounting '~a'...~%" mount-point)
+                            (catch 'system-error
+                              (lambda ()
+                                (umount mount-point))
+                              (lambda args
+                                (let ((errno (system-error-errno args)))
+                                  (format #t "failed to unmount '~a': ~a~%"
+                                          mount-point (strerror errno))))))
+                          (filter (negate known?) (mount-points)))
+                #f))))))
 
 (define (user-unmount-service known-mount-points)
   "Return a service whose sole purpose is to unmount file systems not listed
 in KNOWN-MOUNT-POINTS when it is stopped."
-  (service
-   (documentation "Unmount manually-mounted file systems.")
-   (provision '(user-unmount))
-   (start #~(const #t))
-   (stop #~(lambda args
-             (define (known? mount-point)
-               (member mount-point
-                       (cons* "/proc" "/sys"
-                              '#$known-mount-points)))
-
-             ;; Make sure we don't keep the user's mount points busy.
-             (chdir "/")
-
-             (for-each (lambda (mount-point)
-                         (format #t "unmounting '~a'...~%" mount-point)
-                         (catch 'system-error
-                           (lambda ()
-                             (umount mount-point))
-                           (lambda args
-                             (let ((errno (system-error-errno args)))
-                               (format #t "failed to unmount '~a': ~a~%"
-                                       mount-point (strerror errno))))))
-                       (filter (negate known?) (mount-points)))
-             #f))))
+  (service user-unmount-service-type known-mount-points))
 
 (define %do-not-kill-file
   ;; Name of the file listing PIDs of processes that must survive when halting
   ;; the system.  Typical example is user-space file systems.
   "/etc/dmd/do-not-kill")
 
-(define* (user-processes-service requirements #:key (grace-delay 4))
+(define user-processes-service-type
+  (dmd-service-type
+   (match-lambda
+     ((requirements grace-delay)
+      (dmd-service
+       (documentation "When stopped, terminate all user processes.")
+       (provision '(user-processes))
+       (requirement (cons 'root-file-system
+                          (map file-system->dmd-service-name
+                               requirements)))
+       (start #~(const #t))
+       (stop #~(lambda _
+                 (define (kill-except omit signal)
+                   ;; Kill all the processes with SIGNAL except those listed
+                   ;; in OMIT and the current process.
+                   (let ((omit (cons (getpid) omit)))
+                     (for-each (lambda (pid)
+                                 (unless (memv pid omit)
+                                   (false-if-exception
+                                    (kill pid signal))))
+                               (processes))))
+
+                 (define omitted-pids
+                   ;; List of PIDs that must not be killed.
+                   (if (file-exists? #$%do-not-kill-file)
+                       (map string->number
+                            (call-with-input-file #$%do-not-kill-file
+                              (compose string-tokenize
+                                       (@ (ice-9 rdelim) read-string))))
+                       '()))
+
+                 (define (now)
+                   (car (gettimeofday)))
+
+                 (define (sleep* n)
+                   ;; Really sleep N seconds.
+                   ;; Work around <http://bugs.gnu.org/19581>.
+                   (define start (now))
+                   (let loop ((elapsed 0))
+                     (when (> n elapsed)
+                       (sleep (- n elapsed))
+                       (loop (- (now) start)))))
+
+                 (define lset= (@ (srfi srfi-1) lset=))
+
+                 (display "sending all processes the TERM signal\n")
+
+                 (if (null? omitted-pids)
+                     (begin
+                       ;; Easy: terminate all of them.
+                       (kill -1 SIGTERM)
+                       (sleep* #$grace-delay)
+                       (kill -1 SIGKILL))
+                     (begin
+                       ;; Kill them all except OMITTED-PIDS.  XXX: We would
+                       ;; like to (kill -1 SIGSTOP) to get a fixed list of
+                       ;; processes, like 'killall5' does, but that seems
+                       ;; unreliable.
+                       (kill-except omitted-pids SIGTERM)
+                       (sleep* #$grace-delay)
+                       (kill-except omitted-pids SIGKILL)
+                       (delete-file #$%do-not-kill-file)))
+
+                 (let wait ()
+                   (let ((pids (processes)))
+                     (unless (lset= = pids (cons 1 omitted-pids))
+                       (format #t "waiting for process termination\
+ (processes left: ~s)~%"
+                               pids)
+                       (sleep* 2)
+                       (wait))))
+
+                 (display "all processes have been terminated\n")
+                 #f))
+       (respawn? #f))))))
+
+(define* (user-processes-service file-systems #:key (grace-delay 4))
   "Return the service that is responsible for terminating all the processes so
 that the root file system can be re-mounted read-only, just before
 rebooting/halting.  Processes still running GRACE-DELAY seconds after SIGTERM
 has been sent are terminated with SIGKILL.
 
-The returned service will depend on 'root-file-system' and on all the services
-listed in REQUIREMENTS.
+The returned service will depend on 'root-file-system' and on all the dmd
+services corresponding to FILE-SYSTEMS.
 
 All the services that spawn processes must depend on this one so that they are
 stopped before 'kill' is called."
-  (service
-   (documentation "When stopped, terminate all user processes.")
-   (provision '(user-processes))
-   (requirement (cons 'root-file-system requirements))
-   (start #~(const #t))
-   (stop #~(lambda _
-             (define (kill-except omit signal)
-               ;; Kill all the processes with SIGNAL except those
-               ;; listed in OMIT and the current process.
-               (let ((omit (cons (getpid) omit)))
-                 (for-each (lambda (pid)
-                             (unless (memv pid omit)
-                               (false-if-exception
-                                (kill pid signal))))
-                           (processes))))
-
-             (define omitted-pids
-               ;; List of PIDs that must not be killed.
-               (if (file-exists? #$%do-not-kill-file)
-                   (map string->number
-                        (call-with-input-file #$%do-not-kill-file
-                          (compose string-tokenize
-                                   (@ (ice-9 rdelim) read-string))))
-                   '()))
-
-             (define (now)
-               (car (gettimeofday)))
-
-             (define (sleep* n)
-               ;; Really sleep N seconds.
-               ;; Work around <http://bugs.gnu.org/19581>.
-               (define start (now))
-               (let loop ((elapsed 0))
-                 (when (> n elapsed)
-                   (sleep (- n elapsed))
-                   (loop (- (now) start)))))
-
-             (define lset= (@ (srfi srfi-1) lset=))
-
-             (display "sending all processes the TERM signal\n")
-
-             (if (null? omitted-pids)
-                 (begin
-                   ;; Easy: terminate all of them.
-                   (kill -1 SIGTERM)
-                   (sleep* #$grace-delay)
-                   (kill -1 SIGKILL))
-                 (begin
-                   ;; Kill them all except OMITTED-PIDS.  XXX: We
-                   ;; would like to (kill -1 SIGSTOP) to get a fixed
-                   ;; list of processes, like 'killall5' does, but
-                   ;; that seems unreliable.
-                   (kill-except omitted-pids SIGTERM)
-                   (sleep* #$grace-delay)
-                   (kill-except omitted-pids SIGKILL)
-                   (delete-file #$%do-not-kill-file)))
-
-             (let wait ()
-               (let ((pids (processes)))
-                 (unless (lset= = pids (cons 1 omitted-pids))
-                   (format #t "waiting for process termination\
- (processes left: ~s)~%"
-                           pids)
-                   (sleep* 2)
-                   (wait))))
+  (service user-processes-service-type
+           (list file-systems grace-delay)))
 
-             (display "all processes have been terminated\n")
-             #f))
-   (respawn? #f)))
+
+;;;
+;;; Console & co.
+;;;
+
+(define host-name-service-type
+  (dmd-service-type
+   (lambda (name)
+     (dmd-service
+      (documentation "Initialize the machine's host name.")
+      (provision '(host-name))
+      (start #~(lambda _
+                 (sethostname #$name)))
+      (respawn? #f)))))
 
 (define (host-name-service name)
   "Return a service that sets the host name to @var{name}."
-  (service
-   (documentation "Initialize the machine's host name.")
-   (provision '(host-name))
-   (start #~(lambda _
-              (sethostname #$name)))
-   (respawn? #f)))
+  (service host-name-service-type name))
 
 (define (unicode-start tty)
   "Return a gexp to start Unicode support on @var{tty}."
@@ -310,15 +367,43 @@ stopped before 'kill' is called."
           (else
            (zero? (cdr (waitpid pid))))))))
 
+(define console-keymap-service-type
+  (dmd-service-type
+   (lambda (file)
+     (dmd-service
+      (documentation (string-append "Load console keymap (loadkeys)."))
+      (provision '(console-keymap))
+      (start #~(lambda _
+                 (zero? (system* (string-append #$kbd "/bin/loadkeys")
+                                 #$file))))
+      (respawn? #f)))))
+
 (define (console-keymap-service file)
   "Return a service to load console keymap from @var{file}."
-  (service
-   (documentation (string-append "Load console keymap (loadkeys)."))
-   (provision '(console-keymap))
-   (start #~(lambda _
-              (zero? (system* (string-append #$kbd "/bin/loadkeys")
-                              #$file))))
-   (respawn? #f)))
+  (service console-keymap-service-type file))
+
+(define console-font-service-type
+  (dmd-service-type
+   (match-lambda
+     ((tty font)
+      (let ((device (string-append "/dev/" tty)))
+        (dmd-service
+         (documentation "Load a Unicode console font.")
+         (provision (list (symbol-append 'console-font-
+                                         (string->symbol tty))))
+
+         ;; Start after mingetty has been started on TTY, otherwise the settings
+         ;; are ignored.
+         (requirement (list (symbol-append 'term-
+                                           (string->symbol tty))))
+
+         (start #~(lambda _
+                    (and #$(unicode-start device)
+                         (zero?
+                          (system* (string-append #$kbd "/bin/setfont")
+                                   "-C" #$device #$font)))))
+         (stop #~(const #t))
+         (respawn? #f)))))))
 
 (define* (console-font-service tty #:optional (font "LatGrkCyr-8x16"))
   "Return a service that sets up Unicode support in @var{tty} and loads
@@ -326,24 +411,7 @@ stopped before 'kill' is called."
   ;; Note: 'LatGrkCyr-8x16' has the advantage of providing three common
   ;; scripts as well as glyphs for em dash, quotation marks, and other Unicode
   ;; codepoints notably found in the UTF-8 manual.
-  (let ((device (string-append "/dev/" tty)))
-    (service
-     (documentation "Load a Unicode console font.")
-     (provision (list (symbol-append 'console-font-
-                                     (string->symbol tty))))
-
-     ;; Start after mingetty has been started on TTY, otherwise the
-     ;; settings are ignored.
-     (requirement (list (symbol-append 'term-
-                                       (string->symbol tty))))
-
-     (start #~(lambda _
-                (and #$(unicode-start device)
-                     (zero?
-                      (system* (string-append #$kbd "/bin/setfont")
-                               "-C" #$device #$font)))))
-     (stop #~(const #t))
-     (respawn? #f))))
+  (service console-font-service-type (list tty font)))
 
 (define-record-type* <mingetty-configuration>
   mingetty-configuration make-mingetty-configuration
@@ -365,43 +433,56 @@ stopped before 'kill' is called."
   (allow-empty-passwords? mingetty-configuration-allow-empty-passwords?
                           (default #t)))          ;Boolean
 
-(define* (mingetty-service config)
-  "Return a service to run mingetty according to @var{config}, a
-@code{<mingetty-configuration>} object, which specifies the tty to run, among
-other things."
-  (match config
+(define (mingetty-pam-service conf)
+  "Return the list of PAM service needed for CONF."
+  ;; Let 'login' be known to PAM.  All the mingetty services will have that
+  ;; PAM service, but that's fine because they're all identical and duplicates
+  ;; are removed.
+  (list (unix-pam-service "login"
+                          #:allow-empty-passwords?
+                          (mingetty-configuration-allow-empty-passwords? conf)
+                          #:motd
+                          (mingetty-configuration-motd conf))))
+
+(define mingetty-dmd-service
+  (match-lambda
     (($ <mingetty-configuration> mingetty tty motd auto-login login-program
                                  login-pause? allow-empty-passwords?)
-     (service
-      (documentation "Run mingetty on an tty.")
-      (provision (list (symbol-append 'term- (string->symbol tty))))
-
-      ;; Since the login prompt shows the host name, wait for the 'host-name'
-      ;; service to be done.  Also wait for udev essentially so that the tty
-      ;; text is not lost in the middle of kernel messages (XXX).
-      (requirement '(user-processes host-name udev))
-
-      (start  #~(make-forkexec-constructor
-                 (list (string-append #$mingetty "/sbin/mingetty")
-                       "--noclear" #$tty
-                       #$@(if auto-login
-                              #~("--autologin" #$auto-login)
-                              #~())
-                       #$@(if login-program
-                              #~("--loginprog" #$login-program)
-                              #~())
-                       #$@(if login-pause?
-                              #~("--loginpause")
-                              #~()))))
-      (stop   #~(make-kill-destructor))
-
-      (pam-services
-       ;; Let 'login' be known to PAM.  All the mingetty services will have
-       ;; that PAM service, but that's fine because they're all identical and
-       ;; duplicates are removed.
-       (list (unix-pam-service "login"
-                               #:allow-empty-passwords? allow-empty-passwords?
-                               #:motd motd)))))))
+     (list
+      (dmd-service
+       (documentation "Run mingetty on an tty.")
+       (provision (list (symbol-append 'term- (string->symbol tty))))
+
+       ;; Since the login prompt shows the host name, wait for the 'host-name'
+       ;; service to be done.  Also wait for udev essentially so that the tty
+       ;; text is not lost in the middle of kernel messages (XXX).
+       (requirement '(user-processes host-name udev))
+
+       (start  #~(make-forkexec-constructor
+                  (list (string-append #$mingetty "/sbin/mingetty")
+                        "--noclear" #$tty
+                        #$@(if auto-login
+                               #~("--autologin" #$auto-login)
+                               #~())
+                        #$@(if login-program
+                               #~("--loginprog" #$login-program)
+                               #~())
+                        #$@(if login-pause?
+                               #~("--loginpause")
+                               #~()))))
+       (stop   #~(make-kill-destructor)))))))
+
+(define mingetty-service-type
+  (service-type (name 'mingetty)
+                (extensions (list (service-extension dmd-root-service-type
+                                                     mingetty-dmd-service)
+                                  (service-extension pam-root-service-type
+                                                     mingetty-pam-service)))))
+
+(define* (mingetty-service config)
+  "Return a service to run mingetty according to @var{config}, which specifies
+the tty to run, among other things."
+  (service mingetty-service-type config))
 
 (define-record-type* <nscd-configuration> nscd-configuration
   make-nscd-configuration
@@ -506,38 +587,72 @@ other things."
                                 (string-concatenate
                                  (map cache->config caches)))))))
 
+(define (nscd-dmd-service config)
+  "Return a dmd service for CONFIG, an <nscd-configuration> object."
+  (let ((nscd.conf     (nscd.conf-file config))
+        (name-services (nscd-configuration-name-services config)))
+    (list (dmd-service
+           (documentation "Run libc's name service cache daemon (nscd).")
+           (provision '(nscd))
+           (requirement '(user-processes))
+           (start #~(make-forkexec-constructor
+                     (list (string-append #$(nscd-configuration-glibc config)
+                                          "/sbin/nscd")
+                           "-f" #$nscd.conf "--foreground")
+
+                     #:environment-variables
+                     (list (string-append "LD_LIBRARY_PATH="
+                                          (string-join
+                                           (map (lambda (dir)
+                                                  (string-append dir "/lib"))
+                                                (list #$@name-services))
+                                           ":")))))
+           (stop #~(make-kill-destructor))
+
+           (respawn? #f)))))
+
+(define nscd-activation
+  ;; Actions to take before starting nscd.
+  #~(begin
+      (use-modules (guix build utils))
+      (mkdir-p "/var/run/nscd")
+      (mkdir-p "/var/db/nscd")))                  ;for the persistent cache
+
+(define nscd-service-type
+  (service-type (name 'nscd)
+                (extensions
+                 (list (service-extension activation-service-type
+                                          (const nscd-activation))
+                       (service-extension dmd-root-service-type
+                                          nscd-dmd-service)))
+
+                ;; This can be extended by providing additional name services
+                ;; such as nss-mdns.
+                (compose concatenate)
+                (extend (lambda (config name-services)
+                          (nscd-configuration
+                           (inherit config)
+                           (name-services (append
+                                           (nscd-configuration-name-services config)
+                                           name-services)))))))
+
 (define* (nscd-service #:optional (config %nscd-default-configuration))
   "Return a service that runs libc's name service cache daemon (nscd) with the
 given @var{config}---an @code{<nscd-configuration>} object.  @xref{Name
 Service Switch}, for an example."
-  (let ((nscd.conf (nscd.conf-file config)))
-    (service
-     (documentation "Run libc's name service cache daemon (nscd).")
-     (provision '(nscd))
-     (requirement '(user-processes))
-
-     (activate #~(begin
-                   (use-modules (guix build utils))
-                   (mkdir-p "/var/run/nscd")
-                   (mkdir-p "/var/db/nscd")))     ;for the persistent cache
-
-     (start #~(make-forkexec-constructor
-               (list (string-append #$(nscd-configuration-glibc config)
-                                    "/sbin/nscd")
-                     "-f" #$nscd.conf "--foreground")
-
-               #:environment-variables
-               (list (string-append "LD_LIBRARY_PATH="
-                                    (string-join
-                                     (map (lambda (dir)
-                                            (string-append dir "/lib"))
-                                          (list
-                                           #$@(nscd-configuration-name-services
-                                               config)))
-                                     ":")))))
-     (stop #~(make-kill-destructor))
-
-     (respawn? #f))))
+  (service nscd-service-type config))
+
+(define syslog-service-type
+  (dmd-service-type
+   (lambda (config-file)
+     (dmd-service
+      (documentation "Run the syslog daemon (syslogd).")
+      (provision '(syslogd))
+      (requirement '(user-processes))
+      (start #~(make-forkexec-constructor
+                (list (string-append #$inetutils "/libexec/syslogd")
+                      "--no-detach" "--rcfile" #$config-file)))
+      (stop #~(make-kill-destructor))))))
 
 ;; Snippet adapted from the GNU inetutils manual.
 (define %default-syslog.conf
@@ -561,18 +676,12 @@ Service Switch}, for an example."
      # Log all the mail messages in one place.
      mail.*                                  /var/log/maillog
 "))
+
 (define* (syslog-service #:key (config-file %default-syslog.conf))
   "Return a service that runs @code{syslogd}.
 If configuration file name @var{config-file} is not specified, use some
 reasonable default settings."
-  (service
-   (documentation "Run the syslog daemon (syslogd).")
-   (provision '(syslogd))
-   (requirement '(user-processes))
-   (start #~(make-forkexec-constructor
-             (list (string-append #$inetutils "/libexec/syslogd")
-                   "--no-detach" "--rcfile" #$config-file)))
-   (stop #~(make-kill-destructor))))
+  (service syslog-service-type config-file))
 
 (define* (guix-build-accounts count #:key
                               (group "guixbuild")
@@ -621,61 +730,104 @@ GUIX."
                (format (current-error-port) "warning: \
 failed to register hydra.gnu.org public key: ~a~%" status))))))))
 
