Crontab Commands
Crontab is the utility used for scheduled any script and job in the Operating System Level. It comes with the Linux, HP-UX , Unix and Other Operating System.
It is very usefully utility for scheduling purpose.
To list or display all the scheduled job in crontab:
crontab -l
To add entry or change in existing job in crontab:
crontab -e
Backup of Crontab:
It will make a copy of crontab into crontab_new file.
crontab -l > crontab_new
It will make a copy of crontab into crontab_new file.
Restore of Crontab:
crontab crontab_new
It will set crontab_new as crontab
Crontab have 5 parameters for scheduling the jobs which describe time week day of month as you wish
Five Parameter:
minutes(0-59) Hours(0-23) day_of_month(1-31) month(1-12) day_of_week(0-6) (sunday=0)
Describe in the following example:
0 5 * * * sh backup.sh * * * * * command to be executed - - - - - | | | | | | | | | +----- day of week (0 - 6) (Sunday=0) | | | +------- month (1 - 12) | | +--------- day of month (1 - 31) | +----------- hour (0 - 23) +------------- min (0 - 59)
Example for scheduling
* * * * * #Runs every minute 30 * * * * #Runs at 30 minutes past the hour 15 8 * * * #Runs at 8:15 am every day 15 20 * * * #Runs at 8:15 pm every day 00 14 * * 0 #Runs at 2:00 pm every Sunday 00 5 * * Sun #Runs at 5:00 am every Sunday 30 8 1 * * #Runs at 8:30 am on the first day of every month 00 0-23/2 01 * * #Runs every other hour on the first of every month 00 * * * * #Runs on every hour
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