SYSTEMD.CRON(7)

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-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.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

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

.   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).

.   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.

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

AUTHOR
Dwayne Bent