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Here is the typical field layout for a crontab entry (or multiple entries):
<pre style="font-size:18pt14pt">
.---------------- minute (0 - 59)
| .------------- hour (0 - 23)
The asterisk (*) indicate to run for that unit of time. Below is an example of crontab entries:
<pre style="font-size:14pt"> # Check every minute for logins by user “evil” '''* * * * * who | grep '^evil'''' # # Run a script called "ascript.bash" every odd hour (1,3 5...) during the week '''0 1,3,5,7,9,11,13,15,17,19,21,23 * * 1-5 /home/bob/ascript.bash''' # Run "ascript.bash" every half hour during the week '''0 */2 * * 1-5 /home/bob/ascript''' # Same... just doing it a different way '''0 */2 * * mon,tue,wed,thu,fri /home/bob/ascript'''</pre>
You will learn in the lab how to create and use the crontab utility to run a shell script automatically and periodically that will send an e-mail warning to the system administrator if disk space capacity has reached a level for immediate resolution.