-(define* (guix-service #:key (guix guix) (builder-group "guixbuild")
-                       (build-accounts 10) (authorize-hydra-key? #t)
-                       (use-substitutes? #t)
-                       (extra-options '())
-                       (lsof lsof) (lsh lsh))
-  "Return a service that runs the build daemon from @var{guix}, and has
-@var{build-accounts} user accounts available under @var{builder-group}.
-
-When @var{authorize-hydra-key?} is true, the @code{hydra.gnu.org} public key
-provided by @var{guix} is authorized upon activation, meaning that substitutes
-from @code{hydra.gnu.org} are used by default.
-
-If @var{use-substitutes?} is false, the daemon is run with
-@option{--no-substitutes} (@pxref{Invoking guix-daemon,
-@option{--no-substitutes}}).
-
-Finally, @var{extra-options} is a list of additional command-line options
-passed to @command{guix-daemon}."
-  (define activate
-    ;; Assume that the store has BUILDER-GROUP as its group.  We could
-    ;; otherwise call 'chown' here, but the problem is that on a COW unionfs,
-    ;; chown leads to an entire copy of the tree, which is a bad idea.
-
-    ;; Optionally authorize hydra.gnu.org's key.
-    (and authorize-hydra-key?
-         (hydra-key-authorization guix)))
-
-  (service
-   (documentation "Run the Guix daemon.")
-   (provision '(guix-daemon))
-   (requirement '(user-processes))
-   (start
-    #~(make-forkexec-constructor
-       (list (string-append #$guix "/bin/guix-daemon")
-             "--build-users-group" #$builder-group
-             #$@(if use-substitutes?
-                    '()
-                    '("--no-substitutes"))
-             #$@extra-options)
-
-       ;; Add 'lsof' (for the GC) and 'lsh' (for offloading) to the
-       ;; daemon's $PATH.
-       #:environment-variables
-       (list (string-append "PATH=" #$lsof "/bin:" #$lsh "/bin"))))
-   (stop #~(make-kill-destructor))
-   (user-accounts (guix-build-accounts build-accounts
-                                       #:group builder-group))
-   (user-groups (list (user-group
-                       (name builder-group)
-                       (system? #t)
-
-                       ;; Use a fixed GID so that we can create the
-                       ;; store with the right owner.
-                       (id 30000))))
-   (activate activate)))
+(define-record-type* <guix-configuration>
+  guix-configuration make-guix-configuration
+  guix-configuration?
+  (guix             guix-configuration-guix       ;<package>
+                    (default guix))
+  (build-group      guix-configuration-build-group ;string
+                    (default "guixbuild"))
+  (build-accounts   guix-configuration-build-accounts ;integer
+                    (default 10))
+  (authorize-key?   guix-configuration-authorize-key? ;Boolean
+                    (default #t))
+  (use-substitutes? guix-configuration-use-substitutes? ;Boolean
+                    (default #t))
+  (extra-options    guix-configuration-extra-options ;list of strings
+                    (default '()))
+  (lsof             guix-configuration-lsof       ;<package>
+                    (default lsof))
+  (lsh              guix-configuration-lsh        ;<package>
+                    (default lsh)))
+
+(define %default-guix-configuration
+  (guix-configuration))
+
+(define (guix-dmd-service config)
+  "Return a <dmd-service> for the Guix daemon service with CONFIG."
+  (match config
+    (($ <guix-configuration> guix build-group build-accounts authorize-key?
+                             use-substitutes? extra-options lsof lsh)
+     (list (dmd-service
+            (documentation "Run the Guix daemon.")
+            (provision '(guix-daemon))
+            (requirement '(user-processes))
+            (start
+             #~(make-forkexec-constructor
+                (list (string-append #$guix "/bin/guix-daemon")
+                      "--build-users-group" #$build-group
+                      #$@(if use-substitutes?
+                             '()
+                             '("--no-substitutes"))
+                      #$@extra-options)
+
+                ;; Add 'lsof' (for the GC) and 'lsh' (for offloading) to the
+                ;; daemon's $PATH.
+                #:environment-variables
+                (list (string-append "PATH=" #$lsof "/bin:" #$lsh "/bin"))))
+            (stop #~(make-kill-destructor)))))))
+
+(define (guix-accounts config)
+  "Return the user accounts and user groups for CONFIG."
+  (match config
+    (($ <guix-configuration> _ build-group build-accounts)
+     (cons (user-group
+            (name build-group)
+            (system? #t)
+
+            ;; Use a fixed GID so that we can create the store with the right
+            ;; owner.
+            (id 30000))
+           (guix-build-accounts build-accounts
+                                #:group build-group)))))
+
+(define (guix-activation config)
+  "Return the activation gexp for CONFIG."
+  (match config
+    (($ <guix-configuration> guix build-group build-accounts authorize-key?)
+     ;; Assume that the store has BUILD-GROUP as its group.  We could
+     ;; otherwise call 'chown' here, but the problem is that on a COW unionfs,
+     ;; chown leads to an entire copy of the tree, which is a bad idea.
+
+     ;; Optionally authorize hydra.gnu.org's key.
+     (and authorize-key?
+          (hydra-key-authorization guix)))))
+
+(define guix-service-type
+  (service-type
+   (name 'guix)
+   (extensions
+    (list (service-extension dmd-root-service-type guix-dmd-service)
+          (service-extension account-service-type guix-accounts)
+          (service-extension activation-service-type guix-activation)))))
+
+(define* (guix-service #:optional (config %default-guix-configuration))
+  "Return a service that runs the Guix build daemon according to
+@var{config}."
+  (service guix-service-type config))
+
+
+;;;
+;;; Udev.
+;;;
+
+(define-record-type* <udev-configuration>
+  udev-configuration make-udev-configuration
+  udev-configuration?
+  (udev   udev-configuration-udev                 ;<package>
+          (default udev))
+  (rules  udev-configuration-rules                ;list of <package>
+          (default '())))
 
 (define (udev-rules-union packages)
   "Return the union of the @code{lib/udev/rules.d} directories found in each
@@ -727,118 +879,150 @@ item of @var{packages}."
 KERNEL==\"kvm\", GROUP=\"kvm\", MODE=\"0660\"\n" port))))
                  #:modules '((guix build utils))))
 
+(define udev-dmd-service
+  ;; Return a <dmd-service> for UDEV with RULES.
+  (match-lambda
+    (($ <udev-configuration> udev rules)
+     (let* ((rules     (udev-rules-union (cons* udev (kvm-udev-rule) rules)))
+            (udev.conf (computed-file "udev.conf"
+                                      #~(call-with-output-file #$output
+                                          (lambda (port)
+                                            (format port
+                                                    "udev_rules=\"~a/lib/udev/rules.d\"\n"
+                                                    #$rules))))))
+       (list
+        (dmd-service
+         (provision '(udev))
+
+         ;; Udev needs /dev to be a 'devtmpfs' mount so that new device nodes can
+         ;; be added: see
+         ;; <http://www.linuxfromscratch.org/lfs/view/development/chapter07/udev.html>.
+         (requirement '(root-file-system))
+
+         (documentation "Populate the /dev directory, dynamically.")
+         (start #~(lambda ()
+                    (define find
+                      (@ (srfi srfi-1) find))
+
+                    (define udevd
+                      ;; Choose the right 'udevd'.
+                      (find file-exists?
+                            (map (lambda (suffix)
+                                   (string-append #$udev suffix))
+                                 '("/libexec/udev/udevd" ;udev
+                                   "/sbin/udevd"))))     ;eudev
+
+                    (define (wait-for-udevd)
+                      ;; Wait until someone's listening on udevd's control
+                      ;; socket.
+                      (let ((sock (socket AF_UNIX SOCK_SEQPACKET 0)))
+                        (let try ()
+                          (catch 'system-error
+                            (lambda ()
+                              (connect sock PF_UNIX "/run/udev/control")
+                              (close-port sock))
+                            (lambda args
+                              (format #t "waiting for udevd...~%")
+                              (usleep 500000)
+                              (try))))))
+
+                    ;; Allow udev to find the modules.
+                    (setenv "LINUX_MODULE_DIRECTORY"
+                            "/run/booted-system/kernel/lib/modules")
+
+                    ;; The first one is for udev, the second one for eudev.
+                    (setenv "UDEV_CONFIG_FILE" #$udev.conf)
+                    (setenv "EUDEV_RULES_DIRECTORY"
+                            (string-append #$rules "/lib/udev/rules.d"))
+
+                    (let ((pid (primitive-fork)))
+                      (case pid
+                        ((0)
+                         (exec-command (list udevd)))
+                        (else
+                         ;; Wait until udevd is up and running.  This
+                         ;; appears to be needed so that the events
+                         ;; triggered below are actually handled.
+                         (wait-for-udevd)
+
+                         ;; Trigger device node creation.
+                         (system* (string-append #$udev "/bin/udevadm")
+                                  "trigger" "--action=add")
+
+                         ;; Wait for things to settle down.
+                         (system* (string-append #$udev "/bin/udevadm")
+                                  "settle")
+                         pid)))))
+         (stop #~(make-kill-destructor))
+
+         ;; When halting the system, 'udev' is actually killed by
+         ;; 'user-processes', i.e., before its own 'stop' method was called.
+         ;; Thus, make sure it is not respawned.
+         (respawn? #f)))))))
+
+(define udev-service-type
+  (service-type (name 'udev)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          udev-dmd-service)))
+
+                (compose concatenate)           ;concatenate the list of rules
+                (extend (lambda (config rules)
+                          (match config
+                            (($ <udev-configuration> udev initial-rules)
+                             (udev-configuration
+                              (udev udev)
+                              (rules (append initial-rules rules)))))))))
+
 (define* (udev-service #:key (udev eudev) (rules '()))
   "Run @var{udev}, which populates the @file{/dev} directory dynamically.  Get
 extra rules from the packages listed in @var{rules}."
-  (let* ((rules     (udev-rules-union (cons* udev
-                                             (kvm-udev-rule)
-                                             rules)))
-         (udev.conf (computed-file "udev.conf"
-                                   #~(call-with-output-file #$output
-                                       (lambda (port)
-                                         (format port
-                                                 "udev_rules=\"~a/lib/udev/rules.d\"\n"
-                                                 #$rules))))))
-    (service
-     (provision '(udev))
-
-     ;; Udev needs /dev to be a 'devtmpfs' mount so that new device nodes can
-     ;; be added: see
-     ;; <http://www.linuxfromscratch.org/lfs/view/development/chapter07/udev.html>.
-     (requirement '(root-file-system))
-
-     (documentation "Populate the /dev directory, dynamically.")
-     (start #~(lambda ()
-                (define find
-                  (@ (srfi srfi-1) find))
-
-                (define udevd
-                  ;; Choose the right 'udevd'.
-                  (find file-exists?
-                        (map (lambda (suffix)
-                               (string-append #$udev suffix))
-                             '("/libexec/udev/udevd" ;udev
-                               "/sbin/udevd"))))     ;eudev
-
-                (define (wait-for-udevd)
-                  ;; Wait until someone's listening on udevd's control
-                  ;; socket.
-                  (let ((sock (socket AF_UNIX SOCK_SEQPACKET 0)))
-                    (let try ()
-                      (catch 'system-error
-                        (lambda ()
-                          (connect sock PF_UNIX "/run/udev/control")
-                          (close-port sock))
-                        (lambda args
-                          (format #t "waiting for udevd...~%")
-                          (usleep 500000)
-                          (try))))))
-
-                ;; Allow udev to find the modules.
-                (setenv "LINUX_MODULE_DIRECTORY"
-                        "/run/booted-system/kernel/lib/modules")
-
-                ;; The first one is for udev, the second one for eudev.
-                (setenv "UDEV_CONFIG_FILE" #$udev.conf)
-                (setenv "EUDEV_RULES_DIRECTORY"
-                        (string-append #$rules "/lib/udev/rules.d"))
-
-                (let ((pid (primitive-fork)))
-                  (case pid
-                    ((0)
-                     (exec-command (list udevd)))
-                    (else
-                     ;; Wait until udevd is up and running.  This
-                     ;; appears to be needed so that the events
-                     ;; triggered below are actually handled.
-                     (wait-for-udevd)
-
-                     ;; Trigger device node creation.
-                     (system* (string-append #$udev "/bin/udevadm")
-                              "trigger" "--action=add")
-
-                     ;; Wait for things to settle down.
-                     (system* (string-append #$udev "/bin/udevadm")
-                              "settle")
-                     pid)))))
-     (stop #~(make-kill-destructor))
-
-     ;; When halting the system, 'udev' is actually killed by
-     ;; 'user-processes', i.e., before its own 'stop' method was
-     ;; called.  Thus, make sure it is not respawned.
-     (respawn? #f))))
+  (service udev-service-type
+           (udev-configuration (udev udev) (rules rules))))
+
+(define device-mapping-service-type
+  (dmd-service-type
+   (match-lambda
+     ((target open close)
+      (dmd-service
+       (provision (list (symbol-append 'device-mapping- (string->symbol target))))
+       (requirement '(udev))
+       (documentation "Map a device node using Linux's device mapper.")
+       (start #~(lambda () #$open))
+       (stop #~(lambda _ (not #$close)))
+       (respawn? #f))))))
 
 (define (device-mapping-service target open close)
   "Return a service that maps device @var{target}, a string such as
 @code{\"home\"} (meaning @code{/dev/mapper/home}).  Evaluate @var{open}, a
 gexp, to open it, and evaluate @var{close} to close it."
-  (service
-   (provision (list (symbol-append 'device-mapping- (string->symbol target))))
-   (requirement '(udev))
-   (documentation "Map a device node using Linux's device mapper.")
-   (start #~(lambda () #$open))
-   (stop #~(lambda _ (not #$close)))
-   (respawn? #f)))
+  (service device-mapping-service-type
+           (list target open close)))
+
+(define swap-service-type
+  (dmd-service-type
+   (lambda (device)
+     (define requirement
+       (if (string-prefix? "/dev/mapper/" device)
+           (list (symbol-append 'device-mapping-
+                                (string->symbol (basename device))))
+           '()))
+
+     (dmd-service
+      (provision (list (symbol-append 'swap- (string->symbol device))))
+      (requirement `(udev ,@requirement))
+      (documentation "Enable the given swap device.")
+      (start #~(lambda ()
+                 (restart-on-EINTR (swapon #$device))
+                 #t))
+      (stop #~(lambda _
+                (restart-on-EINTR (swapoff #$device))
+                #f))
+      (respawn? #f)))))
 
 (define (swap-service device)
   "Return a service that uses @var{device} as a swap device."
-  (define requirement
-    (if (string-prefix? "/dev/mapper/" device)
-        (list (symbol-append 'device-mapping-
-                             (string->symbol (basename device))))
-        '()))
-
-  (service
-   (provision (list (symbol-append 'swap- (string->symbol device))))
-   (requirement `(udev ,@requirement))
-   (documentation "Enable the given swap device.")
-   (start #~(lambda ()
-              (restart-on-EINTR (swapon #$device))
-              #t))
-   (stop #~(lambda _
-             (restart-on-EINTR (swapoff #$device))
-             #f))
-   (respawn? #f)))
+  (service swap-service-type device))
 
 (define %base-services
   ;; Convenience variable holding the basic services.
@@ -873,9 +1057,6 @@ This is the GNU operating system, welcome!\n\n")))
           ;; The LVM2 rules are needed as soon as LVM2 or the device-mapper is
           ;; used, so enable them by default.  The FUSE and ALSA rules are
           ;; less critical, but handy.
-          ;;
-          ;; XXX Keep this in sync with the 'udev-service' call in
-          ;; %desktop-services.
           (udev-service #:rules (list lvm2 fuse alsa-utils crda)))))
 
 ;;; base.scm ends here
diff --git a/gnu/services/databases.scm b/gnu/services/databases.scm
index 20f8a6977eb..8fdd222a3bf 100644
--- a/gnu/services/databases.scm
+++ b/gnu/services/databases.scm
@@ -19,12 +19,13 @@
 
 (define-module (gnu services databases)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu system shadow)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages databases)
   #:use-module (guix records)
-  #:use-module (guix store)
   #:use-module (guix gexp)
+  #:use-module (ice-9 match)
   #:export (postgresql-service))
 
 ;;; Commentary:
@@ -33,6 +34,14 @@
 ;;;
 ;;; Code:
 
+(define-record-type* <postgresql-configuration>
+  postgresql-configuration make-postgresql-configuration
+  postgresql-configuration?
+  (postgresql     postgresql-configuration-postgresql ;<package>
+                  (default postgresql))
+  (config-file    postgresql-configuration-file)
+  (data-directory postgresql-configuration-data-directory))
+
 (define %default-postgres-hba
   (plain-file "pg_hba.conf"
               "
@@ -49,6 +58,77 @@ host	all	all	::1/128 	trust"))
                    "hba_file = '" %default-postgres-hba "'\n"
                    "ident_file = '" %default-postgres-ident "\n"))
 
+(define %postgresql-accounts
+  (list (user-group (name "postgres") (system? #t))
+        (user-account
+         (name "postgres")
+         (group "postgres")
+         (system? #t)
+         (comment "PostgreSQL server user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define postgresql-activation
+  (match-lambda
+    (($ <postgresql-configuration> postgresql config-file data-directory)
+     #~(begin
+         (use-modules (guix build utils)
+                      (ice-9 match))
+
+         (let ((user (getpwnam "postgres"))
+               (initdb (string-append #$postgresql "/bin/initdb")))
+           ;; Create db state directory.
+           (mkdir-p #$data-directory)
+           (chown #$data-directory (passwd:uid user) (passwd:gid user))
+
+           ;; Drop privileges and init state directory in a new
+           ;; process.  Wait for it to finish before proceeding.
+           (match (primitive-fork)
+             (0
+              ;; Exit with a non-zero status code if an exception is thrown.
+              (dynamic-wind
+                (const #t)
+                (lambda ()
+                  (setgid (passwd:gid user))
+                  (setuid (passwd:uid user))
+                  (primitive-exit (system* initdb "-D" #$data-directory)))
+                (lambda ()
+                  (primitive-exit 1))))
+             (pid (waitpid pid))))))))
+
+(define postgresql-dmd-service
+  (match-lambda
+    (($ <postgresql-configuration> postgresql config-file data-directory)
+     (let ((start-script
+            ;; Wrapper script that switches to the 'postgres' user before
+            ;; launching daemon.
+            (program-file "start-postgres"
+                          #~(let ((user (getpwnam "postgres"))
+                                  (postgres (string-append #$postgresql
+                                                           "/bin/postgres")))
+                              (setgid (passwd:gid user))
+                              (setuid (passwd:uid user))
+                              (system* postgres
+                                       (string-append "--config-file="
+                                                      #$config-file)
+                                       "-D" #$data-directory)))))
+       (list (dmd-service
+              (provision '(postgres))
+              (documentation "Run the PostgreSQL daemon.")
+              (requirement '(user-processes loopback))
+              (start #~(make-forkexec-constructor #$start-script))
+              (stop #~(make-kill-destructor))))))))
+
+(define postgresql-service-type
+  (service-type (name 'postgresql)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          postgresql-dmd-service)
+                       (service-extension activation-service-type
+                                          postgresql-activation)
+                       (service-extension account-service-type
+                                          (const %postgresql-accounts))))))
+
 (define* (postgresql-service #:key (postgresql postgresql)
                              (config-file %default-postgres-config)
                              (data-directory "/var/lib/postgresql/data"))
@@ -56,60 +136,8 @@ host	all	all	::1/128 	trust"))
 
