etc: Add systemd files for running ‘guix gc’ periodically

* etc/guix-gc.service.in: New file.
* etc/guix-gc.timer: Likewise.
* .gitignore: Ignore generated ‘guix-gc.service’.
* nix/local.mk (nodist_systemdservice_DATA): Add ‘guix-gc.service’ and
‘guix-gc.timer’.
(EXTRA_DIST): Add ‘guix-gc.service.in’ and ‘guix-gc.timer’.
* doc/guix.texi (Binary Installation): Mention the new systemd files.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

.gitignore

@@ -74,6 +74,7 @@
 /etc/guix-daemon.service
 /etc/guix-publish.conf
 /etc/guix-publish.service
+/etc/guix-gc.service
 /etc/init.d/guix-daemon
 /etc/openrc/guix-daemon
 /guix-*

doc/guix.texi

@@ -743,6 +743,18 @@ with these commands:
 # systemctl enable --now gnu-store.mount guix-daemon
 @end example
 
+You may also want to arrange for @command{guix gc} to run periodically:
+
+@example
+# cp ~root/.config/guix/current/lib/systemd/system/guix-gc.service \
+     ~root/.config/guix/current/lib/systemd/system/guix-gc.timer \
+     /etc/systemd/system/
+# systemctl enable --now guix-gc.timer
+@end example
+
+You may want to edit @file{guix-gc.service} to adjust the command line
+options to fit your needs (@pxref{Invoking guix gc}).
+
 If your host distro uses the Upstart init system:
 
 @example

etc/guix-gc.service.in

@@ -0,0 +1,20 @@
+# This is a "service unit file" for the systemd init system to perform a
+# one-shot 'guix gc' operation.  It is meant to be triggered by a timer.
+# Drop it in /etc/systemd/system or similar together with 'guix-gc.timer'
+# to set it up.
+
+[Unit]
+Description=Discard unused Guix store items
+
+[Service]
+Type=oneshot
+# Customize the 'guix gc' arguments to fit your needs.
+ExecStart=@localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix gc -d 1m -F 10G
+PrivateDevices=yes
+PrivateNetwork=yes
+PrivateUsers=no
+ProtectKernelTunables=yes
+ProtectKernelModules=yes
+ProtectControlGroups=yes
+MemoryDenyWriteExecute=yes
+SystemCallFilter=@default @file-system @basic-io @system-service

etc/guix-gc.timer

@@ -0,0 +1,15 @@
+# This is a "timer unit file" for the systemd init system to trigger
+# 'guix-gc.service' periodically.  Drop it in /etc/systemd/system or similar
+# together with 'guix-gc.service' to set it up.
+
+[Unit]
+Description=Discard unused Guix store items
+
+[Timer]
+OnCalendar=weekly
+AccuracySec=1h
+Persistent=true
+RandomizedDelaySec=6000
+
+[Install]
+WantedBy=timers.target

nix/local.mk

@@ -153,7 +153,9 @@ systemdservicedir = $(libdir)/systemd/system
 nodist_systemdservice_DATA =			\
   etc/gnu-store.mount				\
   etc/guix-daemon.service			\
-  etc/guix-publish.service
+  etc/guix-publish.service			\
+  etc/guix-gc.service				\
+  etc/guix-gc.timer
 
 etc/%.mount: etc/%.mount.in	\
 			 $(top_builddir)/config.status
@@ -216,6 +218,8 @@ EXTRA_DIST +=					\
   etc/guix-daemon.conf.in			\
   etc/guix-publish.service.in			\
   etc/guix-publish.conf.in			\
+  etc/guix-gc.service.in			\
+  etc/guix-gc.timer				\
   etc/init.d/guix-daemon.in			\
   etc/openrc/guix-daemon.in