A cron job is the scheduled task by itself which can be very useful for repetitive tasks. The cron is a utility for scheduling a command or script on your server to run automatically at a specified time and date. Removing crontab files for another user requires superuser privileges. Here username specifies the name of the user’s account for which you want to remove a crontab file. If you accidentally type the crontab command without an option, press the interrupt character from your editor.
Command to remove all cron job as root user
crontab -r