 The PostgreSQL daemon loads its runtime configuration from @var{config-file}
 and stores the database cluster in @var{data-directory}."
-  ;; Wrapper script that switches to the 'postgres' user before launching
-  ;; daemon.
-  (define start-script
-    (program-file "start-postgres"
-                  #~(let ((user (getpwnam "postgres"))
-                          (postgres (string-append #$postgresql
-                                                   "/bin/postgres")))
-                      (setgid (passwd:gid user))
-                      (setuid (passwd:uid user))
-                      (system* postgres
-                               (string-append "--config-file=" #$config-file)
-                               "-D" #$data-directory))))
-
-  (define activate
-    #~(begin
-        (use-modules (guix build utils)
-                     (ice-9 match))
-
-        (let ((user (getpwnam "postgres"))
-              (initdb (string-append #$postgresql "/bin/initdb")))
-          ;; Create db state directory.
-          (mkdir-p #$data-directory)
-          (chown #$data-directory (passwd:uid user) (passwd:gid user))
-
-          ;; Drop privileges and init state directory in a new
-          ;; process.  Wait for it to finish before proceeding.
-          (match (primitive-fork)
-            (0
-             ;; Exit with a non-zero status code if an exception is thrown.
-             (dynamic-wind
-               (const #t)
-               (lambda ()
-                 (setgid (passwd:gid user))
-                 (setuid (passwd:uid user))
-                 (primitive-exit (system* initdb "-D" #$data-directory)))
-               (lambda ()
-                 (primitive-exit 1))))
-            (pid (waitpid pid))))))
-
-  (service
-   (provision '(postgres))
-   (documentation "Run the PostgreSQL daemon.")
-   (requirement '(user-processes loopback))
-   (start #~(make-forkexec-constructor #$start-script))
-   (stop #~(make-kill-destructor))
-   (activate activate)
-   (user-groups (list (user-group
-                       (name "postgres")
-                       (system? #t))))
-   (user-accounts (list (user-account
-                         (name "postgres")
-                         (group "postgres")
-                         (system? #t)
-                         (comment "PostgreSQL server user")
-                         (home-directory "/var/empty")
-                         (shell
-                          #~(string-append #$shadow "/sbin/nologin")))))))
+  (service postgresql-service-type
+           (postgresql-configuration
+            (postgresql postgresql)
+            (config-file config-file)
+            (data-directory data-directory))))
diff --git a/gnu/services/dbus.scm b/gnu/services/dbus.scm
new file mode 100644
index 00000000000..e4ecd961c57
--- /dev/null
+++ b/gnu/services/dbus.scm
@@ -0,0 +1,178 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu services dbus)
+  #:use-module (gnu services)
+  #:use-module (gnu services dmd)
+  #:use-module (gnu system shadow)
+  #:use-module (gnu packages glib)
+  #:use-module (gnu packages admin)
+  #:use-module (guix gexp)
+  #:use-module (guix records)
+  #:use-module (srfi srfi-1)
+  #:use-module (ice-9 match)
+  #:export (dbus-root-service-type
+            dbus-service))
+
+;;;
+;;; D-Bus.
+;;;
+
+(define-record-type* <dbus-configuration>
+  dbus-configuration make-dbus-configuration
+  dbus-configuration?
+  (dbus      dbus-configuration-dbus              ;<package>
+             (default dbus))
+  (services  dbus-configuration-services          ;list of <package>
+             (default '())))
+
+(define (dbus-configuration-directory dbus services)
+  "Return a configuration directory for @var{dbus} that includes the
+@code{etc/dbus-1/system.d} directories of each package listed in
+@var{services}."
+  (define build
+    #~(begin
+        (use-modules (sxml simple)
+                     (srfi srfi-1))
+
+        (define (services->sxml services)
+          ;; Return the SXML 'includedir' clauses for DIRS.
+          `(busconfig
+            ,@(append-map (lambda (dir)
+                            `((includedir
+                               ,(string-append dir "/etc/dbus-1/system.d"))
+                              (servicedir         ;for '.service' files
+                               ,(string-append dir "/share/dbus-1/services"))
+                              (servicedir       ;likewise, for auto-activation
+                               ,(string-append
+                                 dir
+                                 "/share/dbus-1/system-services"))))
+                          services)))
+
+        (mkdir #$output)
+        (copy-file (string-append #$dbus "/etc/dbus-1/system.conf")
+                   (string-append #$output "/system.conf"))
+
+        ;; The default 'system.conf' has an <includedir> clause for
+        ;; 'system.d', so create it.
+        (mkdir (string-append #$output "/system.d"))
+
+        ;; 'system-local.conf' is automatically included by the default
+        ;; 'system.conf', so this is where we stuff our own things.
+        (call-with-output-file (string-append #$output "/system-local.conf")
+          (lambda (port)
+            (sxml->xml (services->sxml (list #$@services))
+                       port)))))
+
+  (computed-file "dbus-configuration" build))
+
+(define %dbus-accounts
+  ;; Accounts used by the system bus.
+  (list (user-group (name "messagebus") (system? #t))
+        (user-account
+         (name "messagebus")
+         (group "messagebus")
+         (system? #t)
+         (comment "D-Bus system bus user")
+         (home-directory "/var/run/dbus")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define (dbus-activation config)
+  "Return an activation gexp for D-Bus using @var{config}."
+  #~(begin
+      (use-modules (guix build utils))
+
+      (mkdir-p "/var/run/dbus")
+
+      (let ((user (getpwnam "messagebus")))
+        (chown "/var/run/dbus"
+               (passwd:uid user) (passwd:gid user)))
+
+      (unless (file-exists? "/etc/machine-id")
+        (format #t "creating /etc/machine-id...~%")
+        (let ((prog (string-append #$(dbus-configuration-dbus config)
+                                   "/bin/dbus-uuidgen")))
+          ;; XXX: We can't use 'system' because the initrd's
+          ;; guile system(3) only works when 'sh' is in $PATH.
+          (let ((pid (primitive-fork)))
+            (if (zero? pid)
+                (call-with-output-file "/etc/machine-id"
+                  (lambda (port)
+                    (close-fdes 1)
+                    (dup2 (port->fdes port) 1)
+                    (execl prog)))
+                (waitpid pid)))))))
+
+(define dbus-dmd-service
+  (match-lambda
+    (($ <dbus-configuration> dbus services)
+     (let ((conf (dbus-configuration-directory dbus services)))
+       (list (dmd-service
+              (documentation "Run the D-Bus system daemon.")
+              (provision '(dbus-system))
+              (requirement '(user-processes))
+              (start #~(make-forkexec-constructor
+                        (list (string-append #$dbus "/bin/dbus-daemon")
+                              "--nofork"
+                              (string-append "--config-file=" #$conf
+                                             "/system.conf"))))
+              (stop #~(make-kill-destructor))))))))
+
+(define dbus-root-service-type
+  (service-type (name 'dbus)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          dbus-dmd-service)
+                       (service-extension activation-service-type
+                                          dbus-activation)
+                       (service-extension account-service-type
+                                          (const %dbus-accounts))))
+
+                ;; Extensions consist of lists of packages (representing D-Bus
+                ;; services) that we just concatenate.
+                ;;
+                ;; FIXME: We need 'dbus-daemon-launch-helper' to be
+                ;; setuid-root for auto-activation to work.
+                (compose concatenate)
+
+                ;; The service's parameters field is extended by augmenting
+                ;; its <dbus-configuration> 'services' field.
+                (extend (lambda (config services)
+                          (dbus-configuration
+                           (inherit config)
+                           (services
+                            (append (dbus-configuration-services config)
+                                    services)))))))
+
+(define* (dbus-service #:key (dbus dbus) (services '()))
+  "Return a service that runs the \"system bus\", using @var{dbus}, with
+support for @var{services}.
+
+@uref{http://dbus.freedesktop.org/, D-Bus} is an inter-process communication
+facility.  Its system bus is used to allow system services to communicate and
+be notified of system-wide events.
+
+@var{services} must be a list of packages that provide an
+@file{etc/dbus-1/system.d} directory containing additional D-Bus configuration
+and policy files.  For example, to allow avahi-daemon to use the system bus,
+@var{services} must be equal to @code{(list avahi)}."
+  (service dbus-root-service-type
+           (dbus-configuration (dbus dbus)
+                               (services services))))
+
+;;; dbus.scm ends here
diff --git a/gnu/services/desktop.scm b/gnu/services/desktop.scm
index 346f9169502..cf1ce8269d5 100644
--- a/gnu/services/desktop.scm
+++ b/gnu/services/desktop.scm
@@ -20,7 +20,9 @@
 
 (define-module (gnu services desktop)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu services base)
+  #:use-module (gnu services dbus)
   #:use-module (gnu services avahi)
   #:use-module (gnu services xorg)
   #:use-module (gnu services networking)
@@ -31,16 +33,14 @@
   #:use-module (gnu packages freedesktop)
   #:use-module (gnu packages gnome)
   #:use-module (gnu packages avahi)
-  #:use-module (gnu packages wicd)
   #:use-module (gnu packages polkit)
-  #:use-module ((gnu packages linux)
-                #:select (lvm2 fuse alsa-utils crda))
   #:use-module (guix records)
+  #:use-module (guix packages)
   #:use-module (guix store)
   #:use-module (guix gexp)
+  #:use-module (srfi srfi-1)
   #:use-module (ice-9 match)
-  #:export (dbus-service
-            upower-service
+  #:export (upower-service
             colord-service
             geoclue-application
             %standard-geoclue-applications
@@ -64,133 +64,149 @@
 (define (bool value)
   (if value "true\n" "false\n"))
 
-
-;;;
-;;; D-Bus.
-;;;
 
-(define (dbus-configuration-directory dbus services)
-  "Return a configuration directory for @var{dbus} that includes the
-@code{etc/dbus-1/system.d} directories of each package listed in
-@var{services}."
-  (define build
-    #~(begin
-        (use-modules (sxml simple)
-                     (srfi srfi-1))
-
-        (define (services->sxml services)
-          ;; Return the SXML 'includedir' clauses for DIRS.
-          `(busconfig
-            ,@(append-map (lambda (dir)
-                            `((includedir
-                               ,(string-append dir "/etc/dbus-1/system.d"))
-                              (servicedir         ;for '.service' files
-                               ,(string-append dir "/share/dbus-1/services"))))
-                          services)))
-
-        (mkdir #$output)
-        (copy-file (string-append #$dbus "/etc/dbus-1/system.conf")
-                   (string-append #$output "/system.conf"))
-
-        ;; The default 'system.conf' has an <includedir> clause for
-        ;; 'system.d', so create it.
-        (mkdir (string-append #$output "/system.d"))
-
-        ;; 'system-local.conf' is automatically included by the default
-        ;; 'system.conf', so this is where we stuff our own things.
-        (call-with-output-file (string-append #$output "/system-local.conf")
-          (lambda (port)
-            (sxml->xml (services->sxml (list #$@services))
-                       port)))))
-
-  (computed-file "dbus-configuration" build))
-
-(define* (dbus-service services #:key (dbus dbus))
-  "Return a service that runs the \"system bus\", using @var{dbus}, with
-support for @var{services}.
-
-@uref{http://dbus.freedesktop.org/, D-Bus} is an inter-process communication
-facility.  Its system bus is used to allow system services to communicate and
-be notified of system-wide events.
-
-@var{services} must be a list of packages that provide an
-@file{etc/dbus-1/system.d} directory containing additional D-Bus configuration
-and policy files.  For example, to allow avahi-daemon to use the system bus,
-@var{services} must be equal to @code{(list avahi)}."
-  (let ((conf (dbus-configuration-directory dbus services)))
-    (service
-     (documentation "Run the D-Bus system daemon.")
-     (provision '(dbus-system))
-     (requirement '(user-processes))
-     (start #~(make-forkexec-constructor
-               (list (string-append #$dbus "/bin/dbus-daemon")
-                     "--nofork"
-                     (string-append "--config-file=" #$conf "/system.conf"))))
-     (stop #~(make-kill-destructor))
-     (user-groups (list (user-group
-                         (name "messagebus")
-                         (system? #t))))
-     (user-accounts (list (user-account
-                           (name "messagebus")
-                           (group "messagebus")
-                           (system? #t)
-                           (comment "D-Bus system bus user")
-                           (home-directory "/var/run/dbus")
-                           (shell
-                            #~(string-append #$shadow "/sbin/nologin")))))
-     (activate #~(begin
-                   (use-modules (guix build utils))
-
-                   (mkdir-p "/var/run/dbus")
-
-                   (let ((user (getpwnam "messagebus")))
-                     (chown "/var/run/dbus"
-                            (passwd:uid user) (passwd:gid user)))
-
-                   (unless (file-exists? "/etc/machine-id")
-                     (format #t "creating /etc/machine-id...~%")
-                     (let ((prog (string-append #$dbus "/bin/dbus-uuidgen")))
-                       ;; XXX: We can't use 'system' because the initrd's
-                       ;; guile system(3) only works when 'sh' is in $PATH.
-                       (let ((pid (primitive-fork)))
-                         (if (zero? pid)
-                             (call-with-output-file "/etc/machine-id"
-                               (lambda (port)
-                                 (close-fdes 1)
-                                 (dup2 (port->fdes port) 1)
-                                 (execl prog)))
-                             (waitpid pid))))))))))
+(define (wrapped-dbus-service service program variable value)
+  "Return a wrapper for @var{service}, a package containing a D-Bus service,
+where @var{program} is wrapped such that environment variable @var{variable}
+is set to @var{value} when the bus daemon launches it."
+  (define wrapper
+    (program-file (string-append (package-name service) "-program-wrapper")
+                  #~(begin
+                      (setenv #$variable #$value)
+                      (apply execl (string-append #$service "/" #$program)
+                             (string-append #$service "/" #$program)
+                             (cdr (command-line))))))
+
+  (computed-file (string-append (package-name service) "-wrapper")
+                 #~(begin
+                     (use-modules (guix build utils))
+
+                     (define service-directory
+                       "/share/dbus-1/system-services")
+
+                     (mkdir-p (dirname (string-append #$output
+                                                      service-directory)))
+                     (copy-recursively (string-append #$service
+                                                      service-directory)
+                                       (string-append #$output
+                                                      service-directory))
+                     (symlink (string-append #$service "/etc") ;for etc/dbus-1
+                              (string-append #$output "/etc"))
+
+                     (for-each (lambda (file)
+                                 (substitute* file
+                                   (("Exec[[:blank:]]*=[[:blank:]]*([[:graph:]]+)(.*)$"
+                                     _ original-program arguments)
+                                    (string-append "Exec=" #$wrapper arguments
+                                                   "\n"))))
+                               (find-files #$output "\\.service$")))
+                 #:modules '((guix build utils))))
 
 
 ;;;
 ;;; Upower D-Bus service.
 ;;;
 
-(define* (upower-configuration-file #:key watts-up-pro? poll-batteries?
-                                    ignore-lid? use-percentage-for-policy?
-                                    percentage-low percentage-critical
-                                    percentage-action time-low
-                                    time-critical time-action
-                                    critical-power-action)
-  "Return an upower-daemon configuration file."
-  (plain-file "UPower.conf"
-              (string-append
-               "[UPower]\n"
-               "EnableWattsUpPro=" (bool watts-up-pro?)
-               "NoPollBatteries=" (bool (not poll-batteries?))
-               "IgnoreLid=" (bool ignore-lid?)
-               "UsePercentageForPolicy=" (bool use-percentage-for-policy?)
-               "PercentageLow=" (number->string percentage-low) "\n"
-               "PercentageCritical=" (number->string percentage-critical) "\n"
-               "PercentageAction=" (number->string percentage-action) "\n"
-               "TimeLow=" (number->string time-low) "\n"
-               "TimeCritical=" (number->string time-critical) "\n"
-               "TimeAction=" (number->string time-action) "\n"
-               "CriticalPowerAction=" (match critical-power-action
-                                        ('hybrid-sleep "HybridSleep")
-                                        ('hibernate "Hibernate")
-                                        ('power-off "PowerOff"))
-               "\n")))
+;; TODO: Export.
+(define-record-type* <upower-configuration>
+  upower-configuration make-upower-configuration
+  upower-configuration?
+  (upower        upower-configuration-upower
+                 (default upower))
+  (watts-up-pro? upower-configuration-watts-up-pro?)
+  (poll-batteries? upower-configuration-poll-batteries?)
+  (ignore-lid? upower-configuration-ignore-lid?)
+  (use-percentage-for-policy? upower-configuration-use-percentage-for-policy?)
+  (percentage-low upower-configuration-percentage-low)
+  (percentage-critical upower-configuration-percentage-critical)
+  (percentage-action upower-configuration-percentage-action)
+  (time-low upower-configuration-time-low)
+  (time-critical upower-configuration-time-critical)
+  (time-action upower-configuration-time-action)
+  (critical-power-action upower-configuration-critical-power-action))
+
+(define* upower-configuration-file
+  ;; Return an upower-daemon configuration file.
+  (match-lambda
+    (($ <upower-configuration> upower
+        watts-up-pro? poll-batteries? ignore-lid? use-percentage-for-policy?
+        percentage-low percentage-critical percentage-action time-low
+        time-critical time-action critical-power-action)
+     (plain-file "UPower.conf"
+                 (string-append
+                  "[UPower]\n"
+                  "EnableWattsUpPro=" (bool watts-up-pro?)
+                  "NoPollBatteries=" (bool (not poll-batteries?))
+                  "IgnoreLid=" (bool ignore-lid?)
+                  "UsePercentageForPolicy=" (bool use-percentage-for-policy?)
+                  "PercentageLow=" (number->string percentage-low) "\n"
+                  "PercentageCritical=" (number->string percentage-critical) "\n"
+                  "PercentageAction=" (number->string percentage-action) "\n"
+                  "TimeLow=" (number->string time-low) "\n"
+                  "TimeCritical=" (number->string time-critical) "\n"
+                  "TimeAction=" (number->string time-action) "\n"
+                  "CriticalPowerAction=" (match critical-power-action
+                                           ('hybrid-sleep "HybridSleep")
+                                           ('hibernate "Hibernate")
+                                           ('power-off "PowerOff"))
+                  "\n")))))
+
+(define %upower-accounts                          ;XXX: useful?
+  (list (user-group (name "upower") (system? #t))
+        (user-account
+         (name "upower")
+         (group "upower")
+         (system? #t)
+         (comment "UPower daemon user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define %upower-activation
+  #~(begin
+      (use-modules (guix build utils))
+      (mkdir-p "/var/lib/upower")
+      (let ((user (getpwnam "upower")))
+        (chown "/var/lib/upower"
+               (passwd:uid user) (passwd:gid user)))))
+
+
+(define (upower-dbus-service config)
+  (list (wrapped-dbus-service (upower-configuration-upower config)
+                              "libexec/upowerd"
+                              "UPOWER_CONF_FILE_NAME"
+                              (upower-configuration-file config))))
+
+(define (upower-dmd-service config)
+  "Return a dmd service for UPower with CONFIG."
+  (let ((upower (upower-configuration-upower config))
+        (config (upower-configuration-file config)))
+    (list (dmd-service
+           (documentation "Run the UPower power and battery monitor.")
+           (provision '(upower-daemon))
+           (requirement '(dbus-system udev))
+
+           (start #~(make-forkexec-constructor
+                     (list (string-append #$upower "/libexec/upowerd"))
+                     #:environment-variables
+                     (list (string-append "UPOWER_CONF_FILE_NAME="
+                                          #$config))))
+           (stop #~(make-kill-destructor))))))
+
+(define upower-service-type
+  (service-type (name 'upower)
+                (extensions
+                 (list (service-extension dbus-root-service-type
+                                          upower-dbus-service)
+                       (service-extension dmd-root-service-type
+                                          upower-dmd-service)
+                       (service-extension account-service-type
+                                          (const %upower-accounts))
+                       (service-extension activation-service-type
+                                          (const %upower-activation))
+                       (service-extension udev-service-type
+                                          (compose
+                                           list
+                                           upower-configuration-upower))))))
 
 (define* (upower-service #:key (upower upower)
                          (watts-up-pro? #f)
@@ -208,90 +224,97 @@ and policy files.  For example, to allow avahi-daemon to use the system bus,
 @command{upowerd}}, a system-wide monitor for power consumption and battery
 levels, with the given configuration settings.  It implements the
 @code{org.freedesktop.UPower} D-Bus interface, and is notably used by GNOME."
-  (let ((config (upower-configuration-file
-                 #:watts-up-pro? watts-up-pro?
-                 #:poll-batteries? poll-batteries?
-                 #:ignore-lid? ignore-lid?
-                 #:use-percentage-for-policy? use-percentage-for-policy?
-                 #:percentage-low percentage-low
-                 #:percentage-critical percentage-critical
-                 #:percentage-action percentage-action
-                 #:time-low time-low
-                 #:time-critical time-critical
-                 #:time-action time-action
-                 #:critical-power-action critical-power-action)))
-    (service
-     (documentation "Run the UPower power and battery monitor.")
-     (provision '(upower-daemon))
-     (requirement '(dbus-system udev))
-
-     (start #~(make-forkexec-constructor
-               (list (string-append #$upower "/libexec/upowerd"))
-               #:environment-variables
-               (list (string-append "UPOWER_CONF_FILE_NAME=" #$config))))
-     (stop #~(make-kill-destructor))
-     (activate #~(begin
-                   (use-modules (guix build utils))
-                   (mkdir-p "/var/lib/upower")
-                   (let ((user (getpwnam "upower")))
-                     (chown "/var/lib/upower"
-                            (passwd:uid user) (passwd:gid user)))))
-
-     (user-groups (list (user-group
-                         (name "upower")
-                         (system? #t))))
-     (user-accounts (list (user-account
-                           (name "upower")
-                           (group "upower")
-                           (system? #t)
-                           (comment "UPower daemon user")
-                           (home-directory "/var/empty")
-                           (shell
-                            #~(string-append #$shadow "/sbin/nologin"))))))))
+  (let ((config (upower-configuration
+                 (watts-up-pro? watts-up-pro?)
+                 (poll-batteries? poll-batteries?)
+                 (ignore-lid? ignore-lid?)
+                 (use-percentage-for-policy? use-percentage-for-policy?)
+                 (percentage-low percentage-low)
+                 (percentage-critical percentage-critical)
+                 (percentage-action percentage-action)
+                 (time-low time-low)
+                 (time-critical time-critical)
+                 (time-action time-action)
+                 (critical-power-action critical-power-action))))
+    (service upower-service-type config)))
 
