Schedule Tasks In Linux With CRON

Schedule Tasks In Linux With CRON

                                      There is an utility in Linux known as CRON with which you can start your jobs automatically at a desired time and schedule them to get executed periodically.

                                     Cron utility consists of two parts: The cron daemon and the cron configuration files. Cron daemon is just like any service that is started automatically whenever your system boots. Cron configuration files hold the information of what to do and when to do

1. Edit a Crontab Entry :- crontab -e
2. Select Favorite editor.If You select any other option, use the following command to open in VI editor

            export VISUAL=vi

     3. Create a new crontab file from another user

            crontab -l > name  (Created in Present Working Directory)

     4. Listing the Cron Jobs :- crontab –l

     5. To enlist the cron jobs for a particular user :- crontab –u [USER] –l

Example :- crontab –u root –l

     6. For deleting Crontab entry : - crontab -r

     7. For activating crontab entry : - crontab crontab name

Crontab syntax :-

                                           A crontab file has six fields for specifying minute, hour, day of month, month, day of week and the command to be run at that interval. See below:

• 1: Minute (0-59)
• 2: Hours (0-23)
• 3: Day (0-31)
• 4: Month (0-12 [12 == December])
• 5: Day of the week(0-7 [7 or 0 == sunday])
• /path/to/command - Script or command name to schedule

Easy to remember format:

*     *     *     *     *  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)

Sample :-

1. Created a bash script for making directory

root@IPAM:/home/ictops#vi job.sh

mkdir -p /home/ictops/test1

mkdir -p /home/ictops/test1

      2. Provide Executable permission :- chmod +x /home/ictops/job.sh

      3. Add this batch file “job.sh” into crontab entry for sheduling task

        root@IPAM:/home/ictops#crontab -l > mycron   

            no crontab for root

        root@IPAM:/home/ictops#crontab -e

no crontab for root - using an empty one

root@IPAM:/home/ictops#crontab -l > mycron   

root@IPAM:/home/ictops#crontab  mycron