On 01/05/21 21.52, Lénaïc Huard wrote:
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.
Supposed that I have Linux box with systemd and classical cron. Should systemd timers be preferred over cron?
* 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 its own tasks scheduled by cron whereas he will have access to the log of its own tasks scheduled by systemd timer. 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 parametrized 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 than with the other scheduling methods: git for-each-repo --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@xxxxxxxxx>
Nevertheless, because we are dealing with external dependency (systemd), it should makes sense to enforce this dependency requirement when user choose to use systemd timers so that users on non-systemd boxes (such as Gentoo with OpenRC) don't see errors that forcing them to use systemd. -- An old man doll... just what I always wanted! - Clara