 
 ;;;
 ;;; Colord D-Bus service.
 ;;;
 
+(define %colord-activation
+  #~(begin
+      (use-modules (guix build utils))
+      (mkdir-p "/var/lib/colord")
+      (let ((user (getpwnam "colord")))
+        (chown "/var/lib/colord"
+               (passwd:uid user) (passwd:gid user)))))
+
+(define %colord-accounts
+  (list (user-group (name "colord") (system? #t))
+        (user-account
+         (name "colord")
+         (group "colord")
+         (system? #t)
+         (comment "colord daemon user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define (colord-dmd-service colord)
+  "Return a dmd service for COLORD."
+  ;; TODO: Remove when D-Bus activation works.
+  (list (dmd-service
+         (documentation "Run the colord color management service.")
+         (provision '(colord-daemon))
+         (requirement '(dbus-system udev))
+         (start #~(make-forkexec-constructor
+                   (list (string-append #$colord "/libexec/colord"))))
+         (stop #~(make-kill-destructor)))))
+
+(define colord-service-type
+  (service-type (name 'colord)
+                (extensions
+                 (list (service-extension account-service-type
+                                          (const %colord-accounts))
+                       (service-extension activation-service-type
+                                          (const %colord-activation))
+                       (service-extension dmd-root-service-type
+                                          colord-dmd-service)
+
+                       ;; Colord is a D-Bus service that dbus-daemon can
+                       ;; activate.
+                       (service-extension dbus-root-service-type list)
+
+                       ;; Colord provides "color device" rules for udev.
+                       (service-extension udev-service-type list)))))
+
 (define* (colord-service #:key (colord colord))
   "Return a service that runs @command{colord}, a system service with a D-Bus
 interface to manage the color profiles of input and output devices such as
 screens and scanners.  It is notably used by the GNOME Color Manager graphical
 tool.  See @uref{http://www.freedesktop.org/software/colord/, the colord web
 site} for more information."
-  (service
-   (documentation "Run the colord color management service.")
-   (provision '(colord-daemon))
-   (requirement '(dbus-system udev))
-
-   (start #~(make-forkexec-constructor
-             (list (string-append #$colord "/libexec/colord"))))
-   (stop #~(make-kill-destructor))
-   (activate #~(begin
-                 (use-modules (guix build utils))
-                 (mkdir-p "/var/lib/colord")
-                 (let ((user (getpwnam "colord")))
-                   (chown "/var/lib/colord"
-                          (passwd:uid user) (passwd:gid user)))))
-
-   (user-groups (list (user-group
-                       (name "colord")
-                       (system? #t))))
-   (user-accounts (list (user-account
-                         (name "colord")
-                         (group "colord")
-                         (system? #t)
-                         (comment "colord daemon user")
-                         (home-directory "/var/empty")
-                         (shell
-                          #~(string-append #$shadow "/sbin/nologin")))))))
+  (service colord-service-type colord))
 
 
 ;;;
 ;;; GeoClue D-Bus service.
 ;;;
 
+;; TODO: Export.
+(define-record-type* <geoclue-configuration>
+  geoclue-configuration make-geoclue-configuration
+  geoclue-configuration?
+  (geoclue geoclue-configuration-geoclue
+           (default geoclue))
+  (whitelist geoclue-configuration-whitelist)
+  (wifi-geolocation-url geoclue-configuration-wifi-geolocation-url)
+  (submit-data? geoclue-configuration-submit-data?)
+  (wifi-submission-url geoclue-configuration-wifi-submission-url)
+  (submission-nick geoclue-configuration-submission-nick)
+  (applications geoclue-configuration-applications))
+
 (define* (geoclue-application name #:key (allowed? #t) system? (users '()))
   "Configure default GeoClue access permissions for an application.  NAME is
 the Desktop ID of the application, without the .desktop part.  If ALLOWED? is
@@ -311,21 +334,67 @@ users are allowed."
         (geoclue-application "epiphany" #:system? #f)
         (geoclue-application "firefox" #:system? #f)))
 
-(define* (geoclue-configuration-file #:key whitelist wifi-geolocation-url
-                                     submit-data?
-                                     wifi-submission-url submission-nick
-                                     applications)
+(define* (geoclue-configuration-file config)
   "Return a geoclue configuration file."
   (plain-file "geoclue.conf"
               (string-append
                "[agent]\n"
-               "whitelist=" (string-join whitelist ";") "\n"
+               "whitelist="
+               (string-join (geoclue-configuration-whitelist config)
+                            ";") "\n"
                "[wifi]\n"
-               "url=" wifi-geolocation-url "\n"
-               "submit-data=" (bool submit-data?)
-               "submission-url=" wifi-submission-url "\n"
-               "submission-nick=" submission-nick "\n"
-               (string-join applications "\n"))))
+               "url=" (geoclue-configuration-wifi-geolocation-url config) "\n"
+               "submit-data=" (bool (geoclue-configuration-submit-data? config))
+               "submission-url="
+               (geoclue-configuration-wifi-submission-url config) "\n"
+               "submission-nick="
+               (geoclue-configuration-submission-nick config)
+               "\n"
+               (string-join (geoclue-configuration-applications config)
+                            "\n"))))
+
+(define (geoclue-dbus-service config)
+  (list (wrapped-dbus-service (geoclue-configuration-geoclue config)
+                              "libexec/geoclue"
+                              "GEOCLUE_CONFIG_FILE"
+                              (geoclue-configuration-file config))))
+
+(define (geoclue-dmd-service config)
+  "Return a GeoClue dmd service for CONFIG."
+  ;; TODO: Remove when D-Bus activation works.
+  (let ((geoclue (geoclue-configuration-geoclue config))
+        (config  (geoclue-configuration-file config)))
+    (list (dmd-service
+           (documentation "Run the GeoClue location service.")
+           (provision '(geoclue-daemon))
+           (requirement '(dbus-system))
+
+           (start #~(make-forkexec-constructor
+                     (list (string-append #$geoclue "/libexec/geoclue"))
+                     #:user "geoclue"
+                     #:environment-variables
+                     (list (string-append "GEOCLUE_CONFIG_FILE=" #$config))))
+           (stop #~(make-kill-destructor))))))
+
+(define %geoclue-accounts
+  (list (user-group (name "geoclue") (system? #t))
+        (user-account
+         (name "geoclue")
+         (group "geoclue")
+         (system? #t)
+         (comment "GeoClue daemon user")
+         (home-directory "/var/empty")
+         (shell "/run/current-system/profile/sbin/nologin"))))
+
+(define geoclue-service-type
+  (service-type (name 'geoclue)
+                (extensions
+                 (list (service-extension dbus-root-service-type
+                                          geoclue-dbus-service)
+                       (service-extension dmd-root-service-type
+                                          geoclue-dmd-service)
+                       (service-extension account-service-type
+                                          (const %geoclue-accounts))))))
 
 (define* (geoclue-service #:key (geoclue geoclue)
                           (whitelist '())
@@ -345,70 +414,67 @@ and Epiphany web browsers are able to ask for the user's location, and in the
 case of Icecat and Epiphany, both will ask the user for permission first.  See
 @uref{https://wiki.freedesktop.org/www/Software/GeoClue/, the geoclue web
 site} for more information."
-  (let ((config (geoclue-configuration-file
-                 #:whitelist whitelist
-                 #:wifi-geolocation-url wifi-geolocation-url
-                 #:submit-data? submit-data?
-                 #:wifi-submission-url wifi-submission-url
-                 #:submission-nick submission-nick
-                 #:applications applications)))
-    (service
-     (documentation "Run the GeoClue location service.")
-     (provision '(geoclue-daemon))
-     (requirement '(dbus-system))
-
-     (start #~(make-forkexec-constructor
-               (list (string-append #$geoclue "/libexec/geoclue"))
-               #:user "geoclue"
-               #:environment-variables
-               (list (string-append "GEOCLUE_CONFIG_FILE=" #$config))))
-     (stop #~(make-kill-destructor))
-
-     (user-groups (list (user-group
-                         (name "geoclue")
-                         (system? #t))))
-     (user-accounts (list (user-account
-                           (name "geoclue")
-                           (group "geoclue")
-                           (system? #t)
-                           (comment "GeoClue daemon user")
-                           (home-directory "/var/empty")
-                           (shell
-                            "/run/current-system/profile/sbin/nologin")))))))
+  (service geoclue-service-type
+           (geoclue-configuration
+            (geoclue geoclue)
+            (whitelist whitelist)
+            (wifi-geolocation-url wifi-geolocation-url)
+            (submit-data? submit-data?)
+            (wifi-submission-url wifi-submission-url)
+            (submission-nick submission-nick)
+            (applications applications))))
 
 
 ;;;
 ;;; Polkit privilege management service.
 ;;;
 
+(define %polkit-accounts
+  (list (user-group (name "polkitd") (system? #t))
+        (user-account
+         (name "polkitd")
+         (group "polkitd")
+         (system? #t)
+         (comment "Polkit daemon user")
+         (home-directory "/var/empty")
+         (shell "/run/current-system/profile/sbin/nologin"))))
+
+(define %polkit-pam-services
+  (list (unix-pam-service "polkit-1")))
+
+(define (polkit-dmd-service polkit)
+  "Return the <dmd-service> for POLKIT."
+  ;; TODO: Remove when D-Bus activation works.
+  (list (dmd-service
+         (documentation "Run the polkit privilege management service.")
+         (provision '(polkit-daemon))
+         (requirement '(dbus-system))
+
+         (start #~(make-forkexec-constructor
+                   (list (string-append #$polkit "/lib/polkit-1/polkitd"))))
+         (stop #~(make-kill-destructor)))))
+
+(define polkit-service-type
+  ;; TODO: Make it extensible so it can collect policy files from other
+  ;; services.
+  (service-type (name 'polkit)
+                (extensions
+                 (list (service-extension account-service-type
+                                          (const %polkit-accounts))
+                       (service-extension pam-root-service-type
+                                          (const %polkit-pam-services))
+                       (service-extension dbus-root-service-type
+                                          list)
+                       (service-extension dmd-root-service-type
+                                          polkit-dmd-service)))))
+
 (define* (polkit-service #:key (polkit polkit))
   "Return a service that runs the @command{polkit} privilege management
 service.  By querying the @command{polkit} service, a privileged system
 component can know when it should grant additional capabilities to ordinary
 users.  For example, an ordinary user can be granted the capability to suspend
 the system if the user is logged in locally."
-  (service
-   (documentation "Run the polkit privilege management service.")
-   (provision '(polkit-daemon))
-   (requirement '(dbus-system))
-
-   (start #~(make-forkexec-constructor
-             (list (string-append #$polkit "/lib/polkit-1/polkitd"))))
-   (stop #~(make-kill-destructor))
-
-   (user-groups (list (user-group
-                       (name "polkitd")
-                       (system? #t))))
-   (user-accounts (list (user-account
-                         (name "polkitd")
-                         (group "polkitd")
-                         (system? #t)
-                         (comment "Polkit daemon user")
-                         (home-directory "/var/empty")
-                         (shell
-                          "/run/current-system/profile/sbin/nologin"))))
-
-   (pam-services (list (unix-pam-service "polkit-1")))))
+  (service polkit-service-type polkit))
 
 
 ;;;
@@ -418,6 +484,8 @@ the system if the user is logged in locally."
 (define-record-type* <elogind-configuration> elogind-configuration
   make-elogind-configuration
   elogind-configuration
+  (elogind                         elogind-package
+                                   (default elogind))
   (kill-user-processes?            elogind-kill-user-processes?
                                    (default #f))
   (kill-only-users                 elogind-kill-only-users
@@ -547,67 +615,62 @@ the system if the user is logged in locally."
    ("HybridSleepState" (sleep-list elogind-hybrid-sleep-state))
    ("HybridSleepMode" (sleep-list elogind-hybrid-sleep-mode))))
 
-(define* (elogind-service #:key (elogind elogind)
-                          (config (elogind-configuration)))
+(define (elogind-dmd-service config)
+  "Return a dmd service for elogind, using @var{config}."
+  (let ((config-file (elogind-configuration-file config))
+        (elogind     (elogind-package config)))
+    (list (dmd-service
+           (documentation "Run the elogind login and seat management service.")
+           (provision '(elogind))
+           (requirement '(dbus-system))
+
+           (start #~(make-forkexec-constructor
+                     (list (string-append #$elogind "/libexec/elogind/elogind"))
+                     #:environment-variables
+                     (list (string-append "ELOGIND_CONF_FILE=" #$config-file))))
+           (stop #~(make-kill-destructor))))))
+
+(define elogind-service-type
+  (service-type (name 'elogind)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          elogind-dmd-service)
+                       (service-extension dbus-root-service-type
+                                          (compose list elogind-package))
+                       (service-extension udev-service-type
+                                          (compose list elogind-package))
+                       ;; TODO: Extend polkit(?) and PAM.
+                       ))))
+
+(define* (elogind-service #:key (config (elogind-configuration)))
   "Return a service that runs the @command{elogind} login and seat management
 service.  The @command{elogind} service integrates with PAM to allow other
 system components to know the set of logged-in users as well as their session
 types (graphical, console, remote, etc.).  It can also clean up after users
 when they log out."
-  (let ((config-file (elogind-configuration-file config)))
-    (service
-     (documentation "Run the elogind login and seat management service.")
-     (provision '(elogind))
-     (requirement '(dbus-system))
-
-     (start #~(make-forkexec-constructor
-               (list (string-append #$elogind "/libexec/elogind/elogind"))
-               #:environment-variables
-               (list (string-append "ELOGIND_CONF_FILE=" #$config-file))))
-     (stop #~(make-kill-destructor)))))
+  (service elogind-service-type config))
 
 
 ;;;
 ;;; The default set of desktop services.
 ;;;
+
 (define %desktop-services
   ;; List of services typically useful for a "desktop" use case.
   (cons* (slim-service)
 
+         ;; The D-Bus clique.
          (avahi-service)
          (wicd-service)
          (upower-service)
-         ;; FIXME: The colord, geoclue, and polkit services could all be
-         ;; bus-activated by default, so they don't run at program startup.
-         ;; However, user creation and /var/lib/colord creation happen at
-         ;; service activation time, so we currently add them to the set of
-         ;; default services.
          (colord-service)
          (geoclue-service)
          (polkit-service)
          (elogind-service)
-         (dbus-service (list avahi wicd upower colord geoclue polkit elogind))
+         (dbus-service)
 
          (ntp-service)
 
-         (map (lambda (service)
-                (cond
-                 ;; Provide an nscd ready to use nss-mdns.
-                 ((memq 'nscd (service-provision service))
-                  (nscd-service (nscd-configuration
-                                 (name-services (list nss-mdns)))))
-
-                 ;; Add more rules to udev-service.
-                 ;;
-                 ;; XXX Keep this in sync with the 'udev-service' call in
-                 ;; %base-services.  Here we intend only to add 'upower',
-                 ;; 'colord', and 'elogind'.
-                 ((memq 'udev (service-provision service))
-                  (udev-service #:rules
-                                (list lvm2 fuse alsa-utils crda
-                                      upower colord elogind)))
-
-                 (else service)))
-              %base-services)))
+         %base-services))
 
 ;;; desktop.scm ends here
diff --git a/gnu/services/dmd.scm b/gnu/services/dmd.scm
index 618df91c5e3..6020ffc8ebf 100644
--- a/gnu/services/dmd.scm
+++ b/gnu/services/dmd.scm
@@ -22,13 +22,27 @@
   #:use-module (guix gexp)
   #:use-module (guix store)
   #:use-module (guix monads)
+  #:use-module (guix records)
   #:use-module (guix derivations)                 ;imported-modules, etc.
   #:use-module (gnu services)
+  #:use-module (gnu packages admin)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
-  #:export (dmd-configuration-file))
+  #:export (dmd-root-service-type
+            %dmd-root-service
+            dmd-service-type
+
+            dmd-service
+            dmd-service?
+            dmd-service-documentation
+            dmd-service-provision
+            dmd-service-requirement
+            dmd-service-respawn?
+            dmd-service-start
+            dmd-service-stop
+            dmd-service-auto-start?))
 
 ;;; Commentary:
 ;;;
@@ -36,6 +50,68 @@
 ;;;
 ;;; Code:
 
+
+(define (dmd-boot-gexp services)
+  (mlet %store-monad ((dmd-conf (dmd-configuration-file services)))
+    (return #~(begin
+                ;; Keep track of the booted system.
+                (false-if-exception (delete-file "/run/booted-system"))
+                (symlink (readlink "/run/current-system")
+                         "/run/booted-system")
+
+                ;; Close any remaining open file descriptors to be on the safe
+                ;; side.  This must be the very last thing we do, because
+                ;; Guile has internal FDs such as 'sleep_pipe' that need to be
+                ;; alive.
+                (let loop ((fd 3))
+                  (when (< fd 1024)
+                    (false-if-exception (close-fdes fd))
+                    (loop (+ 1 fd))))
+
+                ;; Start dmd.
+                (execl (string-append #$dmd "/bin/dmd")
+                       "dmd" "--config" #$dmd-conf)))))
+
+(define dmd-root-service-type
+  (service-type
+   (name 'dmd-root)
+   ;; Extending the root dmd service (aka. PID 1) happens by concatenating the
+   ;; list of services provided by the extensions.
+   (compose concatenate)
+   (extend append)
+   (extensions (list (service-extension boot-service-type dmd-boot-gexp)))))
+
+(define %dmd-root-service
+  ;; The root dmd service, aka. PID 1.  Its parameter is a list of
+  ;; <dmd-service> objects.
+  (service dmd-root-service-type '()))
+
+(define-syntax-rule (dmd-service-type proc)
+  "Return a <service-type> denoting a simple dmd service--i.e., the type for a
+service that extends DMD-ROOT-SERVICE-TYPE and nothing else."
+  (service-type
+   (name 'some-dmd-service)
+   (extensions
+    (list (service-extension dmd-root-service-type
+                             (compose list proc))))))
+
+(define-record-type* <dmd-service>
+  dmd-service make-dmd-service
+  dmd-service?
+  (documentation service-documentation            ; string
+                 (default "[No documentation.]"))
+  (provision     service-provision)               ; list of symbols
+  (requirement   service-requirement              ; list of symbols
+                 (default '()))
+  (respawn?      service-respawn?                 ; Boolean
+                 (default #t))
+  (start         service-start)                   ; g-expression (procedure)
+  (stop          service-stop                     ; g-expression (procedure)
+                 (default #~(const #f)))
+  (auto-start?   service-auto-start?              ; Boolean
+                 (default #t)))
+
+
 (define (assert-no-duplicates services)
   "Raise an error if SERVICES provide the same dmd service more than once.
 
diff --git a/gnu/services/lirc.scm b/gnu/services/lirc.scm
index 368f2ba2937..6ae622579d7 100644
--- a/gnu/services/lirc.scm
+++ b/gnu/services/lirc.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 Alex Kost <alezost@gmail.com>
+;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -18,17 +19,65 @@
 
 (define-module (gnu services lirc)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu packages lirc)
-  #:use-module (guix store)
   #:use-module (guix gexp)
+  #:use-module (guix records)
+  #:use-module (ice-9 match)
   #:export (lirc-service))
 
 ;;; Commentary:
 ;;;
-;;; LIRC services.
+;;; LIRC service.
 ;;;
 ;;; Code:
 
+(define-record-type* <lirc-configuration>
+  lirc-configuration make-lirc-configuration
+  lirc-configuation?
+  (lirc          lirc-configuration-lirc          ;<package>
+                 (default lirc))
+  (device        lirc-configuration-device)       ;string
+  (driver        lirc-configuration-driver)       ;string
+  (config-file   lirc-configuration-file)         ;string | file-like object
+  (extra-options lirc-configuration-options       ;list of strings
+                 (default '())))
+
+(define %lirc-activation
+  #~(begin
+      (use-modules (guix build utils))
+      (mkdir-p "/var/run/lirc")))
+
+(define lirc-dmd-service
+  (match-lambda
+    (($ <lirc-configuration> lirc device driver config-file options)
+     (list (dmd-service
+            (provision '(lircd))
+            (documentation "Run the LIRC daemon.")
+            (requirement '(user-processes))
+            (start #~(make-forkexec-constructor
+                      (list (string-append #$lirc "/sbin/lircd")
+                            "--nodaemon"
+                            #$@(if device
+                                   #~("--device" #$device)
+                                   #~())
+                            #$@(if driver
+                                   #~("--driver" #$driver)
+                                   #~())
+                            #$@(if config-file
+                                   #~(#$config-file)
+                                   #~())
+                            #$@options)))
+            (stop #~(make-kill-destructor)))))))
+
+(define lirc-service-type
+  (service-type (name 'lirc)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          lirc-dmd-service)
+                       (service-extension activation-service-type
+                                          (const %lirc-activation))))))
+
 (define* (lirc-service #:key (lirc lirc)
                        device driver config-file
                        (extra-options '()))
@@ -40,26 +89,11 @@ The daemon will use specified @var{device}, @var{driver} and
 
