An example systemd timer. #systemd #timer #systemd.timer #cron #cronjob

README-setup-systemd-timer.md

README

Timers provided by systemd can be used as cronjob replacements. More at man systemd.timer.

Suppose we want to periodically trigger cleanup tasks for a baz utility. We 'll create a baz-cleanup.service which will be triggered by a baz-cleanup.timer.

Define the target service unit

Create a minimal service at /etc/systemd/system/baz-cleanup.service:

[Unit]
Description=Baz Periodic Cleanup

[Service]
Type=simple
ExecStart=/usr/bin/python /opt/baz/cleanup.py
StandardError=journal

We dont provide an [Install] section, since this service is not meant to be enabled on its own (will be triggered by an enabled timer instead).

The actual task at /opt/baz/cleanup.py could be something like:

#!/usr/bin/python
import logging
logging.basicConfig(level=logging.INFO)
logging.info("baz-cleanup: Running periodic cleanup for Baz ...")

Define the timer

Create the timer unit at /etc/systemd/system/baz-cleanup.timer:

[Unit]
Description=Timer for Baz Cleanup

[Timer]
# Define target unit (in case the name part is the same, can be omitted)
Unit=baz-cleanup.service

## Activate target unit based on monotonic timers 

# Time to wait after booting before we run first time
#OnBootSec=10min

# Time between running each consecutive time
#OnUnitActiveSec=30min

## or ..
## Activate target based on wallclock time (calendar event)

# Define a calendar event (see `man systemd.time`)
OnCalendar=*-*-* 12:13:00

[Install]
WantedBy=multi-user.target

Start/Enable the timer

Start the timer. Inspect the journal to verify that the perioric task is actually triggered.

systemctl daemon-reload && systemctl start baz-cleanup.timer

I have a timer running
OnBootSec=10m
OnUnitActiveSec=1m

But the thing kicks off every minute, even right at boot.

I'm using a "oneshot" service...why doesn't it work?

time:

[Unit]
Description=Check to see if we should shut down this compute node.

[Timer]
OnBootSec=10min
OnUnitActiveSec=1m

Unit=sem_scalein_check.service

[Install]
WantedBy=multi-user.target

service:

[Unit]
Description=sem_scaleine_check

[Service]
# OPTIONS should just contain a single word with the queue to check
# i.e
# OPTIONS=semfake
Type=oneshot
EnvironmentFile=/etc/sysconfig/sem_scalein_check
ExecStart=/usr/local/bin/sem_scalein_check.sh $OPTIONS

[Install]
WantedBy=multi-user.target

@sean-abbott I think you want RemainAfterElapse=False in your [Timer] section, and you can change service.type back to simple.

OnUnitActiveSec does not work with oneshot service, because oneshot service status is never active.