How to schedule job using cron tab in Linux

Scheduling the job by using cron tab

Cron tab allows Linux and Unix users to run commands or scripts at a given date and time. You can schedule scripts to be executed periodically. Crontab files can be used for system maintenance, backup and other repetitive tasks. The syntax is powerful and flexible, so you can run a task for every fifteen minutes or at a specific minute on a specific day.

Crontab format

Crontab contains totally 6 fields. The first 5 fields are Minute, Hour, day of month, month , day of week and the last field is command or job to be execution.

To add or update

Use the following command to add or update the job in crontab.

[root@linuxhelp Desktop]# crontab &ndash e

Now the cron file will be open, you can specify the task and also the time to be executed.

To verify

Run the following command to verify or list the created cronjob.

[root@linuxhelp Desktop]# crontab &ndash e
10 17 31 * * mkdir /root/Desktop/folder  touch /root/Desktop/file1.txt

To remove crontab

Use the option " i" and " r" , to remove crontab. It will ask confirmation notification before deleting the cron file.

[root@linuxhelp Desktop]# crontab &ndash i &ndash r
crontab: really delete root' s crontab?

To remove crontab recursively

If you want to delete the cron file recursively without confirmation notification use " &ndash r" option.

[root@linuxhelp Desktop]# crontab &ndash r

To Create cron job for specific user

[root@linuxhelp Desktop]# crontab -u user1 -e

To check cron job for specific user

Verify or list the cron job for specific user.

[root@linuxhelp Desktop]# crontab -u user1 &ndash l
29 16 31 * * mkdir dir

To assign cron job for every 15 mins and every 2 hours.

[root@linuxhelp Desktop]# crontab &ndash e
Cron tab

You can also change the mins and hours setting depends on your options.

To create multiple cron job

Create multiple cron job in single cron file.

[root@linuxhelp Desktop]# crontab &ndash e

Here the multiple jobs will be separated by semicolon ‘ ’ .

Special string in cron tab.

[root@linuxhelp Desktop]# crontab &ndash e

Instead of the first five fields, you can use any one of eight special strings. It will not just save your time but it will improve readability.

Special strings in crontabs

Special character for crontab