Linux: Crontab - Brief

I always get confuse whenever I want to set a new cron job. The confuse is with regard to the options too be set!
For those who new to 'cron', its nothing but, an event scheduler in Linux. That means, you can schedule any script to run at any time you wanted to. Its just the system/server should be up and running!

cron job is specific to every user in Linux/Unix. So, one can't see other's cron unless the necessary privileges or sudo root access given.

Whatever, here is the options in cron:


To check cron jobs:

[root@localhost kiran]# crontab -l
no crontab for root

To set cron jobs:

[root@localhost kiran]# crontab -e

After adding, here is how it looks:

[root@localhost kiran]# crontab -l

##Script to test

00 */2 1-31 * 0,2,3   sh /home/kiran/test.sh >> /dev/null

Every Cron job should be given with 5 options:

• minute -> 0-59
• hour -> 0-23
• day of month -> 1-31
• month -> 1-12 
• day of week -> 0-7 (0 is Sunday )

In the above example:

00 -- 0th Minute

*/2 -- Every 2 hours

1-31 -- Every day (1 to 31)

* -- Every Month

0,2,3 -- Sunday,Tuesday,Wednesday