Crontab Commands
export EDITOR=vi ;to specify a editor to open crontab file.
crontab -e Edit crontab file, or create one if it doesn’t already exist.
crontab -l crontab list of cronjobs , display crontab file contents.
crontab -r Remove your crontab file.
crontab -v Display the last time you edited your crontab file. (This option is only available on a few systems.)
Linux Crontab Format
MIN HOUR DOM MON DOW CMD
Schedule a cron to execute at 2am daily.
This will be useful for scheduling database backup on a daily basis.
0 2 * * * CMD
Asterisk (*) is used for matching all the records.
Schedule a cron to execute twice a day.
Below example command will execute at 5 AM and 5 PM daily. You can specify multiple time stamp by comma separated.
0 5,17 * * * CMD
Schedule a cron to execute on every minutes.
Generally, we don’t require any script to execute on every minute but in some case, you may need to configure it.
* * * * * CMD
Schedule a cron to execute on every Sunday at 5 PM.
This type of cron is useful for doing weekly tasks, like log rotation, etc.
0 17 * * sun CMD
Schedule a cron to execute on every 10 minutes.
If you want to run your script on 10 minutes interval, can configure like below. These type of crons are useful for monitoring.
*/10 * * * * /scripts/monitor.sh
*/10: means to run on every 10 minutes. Same as if you want to execute on every 5 minutes use */5.
Schedule a cron to execute on selected months.
Sometimes we required scheduling a task to be executed for selected months only. Below example script will run in January, May and August months.
* * * jan,may,aug * /script/script.sh
Schedule a cron to execute on selected days.
If you required scheduling a task to be executed for selected days only. Below example will run on each Sunday and Friday at 5 PM.
0 17 * * sun,fri /script/script.sh
Schedule a cron to execute on first sunday of every month.
To schedule a script to execute a script on first Sunday only is not possible by time parameter, But we can use the condition in command fields to do it.
0 2 * * sun [ $(date +%d) -le 07 ] && /script/script.sh
Schedule a cron to execute on every four hours.
If you want to run a script on 4 hours interval. It can be configured like below.
0 */4 * * * CMD
Schedule a cron to execute twice on every Sunday and Monday.
To schedule a task to execute twice on Sunday and Monday only. Use the following settings to do it.
0 4,17 * * sun,mon CMD
Schedule a cron to execute on every 30 Seconds.
To schedule a task to execute on every 30 seconds is not possible by time parameters, But it can be done by schedule same cron twice like below.
* * * * * CMD
* * * * * sleep 30; CMD
Schedule a multiple tasks in single cron.
To configure multiple tasks with single cron, Can be done by separating tasks by the semicolon ( ; ).
* * * * * CMD; /scripts/scrit2.sh
Schedule tasks to execute on yearly ( @yearly ).
@yearly timestamp is similar to “0 0 1 1 *”. It will execute task on the first minute of every year.
@yearly CMD
Schedule tasks to execute on monthly ( @monthly ).
@monthly timestamp is similar to “0 0 1 * *”. It will execute a task in the first minute of the month.
@monthly CMD
Schedule tasks to execute on Weekly ( @weekly ).
@weekly timestamp is similar to “0 0 1 * mon”. It will execute a task in the first minute of the week.
@weekly /bin/script.sh
Schedule tasks to execute on daily ( @daily ).
@daily timestamp is similar to “0 0 * * *”. It will execute a task in the first minute of every day.
@daily CMD
Schedule tasks to execute on hourly ( @hourly ).
@hourly timestamp is similar to “0 * * * *”. It will execute a task in the first minute of every hour.
@hourly CMD
Schedule tasks to execute on system reboot ( @reboot ).
@reboot is useful for those tasks which you want to run on your system startup. It is useful for starting tasks in the background automatically.
@reboot CMD
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