Using SystemD Timers (Like Cron) – Centos

The more I use it, the more I like using SystemD to manage services.  It is sometimes verbose, but in general, it is very easy to use and very powerful.  It can restart failed services, start services automatically, handle logging and rolling for simplistic services, and much more.

SystemD Instead of Cron

Recently, I had to take a SystemD service and make it run on a regular timer.  So, of course, my first thought was using cron… but I’m not a particularly big fan of cron for reasons I won’t go into here.

I found out that SystemD can do this as well!

Creating a SystemD Timer

Let’s say you have a (very) simple service defined like this in SystemD (in /etc/systemd/system/your-service.service):

[Unit]
Description=Do something useful.

[Service]
Type=simple
ExecStart=/opt/your-service/do-something-useful.sh
User=someuser
Group=someuser

Then you can create a timer for it by creating another SystemD file in the same location but ending with “.timer” instead of “.service”. It can handle basically any interval, can start at reboot, and can even time tasks based on the reboot time.

[Unit]
Description=Run service once daily.

[Timer]
OnCalendar=*-*-* 00:30:00
Unit=your-service.service

[Install]
WantedBy=multi-user.target

Once the timer file is made, you can enable it like to:

sudo systemctl daemon-reload
sudo systemctl enable your-service.timer
sudo systemctl start your-service.timer

After this, you can verify the timer is working and check its next (and later on, previous) execution time with this command:

$> systemctl list-timers --all
NEXT                         LEFT          LAST                         PASSED  UNIT                         ACTIVATES
Tue 2019-03-05 20:00:01 UTC  14min left    Mon 2019-03-04 20:00:01 UTC  23h ago systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.service
Wed 2019-03-06 00:30:00 UTC  4h 44min left n/a                          n/a     your-service.timer     your-service.service
n/a                          n/a           n/a                          n/a     systemd-readahead-done.timer systemd-readahead-done.service

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s