Anacron

Run a command with a certain interval in hours, days, weeks and months if the computer is running .
Only @monthly is a valid '@' interval designator.
@reboot is not valid.

Run times

Anacron runs:

Interval	Time
Hourly	x:17
Daily	6:25
Weekly	Sunday on 6:47
Monthly	On the 1st of the month on 6:52

From /etc/crontab:

17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )

Main rule

Always put the code in a script
Start the script with

#! /bin/bash

Then call the script from anacron. If you do not use a script you can get something like

/bin/sh: 1: [[: not found

in the case you used an [[ statement for example

Servers

On servers do not user anacron, use cron

Alternative

Put scripts in a file in /etc/cron.daily, /etc/cron.weekly or /etc/cron.monthly

They are executed after the anacrontab file is processed
Scripts in these directories are processed in alphanumerical order. Scripts starting with a number first

Restart service

systemctl restart anacron.service

Configuration files

File	Remark
/home/user/.local/anacrontab	For user specific entries
/etc/anacrontab	Put the non user entries in this file
/etc/cron.d/anacron
/etc/default/anacron
/etc/init.d/anacron

Environment

Syntax: VAR=VALUE

Command	Remark
`SHELL=/bin/bash`
`PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin`
`HOME=/root`	Or used in crontab only?
`LOGNAME=root`	Used in the From: field the e-mail. Username, may not be changed. Or used in crontab only?
MAILTO=user	User to whom the output of anacron has to be mailed
`START_HOURS_RANGE=10-12`	In this time frame jobs are started. If missed they are skipped for that day
`RANDOM_DELAY=delaytime`	0: off. Other value: Add a delay of 0 to delaytime minutes to the delay time (see commands section)

Comments

Blank lines
White-space only lines
White-space followed by a '#' followed by a comment

Commands

Option	Explanation
`period`	days
`delay`	minutes
`job-identifier`	Make up yourself. “ ” (space) and “/” are not allowed
`command`	Any shell command or script. Field separation with blank spaces or tabs

Syntax	Remark
`period delay job-identifier command`	period is in days
`monthly delay job-identifier command`	daily nor weekly are possible. Use the previous syntax with a period of 1 or 7

Command continuation

Place a '\' and continue the command on the next line

  4 10 backupSomething cp /home \
                          /backup

Options - --

Short, -, nor long, --, options are allowed. There will be an error message: “/bin/sh: 0: Illegal option -”, (long --)
Solution: write a script and have anacron run it

Examples

 # Comment
4 10 backupSomething cp /home /backup
monthly 20 backupSomething cp /home /backup
 
 # An other comment

Test

Run as root

Command	Explanation
anacron -T	Test the anacrontab file
anacron -T -t /home/user/.local/anacrontab	Test the local user's anacrontab file
anacron -nf	Run all commands now regardless the timestamp

Last run date

Check the date when an anacron job has last run in /var/spool/anacron/jobname. The format is yyyymmdd (may depend on the locale setting)

Run in user mode

anacron needs root privileges to run. You can run it in user mode. Do

mkdir -p /home/user/.local/spool/anacron
crontab -e and add:

@reboot /usr/sbin/anacron -s -t $HOME/.local/anacrontab -S $HOME/.local/spool/anacron 
@hourly /usr/sbin/anacron -s -t $HOME/.local/anacrontab -S $HOME/.local/spool/anacron 
@daily /usr/sbin/anacron -s -t $HOME/.local/anacrontab -S $HOME/.local/spool/anacron

@hourly runs at every full hour: [0-24]:00
@daily runs very day at midnight: 0:00

man pages

man 8 anacron
man 5 anacorntab
man run-parts (run scripts or programs in a directory)
man cron

Useful links

Why would anacron not be running

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