anacron til

Author: ryan nemeth

content/til/2025-08-24-anacron.md

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+---
+title: 'Anacron'
+date: '2025-08-24'
+author: Ryan
+layout: post
+categories:
+- Uncategorized
+---
+
+Anacron is designed for tasks that need to run periodically (daily, weekly, monthly) on systems that are not continuously powered on. If a scheduled cron task is missed because the system is off, anacron will run the task once the system is available.
+
+On many systems, anacron is pre-installed. If not, install it with:
+~~~
+$ sudo apt install anacron
+Anacron's configuration is in the /etc/anacrontab file, which includes helpful comments and examples. Here’s an excerpt:
+
+$ sudo vim /etc/anacrontab
+# See anacron(8) and anacrontab(5) for details.
+# These entries replace cron's job entries.
+1       5       cron.daily      run-parts --report /etc/cron.daily
+7       10      cron.weekly     run-parts --report /etc/cron.weekly
+@monthly 15      cron.monthly    run-parts --report /etc/cron.monthly
+~~~
+
+The syntax in the anacrontab file consists of four fields:
+1) The period in days (e.g., 1 for daily, 7 for weekly).
+2) A delay (in minutes) after system startup.
+3) A unique job identifier.
+4) The command to execute.
+
+For example, to run a job every three days with a 10-minute delay:
+~~~
+3 10 test_job /usr/bin/touch /root/anacron_created_this
+~~~
+
+Other examples include:
+~~~
+7 10 test_job /usr/bin/touch /root/anacron_created_this
+@monthly 10 test_job /usr/bin/touch /root/anacron_created_this
+~~~
+
+After editing, verify your anacrontab syntax with:
+~~~
+$ anacron -T
+anacron: /etc/anacrontab: Unknown named period on line 13, skipping
+~~~
+
+If no errors are reported, your anacron entries are correctly formatted.
+
+Consult the anacron man pages for more info.