 Finally, @var{extra-options} is a list of additional command-line options
 passed to @command{lircd}."
-  (service
-   (provision '(lircd))
-   (documentation "Run the LIRC daemon.")
-   (requirement '(user-processes))
-   (start #~(make-forkexec-constructor
-             (list (string-append #$lirc "/sbin/lircd")
-                   "--nodaemon"
-                   #$@(if device
-                          #~("--device" #$device)
-                          #~())
-                   #$@(if driver
-                          #~("--driver" #$driver)
-                          #~())
-                   #$@(if config-file
-                          #~(#$config-file)
-                          #~())
-                   #$@extra-options)))
-   (stop #~(make-kill-destructor))
-   (activate #~(begin
-                 (use-modules (guix build utils))
-                 (mkdir-p "/var/run/lirc")))))
+  (service lirc-service-type
+           (lirc-configuration
+            (lirc lirc)
+            (device device) (driver driver)
+            (config-file config-file)
+            (extra-options extra-options))))
 
 ;;; lirc.scm ends here
diff --git a/gnu/services/networking.scm b/gnu/services/networking.scm
index 50ffac57962..52a843b54b2 100644
--- a/gnu/services/networking.scm
+++ b/gnu/services/networking.scm
@@ -19,7 +19,10 @@
 
 (define-module (gnu services networking)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
+  #:use-module (gnu services dbus)
   #:use-module (gnu system shadow)
+  #:use-module (gnu system linux)                 ;PAM
   #:use-module (gnu packages admin)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages tor)
@@ -27,8 +30,9 @@
   #:use-module (gnu packages ntp)
   #:use-module (gnu packages wicd)
   #:use-module (guix gexp)
-  #:use-module (guix store)
+  #:use-module (guix records)
   #:use-module (srfi srfi-26)
+  #:use-module (ice-9 match)
   #:export (%facebook-host-aliases
             static-networking-service
             dhcp-client-service
@@ -78,6 +82,72 @@ fe80::1%lo0 www.connect.facebook.net
 fe80::1%lo0 apps.facebook.com\n")
 
 
+(define-record-type* <static-networking>
+  static-networking make-static-networking
+  static-networking?
+  (interface static-networking-interface)
+  (ip static-networking-ip)
+  (gateway static-networking-gateway)
+  (provision static-networking-provision)
+  (name-servers static-networking-name-servers)
+  (net-tools static-networking-net-tools))
+
+(define static-networking-service-type
+  (dmd-service-type
+   (match-lambda
+     (($ <static-networking> interface ip gateway provision
+                             name-servers net-tools)
+      (let ((loopback? (memq 'loopback provision)))
+
+        ;; TODO: Eventually replace 'route' with bindings for the appropriate
+        ;; ioctls.
+        (dmd-service
+
+         ;; Unless we're providing the loopback interface, wait for udev to be up
+         ;; and running so that INTERFACE is actually usable.
+         (requirement (if loopback? '() '(udev)))
+
+         (documentation
+          "Bring up the networking interface using a static IP address.")
+         (provision provision)
+         (start #~(lambda _
+                    ;; Return #t if successfully started.
+                    (let* ((addr     (inet-pton AF_INET #$ip))
+                           (sockaddr (make-socket-address AF_INET addr 0)))
+                      (configure-network-interface #$interface sockaddr
+                                                   (logior IFF_UP
+                                                           #$(if loopback?
+                                                                 #~IFF_LOOPBACK
+                                                                 0))))
+                    #$(if gateway
+                          #~(zero? (system* (string-append #$net-tools
+                                                           "/sbin/route")
+                                            "add" "-net" "default"
+                                            "gw" #$gateway))
+                          #t)
+                    #$(if (pair? name-servers)
+                          #~(call-with-output-file "/etc/resolv.conf"
+                              (lambda (port)
+                                (display
+                                 "# Generated by 'static-networking-service'.\n"
+                                 port)
+                                (for-each (lambda (server)
+                                            (format port "nameserver ~a~%"
+                                                    server))
+                                          '#$name-servers)))
+                          #t)))
+         (stop #~(lambda _
+                   ;; Return #f is successfully stopped.
+                   (let ((sock (socket AF_INET SOCK_STREAM 0)))
+                     (set-network-interface-flags sock #$interface 0)
+                     (close-port sock))
+                   (not #$(if gateway
+                              #~(system* (string-append #$net-tools
+                                                        "/sbin/route")
+                                         "del" "-net" "default")
+                              #t))))
+         (respawn? #f)))))))
+
 (define* (static-networking-service interface ip
                                     #:key
                                     gateway
@@ -87,111 +157,70 @@ fe80::1%lo0 apps.facebook.com\n")
   "Return a service that starts @var{interface} with address @var{ip}.  If
 @var{gateway} is true, it must be a string specifying the default network
 gateway."
-  (define loopback?
-    (memq 'loopback provision))
-
-  ;; TODO: Eventually replace 'route' with bindings for the appropriate
-  ;; ioctls.
-  (service
-
-   ;; Unless we're providing the loopback interface, wait for udev to be up
-   ;; and running so that INTERFACE is actually usable.
-   (requirement (if loopback? '() '(udev)))
-
-   (documentation
-    "Bring up the networking interface using a static IP address.")
-   (provision provision)
-   (start #~(lambda _
-              ;; Return #t if successfully started.
-              (let* ((addr     (inet-pton AF_INET #$ip))
-                     (sockaddr (make-socket-address AF_INET addr 0)))
-                (configure-network-interface #$interface sockaddr
-                                             (logior IFF_UP
-                                                     #$(if loopback?
-                                                           #~IFF_LOOPBACK
-                                                           0))))
-              #$(if gateway
-                    #~(zero? (system* (string-append #$net-tools
-                                                     "/sbin/route")
-                                      "add" "-net" "default"
-                                      "gw" #$gateway))
-                    #t)
-              #$(if (pair? name-servers)
-                    #~(call-with-output-file "/etc/resolv.conf"
-                        (lambda (port)
-                          (display
-                           "# Generated by 'static-networking-service'.\n"
-                           port)
-                          (for-each (lambda (server)
-                                      (format port "nameserver ~a~%"
-                                              server))
-                                    '#$name-servers)))
-                    #t)))
-   (stop #~(lambda _
-             ;; Return #f is successfully stopped.
-             (let ((sock (socket AF_INET SOCK_STREAM 0)))
-               (set-network-interface-flags sock #$interface 0)
-               (close-port sock))
-             (not #$(if gateway
-                        #~(system* (string-append #$net-tools
-                                                  "/sbin/route")
-                                   "del" "-net" "default")
-                        #t))))
-   (respawn? #f)))
+  (service static-networking-service-type
+           (static-networking (interface interface) (ip ip)
+                              (gateway gateway)
+                              (provision provision)
+                              (name-servers name-servers)
+                              (net-tools net-tools))))
+
+(define dhcp-client-service-type
+  (dmd-service-type
+   (lambda (dhcp)
+     (define dhclient
+       #~(string-append #$dhcp "/sbin/dhclient"))
+
+     (define pid-file
+       "/var/run/dhclient.pid")
+
+     (dmd-service
+      (documentation "Set up networking via DHCP.")
+      (requirement '(user-processes udev))
+
+      ;; XXX: Running with '-nw' ("no wait") avoids blocking for a minute when
+      ;; networking is unavailable, but also means that the interface is not up
+      ;; yet when 'start' completes.  To wait for the interface to be ready, one
+      ;; should instead monitor udev events.
+      (provision '(networking))
+
+      (start #~(lambda _
+                 ;; When invoked without any arguments, 'dhclient' discovers all
+                 ;; non-loopback interfaces *that are up*.  However, the relevant
+                 ;; interfaces are typically down at this point.  Thus we perform
+                 ;; our own interface discovery here.
+                 (define valid?
+                   (negate loopback-network-interface?))
+                 (define ifaces
+                   (filter valid? (all-network-interface-names)))
+
+                 ;; XXX: Make sure the interfaces are up so that 'dhclient' can
+                 ;; actually send/receive over them.
+                 (for-each set-network-interface-up ifaces)
+
+                 (false-if-exception (delete-file #$pid-file))
+                 (let ((pid (fork+exec-command
+                             (cons* #$dhclient "-nw"
+                                    "-pf" #$pid-file ifaces))))
+                   (and (zero? (cdr (waitpid pid)))
+                        (let loop ()
+                          (catch 'system-error
+                            (lambda ()
+                              (call-with-input-file #$pid-file read))
+                            (lambda args
+                              ;; 'dhclient' returned before PID-FILE was created,
+                              ;; so try again.
+                              (let ((errno (system-error-errno args)))
+                                (if (= ENOENT errno)
+                                    (begin
+                                      (sleep 1)
+                                      (loop))
+                                    (apply throw args))))))))))
+      (stop #~(make-kill-destructor))))))
 
 (define* (dhcp-client-service #:key (dhcp isc-dhcp))
   "Return a service that runs @var{dhcp}, a Dynamic Host Configuration
 Protocol (DHCP) client, on all the non-loopback network interfaces."
-
-  (define dhclient
-    #~(string-append #$dhcp "/sbin/dhclient"))
-
-  (define pid-file
-    "/var/run/dhclient.pid")
-
-  (service
-   (documentation "Set up networking via DHCP.")
-   (requirement '(user-processes udev))
-
-   ;; XXX: Running with '-nw' ("no wait") avoids blocking for a minute when
-   ;; networking is unavailable, but also means that the interface is not up
-   ;; yet when 'start' completes.  To wait for the interface to be ready, one
-   ;; should instead monitor udev events.
-   (provision '(networking))
-
-   (start #~(lambda _
-              ;; When invoked without any arguments, 'dhclient' discovers all
-              ;; non-loopback interfaces *that are up*.  However, the relevant
-              ;; interfaces are typically down at this point.  Thus we perform
-              ;; our own interface discovery here.
-              (define valid?
-                (negate loopback-network-interface?))
-              (define ifaces
-                (filter valid? (all-network-interface-names)))
-
-              ;; XXX: Make sure the interfaces are up so that 'dhclient' can
-              ;; actually send/receive over them.
-              (for-each set-network-interface-up ifaces)
-
-              (false-if-exception (delete-file #$pid-file))
-              (let ((pid (fork+exec-command
-                          (cons* #$dhclient "-nw"
-                                 "-pf" #$pid-file ifaces))))
-                (and (zero? (cdr (waitpid pid)))
-                     (let loop ()
-                       (catch 'system-error
-                         (lambda ()
-                           (call-with-input-file #$pid-file read))
-                         (lambda args
-                           ;; 'dhclient' returned before PID-FILE was created,
-                           ;; so try again.
-                           (let ((errno (system-error-errno args)))
-                             (if (= ENOENT errno)
-                                 (begin
-                                   (sleep 1)
-                                   (loop))
-                                 (apply throw args))))))))))
-   (stop #~(make-kill-destructor))))
+  (service dhcp-client-service-type dhcp))
 
 (define %ntp-servers
   ;; Default set of NTP servers.
@@ -199,19 +228,30 @@ Protocol (DHCP) client, on all the non-loopback network interfaces."
     "1.pool.ntp.org"
     "2.pool.ntp.org"))
 
-(define* (ntp-service #:key (ntp ntp)
-                      (servers %ntp-servers))
-  "Return a service that runs the daemon from @var{ntp}, the
-@uref{http://www.ntp.org, Network Time Protocol package}.  The daemon will
-keep the system clock synchronized with that of @var{servers}."
-  ;; TODO: Add authentication support.
-
-  (define config
-    (string-append "driftfile /var/run/ntp.drift\n"
-                   (string-join (map (cut string-append "server " <>)
-                                     servers)
-                                "\n")
-                   "
+
+;;;
+;;; NTP.
+;;;
+
+;; TODO: Export.
+(define-record-type* <ntp-configuration>
+  ntp-configuration make-ntp-configuration
+  ntp-configuration?
+  (ntp      ntp-configuration-ntp
+            (default ntp))
+  (servers  ntp-configuration-servers))
+
+(define ntp-dmd-service
+  (match-lambda
+    (($ <ntp-configuration> ntp servers)
+     (let ()
+       ;; TODO: Add authentication support.
+       (define config
+         (string-append "driftfile /var/run/ntp.drift\n"
+                        (string-join (map (cut string-append "server " <>)
+                                          servers)
+                                     "\n")
+                        "
 # Disable status queries as a workaround for CVE-2013-5211:
 # <http://support.ntp.org/bin/view/Main/SecurityNotice#DRDoS_Amplification_Attack_using>.
 restrict default kod nomodify notrap nopeer noquery
@@ -221,55 +261,154 @@ restrict -6 default kod nomodify notrap nopeer noquery
 restrict 127.0.0.1
 restrict -6 ::1\n"))
 
-  (let ((ntpd.conf (plain-file "ntpd.conf" config)))
-    (service
-     (provision '(ntpd))
-     (documentation "Run the Network Time Protocol (NTP) daemon.")
-     (requirement '(user-processes networking))
-     (start #~(make-forkexec-constructor
-               (list (string-append #$ntp "/bin/ntpd") "-n"
-                     "-c" #$ntpd.conf
-                     "-u" "ntpd")))
-     (stop #~(make-kill-destructor))
-     (user-accounts (list (user-account
-                           (name "ntpd")
-                           (group "nogroup")
-                           (system? #t)
-                           (comment "NTP daemon user")
-                           (home-directory "/var/empty")
-                           (shell
-                            #~(string-append #$shadow "/sbin/nologin"))))))))
+       (define ntpd.conf
+         (plain-file "ntpd.conf" config))
+
+       (list (dmd-service
+              (provision '(ntpd))
+              (documentation "Run the Network Time Protocol (NTP) daemon.")
+              (requirement '(user-processes networking))
+              (start #~(make-forkexec-constructor
+                        (list (string-append #$ntp "/bin/ntpd") "-n"
+                              "-c" #$ntpd.conf "-u" "ntpd")))
+              (stop #~(make-kill-destructor))))))))
+
+(define %ntp-accounts
+  (list (user-account
+         (name "ntpd")
+         (group "nogroup")
+         (system? #t)
+         (comment "NTP daemon user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define ntp-service-type
+  (service-type (name 'ntp)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          ntp-dmd-service)
+                       (service-extension account-service-type
+                                          (const %ntp-accounts))))))
+
+(define* (ntp-service #:key (ntp ntp)
+                      (servers %ntp-servers))
+  "Return a service that runs the daemon from @var{ntp}, the
+@uref{http://www.ntp.org, Network Time Protocol package}.  The daemon will
+keep the system clock synchronized with that of @var{servers}."
+  (service ntp-service-type
+           (ntp-configuration (ntp ntp) (servers servers))))
+
+
+;;;
+;;; Tor.
+;;;
+
+(define %tor-accounts
+  ;; User account and groups for Tor.
+  (list (user-group (name "tor") (system? #t))
+        (user-account
+         (name "tor")
+         (group "tor")
+         (system? #t)
+         (comment "Tor daemon user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define (tor-dmd-service tor)
+  "Return a <dmd-service> running TOR."
+  (let ((torrc (plain-file "torrc" "User tor\n")))
+    (list (dmd-service
+           (provision '(tor))
+
+           ;; Tor needs at least one network interface to be up, hence the
+           ;; dependency on 'loopback'.
+           (requirement '(user-processes loopback))
+
+           (start #~(make-forkexec-constructor
+                     (list (string-append #$tor "/bin/tor") "-f" #$torrc)))
+           (stop #~(make-kill-destructor))
+           (documentation "Run the Tor anonymous network overlay.")))))
+
+(define tor-service-type
+  (service-type (name 'tor)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          tor-dmd-service)
+                       (service-extension account-service-type
+                                          (const %tor-accounts))))))
 
 (define* (tor-service #:key (tor tor))
   "Return a service to run the @uref{https://torproject.org,Tor} daemon.
 
 The daemon runs with the default settings (in particular the default exit
 policy) as the @code{tor} unprivileged user."
-  (let ((torrc (plain-file "torrc" "User tor\n")))
-    (service
-     (provision '(tor))
-
-     ;; Tor needs at least one network interface to be up, hence the
-     ;; dependency on 'loopback'.
-     (requirement '(user-processes loopback))
-
-     (start #~(make-forkexec-constructor
-               (list (string-append #$tor "/bin/tor") "-f" #$torrc)))
-     (stop #~(make-kill-destructor))
-
-     (user-groups   (list (user-group
-                           (name "tor")
-                           (system? #t))))
-     (user-accounts (list (user-account
-                           (name "tor")
-                           (group "tor")
-                           (system? #t)
-                           (comment "Tor daemon user")
-                           (home-directory "/var/empty")
-                           (shell
-                            #~(string-append #$shadow "/sbin/nologin")))))
-
-     (documentation "Run the Tor anonymous network overlay."))))
+  (service tor-service-type tor))
+
+
+;;;
+;;; BitlBee.
+;;;
+
+(define-record-type* <bitlbee-configuration>
+  bitlbee-configuration make-bitlbee-configuration
+  bitlbee-configuration?
+  (bitlbee bitlbee-configuration-bitlbee
+           (default bitlbee))
+  (interface bitlbee-configuration-interface)
+  (port bitlbee-configuration-port)
+  (extra-settings bitlbee-configuration-extra-settings))
+
+(define bitlbee-dmd-service
+  (match-lambda
+    (($ <bitlbee-configuration> bitlbee interface port extra-settings)
+     (let ((conf (plain-file "bitlbee.conf"
+                             (string-append "
+  [settings]
+  User = bitlbee
+  ConfigDir = /var/lib/bitlbee
+  DaemonInterface = " interface "
+  DaemonPort = " (number->string port) "
+" extra-settings))))
+
+       (list (dmd-service
+              (provision '(bitlbee))
+              (requirement '(user-processes loopback))
+              (start #~(make-forkexec-constructor
+                        (list (string-append #$bitlbee "/sbin/bitlbee")
+                              "-n" "-F" "-u" "bitlbee" "-c" #$conf)))
+              (stop  #~(make-kill-destructor))))))))
+
+(define %bitlbee-accounts
+  ;; User group and account to run BitlBee.
+  (list (user-group (name "bitlbee") (system? #t))
+        (user-account
+         (name "bitlbee")
+         (group "bitlbee")
+         (system? #t)
+         (comment "BitlBee daemon user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define %bitlbee-activation
+  ;; Activation gexp for BitlBee.
+  #~(begin
+      (use-modules (guix build utils))
+
+      ;; This directory is used to store OTR data.
+      (mkdir-p "/var/lib/bitlbee")
+      (let ((user (getpwnam "bitlbee")))
+        (chown "/var/lib/bitlbee"
+               (passwd:uid user) (passwd:gid user)))))
+
+(define bitlbee-service-type
+  (service-type (name 'bitlbee)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          bitlbee-dmd-service)
+                       (service-extension account-service-type
+                                          (const %bitlbee-accounts))
+                       (service-extension activation-service-type
+                                          (const %bitlbee-activation))))))
 
 (define* (bitlbee-service #:key (bitlbee bitlbee)
                           (interface "127.0.0.1") (port 6667)
@@ -284,57 +423,52 @@ come from any networking interface.
 
