Task scheduling

The are two common ways to schedule the unattended execution of programs: at and cron.

Usually at is installed without any default rule, cron, instead is installed and required for the execution of various system event (Read: NEVER disable cron).
Cron's system config file is /etc/crontab, users can store their own cron jobs in /var/spool/cron
Many distro provide (or require) anacron in order to execute "missed" cron jobs (planned at an hour when the system was off).
As usual, besides the common textual nature, there can be different graphical tools to manage and configure cronjobs.

Analyzing the system cron configuration files is often useful. Let's see a brief overview of the major distros:

FEDORA cronjobs are configured in /etc/crontab, in the directories /etc/cron.hourly/, /etc/cron.daily/, /etc/cron.weekly, /etc/cron.monthly, /var/spoll/cron/ (cron files per single users), /etc/cron.d.
The graphical tool used is KCron (Menu System Tools - Task Scheduler).

MANDRAKE cron activities are configured exactly in the same files and directories used by RedHat.

SLACKWARE doesn't use the usual /etc/crontab file and stores the systems's cron jobs in the /var/spool/cron/crontabs/root file, the same directory can contain the cron jobs of the single users.
Similarly to other distros, in the directories /etc/cron.hourly/, /etc/cron.daily/, /etc/cron.weekly, /etc/cron.monthly can be placed scripts to be executed at the relative interval. Slack uses dcron, which is an essential and simple cron implementation rewritten from scratch.

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