09 Jun 2013

Use Systemd as a Cron Replacement

Since systemd 197 timer units support calendar time events, which makes systemd a full cron replacement. Why one would replace the good old cron? Well, because systemd is good at executing stuff and monitor its state!

with the help of journalctl you get last status and logging output, which is a great thing to debug failing jobs:

$ systemctl status reflector-update.service
reflector-update.service - "Update pacman's mirrorlist using reflector"
   Loaded: loaded
(/etc/systemd/system/timer-weekly.target.wants/reflector-update.service)
   Active: inactive (dead)

Jun 09 17:58:30 higgsboson reflector[30109]: rating http://www.gtlib.gatech.edu/pub/archlinux/
Jun 09 17:58:30 higgsboson reflector[30109]: rating rsync://rsync.gtlib.gatech.edu/archlinux/
Jun 09 17:58:30 higgsboson reflector[30109]: rating http://lug.mtu.edu/archlinux/
Jun 09 17:58:30 higgsboson reflector[30109]: Server Rate       Time
...

there are a lot of useful systemd unit options like IOSchedulingPriority, Nice or JobTimeoutSec
it is possible to let depend units on other services, like mounting the nfs host before starting the mysql-backup.service or depending on the network.target.

So let’s get it started. The first thing you might want to do, is to replace the default scripts located in the runparts directories /etc/cron.{daily,hourly,monthly,weekly}.

On my distribution (archlinux) these are logrotate, man-db, shadow and updatedb: For convenience I created a structure like /etc/cron.*:

$ mkdir /etc/systemd/system/timer-{hourly,daily,weekly}.target.wants

and added the following timer.

$ cd /etc/systemd/system
$ wget https://blog.thalheim.io/downloads/timers.tar
$ tar -xvf timers.tar && rm timers.tar

[Unit]
Description=Hourly Timer

[Timer]
OnBootSec=5min
OnUnitActiveSec=1h
Unit=timer-hourly.target

[Install]
WantedBy=basic.target

[Unit]
Description=Hourly Timer Target
StopWhenUnneeded=yes

[Unit]
Description=Daily Timer

[Timer]
OnBootSec=10min
OnUnitActiveSec=1d
Unit=timer-daily.target

[Install]
WantedBy=basic.target

[Unit]
Description=Daily Timer Target
StopWhenUnneeded=yes

[Unit]
Description=Weekly Timer

[Timer]
OnBootSec=15min
OnUnitActiveSec=1w
Unit=timer-weekly.target

[Install]
WantedBy=basic.target

[Unit]
Description=Weekly Timer Target
StopWhenUnneeded=yes

… and enable them:

$ systemctl enable timer-hourly.timer
$ systemctl enable timer-daily.timer
$ systemctl enable timer-weekly.timer

These directories work like their cron equivalents, each service file located in such a directory will be executed at the given time.

Now move on to the service files. If you’re not running Arch, the paths might be different on your system.

$ cd /etc/systemd/system
$ wget https://blog.higgsboson.tk/downloads/services.tar
$ tar -xvf services.tar && rm services.tar

[Unit]
Description=Update man-db

[Service]
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
ExecStart=/usr/bin/logrotate /etc/logrotate.conf

[Unit]
Description=Update man-db

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

[Unit]
Description=Update mlocate database

[Service]
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
ExecStart=/usr/bin/updatedb

[Unit]
Description=Verify integrity of password and group files

[Service]
Type=oneshot
ExecStart=/usr/sbin/pwck -r
ExecStart=/usr/sbin/grpck -r

At last but not least you can disable cron:

$ systemctl stop cronie && systemctl disable cronie

If you want to execute at a special calendar events for example “every first day in a month” use the “OnCalendar=” option in the timer file. example:

[Unit]
Description=Daily Timer

[Timer]
OnCalendar=*-*-1 0:0:O
Unit=send-bill.target

[Install]
WantedBy=basic.target

That’s all for the moment. Have a good time using the power of systemd!

