THE VIRTUAL SERVER HANDBOOK

Managing with Cron

 Cron enables you to schedule things to be done automatically. Cron is the

system scheduler for Unix. Using Cron, you can schedule events to occur

daily, weekly, monthly, hourly or whenever. Any command or set of

commands you can run from a Telnet prompt can be run from Cron. For

detailed information on Cron you can Telnet to your server and type "man 5

Crontab" at the command prompt. Much of the information in this section is

taken from the man (manual) page written by Paul Vixie.

Each Virtual Server can load its own Cron job to execute scheduled tasks.

The most effective way to use Cron is to load the scheduled tasks into the

Cron daemon from a file that you have created and stored on the Virtual

Server. Although it is possible to manipulate Cron directly, loading Cron

jobs from pre formatted files will ensure that you have a copy of the file

around for editing and for archival purposes. A common place to put such a

Cron file is in a directory called " Cronfiles" in your ~/etc directory.

To make the "Cronfiles" directory

1.

Connect to your Virtual Server via Telnet.

2.

Enter:

% cd ~/etc

% mkdir cronfiles

You can then store the file(s) holding your Cron information in this

directory. After you have made the Cron file, you need to load it into the

Cron program (daemon).

To load a file into the Cron program

1.

Change directories to where the file is located on your Virtual Server.

% cd ~/etc/cronfiles

If you have placed a Cron file in the directory named my_ cron_file, load

the file into the Cron program by typing:

% crontab my_cron_file

A copy of the Cron file you created is in memory in the Cron program. To

view Cron s copy in memory, you can call the Cron program with the "list"

option:

% crontab  l

Cron has other command line options such as "edit" and "remove". These

commands will allow you to manipulate the information that Cron has in

memory. For example, if you wanted to add another event to the Cron

information, you could use the Crontab  e option:

% crontab  e

This will take the copy of the entry that is stored in the Cron programs

memory, and allow you to edit it. This is however a less preferable option

than changing the physical file and re loading it into Cron because the

changes will not be physically stored anywhere accept in Cron's memory.

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