systemd-crontab-generator — translate cron schedules in systemd Units

systemd-crontab-generator  is  a  systemd.generator(7)  translating  classic  cron  “FILES”  into  native
       systemd.timer(5)/systemd.service(5) pairs.

       It runs automatically
         •  during early boot,
         •  a second time by cron-after-var.service if /var is a separate mount-point, in order to process  user
            crontabs in /var/spool/cron/crontabs,
         •  after each update to /etc/crontab† and /etc/anacrontab†, and
         •  when packages add files under /etc/cron.d†
       (†: monitored by cron-update.path).

systemctllist-timers shows an overview of current timers and when they'll elapse.

       If you see something to the effect of
             /usr/lib/systemd/system-generators/systemd-crontab-generatorfailedwitherrorcode1.
       in  the  journal,  you can run /usr/lib/systemd/system-generators/systemd-crontab-generator/tmp/test for
       more verbose output.

/etc/crontab              Administrator's system crontab, see crontab(5).
       /etc/cron.d               System crontabs managed by packages live here.
       /etc/anacrontabanacrontab(5)
       /var/spool/cron/crontabs  Users' crontabs live here.
       /run/systemd/generator    Automatically generated units go here.
       /run/crond.reboot         If this file exists, @reboot jobs aren't re-generated.  Managed automatically.
       /var/lib/systemd/timerssystemd.timer(5)s with the Persistent flag set store their timestamps here.

       systemd-crontab-generator — translate cron schedules in systemd Units

crontab(5), systemd.unit(5), systemd.timer(5), systemd.cron(7)

systemd-cron 2.5.1-2                               2023-08-13                       SYSTEMD-CRONTAB-GENERATOR(8)

/usr/lib/systemd/system-generators/systemd-crontab-generatoroutput-dir