What is crontab in Linux

Here in this post, we will be checking is What is crontab in Linux, Crontab syntax, crontab schedule, and how to edit the crontab, how to list the crontab content

What are Cron and Crontab

• Cron is a utility in which we can schedule jobs on a Unix system.
• Cron is driven by a crontab file, a configuration file that specifies shell commands to run periodically on a given schedule.
• Every user can have their own crontab file.
• Crontab file contains the cron strings and executable file
• cron strings is a set of five or six fields separated by white space that represents a set of times
• We can use crontab as an alternative for scheduling concurrent programs at application level.

Syntax of Crontab

Example of Crontab

00,15,30,45 * * * 1-6 /u01/app/check_load.sh
15,35,55 08-22 * * 1-6 /home/applmgr/scripts/check_forms_sessions.sh

Expression in Cron

How to edit the Crontab

crontab -e
If you are doing with root user and want to edit for particuler user
crontab -e <username>

How to list the crontab

crontab -l
If you are doing with root user and want to edit for particuler user
crontab -l <username>

How to remove the crontab file

crontab -r
If you are doing with root user and want to edit for a particular user
crontab -r <username>

Cron deamon

There runs a background process called cron daemon which runs the scripts in the crontab file as per the schedule. You can check that as

ps -ef|grep cron

I hope all this information on What is crontab in Linux, Crontab syntax, crontab schedule, and how to edit the crontab,how to list the crontab content help you in daily activities

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