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UNIX in a Nutshell: System V Edition

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UNIX Commands
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crontab

crontab [file]
crontab flags [user]

Run crontab on your current crontab file, or specify a crontab file to add to the crontab directory. A privileged user can run crontab for another user by supplying a user after any of the flags. A crontab file is a list of commands, one per line, that will execute automatically at a given time. Numbers are supplied before each command to specify the execution time. The numbers appear in five fields, as follows:


Minute	0-59
Hour	0-23
Day of month	1-31
Month	1-12
Day of week	0-6, with 0 = Sunday

Use a comma between multiple values, a hyphen to indicate a range, and an asterisk to indicate all possible values. For example, assuming the crontab entries below:

59 3 * * 5	find / -print | backup_program
0 0 1,15 * *	echo "Timesheets due" | mail user

The first command backs up the system files every Friday at 3:59 a.m., and the second command mails a reminder on the 1st and 15th of each month.

Flags

-e

Edit the user's current crontab file (or create one).

-l

List the user's file in the crontab directory.

-r

Delete the user's file in the crontab directory.


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