NAME

systemd.crom — systemd units for cron periodic jobs

SYNOPSIS

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

DESCRIPTION

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).

FILES

/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.
/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.

UNITS

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 (via sendmail(1), which can be overridden with $SENDMAIL) 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 (‘:’):

nonempty: exit silently if the unit produced no output (equivalent to CRON_MAIL_SUCCESS=nonempty) for OnSuccess=),
nometadata: don't include systemctl status output, don't add usual journalctl metadata to the output (equivalent to CRON_MAIL_FORMAT=nometadata), and
verbose: log reason before exiting silently.

(upper-case arguments are ignored).

Overriding this via systemctl edit can be useful, especially for units under /etc/cron.*.

BUGS

Do not use with a cron daemon or anacron, otherwise scripts may be executed multiple times.

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

EXTENSIONS

The generator can optionally turn any crontabs in persistent timers with the PERSISTENT=true flag, while a regular cron and anacron setup won't catch up on the missed executions of crontabs on reboot.

EXAMPLES

Start cron units

# systemctl start cron.target

Start cron units on boot

# systemctl enable cron.target

View script output

# journalctl -u cron-daily

Override some generated timer start time

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

and add

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

Override cron-daily.service priority, useful for old computers

# systemctl edit cron-daily.service

and add

[Service]
CPUSchedulingPolicy=idle
IOSchedulingClass=idle

Example service file executed every hour

[Unit]
Description=Update the man db

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

[Install]
WantedBy=cron-hourly.target

NOTES

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

DIAGNOSTICS

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