 In addition, @var{extra-settings} specifies a string to append to the
 configuration file."
-  (let ((conf (plain-file "bitlbee.conf"
-                          (string-append "
-  [settings]
-  User = bitlbee
-  ConfigDir = /var/lib/bitlbee
-  DaemonInterface = " interface "
-  DaemonPort = " (number->string port) "
-" extra-settings))))
-    (service
-     (provision '(bitlbee))
-     (requirement '(user-processes loopback))
-     (activate #~(begin
-                   (use-modules (guix build utils))
-
-                   ;; This directory is used to store OTR data.
-                   (mkdir-p "/var/lib/bitlbee")
-                   (let ((user (getpwnam "bitlbee")))
-                     (chown "/var/lib/bitlbee"
-                            (passwd:uid user) (passwd:gid user)))))
-     (start #~(make-forkexec-constructor
-               (list (string-append #$bitlbee "/sbin/bitlbee")
-                     "-n" "-F" "-u" "bitlbee" "-c" #$conf)))
-     (stop  #~(make-kill-destructor))
-     (user-groups   (list (user-group (name "bitlbee") (system? #t))))
-     (user-accounts (list (user-account
-                           (name "bitlbee")
-                           (group "bitlbee")
-                           (system? #t)
-                           (comment "BitlBee daemon user")
-                           (home-directory "/var/empty")
-                           (shell #~(string-append #$shadow
-                                                   "/sbin/nologin"))))))))
+  (service bitlbee-service-type
+           (bitlbee-configuration
+            (bitlbee bitlbee)
+            (interface interface) (port port)
+            (extra-settings extra-settings))))
+
+
+;;;
+;;; Wicd.
+;;;
+
+(define %wicd-activation
+  ;; Activation gexp for Wicd.
+  #~(begin
+      (use-modules (guix build utils))
+
+      (mkdir-p "/etc/wicd")
+      (let ((file-name "/etc/wicd/dhclient.conf.template.default"))
+        (unless (file-exists? file-name)
+          (copy-file (string-append #$wicd file-name)
+                     file-name)))))
+
+(define (wicd-dmd-service wicd)
+  "Return a dmd service for WICD."
+  (list (dmd-service
+         (documentation "Run the Wicd network manager.")
+         (provision '(networking))
+         (requirement '(user-processes dbus-system loopback))
+         (start #~(make-forkexec-constructor
+                   (list (string-append #$wicd "/sbin/wicd")
+                         "--no-daemon")))
+         (stop #~(make-kill-destructor)))))
+
+(define wicd-service-type
+  (service-type (name 'wicd)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          wicd-dmd-service)
+                       (service-extension dbus-root-service-type
+                                          list)
+                       (service-extension activation-service-type
+                                          (const %wicd-activation))))))
 
 (define* (wicd-service #:key (wicd wicd))
   "Return a service that runs @url{https://launchpad.net/wicd,Wicd}, a network
 manager that aims to simplify wired and wireless networking."
-  (service
-   (documentation "Run the Wicd network manager.")
-   (provision '(networking))
-   (requirement '(user-processes dbus-system loopback))
-   (start #~(make-forkexec-constructor
-             (list (string-append #$wicd "/sbin/wicd")
-                   "--no-daemon")))
-   (stop #~(make-kill-destructor))
-   (activate
-    #~(begin
-        (use-modules (guix build utils))
-        (mkdir-p "/etc/wicd")
-        (let ((file-name "/etc/wicd/dhclient.conf.template.default"))
-          (unless (file-exists? file-name)
-            (copy-file (string-append #$wicd file-name)
-                       file-name)))))))
+  (service wicd-service-type wicd))
 
 ;;; networking.scm ends here
diff --git a/gnu/services/ssh.scm b/gnu/services/ssh.scm
index 3fa0976054d..d3a6cfb33ac 100644
--- a/gnu/services/ssh.scm
+++ b/gnu/services/ssh.scm
@@ -18,8 +18,9 @@
 
 (define-module (gnu services ssh)
   #:use-module (guix gexp)
-  #:use-module (guix store)
+  #:use-module (guix records)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu system linux)                 ; 'pam-service'
   #:use-module (gnu packages lsh)
   #:export (lsh-service))
@@ -30,11 +31,32 @@
 ;;;
 ;;; Code:
 
+;; TODO: Export.
+(define-record-type* <lsh-configuration>
+  lsh-configuration make-lsh-configuration
+  lsh-configuration?
+  (lsh lsh-configuration-lsh
+       (default lsh))
+  (daemonic? lsh-configuration-daemonic?)
+  (host-key lsh-configuration-host-key)
+  (interfaces lsh-configuration-interfaces)
+  (port-number lsh-configuration-port-number)
+  (allow-empty-passwords? lsh-configuration-allow-empty-passwords?)
+  (root-login? lsh-configuration-root-login?)
+  (syslog-output? lsh-configuration-syslog-output?)
+  (pid-file? lsh-configuration-pid-file?)
+  (pid-file lsh-configuration-pid-file)
+  (x11-forwarding? lsh-configuration-x11-forwarding?)
+  (tcp/ip-forwarding? lsh-configuration-tcp/ip-forwarding?)
+  (password-authentication? lsh-configuration-password-authentication?)
+  (public-key-authentication? lsh-configuration-public-key-authentication?)
+  (initialize? lsh-configuration-initialize?))
+
 (define %yarrow-seed
   "/var/spool/lsh/yarrow-seed-file")
 
-(define (activation lsh host-key)
-  "Return the gexp to activate the LSH service for HOST-KEY."
+(define (lsh-initialization lsh host-key)
+  "Return the gexp to initialize the LSH service for HOST-KEY."
   #~(begin
       (unless (file-exists? #$%yarrow-seed)
         (system* (string-append #$lsh "/bin/lsh-make-seed")
@@ -70,6 +92,88 @@
                   (waitpid keygen)
                   (waitpid write-key))))))))))
 
+(define (lsh-activation config)
+  "Return the activation gexp for CONFIG."
+  #~(begin
+      (use-modules (guix build utils))
+      (mkdir-p "/var/spool/lsh")
+      #$(if (lsh-configuration-initialize? config)
+            (lsh-initialization (lsh-configuration-lsh config)
+                                (lsh-configuration-host-key config))
+            #t)))
+
+(define (lsh-dmd-service config)
+  "Return a <dmd-service> for lsh with CONFIG."
+  (define lsh (lsh-configuration-lsh config))
+  (define pid-file (lsh-configuration-pid-file config))
+  (define pid-file? (lsh-configuration-pid-file? config))
+  (define daemonic? (lsh-configuration-daemonic? config))
+  (define interfaces (lsh-configuration-interfaces config))
+
+  (define lsh-command
+    (append
+     (cons #~(string-append #$lsh "/sbin/lshd")
+           (if daemonic?
+               (let ((syslog (if (lsh-configuration-syslog-output? config)
+                                 '()
+                                 (list "--no-syslog"))))
+                 (cons "--daemonic"
+                       (if pid-file?
+                           (cons #~(string-append "--pid-file=" #$pid-file)
+                                 syslog)
+                           (cons "--no-pid-file" syslog))))
+               (if pid-file?
+                   (list #~(string-append "--pid-file=" #$pid-file))
+                   '())))
+     (cons* #~(string-append "--host-key="
+                             #$(lsh-configuration-host-key config))
+            #~(string-append "--password-helper=" #$lsh "/sbin/lsh-pam-checkpw")
+            #~(string-append "--subsystems=sftp=" #$lsh "/sbin/sftp-server")
+            "-p" (number->string (lsh-configuration-port-number config))
+            (if (lsh-configuration-password-authentication? config)
+                "--password" "--no-password")
+            (if (lsh-configuration-public-key-authentication? config)
+                "--publickey" "--no-publickey")
+            (if (lsh-configuration-root-login? config)
+                "--root-login" "--no-root-login")
+            (if (lsh-configuration-x11-forwarding? config)
+                "--x11-forward" "--no-x11-forward")
+            (if (lsh-configuration-tcp/ip-forwarding? config)
+                "--tcpip-forward" "--no-tcpip-forward")
+            (if (null? interfaces)
+                '()
+                (list (string-append "--interfaces="
+                                     (string-join interfaces ",")))))))
+
+  (define requires
+    (if (and daemonic? (lsh-configuration-syslog-output? config))
+        '(networking syslogd)
+        '(networking)))
+
+  (list (dmd-service
+         (documentation "GNU lsh SSH server")
+         (provision '(ssh-daemon))
+         (requirement requires)
+         (start #~(make-forkexec-constructor (list #$@lsh-command)))
+         (stop  #~(make-kill-destructor)))))
+
+(define (lsh-pam-services config)
+  "Return a list of <pam-services> for lshd with CONFIG."
+  (list (unix-pam-service
+         "lshd"
+         #:allow-empty-passwords?
+         (lsh-configuration-allow-empty-passwords? config))))
+
+(define lsh-service-type
+  (service-type (name 'lsh)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          lsh-dmd-service)
+                       (service-extension pam-root-service-type
+                                          lsh-pam-services)
+                       (service-extension activation-service-type
+                                          lsh-activation)))))
+
 (define* (lsh-service #:key
                       (lsh lsh)
                       (daemonic? #t)
@@ -114,58 +218,20 @@ passwords, and @var{root-login?} specifies whether to accept log-ins as
 root.
 
 The other options should be self-descriptive."
-  (define lsh-command
-    (append
-     (cons #~(string-append #$lsh "/sbin/lshd")
-           (if daemonic?
-               (let ((syslog (if syslog-output? '()
-                                 (list "--no-syslog"))))
-                 (cons "--daemonic"
-                       (if pid-file?
-                           (cons #~(string-append "--pid-file=" #$pid-file)
-                                 syslog)
-                           (cons "--no-pid-file" syslog))))
-               (if pid-file?
-                   (list #~(string-append "--pid-file=" #$pid-file))
-                   '())))
-     (cons* #~(string-append "--host-key=" #$host-key)
-            #~(string-append "--password-helper=" #$lsh "/sbin/lsh-pam-checkpw")
-            #~(string-append "--subsystems=sftp=" #$lsh "/sbin/sftp-server")
-            "-p" (number->string port-number)
-            (if password-authentication? "--password" "--no-password")
-            (if public-key-authentication?
-                "--publickey" "--no-publickey")
-            (if root-login?
-                "--root-login" "--no-root-login")
-            (if x11-forwarding?
-                "--x11-forward" "--no-x11-forward")
-            (if tcp/ip-forwarding?
-                "--tcpip-forward" "--no-tcpip-forward")
-            (if (null? interfaces)
-                '()
-                (list (string-append "--interfaces="
-                                     (string-join interfaces ",")))))))
-
-  (define requires
-    (if (and daemonic? syslog-output?)
-        '(networking syslogd)
-        '(networking)))
-
-  (service
-   (documentation "GNU lsh SSH server")
-   (provision '(ssh-daemon))
-   (requirement requires)
-   (start #~(make-forkexec-constructor (list #$@lsh-command)))
-   (stop  #~(make-kill-destructor))
-   (pam-services
-    (list (unix-pam-service
-           "lshd"
-           #:allow-empty-passwords? allow-empty-passwords?)))
-   (activate #~(begin
-                 (use-modules (guix build utils))
-                 (mkdir-p "/var/spool/lsh")
-                 #$(if initialize?
-                       (activation lsh host-key)
-                       #t)))))
+  (service lsh-service-type
+           (lsh-configuration (lsh lsh) (daemonic? daemonic?)
+                              (host-key host-key) (interfaces interfaces)
+                              (port-number port-number)
+                              (allow-empty-passwords? allow-empty-passwords?)
+                              (root-login? root-login?)
+                              (syslog-output? syslog-output?)
+                              (pid-file? pid-file?) (pid-file pid-file)
+                              (x11-forwarding? x11-forwarding?)
+                              (tcp/ip-forwarding? tcp/ip-forwarding?)
+                              (password-authentication?
+                               password-authentication?)
+                              (public-key-authentication?
+                               public-key-authentication?)
+                              (initialize? initialize?))))
 
 ;;; ssh.scm ends here
diff --git a/gnu/services/web.scm b/gnu/services/web.scm
index c6b4153d05a..84bb30d8fd0 100644
--- a/gnu/services/web.scm
+++ b/gnu/services/web.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 David Thompson <davet@gnu.org>
+;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -18,12 +19,13 @@
 
 (define-module (gnu services web)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu system shadow)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages web)
   #:use-module (guix records)
-  #:use-module (guix store)
   #:use-module (guix gexp)
+  #:use-module (ice-9 match)
   #:export (nginx-service))
 
 ;;; Commentary:
@@ -32,6 +34,14 @@
 ;;;
 ;;; Code:
 
+(define-record-type* <nginx-configuration>
+  nginx-configuration make-nginx-configuration
+  nginx-configuration?
+  (nginx         nginx-configuration-nginx)         ;<package>
+  (log-directory nginx-configuration-log-directory) ;string
+  (run-directory nginx-configuration-run-directory) ;string
+  (file          nginx-configuration-file))         ;string | file-like
+
 (define (default-nginx-config log-directory run-directory)
   (plain-file "nginx.conf"
               (string-append
@@ -45,6 +55,58 @@
                "}\n"
                "events {}\n")))
 
+(define %nginx-accounts
+  (list (user-group (name "nginx") (system? #t))
+        (user-account
+         (name "nginx")
+         (group "nginx")
+         (system? #t)
+         (comment "nginx server user")
+         (home-directory "/var/empty")
+         (shell #~(string-append #$shadow "/sbin/nologin")))))
+
+(define nginx-activation
+  (match-lambda
+    (($ <nginx-configuration> nginx log-directory run-directory config-file)
+     #~(begin
+         (use-modules (guix build utils))
+
+         (format #t "creating nginx log directory '~a'~%" #$log-directory)
+         (mkdir-p #$log-directory)
+         (format #t "creating nginx run directory '~a'~%" #$run-directory)
+         (mkdir-p #$run-directory)
+         ;; Check configuration file syntax.
+         (system* (string-append #$nginx "/bin/nginx")
+                  "-c" #$config-file "-t")))))
+
+(define nginx-dmd-service
+  (match-lambda
+    (($ <nginx-configuration> nginx log-directory run-directory config-file)
+     (let* ((nginx-binary #~(string-append #$nginx "/sbin/nginx"))
+            (nginx-action
+             (lambda args
+               #~(lambda _
+                   (zero?
+                    (system* #$nginx-binary "-c" #$config-file #$@args))))))
+
+       ;; TODO: Add 'reload' action.
+       (list (dmd-service
+              (provision '(nginx))
+              (documentation "Run the nginx daemon.")
+              (requirement '(user-processes loopback))
+              (start (nginx-action "-p" run-directory))
+              (stop (nginx-action "-s" "stop"))))))))
+
+(define nginx-service-type
+  (service-type (name 'nginx)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          nginx-dmd-service)
+                       (service-extension activation-service-type
+                                          nginx-activation)
+                       (service-extension account-service-type
+                                          (const %nginx-accounts))))))
+
 (define* (nginx-service #:key (nginx nginx)
                         (log-directory "/var/log/nginx")
                         (run-directory "/var/run/nginx")
@@ -54,41 +116,9 @@
 
 The nginx daemon loads its runtime configuration from CONFIG-FIGLE, stores log
 files in LOG-DIRECTORY, and stores temporary runtime files in RUN-DIRECTORY."
-  (define nginx-binary
-    #~(string-append #$nginx "/sbin/nginx"))
-
-  (define (nginx-action . args)
-    #~(lambda _
-        (zero?
-         (system* #$nginx-binary "-c" #$config-file #$@args))))
-
-  (define activate
-    #~(begin
-        (use-modules (guix build utils))
-        (format #t "creating nginx log directory '~a'~%" #$log-directory)
-        (mkdir-p #$log-directory)
-        (format #t "creating nginx run directory '~a'~%" #$run-directory)
-        (mkdir-p #$run-directory)
-        ;; Check configuration file syntax.
-        (system* #$nginx-binary "-c" #$config-file "-t")))
-
-  (define nologin #~(string-append #$shadow "/sbin/nologin"))
-
-  ;; TODO: Add 'reload' action.
-  (service
-   (provision '(nginx))
-   (documentation "Run the nginx daemon.")
-   (requirement '(user-processes loopback))
-   (start (nginx-action "-p" run-directory))
-   (stop (nginx-action "-s" "stop"))
-   (activate activate)
-   (user-groups (list (user-group
-                       (name "nginx")
-                       (system? #t))))
-   (user-accounts (list (user-account
-                         (name "nginx")
-                         (group "nginx")
-                         (system? #t)
-                         (comment "nginx server user")
-                         (home-directory "/var/empty")
-                         (shell nologin))))))
+  (service nginx-service-type
+           (nginx-configuration
+            (nginx nginx)
+            (log-directory log-directory)
+            (run-directory run-directory)
+            (file config-file))))
diff --git a/gnu/services/xorg.scm b/gnu/services/xorg.scm
index 9c96aab2b8d..812cb3f7254 100644
--- a/gnu/services/xorg.scm
+++ b/gnu/services/xorg.scm
@@ -20,6 +20,7 @@
 (define-module (gnu services xorg)
   #:use-module (gnu artwork)
   #:use-module (gnu services)
+  #:use-module (gnu services dmd)
   #:use-module (gnu system linux)                 ; 'pam-service'
   #:use-module ((gnu packages base) #:select (canonical-package))
   #:use-module (gnu packages guile)
@@ -212,6 +213,95 @@ which should be passed to this script as the first argument.  If not, the
   ;; contains the actual theme files.
   "0.x")
 
+(define-record-type* <slim-configuration>
+  slim-configuration make-slim-configuration
+  slim-configuration?
+  (slim slim-configuration-slim
+        (default slim))
+  (allow-empty-passwords? slim-configuration-allow-empty-passwords?)
+  (auto-login? slim-configuration-auto-login?)
+  (default-user slim-configuration-default-user)
+  (theme slim-configuration-theme)
+  (theme-name slim-configuration-theme-name)
+  (xauth slim-configuration-xauth
+         (default xauth))
+  (dmd slim-configuration-dmd
+       (default dmd))
+  (bash slim-configuration-bash
+        (default bash))
+  (auto-login-session slim-configuration-auto-login-session)
+  (startx slim-configuration-startx))
+
+(define (slim-pam-service config)
+  "Return a PAM service for @command{slim}."
+  (list (unix-pam-service
+         "slim"
+         #:allow-empty-passwords?
+         (slim-configuration-allow-empty-passwords? config))))
+
+(define (slim-dmd-service config)
+  (define slim.cfg
+    (let ((xinitrc (xinitrc #:fallback-session
+                            (slim-configuration-auto-login-session config)))
+          (slim    (slim-configuration-slim config))
+          (xauth   (slim-configuration-xauth config))
+          (startx  (slim-configuration-startx config))
+          (dmd     (slim-configuration-dmd config))
+          (theme-name (slim-configuration-theme-name config)))
+      (mixed-text-file "slim.cfg"  "
+default_path /run/current-system/profile/bin
+default_xserver " startx "
+xserver_arguments :0 vt7
+xauth_path " xauth "/bin/xauth
+authfile /var/run/slim.auth
+
+# The login command.  '%session' is replaced by the chosen session name, one
+# of the names specified in the 'sessions' setting: 'wmaker', 'xfce', etc.
+login_cmd  exec " xinitrc " %session
+sessiondir /run/current-system/profile/share/xsessions
+session_msg session (F1 to change):
+
+halt_cmd " dmd "/sbin/halt
+reboot_cmd " dmd "/sbin/reboot\n"
+(if (slim-configuration-auto-login? config)
+    (string-append "auto_login yes\ndefault_user "
+                   (slim-configuration-default-user config) "\n")
+    "")
+(if theme-name
+    (string-append "current_theme " theme-name "\n")
+    ""))))
+
+  (define theme
+    (slim-configuration-theme config))
+
+  (list (dmd-service
+         (documentation "Xorg display server")
+         (provision '(xorg-server))
+         (requirement '(user-processes host-name udev))
+         (start
+          #~(lambda ()
+              ;; A stale lock file can prevent SLiM from starting, so remove it to
+              ;; be on the safe side.
+              (false-if-exception (delete-file "/var/run/slim.lock"))
+
+              (fork+exec-command
+               (list (string-append #$slim "/bin/slim") "-nodaemon")
+               #:environment-variables
+               (list (string-append "SLIM_CFGFILE=" #$slim.cfg)
+                     #$@(if theme
+                            (list #~(string-append "SLIM_THEMESDIR=" #$theme))
+                            #~())))))
+         (stop #~(make-kill-destructor))
+         (respawn? #t))))
+
+(define slim-service-type
+  (service-type (name 'slim)
+                (extensions
+                 (list (service-extension dmd-root-service-type
+                                          slim-dmd-service)
+                       (service-extension pam-root-service-type
+                                          slim-pam-service)))))
+
 (define* (slim-service #:key (slim slim)
                        (allow-empty-passwords? #t) auto-login?
                        (default-user "")
@@ -246,54 +336,14 @@ If @var{theme} is @code{#f}, the use the default log-in theme; otherwise
 @var{theme} must be a gexp denoting the name of a directory containing the
 theme to use.  In that case, @var{theme-name} specifies the name of the
 theme."
-
-  (define slim.cfg
-    (let ((xinitrc (xinitrc #:fallback-session auto-login-session)))
-      (mixed-text-file "slim.cfg"  "
-default_path /run/current-system/profile/bin
-default_xserver " startx "
-xserver_arguments :0 vt7
-xauth_path " xauth "/bin/xauth
-authfile /var/run/slim.auth
-
-# The login command.  '%session' is replaced by the chosen session name, one
-# of the names specified in the 'sessions' setting: 'wmaker', 'xfce', etc.
-login_cmd  exec " xinitrc " %session
-sessiondir /run/current-system/profile/share/xsessions
-session_msg session (F1 to change):
-
-halt_cmd " dmd "/sbin/halt
-reboot_cmd " dmd "/sbin/reboot\n"
-            (if auto-login?
-                (string-append "auto_login yes\ndefault_user " default-user "\n")
-                "")
-            (if theme-name
-                (string-append "current_theme " theme-name "\n")
-               ""))))
-
-  (service
-   (documentation "Xorg display server")
-   (provision '(xorg-server))
-   (requirement '(user-processes host-name udev))
-   (start
-    #~(lambda ()
-        ;; A stale lock file can prevent SLiM from starting, so remove it
-        ;; to be on the safe side.
-        (false-if-exception (delete-file "/var/run/slim.lock"))
-
-        (fork+exec-command
-         (list (string-append #$slim "/bin/slim") "-nodaemon")
-         #:environment-variables
-         (list (string-append "SLIM_CFGFILE=" #$slim.cfg)
-               #$@(if theme
-                      (list #~(string-append "SLIM_THEMESDIR=" #$theme))
-                      #~())))))
-   (stop #~(make-kill-destructor))
-   (respawn? #t)
-   (pam-services
-    ;; Tell PAM about 'slim'.
-    (list (unix-pam-service
-           "slim"
-           #:allow-empty-passwords? allow-empty-passwords?)))))
+  (service slim-service-type
+           (slim-configuration
+            (slim slim)
+            (allow-empty-passwords? allow-empty-passwords?)
+            (auto-login? auto-login?) (default-user default-user)
+            (theme theme) (theme-name theme-name)
+            (xauth xauth) (dmd dmd) (bash bash)
+            (auto-login-session auto-login-session)
+            (startx startx))))
 
