
Automate Your Life with cron #70
Chapter 9, Administration and Automation
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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 ...