Crontab

2009-09-06T11:20:52Z

Polymath69: Cleared up some misconceptions and misinformations

Scheduling jobs on [[linux]] requires two parts. The first part is having the crond daemon running. The second part is using the [[crontab]] command to create a schedule. The schedule is a list of jobs with times that you'd like to have run.

There are two versions of the command that you will use most of the time.

crontab -e
To edit your crontab file.

crontab -l
To list your crontab file.

crontab -l > crontabbackup.txt
Another use of the -l switch allows you to send the schedule to a file.

crontab crontabbackup.txt
If you use the crontab -l option and send the output to a file as was shown in the prior command example, you can take that schedule and import it into another schedule. All you have to do is use [[crontab]] and supply your backed up schedule file. This is a great trick for [[knoppix]]. The creative use of this format of the command would be to import your schedule from a [[USB]] thumb drive or a hard drive partion. You could even store the file on a MS Windows partition as long as the file is in [[linux]] format versus MS-DOS format.

man 5 crontab
Use this man command to read about the formatting requirements for your '''crontab''' files.

Note: there are two main types of crontab --
each user's crontab located in the directory /var/spool/cron/crontabs/''user'', and the main
system crontab '''/etc/crontab'''.
The '''crontab -e''' command will edit only the
per-user crontab files. Use '''sudo vi /etc/crontab'''
to edit the systemwide crontab, but use this with
caution or as a last resort as this command will
bypass the syntax checking enforced by '''crontab -e'''.

== External links ==
* [http://www.math-linux.com/spip.php?article45 Crontab : Scheduling Tasks]
[[Category:Useful Linux Commands]]

* [http://www.hxpi.com/cron_sandbox.php A safe place to experiment with crontab commands is Cron Sandbox at HxPI where you can see straightaway a future schedule of run times for whatever crontab parameters you type in.]

Knoppix Documentation Wiki - User contributions [en]

Crontab