crontab is used for executing scheduled processes. For example, you can run database backup everyday using schell script.
crontab -l
Above command list the all available crontab command.
crontab -e
This command can be used to edit crontab command fro your preference.
Sample crontab command is shown below. This script.sh script is executed every day at midnight.
0 0 means zero minute at zero hours(midnight).
0 0 * * * /home/sujith/script.sh
