Understanding "crontab"

If we need to run a specific task repetitively, then the solution is to use crontab.

The syntax of the command is as follows:

$  crontab    –e

This will open a new editor. The following diagram is the syntax to add tasks. The fields to use for repeating tasks at what time are explained here:

Finally, to save the jobs, use the following:

wq        # save and quite crontab job

The following are a few examples of the crontab command:

• Use the following command to run a script every 5 minutes, every day:

  5 * * * *      $HOME/bin/daily.job >> $HOME/tmp/out  2>&1
  

• Use the following command to run 5 minutes after midnight every day:

  5 0 * * *      $HOME/bin/daily.job >> $HOME/tmp/out  2>&1
  

• Use the following command to run at 2.15 P.M. on the first of every month—the output is mailed to Paul:

  15 14 1 * * *     $HOME/bin/monthly
  

• Use the following command to run at 10 P.M. on weekdays, send the e-mail to <[email protected]>:

  0 22 * *  1-5   sendmail...