NAME

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

SYNOPSIS

/usr/lib/systemd/system-generators/systemd-crontab-generator output-dir

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).

/etc/crontab: Administrator's system crontab, see crontab(5).
/etc/cron.d: System crontabs managed by packages live here.
/etc/anacrontab: anacrontab(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/timers: systemd.timer(5)s with the Persistent flag set store their timestamps here.

systemctl list-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-generator
  failed with error code 1.

in the journal, you can run /usr/lib/systemd/system-generators/systemd-crontab-generator /tmp/test for more verbose output.