| Lesson 9 | Periodic processes |
| Objective | Describe the main ways to automate a periodic process. |
Unix Periodic Processes
Some UNIX processes, such as those associated with the kernel, run at all times. However, you will want some applications to run only at specific times. For example, you may want to schedule a backup of your system at only those times when the backup will not adversely affect network performance. Other common tasks include automatically deleting files, using tar on old log files, and scheduling periodic maintenance. Any process that you want to schedule is called a periodic process. One of the standard UNIX daemons that allows you to automate periodic processes is
cron.
What is cron?
The cron daemon allows you to perform two functions:
- Automate the running of processes and applications
- Schedule a certain time for this process to run on a system
If you configure cron correctly, it will run at boot time, then continue running until you issue a kill command or shut the system down.
Other ways to automate
You can use the at command in much the same way as cron. The at command, however, runs a program at one specified time.
The batch command executes commands entered from standard
input. This command functions much like the at command, but does not bog down the system.
Continuing with cron
The next lesson will continue our exploration of cron. You will learn how to configure a cron job and get some practice,
too.
daemon: A daemon is a process that is not associated with any terminal and which is dedicated to handling a particular task.
kernel: The kernel is the core of the UNIX operating system. The kernel remains hidden from typical users.
tar:The tar utility is an archiving program that allows you to back up directories or files quickly. It is used in many smaller backups and less sophisticated archiving procedures.