Users And Access Permissions - Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual

For file compression, the obvious choice is gzip or, for a even better compression ratio,
bzip2. Just enter gzip testarchive.tar (or bzip2 testarchive.tar,
but gzip is used in this example). With ls, now see that the file testarchive.tar
is no longer there and that the file testarchive.tar.gz has been created instead.
This file is much smaller and therefore much better suited for transfer via e-mail or
storage on a USB stick.
Now, unpack this file in the test2 directory created earlier. To do so, enter cp
testarchive.tar.gz test2 to copy the file to that directory. Change to the
directory with cd test2. A compressed archive with the .tar.gz extension can
be unzipped with the gunzip command. Enter gunzip testarchive.tar.gz,
which results in the file testarchive.tar, which then needs to be extracted or
untarred with tar -xvf testarchive.tar. You can also unzip and extract a
compressed archive in one step with tar -xvf testarchive.tar.gz (adding
the -z option is no longer required). With ls, you can see that a new test directory
has been created with the same contents as your test directory in your home directory.
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 365), 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
Working with the Shell 361