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authorLibravatar Lénaïc Huard <lenaic@lhuard.fr>2021-09-04 22:55:00 +0200
committerLibravatar Junio C Hamano <gitster@pobox.com>2021-09-07 10:57:04 -0700
commitb681b191f923267aab80ae7f7ab2f85a692e8833 (patch)
tree2e803824a5ebf0d164924867c383bb81469471ff /Documentation
parentmaintenance: `git maintenance run` learned `--scheduler=<scheduler>` (diff)
downloadtgif-b681b191f923267aab80ae7f7ab2f85a692e8833.tar.xz
maintenance: add support for systemd timers on Linux
The existing mechanism for scheduling background maintenance is done through cron. On Linux systems managed by systemd, systemd provides an alternative to schedule recurring tasks: systemd timers. The main motivations to implement systemd timers in addition to cron are: * cron is optional and Linux systems running systemd might not have it installed. * The execution of `crontab -l` can tell us if cron is installed but not if the daemon is actually running. * With systemd, each service is run in its own cgroup and its logs are tagged by the service inside journald. With cron, all scheduled tasks are running in the cron daemon cgroup and all the logs of the user-scheduled tasks are pretended to belong to the system cron service. Concretely, a user that doesn’t have access to the system logs won’t have access to the log of their own tasks scheduled by cron whereas they will have access to the log of their own tasks scheduled by systemd timer. Although `cron` attempts to send email, that email may go unseen by the user because these days, local mailboxes are not heavily used anymore. In order to schedule git maintenance, we need two unit template files: * ~/.config/systemd/user/git-maintenance@.service to define the command to be started by systemd and * ~/.config/systemd/user/git-maintenance@.timer to define the schedule at which the command should be run. Those units are templates that are parameterized by the frequency. Based on those templates, 3 timers are started: * git-maintenance@hourly.timer * git-maintenance@daily.timer * git-maintenance@weekly.timer The command launched by those three timers are the same as with the other scheduling methods: /path/to/git for-each-repo --exec-path=/path/to --config=maintenance.repo maintenance run --schedule=%i with the full path for git to ensure that the version of git launched for the scheduled maintenance is the same as the one used to run `maintenance start`. The timer unit contains `Persistent=true` so that, if the computer is powered down when a maintenance task should run, the task will be run when the computer is back powered on. Signed-off-by: Lénaïc Huard <lenaic@lhuard.fr> Acked-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/git-maintenance.txt58
1 files changed, 53 insertions, 5 deletions
diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 576290b5c6..e2cfb68ab5 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -179,14 +179,16 @@ OPTIONS
`maintenance.<task>.enabled` configured as `true` are considered.
See the 'TASKS' section for the list of accepted `<task>` values.
---scheduler=auto|crontab|launchctl|schtasks::
+--scheduler=auto|crontab|systemd-timer|launchctl|schtasks::
When combined with the `start` subcommand, specify the scheduler
for running the hourly, daily and weekly executions of
`git maintenance run`.
- Possible values for `<scheduler>` are `auto`, `crontab` (POSIX),
- `launchctl` (macOS), and `schtasks` (Windows).
- When `auto` is specified, the appropriate platform-specific
- scheduler is used. Default is `auto`.
+ Possible values for `<scheduler>` are `auto`, `crontab`
+ (POSIX), `systemd-timer` (Linux), `launchctl` (macOS), and
+ `schtasks` (Windows). When `auto` is specified, the
+ appropriate platform-specific scheduler is used; on Linux,
+ `systemd-timer` is used if available, otherwise
+ `crontab`. Default is `auto`.
TROUBLESHOOTING
@@ -286,6 +288,52 @@ schedule to ensure you are executing the correct binaries in your
schedule.
+BACKGROUND MAINTENANCE ON LINUX SYSTEMD SYSTEMS
+-----------------------------------------------
+
+While Linux supports `cron`, depending on the distribution, `cron` may
+be an optional package not necessarily installed. On modern Linux
+distributions, systemd timers are superseding it.
+
+If user systemd timers are available, they will be used as a replacement
+of `cron`.
+
+In this case, `git maintenance start` will create user systemd timer units
+and start the timers. The current list of user-scheduled tasks can be found
+by running `systemctl --user list-timers`. The timers written by `git
+maintenance start` are similar to this:
+
+-----------------------------------------------------------------------
+$ systemctl --user list-timers
+NEXT LEFT LAST PASSED UNIT ACTIVATES
+Thu 2021-04-29 19:00:00 CEST 42min left Thu 2021-04-29 18:00:11 CEST 17min ago git-maintenance@hourly.timer git-maintenance@hourly.service
+Fri 2021-04-30 00:00:00 CEST 5h 42min left Thu 2021-04-29 00:00:11 CEST 18h ago git-maintenance@daily.timer git-maintenance@daily.service
+Mon 2021-05-03 00:00:00 CEST 3 days left Mon 2021-04-26 00:00:11 CEST 3 days ago git-maintenance@weekly.timer git-maintenance@weekly.service
+-----------------------------------------------------------------------
+
+One timer is registered for each `--schedule=<frequency>` option.
+
+The definition of the systemd units can be inspected in the following files:
+
+-----------------------------------------------------------------------
+~/.config/systemd/user/git-maintenance@.timer
+~/.config/systemd/user/git-maintenance@.service
+~/.config/systemd/user/timers.target.wants/git-maintenance@hourly.timer
+~/.config/systemd/user/timers.target.wants/git-maintenance@daily.timer
+~/.config/systemd/user/timers.target.wants/git-maintenance@weekly.timer
+-----------------------------------------------------------------------
+
+`git maintenance start` will overwrite these files and start the timer
+again with `systemctl --user`, so any customization should be done by
+creating a drop-in file, i.e. a `.conf` suffixed file in the
+`~/.config/systemd/user/git-maintenance@.service.d` directory.
+
+`git maintenance stop` will stop the user systemd timers and delete
+the above mentioned files.
+
+For more details, see `systemd.timer(5)`.
+
+
BACKGROUND MAINTENANCE ON MACOS SYSTEMS
---------------------------------------