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18.1.6 Cleaning Up
After this crash course, you should be familiar with the basics of the Linux shell or
command line. You may want to clean up your home directory by deleting the various
test files and directories using the rm and rmdir commands. In
Section 18.3, "Important
Linux Commands"
(page 361), find a list of the most important commands and a brief
description of their functions.
18.2 Users and Access Permissions
Since its inception in the early 1990s, Linux has been developed as a multiuser system.
Any number of users can work on it simultaneously. Users need to log in to the system
before starting a session at their workstations. Each user has a username with a corre-
sponding password. This differentiation of users guarantees that unauthorized users
cannot see files for which they do not have permission. Larger changes to the system,
such as installing new programs, are also usually impossible or restricted for normal
users. Only the root user, or super user, has the unrestricted capacity to make changes
to the system and unlimited access to all files. Those who use this concept wisely, only
logging in with full root access when necessary, can cut back the risk of unintentional
loss of data. Because under normal circumstances only root can delete system files or
format hard disks, the threat from the Trojan horse effect or from accidentally entering
destructive commands can be significantly reduced.
18.2.1 File System Permissions
Basically, every file in a Linux file system belongs to a user and a group. Both of these
proprietary groups and all others can be authorized to write, read, or execute these files.
A group, in this case, can be defined as a set of connected users with certain collective
rights. For example, call a group working on a certain project project3. Every user
in a Linux system is a member of at least one proprietary group, normally users.
There can be as many groups in a system as needed, but only root is able to add
groups. Every user can find out, with the command groups, of which groups he is a
member.
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Installation and Administration
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Table of Contents
Troubleshooting
