108 lines
4.7 KiB
Markdown
108 lines
4.7 KiB
Markdown
---
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layout: post
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title: "Use systemd as a cron replacement"
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date: 2013-06-09 18:22
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comments: true
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categories:
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- systemd
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- linux
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- cron
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description: "HOWTO: Replace cron with systemd"
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---
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Since systemd 197 timer units support calendar time events, which makes systemd a
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full cron replacement. Why one would replace the good old cron? Well, because systemd
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is good at executing stuff and monitor its state!
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* with the help of journalctl you get last status and logging output, which is a
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great thing to debug failing jobs:
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```
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$ systemctl status reflector-update.service
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reflector-update.service - "Update pacman's mirrorlist using reflector"
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Loaded: loaded
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(/etc/systemd/system/timer-weekly.target.wants/reflector-update.service)
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Active: inactive (dead)
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Jun 09 17:58:30 higgsboson reflector[30109]: rating http://www.gtlib.gatech.edu/pub/archlinux/
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Jun 09 17:58:30 higgsboson reflector[30109]: rating rsync://rsync.gtlib.gatech.edu/archlinux/
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Jun 09 17:58:30 higgsboson reflector[30109]: rating http://lug.mtu.edu/archlinux/
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Jun 09 17:58:30 higgsboson reflector[30109]: Server Rate Time
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...
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```
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* there are a lot of useful [systemd unit options](http://www.freedesktop.org/software/systemd/man/systemd.exec.html) like `IOSchedulingPriority`, `Nice` or `JobTimeoutSec`
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* it is possible to let depend units on other services, like mounting the nfs host
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before starting the mysql-backup.service or depending on the network.target.
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So let's get it started. The first thing you might want to do, is to replace the
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default scripts located in the [runparts](http://superuser.com/questions/402781/what-is-run-parts-in-etc-crontab-and-how-do-i-use-it)
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directories /etc/cron.{daily,hourly,monthly,weekly}.
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On my distribution (archlinux) these are logrotate, man-db, shadow and updatedb:
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For convenience I created a structure like /etc/cron.\*:
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mkdir /etc/systemd/system/timer-{hourly,daily,weekly}.target.wants
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and added the following timer.
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cd /etc/systemd/system
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wget https://blog.higgsboson.tk/downloads/timers.tar
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tar -xvf timers.tar && rm timers.tar
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{% include_code /etc/systemd/system/timer-hourly.timer lang:ini cron-replacement/timer-hourly.timer %}
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{% include_code /etc/systemd/system/timer-hourly.target lang:ini cron-replacement/timer-hourly.target %}
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{% include_code /etc/systemd/system/timer-daily.timer lang:ini cron-replacement/timer-daily.timer %}
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{% include_code /etc/systemd/system/timer-daily.target lang:ini cron-replacement/timer-daily.target %}
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{% include_code /etc/systemd/system/timer-weekly.timer lang:ini cron-replacement/timer-weekly.timer %}
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{% include_code /etc/systemd/system/timer-weekly.target lang:ini cron-replacement/timer-weekly.target %}
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... and enable them:
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systemctl enable timer-hourly.timer
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systemctl enable timer-daily.timer
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systemctl enable timer-weekly.timer
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These directories work like their cron equivalents, each service file located in
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such a directory will be executed at the given time.
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Now move on to the service files. If you're not running Arch, the paths might be different on your system.
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cd /etc/systemd/system
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wget https://blog.higgsboson.tk/downloads/services.tar
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tar -xvf services.tar && rm services.tar
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{% include_code /etc/systemd/system/timer-daily.target.wants/logrotate.service lang:ini cron-replacement/logrotate.service %}
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{% include_code /etc/systemd/system/timer-daily.target.wants/man-db-update.service lang:ini cron-replacement/man-db-update.service %}
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{% include_code /etc/systemd/system/timer-daily.target.wants/mlocate-update.service lang:ini cron-replacement/mlocate-update.service %}
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{% include_code /etc/systemd/system/timer-daily.target.wants/verify-shadow.service lang:ini cron-replacement/verify-shadow.service %}
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At last but not least you can disable cron:
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systemctl stop cronie && systemctl disable cronie
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If you want to execute at a special calendar events for example "every first day in a month" use the ["OnCalendar=" option](http://www.freedesktop.org/software/systemd/man/systemd.time.html) in the timer file.
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example:
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``` ini send-bill.timer
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[Unit]
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Description=Daily Timer
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[Timer]
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OnCalendar=*-*-1 0:0:O
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Unit=send-bill.target
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[Install]
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WantedBy=basic.target
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```
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That's all for the moment. Have a good time using the power of systemd!
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Below some service files, I use:
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{% include_code /etc/systemd/system/timer-weekly.target.wants/reflector-update.service lang:ini cron-replacement/reflector-update.service %}
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{% include_code /etc/systemd/system/timer-weekly.target.wants/pkgstats.service lang:ini cron-replacement/pkgstats.service %}
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[See this link](https://bbs.archlinux.org/viewtopic.php?id=162989) for details about my shell-based pacman notifier
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{% include_code /etc/systemd/system/timer-daily.target.wants/pacman-update.service lang:ini cron-replacement/pacman-update.service %}
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