Below some service files, I use:

[Unit]
Description="Update pacman's mirrorlist using reflector"

[Service]
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
Type=oneshot
ExecStart=/usr/bin/reflector --verbose -l 5 --sort rate --save /etc/pacman.d/mirrorlist

[Unit]
Description=Run pkgstats

[Service]
User=nobody
ExecStart=/usr/bin/pkgstats

See this link for details about my shell-based pacman notifier

[Unit]
Description=Update pacman's package cache

[Service]
Nice=19
Type=oneshot
IOSchedulingClass=2
IOSchedulingPriority=7
Environment=CHECKUPDATE_DB=/var/lib/pacman/checkupdate
ExecStartPre=/bin/sh -c "/usr/bin/checkupdates &gt; /var/log/pacman-updates.log"
ExecStart=/usr/bin/pacman --sync --upgrades --downloadonly --noconfirm --dbpath=/var/lib/pacman/checkupdate

Archived comments

Imported from Disqus, which this blog used before switching to giscus.

Profpatsch 12 Nov 2013

What about cronjobs I want to execute in my useraccount?

Like automatic home folder backups every 3 hours?

Mic92 13 Nov 2013

You have basicly 2 options: 1. create a custom timer in the context of
systemd/user (https://wiki.archlinux.org/.... 2. set
the User variable in the service file.

Buddlespit 10 May 2014

This backs up my home to my home on the server:

[Unit]
Description=Backup ~/
Wants=timer-weekly.timer

[Service]
User=pat
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
ExecStart=/usr/bin/rsync --delete -azvv -e ssh /home/pat/ pat@192.168.1.13:/home/pat/backup

[Install]
WantedBy=timer-weekly.target

Ken 17 Sep 2014

I have the hourly daily weekly systemd cron replacement running but with one problem.

If I set up an hourly service "test.service" and enable it with:

"systemctl enable test.service"

a link to "test.service" is created in "timer-hourly.target.wants" as it should be.

I then remove it with:

"systemctl disable test.service"

the "timer-hourly.target.wants" directory is removed rather than just the link.

(if there are other links in "timer-hourly.target.wants" the directory survives)

What am I doing wrong ?

systemd 215

Mic92 19 Sep 2014

Sound good to me, what behaviour did you expect?

Ken 21 Sep 2014

Didn't expect the wants directory to disappear but now I realise the wants directories are created and deleted as required. Thanks for your comment.

ferrvittorio 09 Nov 2014

Hi. What about if I tried to setup a daily shutdown at 2200. I am landing here from suse cron and I am not yet familiar.
Might the following suffice?

daily-shutdown.timer

[Unit]
Description="daily shutdown"
OnCalendar=*-*-* 22:0:0
Unit=daily-shutdown.timer

[Service]
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
Type=oneshot
ExecStart=/path/to/shutdown

Mic92 10 Nov 2014

the timer spec is correct should work, but you have to put service section in a separate file (if the name is the same except the suffix it will be pulled in by your timer)

daily-shutdown.timer
[Unit]
Description="daily shutdown"

[Timer]
OnCalendar=22:00

[Install]
WantedBy=multi-user.target

daily-shutdown.service
[Service]
Nice=19
IOSchedulingClass=2
IOSchedulingPriority=7
Type=oneshot
ExecStart=/path/to/shutdown

Enable it and start it with:
$ systemctl enable daily-shutdown.timer
$ systemctl start daily-shutdown.timer

To verify if it works use the subcommand:

$ systemctl list-timers

This will list, when the timer is scheduled.

ferrvittorio 11 Nov 2014

Hi! Unit did shutdown, but .. something went really wrong!

LXDE refused to let me log back in, even as root. Login attempt as user jumped me at lxde screen, root loogin forced box to shut down!

For now I removed offending timer/service

What is your opinion

Edit: not LXDE, but LIGHTDM