Linux Desktop Hacks

Automate Your Life with cron #70

Chapter 9, Administration and Automation

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HACK

An important point to note is that cron does not actually perform these

activities itself. cron’s only function is to trigger a specific process or series of

commands at a certain time. When the specified time occurs, the com-

mands and tools that are needed to complete the activity are run. As such, to

automate a process on your computer, you need to determine how you can

complete your task with a series of command-line tools. This usually means

you need to create a script with the commands for cron to run at specified

intervals.

Create a Cronjob

The cron program reads in a special file called a crontab. This file specifies

jobs to be run and their times. You can access this file by running:

foo@bar:~$ crontab -e

This command uses the system’s default command-line editor so that you

can edit the crontab. If you want to set this editor to a different one (such as

jed), set the

$EDITOR environment variable prior to editing crontab:

foo@bar:~$ export EDITOR=jed

If this is your first use of cron, it is likely that your crontab is empty; unless

some special system cronjobs were added (these automatically added

crontabs are quite common in a number of Linux tools and utilities). Each

cronjob consists of a single line containing the time of the cronjob, as well

as the command to run.

A simple example of a crontab entry is:

30 ...