Linux  Command: crontab

 usage:  crontab [-u user] file

        crontab [-u user] [ -e | -l | -r ]

                (default operation is replace, per 1003.2)

        -e      (edit user's crontab)

        -l      (list user's crontab)

        -r      (delete user's crontab)

        -i      (prompt before deleting user's crontab)

Lines that can be in the crontab file.

minute (0-59),

hour (0-23),

day of the month (1-31),

month of the year (1-12),

day of the week (0-6 with 0=Sunday).

Examples

crontab -e = edits the crontab file to be used.

0 12 14 2 * mailx john%Happy Birthday!%Time for lunch.

#crontab -e

 */1 * * * * php /var/www/html/poller.php > /dev/null 2>&1

 0 1 * * * nice -n 15 /var/www/backup.sh