[systemd-devel] How to chain services driven by a timer?

[Andrei Borzenkov]

On Thu, Apr 11, 2024 at 12:07 AM Brian Reichert <reichert at numachi.com> wrote:
>
> On Wed, Apr 10, 2024 at 01:47:47PM -0600, Dan Nicholson wrote:
> > Restarting the timer doesn't make the service run immediately. Are you
> > sure logrotate.service has run again since you made this change? Just
> > simulate the timer and start logrotate.service again. All the timer
> > does is activate the service. For testing you don't need to wait for
> > that to happen.
>
> Ok, that is a helpful detail.
>
> Restarting logrotate.service does now cause my post-logrotate.service
> to subsequently start.
>
> On a lark, I augmented the stock logrotate.service with some
> instrumentation to show me when 'logrotate' completes, in addition to
> maintaining a log file:
>
>   #ExecStart=/usr/sbin/logrotate /etc/logrotate.conf
>   ExecStart=/usr/sbin/logrotate -l /var/log/logrotate.log /etc/logrotate.conf
>   ExecStartPost=/usr/bin/logger 'XXX log rotation completed'
>
> My service is being run (yay!), but I'm wary of the out-of-order
> messaging here:
>

Show full unit definition for both logrotate.service and your service.

>   10-153-68-34:~ # journalctl -o short-precise --no-pager -u logrotate.service -u post-logrotate.service | tail -6
>   Apr 10 16:57:54.061053 10-153-68-34 systemd[1]: Started Activities after logrotation.
>   Apr 10 16:57:54.061140 10-153-68-34 systemd[1]: Stopped Rotate log files.
>   Apr 10 16:57:54.062219 10-153-68-34 systemd[1]: Starting Rotate log files...
>   Apr 10 16:57:54.104300 10-153-68-34 root[5899]: XXX post log rotation
>   Apr 10 16:57:55.367522 10-153-68-34 root[5903]: XXX log rotation completed
>   Apr 10 16:57:55.368789 10-153-68-34 systemd[1]: Started Rotate log files.
>
> And systemctl shows the new post-logrotate.service started slightly
> before logrotate.service ended:
>
>   10-153-68-34:~ # systemctl show logrotate.service --property ExecMainExitTimestamp
>   ExecMainExitTimestamp=Wed 2024-04-10 16:57:55 EDT
>   10-153-68-34:~ # systemctl show post-logrotate.service --property ExecMainStartTimestamp
>   ExecMainStartTimestamp=Wed 2024-04-10 16:57:54 EDT
>
> (I really wish I had higher-resolution timestamps here.)
>
> That log file's mtime:
>
>   10-153-68-34:~ # ls -ldtr --full-time /var/log/logrotate.log
>   -rw-r--r-- 1 root root 1607975 2024-04-10 16:57:55.094420531 -0400 /var/log/logrotate.log
>
> Hopefully someone here can assure me this is just due to an artifact
> of bookkeeping. I'm specifically trying to avoid doing any work
> while logrotate is running.
>
> That I got even this far is really great, so I appreciate all of the
> guidance!
>
> > --
> > Dan
>
> --
> Brian Reichert                          <reichert at numachi.com>
> BSD admin/developer at large