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systemd.cron

systemd units for cron periodic jobs

cron.target
cron-update.path, cron-update.service
cron-mail@.service

These units provide the functionality usually afforded by the cron daemon — running scripts in /etc/cron.schedule directories and sending mail on failure.

Crontabs are monitored by cron-update.path and are automatically translated by systemd-crontab-generator(8).

/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.
/dev/shm/systemd-cron.*
Queues and tokens used for and .

/etc/cron.hourly
Directory for scripts to be executed every hour.
/etc/cron.daily
Directory for scripts to be executed every day.
/etc/cron.weekly
Directory for scripts to be executed every week.
/etc/cron.monthly
Directory for scripts to be executed every month.
/etc/cron.yearly
Directory for scripts to be executed every year.

/usr/lib/systemd/system/schedule.timer
 
/etc/systemd/system/schedule.timer
Native systemd timers will override cron jobs with the same name.

You can also use this mechanism to mask an unneeded crontab provided by a package via systemctl mask package.timer.

File names of crontabs in /etc/cron.d and scripts in /etc/cron.schedule must consist only of ascii(7) alphanumerics, underscores (‘’), and dashes (‘-’) (match the C-locale regular expression "^[[:alnum:]_-]*$"); they will be ignored otherwise. 0anacron and anacron are always ignored.

cron.target
Target unit which starts the others, needs to be enabled to use systemd-cron.
cron-update.path
Monitors FILES and calls
cron-update.service
which runs systemctl daemon-reload to re-run the generator.

cron-mail@.service
Sends mail in case a cron service unit fails, succeeds, or succeeds-but-only-if-it-wrote-something. The instance name (the bit after the @) is the unit name, followed by optional arguments delimited by colons (‘’):
exit silently if the unit produced no output (equivalent to CRON_MAIL_SUCCESS=nonempty) for OnSuccess=),
don't include systemctl status output, don't add usual journalctl metadata to the output (equivalent to CRON_MAIL_FORMAT=nometadata), and
log reason before exiting silently.
(upper-case arguments are ignored).

Overriding this via systemctl edit can be useful, especially for units under /etc/cron.*: set $SENDMAIL or $MAILFROM to override the defaults (sendmail(1) and "root", respectively).

$SENDMAIL can be also be set from the global systemd environment (systemctl show-environment).

Do use with a cron daemon or anacron, otherwise scripts may be executed multiple times.

All services are run with Type=, which means you can't use systemd-cron to launch long lived forking daemons.

Units for non-persistent jobs from crontab(5)s are generated with sequential names, so if a job changes (by direct editing or by removing (commenting out) a previous job) , and mail is sent for that job, some configuration may be wrong (too new) and systemctl status may be confusing. The journal output and e-mail subject are correct. Setting will work around this (but break existing systemctl edit overrides).

Jobs with PERSISTENT= and @-keyword are started on boot if a run was missed while the system was off. A regular cron and anacron setup won't catch up on the missed executions of crontabs on reboot.

Generated units log to the journal with set to the job line (systemd.journal-fields(7)).

# systemctl start cron.target

# systemctl enable cron.target

# journalctl -u cron-daily

# systemctl edit cron-geoip-database-contrib-root-1.timer

and add

[Timer]
OnCalendar=
OnCalendar=*-*-* 18:36:00

# systemctl edit cron-daily.service

and add

[Service]
CPUSchedulingPolicy=idle
IOSchedulingClass=idle

[Unit]
Description=Update the man db

[Service]
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
ExecStart=/usr/bin/mandb --quiet

[Install]
WantedBy=cron-hourly.target

The exact times scripts are executed is determined by the values of the special calendar events , , , , and defined in systemd.time(7).

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

crontab(1), systemd(1), crontab(5), systemd.service(5), systemd.timer(5), systemd.unit(5), systemd.time(7), run-parts(8), systemd-crontab-generator(8)