Introduction to Periodic Processes

City College of San Francisco - CS260A
Unix/Linux System Administration
Module: Periodic Processes

Introduction

On many functioning linux systems there are tasks that need to be performed automatically. Most of these tasks are automated simply for convenience. Some tasks should only be performed when the system is otherwise idle, such as the early hours of the morning. Examples of tasks that are automated include:

updating system databases such as the whatis and locate database
installing system updates
performing backups
any maintenance task that requires significant system resources or that requires the system to be quiescent while it is performed

These tasks can be divided into three subgroups based on when they must be performed:

tasks that must be done once at a predetermined time. These tasks are submitted using atd.
tasks that must be done periodically, such as once each week. These tasks are managed by crond.
tasks that must be done periodically, but whose execution must be guaranteed as much as possible. These tasks are managed by a combination of crond and anacron.

We will begin our study with the most-used periodic process facility, cron.

Preview question: Check to see if the subsystem crond is running on your system. If so, display the contents of its master configuration file /etc/crontab.

This page was made entirely with free software on linux:
Nvu, Kompozer and Openoffice.org