crontab

Crontab command

#export to the file

crontab -l > filename

# import from the file

crontab filename 

# import from the file for the specific user

crontab -u user filename 

# edit

crontab -e 

# delete all

crontab -r 

Crontab special usage 

Entry	Description	Equivalent To
@reboot	Run once, at startup.	None
@yearly	Run once a year	0 0 1 1 *
@annually	(same as @yearly)	0 0 1 1 *
@monthly	Run once a month	0 0 1 * *
@weekly	Run once a week	0 0 * * 0
@daily	Run once a day	0 0 * * *
@midnight	(same as @daily)	0 0 * * *
@hourly	Run once an hour	0 * * * *

reference from http://en.wikipedia.org/wiki/Cron

Crontab Example

# .---------------- minute (0 - 59) # | .------------- hour (0 - 23) # | | .---------- day of month (1 - 31) # | | | .------- month (1 - 12) OR jan,feb,mar,apr ... # | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat # | | | | | # * * * * * command to be executed

min	hour	day/month	month	day/week	Execution time
30	0	1	1,6,12	*	-- 00:30 Hrs  on 1st of Jan, June & Dec.
:
0	20	*	10	1-5	--8.00 PM every weekday (Mon-Fri) only in Oct.
:
0	0	1,10,15	*	*	-- midnight on 1st ,10th & 15th of month
:
5,10	0	10	*	1	-- At 12.05,12.10 every Monday & on 10th of every month
:

 

*/8 * * * * root init 6

After 8 minutes , execute "reboot" command

ps: "*/8" in the minute time field is equivalent to "0,8,16,24,32,48,56"