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page 35

2.3.1 Security

Security is not a significant problem for a computer that is not connected to a network, and

passwords will protect it from ‘honest thieves’. When connected to a network there is potential for

security problems. These problems become more serious when the computer is connected to the

network 24 hours a day. General rules to keep a computer safe (this applies to non-Linux comput-

ers also) are:

keep user passwords safe - these can be the start of a security breach protect the root password - loosing this throws the system wide open

shut down unneeded programs - network programs sometime have bugs that open doors apply patches - software updates help close security holes

2.4 INTERMEDIATE CONCEPTS

Above the basic features of the Linux system are a number of more advanced features and

commands. Some of these are listed below.

pine a simple interface for mail usage

mail a somewhat bothersome mail tool (see pine). man func bring up a manual page for ’func’

man -k stringbrings up information on ’string’

tar -xvf file.tar extract files from an archive file ’file.tar’

tar cvf - files > file.tar put ’files’ into an archive file ’file.tar’

2.4.1 Shells

When one logs into a Linux system, you are actually running a program (shell) this is in some

ways similar to DOS. In the standard shell you are given a prompt, where you type your com-

mand. If it is not a built-in command, it searches on the disk according to a user-specified search

path, for an executable program of that name. Almost all commands are programs that are run in

page 36

this manner. There are also executable shell scripts, similar to command files on DOS. Linux is limited to running a program of a size equal to the sum of its memory, and swap space. As the system is multi-tasking, any program (or part thereof) that is not currently being run when extra memory is required, is swapped (moved) out to the disk, until it is ready to run again.

In shells there are environment variables set. Some of the commands that can be used to view these are shown below. They can be set by editing the appropriate text files.

alias

prints a list of command aliases

printenv

prints a list of the environment variables

set

prints a list of the environment variables

2.4.2 X-Windows

The GUI in Linux is actually two programs working together. The basic program is called X windows, and it provides basic connection to the screen, mouse, keyboard and sound card. The look-and-feel of the GUI is provided by the window manager. One simple window manager is called ‘fvwm’ and it can behave like Windows 95/98. Newer window managers include Gnome and KDE. While these both provide similar capabilities and features, most users develop personal preferences for a single window manager.

2.4.3 Configuring

Devices and settings can be configured under X-windows using graphical tools. Settings can also be configured with text files, but this is not necessary. Examples of settings that the user or root might want to change are:

Modem properties for internet connection

Network card properties for connection to a LAN

Printer type and location