Crontab

Linux has it's own scheduler, named cron (derived from Greek chronos (χρόνος), meaning time). The Debian package contains the version written by Paul Vixie.

Cron operates by having a daemon crond running in the background, that checks once every minute to see if there are scheduled tasks to run. Tasks can be scheduled by each user by making entries in a file named a crontab. Each user has his own crontab, that cron saves in /var/spool/cron/crontabs/<username>. Furthermore, there's a general crontab in /etc, aptly named crontab. This crontab under Debian has 3 default entries:

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
# m h dom mon dow user  command
17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
#

you can schedule tasks directly in the 3 folders.

To see the current users crontab

>crontab -l

To see a users crontab

>crontab -u 'username' -l

To edit the current users crontab

>crontab -e

Now you can schedule your task

# +---------------- minute (0 - 59)
# |  +------------- hour (0 - 23)
# |  |  +---------- day of month (1 - 31)
# |  |  |  +------- month (1 - 12)
# |  |  |  |  +---- day of week (0 - 6) (Sunday=0 or 7)
# |  |  |  |  |
  *  *  *  *  *  command to be executed (full path to command/script)