This post will guide you how to use anacron tool to run commands or your own scripts periodically under Linux operating system. How do I setup anacron jobs in its configuration file /etc/anacrontab in Linux. How to run daily, weekly, and monthly scheduled jobs with anacron tool in Linux.
What is Anacron?
NAME
anacron – runs commands periodically
SYNOPSIS
anacron [-s] [-f] [-n] [-d] [-q] [-t anacrontab] [-S spooldir] [job] anacron [-S spooldir] -u [-t anacrontab] [job] anacron [-V|-h] anacron -T [-t anacrontab]
DESCRIPTION
Anacron is used to execute commands periodically, with a frequency specified in days. Unlike cron, it does not assume that the machine is running continuously. Hence, it can be used on machines that are not running 24 hours a day to control regular jobs as daily, weekly, and monthly jobs.
Anacron reads a list of jobs from the /etc/anacrontab configuration file (see anacrontab(5)). This file contains the list of jobs that Anacron controls. Each job entry specifies a period in days, a delay in minutes, a unique job identifier, and a shell command.
/etc/anacrontab – configuration file for Anacron
The /etc/anacrontab configuration file describes the jobs controlled by anacron(8). It can contain three types of lines: job-description lines, environment assignments, or empty lines.
Job-description lines can have the following format:
period in days delay in minutes job-identifier command
The period in days variable specifies the frequency of execution of a job in days. This variable can be represented by an integer or a macro (@daily, @weekly, @monthly), where @daily denotes the same value as the integer 1, @weekly the same as 7, and @monthly specifies that the job is run once a month, independent on the length of the month.
The delay in minutes variable specifies the number of minutes anacron waits, if necessary, before executing a job. This variable is represented by an integer where 0 means no delay.
The job-identifier variable specifies a unique name of a job which is used in the log files.
The command variable specifies the command to execute. The command can either be a command such as ls /proc >> /tmp/proc or a command to execute a custom script.
Issue the following command to check the configuration file /etc/anacrontab:
#cat /etc/anacrontab
Outputs:
[root@osetc_x8664 ~]# cat /etc/anacrontab
# /etc/anacrontab: configuration file for anacron
# See anacron(8) and anacrontab(5) for details.
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45
# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22
#period in days delay in minutes job-identifier command
1 5 cron.daily nice run-parts /etc/cron.daily
7 25 cron.weekly nice run-parts /etc/cron.weekly
@monthly 45 cron.monthly nice run-parts /etc/cron.monthly
Where,
The START_HOURS_RANGE variable will define an interval when the scheduled jobs can be run in your system.
The RANDOM_DELAY variable will denote the maximum number of minutes that will be added to the delay in minutes variable. and a random value between 0 and 45 will be added to the startup delay of each job.
Cron.daily will run at 3:05AM
Cron.weekly will run at 3:25AM
Cron.monthly will run at 3:45AM
Linux Anacron Example
This example shows how to set up an Anacron job similar in functionality to /etc/crontab which starts all regular jobs between 6:00 and 8:00 only. A RANDOM_DELAY which can be 30 minutes at the most is specified. Jobs will run serialized in a queue where each job is started only after the previous one is finished. You need to edit the /etc/anacrontab file with vi/vim editor, type:
#vim /etc/anacrontab
Adding the below lines into the configuration file:
# environment variables SHELL=/bin/sh PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root RANDOM_DELAY=30 # Anacron jobs will start between 6am and 8am. START_HOURS_RANGE=6-8 # delay will be 5 minutes + RANDOM_DELAY for cron.daily 1 5 cron.daily nice run-parts /etc/cron.daily 7 0 cron.weekly nice run-parts /etc/cron.weekly @monthly 0 cron.monthly nice run-parts /etc/cron.monthly