 ;;; xorg.scm ends here
diff --git a/gnu/system.scm b/gnu/system.scm
index 5eaafed6ae2..b32d26bc8e6 100644
--- a/gnu/system.scm
+++ b/gnu/system.scm
@@ -87,8 +87,6 @@
             operating-system-locale-directory
             operating-system-boot-script
 
-            file-union
-
             local-host-aliases
             %setuid-programs
             %base-packages
@@ -162,41 +160,6 @@
 
 
 ;;;
-;;; Derivation.
-;;;
-
-(define* (file-union name files)
-  "Return a derivation that builds a directory containing all of FILES.  Each
-item in FILES must be a list where the first element is the file name to use
-in the new directory, and the second element is a gexp denoting the target
-file."
-  (define builder
-    #~(begin
-        (mkdir #$output)
-        (chdir #$output)
-        #$@(map (match-lambda
-                 ((target source)
-                  #~(symlink #$source #$target)))
-                files)))
-
-  (gexp->derivation name builder))
-
-(define (directory-union name things)
-  "Return a directory that is the union of THINGS."
-  (match things
-    ((one)
-     ;; Only one thing; return it.
-     (with-monad %store-monad (return one)))
-    (_
-     (gexp->derivation name
-                       #~(begin
-                           (use-modules (guix build union))
-                           (union-build #$output '#$things))
-                       #:modules '((guix build union))
-                       #:local-build? #t))))
-
-
-;;;
 ;;; Services.
 ;;;
 
@@ -244,18 +207,7 @@ as 'needed-for-boot'."
                                   (string->symbol (mapped-device-target md))))
                  (device-mappings fs))))
 
-  (map (lambda (fs)
-         (match fs
-           (($ <file-system> device title target type flags opts
-                             #f check? create?)
-            (file-system-service device target type
-                                 #:title title
-                                 #:requirements (requirements fs)
-                                 #:check? check?
-                                 #:create-mount-point? create?
-                                 #:options opts
-                                 #:flags flags))))
-       file-systems))
+  (map file-system-service file-systems))
 
 (define (mapped-device-user device file-systems)
   "Return a file system among FILE-SYSTEMS that uses DEVICE, or #f."
@@ -302,10 +254,11 @@ from the initrd."
   "Return the list of swap services for OS."
   (map swap-service (operating-system-swap-devices os)))
 
-(define (essential-services os)
+(define* (essential-services os #:key container?)
   "Return the list of essential services for OS.  These are special services
 that implement part of what's declared in OS are responsible for low-level
-bookkeeping."
+bookkeeping.  CONTAINER? determines whether to return the list of services for
+a container or that of a \"bare metal\" system."
   (define known-fs
     (map file-system-mount-point (operating-system-file-systems os)))
 
@@ -315,17 +268,36 @@ bookkeeping."
          (unmount   (user-unmount-service known-fs))
          (swaps     (swap-services os))
          (procs     (user-processes-service
-                     (map (compose first service-provision)
-                          other-fs)))
+                     (map service-parameters other-fs)))
          (host-name (host-name-service (operating-system-host-name os))))
-    (cons* host-name procs root-fs unmount
-           (append other-fs mappings swaps))))
-
-(define (operating-system-services os)
+    (cons* %boot-service
+
+           ;; %DMD-ROOT-SERVICE must come first so that the gexp that execs
+           ;; dmd comes last in the boot script (XXX).
+           %dmd-root-service %activation-service
+
+           (pam-root-service (operating-system-pam-services os))
+           (account-service (append (operating-system-accounts os)
+                                    (operating-system-groups os))
+                            (operating-system-skeletons os))
+           (operating-system-etc-service os)
+           host-name procs root-fs unmount
+           (service setuid-program-service-type
+                    (operating-system-setuid-programs os))
+           (append other-fs mappings swaps
+
+                   ;; Add the firmware service, unless we are building for a
+                   ;; container.
+                   (if container?
+                       '()
+                       (list (service firmware-service-type
+                                      (operating-system-firmware os))))))))
+
+(define* (operating-system-services os #:key container?)
   "Return all the services of OS, including \"internal\" services that do not
 explicitly appear in OS."
   (append (operating-system-user-services os)
-          (essential-services os)))
+          (essential-services os #:container? container?)))
 
 
 ;;;
@@ -388,28 +360,27 @@ This is the GNU system.  Welcome.\n")
 (define (emacs-site-file)
   "Return the Emacs 'site-start.el' file.  That file contains the necessary
 settings for 'guix.el' to work out-of-the-box."
-  (gexp->file "site-start.el"
-              #~(progn
-                 ;; Add the "normal" elisp directory to the search path;
-                 ;; guix.el may be there.
-                 (add-to-list
-                  'load-path
-                  "/run/current-system/profile/share/emacs/site-lisp")
+  (scheme-file "site-start.el"
+               #~(progn
+                  ;; Add the "normal" elisp directory to the search path;
+                  ;; guix.el may be there.
+                  (add-to-list
+                   'load-path
+                   "/run/current-system/profile/share/emacs/site-lisp")
 
-                 ;; Attempt to load guix.el.
-                 (require 'guix-init nil t)
+                  ;; Attempt to load guix.el.
+                  (require 'guix-init nil t)
 
-                 ;; Attempt to load geiser.
-                 (require 'geiser-install nil t))))
+                  ;; Attempt to load geiser.
+                  (require 'geiser-install nil t))))
 
 (define (emacs-site-directory)
   "Return the Emacs site directory, aka. /etc/emacs."
-  (mlet %store-monad ((file (emacs-site-file)))
-    (gexp->derivation "emacs"
-                      #~(begin
-                          (mkdir #$output)
-                          (chdir #$output)
-                          (symlink #$file "site-start.el")))))
+  (computed-file "emacs"
+                 #~(begin
+                     (mkdir #$output)
+                     (chdir #$output)
+                     (symlink #$(emacs-site-file) "site-start.el"))))
 
 (define (user-shells os)
   "Return the list of all the shells used by the accounts of OS.  These may be
@@ -417,49 +388,43 @@ gexps or strings."
   (map user-account-shell (operating-system-accounts os)))
 
 (define (shells-file shells)
-  "Return a derivation that builds a shell list for use as /etc/shells based
-on SHELLS.  /etc/shells is used by xterm, polkit, and other programs."
-  (gexp->derivation "shells"
-                    #~(begin
-                        (use-modules (srfi srfi-1))
-
-                        (define shells
-                          (delete-duplicates (list #$@shells)))
-
-                        (call-with-output-file #$output
-                          (lambda (port)
-                            (display "\
+  "Return a file-like object that builds a shell list for use as /etc/shells
+based on SHELLS.  /etc/shells is used by xterm, polkit, and other programs."
+  (computed-file "shells"
+                 #~(begin
+                     (use-modules (srfi srfi-1))
+
+                     (define shells
+                       (delete-duplicates (list #$@shells)))
+
+                     (call-with-output-file #$output
+                       (lambda (port)
+                         (display "\
 /bin/sh
 /run/current-system/profile/bin/sh
 /run/current-system/profile/bin/bash\n" port)
-                            (for-each (lambda (shell)
-                                        (display shell port)
-                                        (newline port))
-                                      shells))))))
-
-(define* (etc-directory #:key
-                        (locale "C") (timezone "Europe/Paris")
-                        (issue "Hello!\n")
-                        (skeletons '())
-                        (pam-services '())
-                        (profile "/run/current-system/profile")
-                        hosts-file nss (shells '())
-                        (sudoers-file (plain-file "sudoers" "")))
-  "Return a derivation that builds the static part of the /etc directory."
-  (mlet* %store-monad
-      ((pam.d ->   (pam-services->directory pam-services))
-       (login.defs (text-file "login.defs" "# Empty for now.\n"))
-       (shells     (shells-file shells))
-       (emacs      (emacs-site-directory))
-       (issue      (text-file "issue" issue))
-       (nsswitch   (text-file "nsswitch.conf"
-                              (name-service-switch->string nss)))
-
-       ;; Startup file for POSIX-compliant login shells, which set system-wide
-       ;; environment variables.
-       (profile    (text-file* "profile"  "\
-export LANG=\"" locale "\"
-export TZ=\"" timezone "\"
+                         (for-each (lambda (shell)
+                                     (display shell port)
+                                     (newline port))
+                                   shells))))))
+
+(define* (operating-system-etc-service os)
+  "Return a <service> that builds containing the static part of the /etc
+directory."
+  (let ((login.defs (plain-file "login.defs" "# Empty for now.\n"))
+
+        (shells     (shells-file (user-shells os)))
+        (emacs      (emacs-site-directory))
+        (issue      (plain-file "issue" (operating-system-issue os)))
+        (nsswitch   (plain-file "nsswitch.conf"
+                                (name-service-switch->string
+                                 (operating-system-name-service-switch os))))
+
+        ;; Startup file for POSIX-compliant login shells, which set system-wide
+        ;; environment variables.
+        (profile    (mixed-text-file "profile"  "\
+export LANG=\"" (operating-system-locale os) "\"
+export TZ=\"" (operating-system-timezone os) "\"
 export TZDIR=\"" tzdata "/share/zoneinfo\"
 
 # Tell 'modprobe' & co. where to look for modules.
@@ -516,7 +481,7 @@ then
 fi
 "))
 
-       (bashrc    (text-file "bashrc" "\
+        (bashrc    (plain-file "bashrc" "\
 # Bash-specific initialization.
 
 # The 'bash-completion' package.
@@ -526,25 +491,23 @@ then
   # completion loader that searches its own completion files as well
   # as those in ~/.guix-profile and /run/current-system/profile.
   source /run/current-system/profile/etc/profile.d/bash_completion.sh
-fi\n"))
-       (skel ->   (skeleton-directory skeletons)))
-    (file-union "etc"
-                `(("services" ,#~(string-append #$net-base "/etc/services"))
-                  ("protocols" ,#~(string-append #$net-base "/etc/protocols"))
-                  ("rpc" ,#~(string-append #$net-base "/etc/rpc"))
-                  ("emacs" ,#~#$emacs)
-                  ("pam.d" ,#~#$pam.d)
-                  ("login.defs" ,#~#$login.defs)
-                  ("issue" ,#~#$issue)
-                  ("nsswitch.conf" ,#~#$nsswitch)
-                  ("skel" ,#~#$skel)
-                  ("shells" ,#~#$shells)
-                  ("profile" ,#~#$profile)
-                  ("bashrc" ,#~#$bashrc)
-                  ("hosts" ,#~#$hosts-file)
-                  ("localtime" ,#~(string-append #$tzdata "/share/zoneinfo/"
-                                                 #$timezone))
-                  ("sudoers" ,sudoers-file)))))
+fi\n")))
+    (etc-service
+     `(("services" ,#~(string-append #$net-base "/etc/services"))
+       ("protocols" ,#~(string-append #$net-base "/etc/protocols"))
+       ("rpc" ,#~(string-append #$net-base "/etc/rpc"))
+       ("emacs" ,#~#$emacs)
+       ("login.defs" ,#~#$login.defs)
+       ("issue" ,#~#$issue)
+       ("nsswitch.conf" ,#~#$nsswitch)
+       ("shells" ,#~#$shells)
+       ("profile" ,#~#$profile)
+       ("bashrc" ,#~#$bashrc)
+       ("hosts" ,#~#$(or (operating-system-hosts-file os)
+                         (default-/etc/hosts (operating-system-host-name os))))
+       ("localtime" ,#~(string-append #$tzdata "/share/zoneinfo/"
+                                      #$(operating-system-timezone os)))
+       ("sudoers" ,(operating-system-sudoers-file os))))))
 
 (define (operating-system-profile os)
   "Return a derivation that builds the system profile of OS."
@@ -561,18 +524,14 @@ fi\n"))
    (home-directory "/root")))
 
 (define (operating-system-accounts os)
-  "Return the user accounts for OS, including an obligatory 'root' account."
-  (define users
-    ;; Make sure there's a root account.
-    (if (find (lambda (user)
-                (and=> (user-account-uid user) zero?))
-              (operating-system-users os))
-        (operating-system-users os)
-        (cons %root-account (operating-system-users os))))
-
-  (append users
-          (append-map service-user-accounts
-                      (operating-system-services os))))
+  "Return the user accounts for OS, including an obligatory 'root' account,
+and excluding accounts requested by services."
+  ;; Make sure there's a root account.
+  (if (find (lambda (user)
+              (and=> (user-account-uid user) zero?))
+            (operating-system-users os))
+      (operating-system-users os)
+      (cons %root-account (operating-system-users os))))
 
 (define (maybe-string->file file-name thing)
   "If THING is a string, return a <plain-file> with THING as its content.
@@ -607,31 +566,9 @@ use 'plain-file' instead~%")
 
 (define (operating-system-etc-directory os)
   "Return that static part of the /etc directory of OS."
-  (mlet* %store-monad
-      ((services -> (operating-system-services os))
-       (pam-services ->
-                     ;; Services known to PAM.
-                     (append (operating-system-pam-services os)
-                             (append-map service-pam-services services)))
-       (profile-drv (operating-system-profile os))
-       (skeletons   (operating-system-skeletons os))
-       (/etc/hosts  (maybe-file->monadic
-                     "hosts"
-                     (or (operating-system-hosts-file os)
-                         (default-/etc/hosts (operating-system-host-name os)))))
-       (shells ->   (user-shells os)))
-   (etc-directory #:pam-services pam-services
-                  #:skeletons skeletons
-                  #:issue (operating-system-issue os)
-                  #:locale (operating-system-locale os)
-                  #:nss (operating-system-name-service-switch os)
-                  #:timezone (operating-system-timezone os)
-                  #:hosts-file /etc/hosts
-                  #:shells shells
-                  #:sudoers-file (maybe-string->file
-                                  "sudoers"
-                                  (operating-system-sudoers-file os))
-                  #:profile profile-drv)))
+  (etc-directory
+   (fold-services (operating-system-services os)
+                  #:target-type etc-service-type)))
 
 (define %setuid-programs
   ;; Default set of setuid-root programs.
@@ -652,176 +589,23 @@ use 'plain-file' instead~%")
 root ALL=(ALL) ALL
 %wheel ALL=(ALL) ALL\n"))
 
-(define (user-group->gexp group)
-  "Turn GROUP, a <user-group> object, into a list-valued gexp suitable for
-'active-groups'."
-  #~(list #$(user-group-name group)
-          #$(user-group-password group)
-          #$(user-group-id group)
-          #$(user-group-system? group)))
-
-(define (user-account->gexp account)
-  "Turn ACCOUNT, a <user-account> object, into a list-valued gexp suitable for
-'activate-users'."
-  #~`(#$(user-account-name account)
-      #$(user-account-uid account)
-      #$(user-account-group account)
-      #$(user-account-supplementary-groups account)
-      #$(user-account-comment account)
-      #$(user-account-home-directory account)
-      ,#$(user-account-shell account)             ; this one is a gexp
-      #$(user-account-password account)
-      #$(user-account-system? account)))
-
-(define (modprobe-wrapper)
-  "Return a wrapper for the 'modprobe' command that knows where modules live.
-
-This wrapper is typically invoked by the Linux kernel ('call_modprobe', in
-kernel/kmod.c), a situation where the 'LINUX_MODULE_DIRECTORY' environment
-variable is not set---hence the need for this wrapper."
-  (let ((modprobe "/run/current-system/profile/bin/modprobe"))
-    (gexp->script "modprobe"
-                  #~(begin
-                      (setenv "LINUX_MODULE_DIRECTORY"
-                              "/run/booted-system/kernel/lib/modules")
-                      (apply execl #$modprobe
-                             (cons #$modprobe (cdr (command-line))))))))
-
 (define* (operating-system-activation-script os #:key container?)
   "Return the activation script for OS---i.e., the code that \"activates\" the
 stateful part of OS, including user accounts and groups, special directories,
 etc."
-  (define %modules
-    '((gnu build activation)
-      (gnu build linux-boot)
-      (gnu build linux-modules)
-      (gnu build file-systems)
-      (guix build utils)
-      (guix build syscalls)
-      (guix elf)))
-
-  (define (service-activations services)
-    ;; Return the activation scripts for SERVICES.
-    (let ((gexps (filter-map service-activate services)))
-      (sequence %store-monad (map (cut gexp->file "activate-service.scm" <>)
-                                  gexps))))
-
-  (mlet* %store-monad ((services -> (operating-system-services os))
-                       (actions  (service-activations services))
-                       (etc      (operating-system-etc-directory os))
-                       (modules  (imported-modules %modules))
-                       (compiled (compiled-modules %modules))
-                       (modprobe (modprobe-wrapper))
-                       (firmware (directory-union
-                                  "firmware" (operating-system-firmware os)))
-                       (accounts -> (operating-system-accounts os)))
-    (define setuid-progs
-      (operating-system-setuid-programs os))
-
-    (define user-specs
-      (map user-account->gexp accounts))
-
-    (define groups
-      (append (operating-system-groups os)
-              (append-map service-user-groups services)))
-
-    (define group-specs
-      (map user-group->gexp groups))
-
-    (assert-valid-users/groups accounts groups)
-
-    (gexp->file "activate"
-                #~(begin
-                    (eval-when (expand load eval)
-                      ;; Make sure 'use-modules' below succeeds.
-                      (set! %load-path (cons #$modules %load-path))
-                      (set! %load-compiled-path
-                            (cons #$compiled %load-compiled-path)))
-
-                    (use-modules (gnu build activation))
-
-                    ;; Make sure /bin/sh is valid and current.
-                    (activate-/bin/sh
-                     (string-append #$(canonical-package bash)
-                                    "/bin/sh"))
-
-                    ;; Populate /etc.
-                    (activate-etc #$etc)
-
-                    ;; Add users and user groups.
-                    (setenv "PATH"
-                            (string-append #$(@ (gnu packages admin) shadow)
-                                           "/sbin"))
-                    (activate-users+groups (list #$@user-specs)
-                                           (list #$@group-specs))
-
-                    ;; Activate setuid programs.
-                    (activate-setuid-programs (list #$@setuid-progs))
-
-                    ;; Tell the kernel to use our 'modprobe' command.
-                    (activate-modprobe #$modprobe)
-
-                    ;; Tell the kernel where firmware is, unless we are
-                    ;; activating a container.
-                    #$@(if container?
-                           #~()
-                           ;; Tell the kernel where firmware is.
-                           #~((activate-firmware
-                               (string-append #$firmware "/lib/firmware"))
-                              ;; Let users debug their own processes!
-                              (activate-ptrace-attach)))
-
-                    ;; Run the services' activation snippets.
-                    ;; TODO: Use 'load-compiled'.
-                    (for-each primitive-load '#$actions)
-
-                    ;; Set up /run/current-system.
-                    (activate-current-system)))))
+  (let* ((services   (operating-system-services os #:container? container?))
+         (activation (fold-services services
+                                    #:target-type activation-service-type)))
+    (activation-service->script activation)))
 
