NAME

systemd.cron - systemd cron units

SYNOPSIS

cron.target, cron-hourly.timer, cron-hourly.target, cron-hourly.service, cron-daily.timer, cron-daily.target, cron-daily.service, cron-weekly.timer, cron-weekly.target, cron-weekly.service, cron-monthly.timer, cron-monthly.target, cron-monthly.service, cron-yearly.timer, cron-yearly.target, cron-yearly.service, cron-update.path, cron-update.service.

DESCRIPTION

These units provide cron daemon functionality by running scripts in cron directories.
The crontabs are monitored by cron-update.path and are automatically translated by systemd-crontab-generator(8) .

FILES

/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.
/etc/cron.d: Directory for crontabs to be executed on a custom schedule. The files in this folder must follow the crontab(5) layout.
If there exists a timer of the same name + '.timer' in /lib/systemd/system or /etc/systemd/system, this crontab will be ignored to enable a smooth migration to native timers.
You can also use this to mask an unneeded crontab provide by a package:
ln -s /dev/null /etc/systemd/system/[package].timer

SYSTEM UNITS

cron.target: The target unit which starts the others. This should be enabled and started to use cron functionality.
cron-schedule.timer: The timer units which pull the cron-schedule.target units at the appropriate time. Started and stopped by the cron.target unit. These units cannot be controlled manually.
cron-schedule.target: The targets invoke all service units wanted by them, including cron-schedule.service.
cron-schedule.service: The service units which run scripts in the cron directories. Started and stopped by the cron-schedule.target units. These units cannot be controlled manually. You can use journalctl(1) to view the output of scripts run from these units.

LIMITATIONS

This cron replacement only send mails on failure. The log of jobs is saved in systemd journal. Do not use with a cron daemon or anacron, otherwise scripts may be executed multiple times.
All services are run with Type=oneshot , that means you can't use systemd-cron to launch long lived forking daemons.

EXTENSIONS

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

EXAMPLES

Start cron units

# systemctl start cron.target

Start cron units on boot

# systemctl enable cron.target

View script output

# journalctl -u cron-hourly
# journalctl -u cron-daily
# journalctl -u cron-weekly
# journalctl -u cron-monthly
# journalctl -u cron-yearly

Override some generated timer start time

# systemctl edit cron-geoip-database-contrib-root-<...>.timer --full
keep existing statements, but change this one:
[Timer]
OnCalendar=*-*-* 18:36:00

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

# systemctl edit cron-daily.service
this will open a blank editor when you can type a drop-in configuration file that will extend the current .service
[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

1.: The exact times scripts are executed is determined by the values of the special calendar events hourly, daily, weekly, monthly, and yearly defined by systemd.time(7).
2.: run-parts(8) is used to run scripts. Scripts must be executable by root to run.

DIAGNOSTICS

With systemd >= 209, you can execute "systemctl list-timers" to have a overview of timers and know when they will elapse.

AUTHOR

Dwayne Bent

systemd-cron 1.15.19