Cron jobs are tasks or jobs which are scheduled to run repeatedly at specific time like hourly, daily or weekly. We make use of "crontab" command in Linux to setup a cron job.
crontab program can be called with following options:
crontab -e to edit crontab file crontab -l show existing cronjobs crontab -r remove crontab file
A crontab file contains cron jobs. each job or task is seperated by a new line. Each entry of task or job consists of six fields and each field is seperated by a space:
minute hour day month weekday command
If we want to send output of a task or job to some specific email address to notify about job, we can put following line at top of the crontab file:
MAILTO=username@domain-name.com
Examples :-
Set cron to run a task every minute
* * * * * /home/script/backup.php
Set cron to run a task once in an hour
0 * * * * /home/script/backup.php
Set cron to run a task once in a day
0 0 * * * /home/script/backup.php
Set cron to run a task on 1st and 15th of every month
0 0 1,15 * * /home/script/backup.php
Set cron to run on every monday
0 0 * * 1 /home/script/backup.php
To specify a range you can use you can use - (minus) sign like 1-5.
To specify multiple values you can seperate them by , (comma) like 1,5,9