 (define* (operating-system-boot-script os #:key container?)
   "Return the boot script for OS---i.e., the code started by the initrd once
 we're running in the final root.  When CONTAINER? is true, skip all
 hardware-related operations as necessary when booting a Linux container."
-  (mlet* %store-monad ((services -> (operating-system-services os))
-                       (activate (operating-system-activation-script os))
-                       (dmd-conf (dmd-configuration-file services)))
-    (gexp->file "boot"
-                #~(begin
-                    (use-modules (guix build utils))
-
-                    ;; Clean out /tmp and /var/run.
-                    ;;
-                    ;; XXX This needs to happen before service activations, so
-                    ;; it has to be here, but this also implicitly assumes
-                    ;; that /tmp and /var/run are on the root partition.
-                    (false-if-exception (delete-file-recursively "/tmp"))
-                    (false-if-exception (delete-file-recursively "/var/run"))
-                    (false-if-exception (mkdir "/tmp"))
-                    (false-if-exception (chmod "/tmp" #o1777))
-                    (false-if-exception (mkdir "/var/run"))
-                    (false-if-exception (chmod "/var/run" #o755))
-
-                    ;; Activate the system.
-                    ;; TODO: Use 'load-compiled'.
-                    (primitive-load #$activate)
-
-                    ;; Keep track of the booted system.
-                    (false-if-exception (delete-file "/run/booted-system"))
-                    (symlink (readlink "/run/current-system")
-                             "/run/booted-system")
-
-                    ;; Close any remaining open file descriptors to be on the
-                    ;; safe side.  This must be the very last thing we do,
-                    ;; because Guile has internal FDs such as 'sleep_pipe'
-                    ;; that need to be alive.
-                    (let loop ((fd 3))
-                      (when (< fd 1024)
-                        (false-if-exception (close-fdes fd))
-                        (loop (+ 1 fd))))
-
-                    ;; Start dmd.
-                    (execl (string-append #$dmd "/bin/dmd")
-                           "dmd" "--config" #$dmd-conf)))))
+  (let* ((services (operating-system-services os #:container? container?))
+         (boot     (fold-services services)))
+    ;; BOOT is the script as a monadic value.
+    (service-parameters boot)))
 
 (define (operating-system-root-file-system os)
   "Return the root file system of OS."
@@ -908,19 +692,20 @@ this file is the reconstruction of GRUB menu entries for old configurations."
   "Return a derivation that builds OS."
   (mlet* %store-monad
       ((profile     (operating-system-profile os))
-       (etc         (operating-system-etc-directory os))
+       (etc ->      (operating-system-etc-directory os))
        (boot        (operating-system-boot-script os))
        (kernel  ->  (operating-system-kernel os))
        (initrd      (operating-system-initrd-file os))
        (locale      (operating-system-locale-directory os))
        (params      (operating-system-parameters-file os)))
-    (file-union "system"
-                `(("boot" ,#~#$boot)
-                  ("kernel" ,#~#$kernel)
-                  ("parameters" ,#~#$params)
-                  ("initrd" ,initrd)
-                  ("profile" ,#~#$profile)
-                  ("locale" ,#~#$locale)          ;used by libc
-                  ("etc" ,#~#$etc)))))
+    (lower-object
+     (file-union "system"
+                 `(("boot" ,#~#$boot)
+                   ("kernel" ,#~#$kernel)
+                   ("parameters" ,#~#$params)
+                   ("initrd" ,initrd)
+                   ("profile" ,#~#$profile)
+                   ("locale" ,#~#$locale)         ;used by libc
+                   ("etc" ,#~#$etc))))))
 
 ;;; system.scm ends here
diff --git a/gnu/system/install.scm b/gnu/system/install.scm
index 560d64b5d4f..a91c5c3533f 100644
--- a/gnu/system/install.scm
+++ b/gnu/system/install.scm
@@ -24,6 +24,7 @@
   #:use-module (guix monads)
   #:use-module ((guix store) #:select (%store-prefix))
   #:use-module (guix profiles)
+  #:use-module (gnu services dmd)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages bash)
   #:use-module (gnu packages linux)
@@ -159,68 +160,74 @@ current store is on a RAM disk."
                (mount "/.rw-store" #$(%store-prefix) "" MS_MOVE)
                (rmdir "/.rw-store"))))))
 
+(define cow-store-service-type
+  (dmd-service-type
+   (lambda _
+     (dmd-service
+      (requirement '(root-file-system user-processes))
+      (provision '(cow-store))
+      (documentation
+       "Make the store copy-on-write, with writes going to \
+the given target.")
+
+      ;; This is meant to be explicitly started by the user.
+      (auto-start? #f)
+
+      (start #~(case-lambda
+                 ((target)
+                  #$(make-cow-store #~target)
+                  target)
+                 (else
+                  ;; Do nothing, and mark the service as stopped.
+                  #f)))
+      (stop #~(lambda (target)
+                ;; Delete the temporary directory, but leave everything
+                ;; mounted as there may still be processes using it since
+                ;; 'user-processes' doesn't depend on us.  The 'user-unmount'
+                ;; service will unmount TARGET eventually.
+                (delete-file-recursively
+                 (string-append target #$%backing-directory))))))))
+
 (define (cow-store-service)
   "Return a service that makes the store copy-on-write, such that writes go to
 the user's target storage device rather than on the RAM disk."
   ;; See <http://bugs.gnu.org/18061> for the initial report.
-  (service
-   (requirement '(root-file-system user-processes))
-   (provision '(cow-store))
-   (documentation
-    "Make the store copy-on-write, with writes going to \
-the given target.")
-
-   ;; This is meant to be explicitly started by the user.
-   (auto-start? #f)
-
-   (start #~(case-lambda
-              ((target)
-               #$(make-cow-store #~target)
-               target)
-              (else
-               ;; Do nothing, and mark the service as stopped.
-               #f)))
-   (stop #~(lambda (target)
-             ;; Delete the temporary directory, but leave everything
-             ;; mounted as there may still be processes using it
-             ;; since 'user-processes' doesn't depend on us.  The
-             ;; 'user-unmount' service will unmount TARGET
-             ;; eventually.
-             (delete-file-recursively
-              (string-append target #$%backing-directory))))))
-
-(define (configuration-template-service)
-  "Return a dummy service whose purpose is to install an operating system
-configuration template file in the installation system."
-
-  (define search
-    (cut search-path %load-path <>))
-  (define templates
-    (map (match-lambda
-           ((file '-> target)
-            (list (local-file (search file))
-                  (string-append "/etc/configuration/" target))))
-         '(("gnu/system/examples/bare-bones.tmpl" -> "bare-bones.scm")
-           ("gnu/system/examples/desktop.tmpl" -> "desktop.scm"))))
-
-  (service
-   (requirement '(root-file-system))
-   (provision '(os-config-template))
-   (documentation
-    "This dummy service installs an OS configuration template.")
-   (start #~(const #t))
-   (stop  #~(const #f))
-   (activate
-    #~(begin
-        (use-modules (ice-9 match)
-                     (guix build utils))
+  (service cow-store-service-type 'mooooh!))
+
+
+(define (/etc/configuration-files _)
+  "Return a list of tuples representing configuration templates to add to
+/etc."
+  (define (file f)
+    (local-file (search-path %load-path
+                             (string-append "gnu/system/examples/" f))))
+
+  (define directory
+    (computed-file "configuration-templates"
+                   #~(begin
+                       (mkdir #$output)
+                       (for-each (lambda (file target)
+                                   (copy-file file
+                                              (string-append #$output "/"
+                                                             target)))
+                                 '(#$(file "bare-bones.tmpl")
+                                   #$(file "desktop.tmpl"))
+                                 '("bare-bones.scm"
+                                   "desktop.scm"))
+                       #t)
+                   #:modules '((guix build utils))))
+
+  `(("configuration" ,directory)))
+
+(define configuration-template-service-type
+  (service-type (name 'configuration-template)
+                (extensions
+                 (list (service-extension etc-service-type
+                                          /etc/configuration-files)))))
+
+(define %configuration-template-service
+  (service configuration-template-service-type #t))
 
-        (mkdir-p "/etc/configuration")
-        (for-each (match-lambda
-                    ((file target)
-                     (unless (file-exists? target)
-                       (copy-file file target))))
-                  '#$templates)))))
 
 (define %nscd-minimal-caches
   ;; Minimal in-memory caching policy for nscd.
@@ -262,7 +269,7 @@ You have been warned.  Thanks for being so brave.
                              (login-program (log-to-info))))
 
           ;; Documentation add-on.
-          (configuration-template-service)
+          %configuration-template-service
 
           ;; A bunch of 'root' ttys.
           (normal-tty "tty3")
@@ -276,7 +283,7 @@ You have been warned.  Thanks for being so brave.
           ;; The build daemon.  Register the hydra.gnu.org key as trusted.
           ;; This allows the installation process to use substitutes by
           ;; default.
-          (guix-service #:authorize-hydra-key? #t)
+          (guix-service (guix-configuration (authorize-key? #t)))
 
           ;; Start udev so that useful device nodes are available.
           ;; Use device-mapper rules for cryptsetup & co; enable the CRDA for
diff --git a/gnu/system/linux.scm b/gnu/system/linux.scm
index 10e72e905a5..cd14bc97be0 100644
--- a/gnu/system/linux.scm
+++ b/gnu/system/linux.scm
@@ -20,6 +20,7 @@
   #:use-module (guix records)
   #:use-module (guix derivations)
   #:use-module (guix gexp)
+  #:use-module (gnu services)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
@@ -28,7 +29,10 @@
             pam-entry
             pam-services->directory
             unix-pam-service
-            base-pam-services))
+            base-pam-services
+
+            pam-root-service-type
+            pam-root-service))
 
 ;;; Commentary:
 ;;;
@@ -98,8 +102,8 @@ dumped in /etc/pam.d/NAME, where NAME is the name of SERVICE."
 
           (mkdir #$output)
           (for-each (match-lambda
-                     ((name file)
-                      (symlink file (string-append #$output "/" name))))
+                      ((name file)
+                       (symlink file (string-append #$output "/" name))))
 
                     ;; Since <pam-service> objects cannot be compared with
                     ;; 'equal?' since they contain gexps, which contain
@@ -188,4 +192,24 @@ authenticate to run COMMAND."
                '("useradd" "userdel" "usermod"
                  "groupadd" "groupdel" "groupmod"))))
 
+
+;;;
+;;; PAM root service.
+;;;
+
+(define (/etc-entry services)
+  `(("pam.d" ,(pam-services->directory services))))
+
+(define pam-root-service-type
+  (service-type (name 'pam)
+                (extensions (list (service-extension etc-service-type
+                                                     /etc-entry)))
+                (compose concatenate)
+                (extend append)))
+
+(define (pam-root-service base)
+  "The \"root\" PAM service, which collects <pam-service> instance and turns
+them into a /etc/pam.d directory, including the <pam-service> listed in BASE."
+  (service pam-root-service-type base))
+
 ;;; linux.scm ends here
diff --git a/gnu/system/shadow.scm b/gnu/system/shadow.scm
index ddd5f668743..3f49c1fc9f0 100644
--- a/gnu/system/shadow.scm
+++ b/gnu/system/shadow.scm
@@ -22,12 +22,14 @@
   #:use-module (guix store)
   #:use-module (guix sets)
   #:use-module (guix ui)
+  #:use-module (gnu services)
   #:use-module ((gnu system file-systems)
                 #:select (%tty-gid))
   #:use-module ((gnu packages admin)
                 #:select (shadow))
   #:use-module (gnu packages bash)
   #:use-module (gnu packages guile-wm)
+  #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
@@ -54,7 +56,9 @@
             skeleton-directory
             %base-groups
             %base-user-accounts
-            assert-valid-users/groups))
+
+            account-service-type
+            account-service))
 
 ;;; Commentary:
 ;;;
@@ -87,31 +91,32 @@
   (system?        user-group-system?              ; Boolean
                   (default #f)))
 
+
 (define %base-groups
   ;; Default set of groups.
   (let-syntax ((system-group (syntax-rules ()
                                ((_ args ...)
                                 (user-group (system? #t) args ...)))))
     (list (system-group (name "root") (id 0))
-          (system-group (name "wheel"))              ; root-like users
-          (system-group (name "users"))              ; normal users
-          (system-group (name "nogroup"))            ; for daemons etc.
+          (system-group (name "wheel"))           ; root-like users
+          (system-group (name "users"))           ; normal users
+          (system-group (name "nogroup"))         ; for daemons etc.
 
           ;; The following groups are conventionally used by things like udev to
           ;; control access to hardware devices.
           (system-group (name "tty") (id %tty-gid))
           (system-group (name "dialout"))
           (system-group (name "kmem"))
-          (system-group (name "input"))              ; input devices, from udev
+          (system-group (name "input"))           ; input devices, from udev
           (system-group (name "video"))
           (system-group (name "audio"))
-          (system-group (name "netdev"))             ; used in avahi-dbus.conf
+          (system-group (name "netdev"))          ; used in avahi-dbus.conf
           (system-group (name "lp"))
           (system-group (name "disk"))
           (system-group (name "floppy"))
           (system-group (name "cdrom"))
           (system-group (name "tape"))
-          (system-group (name "kvm")))))             ; for /dev/kvm
+          (system-group (name "kvm")))))          ; for /dev/kvm
 
 (define %base-user-accounts
   ;; List of standard user accounts.  Note that "root" is a special case, so
@@ -224,4 +229,81 @@ of user '~a' is undeclared")
                           (user-account-supplementary-groups user)))
               users)))
 
+
+;;;
+;;; Service.
+;;;
+
+(define (user-group->gexp group)
+  "Turn GROUP, a <user-group> object, into a list-valued gexp suitable for
+'active-groups'."
+  #~(list #$(user-group-name group)
+          #$(user-group-password group)
+          #$(user-group-id group)
+          #$(user-group-system? group)))
+
+(define (user-account->gexp account)
+  "Turn ACCOUNT, a <user-account> object, into a list-valued gexp suitable for
+'activate-users'."
+  #~`(#$(user-account-name account)
+      #$(user-account-uid account)
+      #$(user-account-group account)
+      #$(user-account-supplementary-groups account)
+      #$(user-account-comment account)
+      #$(user-account-home-directory account)
+      ,#$(user-account-shell account)             ; this one is a gexp
+      #$(user-account-password account)
+      #$(user-account-system? account)))
+
+(define (account-activation accounts+groups)
+  "Return a gexp that activates ACCOUNTS+GROUPS, a list of <user-account> and
+<user-group> objects.  Raise an error if a user account refers to a undefined
+group."
+  (define accounts
+    (filter user-account? accounts+groups))
+
+  (define user-specs
+    (map user-account->gexp accounts))
+
+  (define groups
+    (filter user-group? accounts+groups))
+
+  (define group-specs
+    (map user-group->gexp groups))
+
+  (assert-valid-users/groups accounts groups)
+
+  ;; Add users and user groups.
+  #~(begin
+      (setenv "PATH"
+              (string-append #$(@ (gnu packages admin) shadow) "/sbin"))
+      (activate-users+groups (list #$@user-specs)
+                             (list #$@group-specs))))
+
+(define (etc-skel arguments)
+  "Filter out among ARGUMENTS things corresponding to skeletons, and return
+the /etc/skel directory for those."
+  (let ((skels (filter pair? arguments)))
+    `(("skel" ,(skeleton-directory skels)))))
+
+(define account-service-type
+  (service-type (name 'account)
+
+                ;; Concatenate <user-account>, <user-group>, and skeleton
+                ;; lists.
+                (compose concatenate)
+                (extend append)
+
+                (extensions
+                 (list (service-extension activation-service-type
+                                          account-activation)
+                       (service-extension etc-service-type
+                                          etc-skel)))))
+
+(define (account-service accounts+groups skeletons)
+  "Return a <service> that takes care of user accounts and user groups, with
+ACCOUNTS+GROUPS as its initial list of accounts and groups."
+  (service account-service-type
+           (append skeletons accounts+groups)))
+
 ;;; shadow.scm ends here
diff --git a/po/guix/POTFILES.in b/po/guix/POTFILES.in
index c0f169eca4c..af46dac0e06 100644
--- a/po/guix/POTFILES.in
+++ b/po/guix/POTFILES.in
@@ -1,6 +1,7 @@
 # List of source files which contain translatable strings.
 # This should be source files of the various tools, and not package modules.
 gnu/packages.scm
+gnu/services.scm
 gnu/system.scm
 gnu/services/dmd.scm
 gnu/system/shadow.scm
diff --git a/tests/services.scm b/tests/services.scm
new file mode 100644
index 00000000000..b4e2cb0b305
--- /dev/null
+++ b/tests/services.scm
@@ -0,0 +1,91 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-services)
+  #:use-module (gnu services)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-64))
+
+(test-begin "services")
+
+(test-equal "fold-services"
+  ;; Make sure 'fold-services' returns the right result.  The numbers come
+  ;; from services of type T3; 'xyz 60' comes from the service of type T2,
+  ;; where 60 = 15 × 4 = (1 + 2 + 3 + 4 + 5) × 4.
+  '(initial-value 5 4 3 2 1 xyz 60)
+  (let* ((t1 (service-type (name 't1) (extensions '())
+                           (compose concatenate)
+                           (extend cons)))
+         (t2 (service-type (name 't2)
+                           (extensions
+                            (list (service-extension t1
+                                                     (cut list 'xyz <>))))
+                           (compose (cut reduce + 0 <>))
+                           (extend *)))
+         (t3 (service-type (name 't3)
+                           (extensions
+                            (list (service-extension t2 identity)
+                                  (service-extension t1 list)))))
+         (r  (fold-services (cons* (service t1 'initial-value)
+                                   (service t2 4)
+                                   (map (lambda (x)
+                                          (service t3 x))
+                                        (iota 5 1)))
+                            #:target-type t1)))
+    (and (eq? (service-kind r) t1)
+         (service-parameters r))))
+
+(test-assert "fold-services, ambiguity"
+  (let* ((t1 (service-type (name 't1) (extensions '())
+                           (compose concatenate)
+                           (extend cons)))
+         (t2 (service-type (name 't2)
+                           (extensions
+                            (list (service-extension t1 list)))))
+         (s  (service t2 42)))
+    (guard (c ((ambiguous-target-service-error? c)
+               (and (eq? (ambiguous-target-service-error-target-type c)
+                         t1)
+                    (eq? (ambiguous-target-service-error-service c)
+                         s))))
+      (fold-services (list (service t1 'first)
+                           (service t1 'second)
+                           s)
+                     #:target-type t1)
+      #f)))
+
+(test-assert "fold-services, missing target"
+  (let* ((t1 (service-type (name 't1) (extensions '())))
+         (t2 (service-type (name 't2)
+                           (extensions
+                            (list (service-extension t1 list)))))
+         (s  (service t2 42)))
+    (guard (c ((missing-target-service-error? c)
+               (and (eq? (missing-target-service-error-target-type c)
+                         t1)
+                    (eq? (missing-target-service-error-service c)
+                         s))))
+      (fold-services (list s) #:target-type t1)
+      #f)))
+
+(test-end)
+
+
+(exit (= (test-runner-fail-count (test-runner-current)) 0))