A linux demon useful to schedule tasks (i.e., execute some scripts).

To edit contab file:

crontab -e

To list the scheduled tasks:

crontab -l

Example:

0 3 * * * /home/user/crontab_backup.sh > /dev/null 2> /home/user/crontab_backup.error

this command executes the script crontab_backup.sh that is in the directory /home/user every day at 3am. The output of the script is discharged (i.e., stdout is redirected to /dev/null), while errors (writes on stderr) are redirected in the crontab_backup.error located in the directory /home/user.

Examples regarding the scheduling:

• 0 3 * * 2,4,6 : The command is executed at 3am the days of the week number with numbers 2, 4 and 6 (numbers are: 0-Sunday, 1-Monday, 2-Tuesday, 3-Wednesday, 4-Thursday, 5-Friday, 6-Saturday)
• 30 3 * * * : The command is executed at 3:30am every day
• 30 3 1 * * : The command is executed ad 3:30am every first day of every month