Anacron

Anacron is a task scheduler similar to cron except that it does not require the system to run continuously. It can be used to run the daily, weekly, and monthly jobs usually run by cron.

To use the Anacron service, you must have the anacron RPM package installed. To determine if the package is installed, use the command rpm -q anacron.

Configuration File

Anacron tasks are listed in the configuration file /etc/anacron. Each line in the configuration file corresponds to a task and has the format:

period   delay   job-identifier  command

period — frequency (in days) to execute the command
delay — delay time in minutes
job-identifier — description of the task, used in Anacron messages and as the name of the job's timestamp file, can contain any non-blank characters (except slashes).
command — command to execute

For each tasks, Anacron determines if the task has been executed within the period specified in the period field of the configuration file. If it has not been executed within the given period, Anacron executes the command specified in the command field after waiting the number of minutes specified in the delay field.

After the task is completed, Anacron records the date in a timestamp file in the /var/spool/anacron directory. Only the date is used (not the time), and the value of the job-identifier is used as the filename for the timestamp file.

Environment variables such as SHELL and PATH can be defined at the top of /etc/anacron as with the cron configuration file.

The default configuration file looks similar to the following:

# /etc/anacrontab: configuration file for anacron

# See anacron(8) and anacrontab(5) for details.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# These entries are useful for a Red Hat Linux system.
1       5       cron.daily              run-parts /etc/cron.daily
7       10      cron.weekly             run-parts /etc/cron.weekly
30      15      cron.monthly    run-parts /etc/cron.monthly

Figure 22-1. Default anacrontab

As you can see in Figure 22-1, the anacrontab for Red Hat Linux is configured to make sure the daily, weekly, and monthly cron tasks are run.

Starting and Stopping the Service

To start the anacron service, use the command /sbin/service anacron start. To stop the service, use the command /sbin/service anacron stop. It is recommended that you start the service at boot time. Refer to Chapter 8 for details on starting the anacron service automatically at boot time.