Chapter 1. The Philosophy of System Administration

9

to months. The

crontab

command is used to manipulate the files that control the

cron

daemon that

actually schedules each

cron

job for execution.

The

at

command (and the closely related command

batch

) are more appropriate for scheduling

the execution of one time scripts or commands. These commands implement a rudimentary batch

subsystem consisting of multiple queues with varying scheduling priorities (known as niceness levels,

due to the name of the command  

nice

  used to change priorities of running programs). Both

at

and

batch

are perfect for tasks that must start at a given time, but are not time critical in terms of

finishing.

Next are the various scripting languages. These are the "programming languages" that the average

system administrator uses to automate manual operations. There are many scripting languages (and

each system administrator tends to have a personal favorite), but the following are currently the most

common:

The

bash

command shell

The

perl

scripting language

Over and above the obvious differences between these languages, the biggest difference is in the way

in which these languages interact with other utility programs on a Red Hat Linux system. Shell scripts

tend to make more extensive use of the many small utility programs (for example, to perform character

string manipulation), while

perl

scripts perform more of these types of operations using features built

into the language itself.

This means that, in order to truly master shell scripting, you will need to be familiar with the many

utility programs (such as

grep

and

sed

) that are part of Red Hat Linux. Learning

perl

, on the other

hand, is a more "self contained" process. However, many

perl

language constructs are based on the

syntax of various traditional UNIX utility programs, and as such will be familiar to those Red Hat

Linux system administrators with shell scripting experience.

1.11.2. Documentation and Communication

In the areas of documentation and communication, there is little that is specific to Red Hat Linux.

Since documentation and communication can consist of anything from adding comments to a text 

based configuration file to updating a webpage or sending an email, a system administrator using Red

Hat Linux will need access to text editors, HTML editors, and mail clients.

Here is a small sample of the many text editors available under Red Hat Linux:

The gedit text editor

The Emacs text editor

The

Vim

text editor

The gedit text editor is a strictly graphical application (in other words, it requires an active X Window

System environment), while

vim

and Emacs are primarily text based in nature.

The subject of the best text editor has sparked debate for nearly as long as computers have existed,

and will continue to do so. Therefore, the best approach is to try each editor for yourself, and use what

works best for you.

For HTML editors, system administrators can use the Composer function of the Mozilla Web browser,

or Quanta, a standalone HTML editor. Of course, some system administrators prefer to hand code

their HTML, making a regular text editor a perfectly acceptable tool as well.

As far as email is concerned, Red Hat Linux includes the Evolution graphical email client, the Mozilla

email client (which is also graphical), and the text based email clients pine and mutt. As with text

editors, the choice of an email client tends to be a personal one; therefore, the best approach is to try

each client for yourself, and use what works best for you.