Currently the service cannot be restarted, because the gnu store mount makes
it read-only. So fix this by removing the mount when starting the service.

"-" to accept failures, in case the command doesn't finish successfully,
chances are, the store can be mounted as RW, so continue.
"+" to run as root

Fixes: #4744

* etc/guix-daemon.service.in
(Service)<ExecStartPre>: Stop gnu-store.mount
(Service)<ExecStartPost>: Start gnu-store.mount

Change-Id: I296f5d8805497f8a7364b68d627eb6d4fc05dbff

This mitigates a race condition described in #576. The 'Type=exec'
option ensures that systemd only starts follow-up units after the
guix-daemon binary has started. By then, the mount points are collected
in a private namespace and will not be affected. Without this option,
'gnu-store.mount' could win the race and remount everything read-only
before guix-daemon has acquired a read-write view.

Fixes #2270

* etc/guix-daemon.service.in: Mitigate mount race condition

Change-Id: I5d28ebc38b0c10e6d2aa8e65353757ef13d5bad3
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

This fixes issue for rootless guix daemon where store being remounted
read-only by gnu-store.mount is propagated to the guix daemon making
guix daemon not able to modify it.

* etc/guix-daemon.service.in: Disable host filesystem mount propagation.

Change-Id: Ib1abc387ee15d2b04d6f70c121244943cd0ad8c6
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Modified-by: Ludovic Courtès <ludo@gnu.org>

* etc/guix-daemon.service.in (ExecStart): Remove ‘--build-users-group’.
(Environment): Add ‘GUIX_STATE_DIRECTORY’.
(Before, User, AmbientCapabilities, PrivateMounts, BindPaths): New fields.
* etc/gnu-store.mount.in (Before): Remove.
(WantedBy): Change to ‘multi-user.target’.

Change-Id: Id826b8ab535844b6024d777f6bd15fd49db6d65e

Having substitute URLs explicitly listed in the service startup file
makes it clearer what should be modified to permanently change the list
of substitute URLs.

* config-daemon.ac: Rename ‘guix_substitute_urls’ to
‘GUIX_SUBSTITUTE_URLS’ and substitute it.
* nix/local.mk (etc/guix-%.service, etc/init.d/guix-daemon)
(etc/guix-%.conf): Substitute it.
* etc/guix-daemon.conf.in, etc/guix-daemon.service.in,
etc/init.d/guix-daemon.in: Add an explicit ‘--substitute-urls’ option.

Change-Id: Ie491b7fab5c42e54dca582801c03805a85de2bf9

The "syslog" method has been deprecated for years, and issues a warning:

  Standard output type syslog is obsolete, automatically updating to
  journal. Please update your unit file, and consider removing the setting
  altogether.

Fixes: #48323

* etc/guix-daemon.service.in (StandardOutput): Use "journal"
(StandardError): Likewise.
* etc/guix-publish.service.in (StandardOutput): Likewise.
(StandardError): Likewise.

* etc/guix-daemon.service.in (RemainAfterExit): Don't.
* etc/guix-publish.service.in (RemainAfterExit): Likewise don't.

* etc/guix-daemon.service.in (Restart): ‘Always’ do.
* etc/guix-publish.service.in (Restart): Likewise.

* etc/guix-daemon.service.in (OOMPolicy): Continue.

Also ensure prompt_yes_no always print the message with a trailing space,
which is more pleasing to the eye.

* etc/guix-daemon.conf.in <--discover=no>: New guix-daemon option.
* etc/guix-daemon.service.in: Likewise.
* etc/init.d/guix-daemon.in: Likewise.
* etc/openrc/guix-daemon.in: Likewise.
* etc/guix-install.sh (configure_substitute_discovery): New procedure.
(sys_enable_guix_daemon): Ask the user whether automatic substitute discovery
should be enabled.  Set the '--discover' argument accordingly.
(prompt_yes_no): Add a trailing space to the message.
(sys_authorize_build_farms): Remove trailing space from the message argument.
* NEWS (Distribution): Add news.