| openSUSE Documentation Part III. System / Chapter 19. Working with the Shell | ||||
|---|---|---|---|---|
 | 18.4. For More Information | 19.2. Users and Access Permissions |  | |
| openSUSE Documentation Part III. System / Chapter 19. Working with the Shell | ||||
|---|---|---|---|---|
| 18.4. For More Information | 19.2. Users and Access Permissions | | |
Contents
Abstract
Although graphical user interfaces have become very important and user-friendly, using them is not the only way to communicate with your system. A command line interpreter, in Unix/Linux called a shell, provides a highly flexible and efficient means for text-oriented communication with your system.
In administration, shell-based applications are especially important for controlling computers over slow network links or if you want to perform tasks as administrator on the command line.
This chapter deals with a couple of basics you need to know for making efficient use of the command line: the directory structure of Linux, the user and permission concept of Linux, an overview of important shell commands, and a short introduction to the vi editor, which is a default editor always available in Unix and Linux systems.
For UNIX or Linux several shells are available which differ slightly in behavior and in the commands they accept. The default shell in openSUSE® is Bash (GNU Bourne-Again Shell).
If you are logged in to a graphical user interface, you can start a
(login) shell parallel to the user interface or in a terminal window within
the graphical user interface. Press Ctrl+Alt+F2 to leave the graphical user interface and access a login shell.
After login, the prompt shows your login name followed by
@ and the hostname of your computer. The hostname is
followed by a colon and the path to the current directory. If you have
logged in as system administrator, root, Bash indicates this with
a hash symbol, #. Directly after login, the current
directory is usually the home directory of the user account with which you
have logged in, indicated by the tilde symbol, ~. When
you are logged in on a remote computer the information provided by the
prompt always shows you which system you are currently working on. You can
now enter commands and execute tasks. To log out from the shell, enter
exit and press Alt+F7 to switch back to the graphical user interface. You will find
your desktop and the applications running on it unchanged.
To start a terminal window within the graphical user interface in KDE or GNOME press Alt+F2 and enter xterm (or click the Konsole or GNOME terminal icon in the panel). This opens a terminal window on your desktop. As you are already logged in to your desktop the prompt shows the usual login and path information. You can now enter commands and execute tasks just like in any shell which runs parallel to your desktop. To close the terminal window press Alt+F4 .
The Konsole or the GNOME Terminal window appears, displaying the
prompt at the first line, see Figure 19.1, “Example of a Bash Terminal Window”. The prompt usually shows your login name (in this example,
tux), the hostname of your computer (here,
knox), and the current path (in this case, your
home directory, indicated by the tilde symbol,
~). When you are logged in on a remote computer
this information always shows you which system you are currently
working on. When the cursor placed behind this prompt, you can send
commands directly to your computer system.
Because the shell does not offer a graphical overview of directories and files like the tree view in a file manager, it is useful to have some basic knowledge of the default directory structure in Linux.
The following table provides a short overview of the most important higher-level directories you find on a Linux system. Find more detailed information about the directories and important subdirectories in the following list.
Table 19.1. Overview of a Standard Directory Tree
|
Directory |
Contents |
|---|---|
|
Root directory—the starting point of the directory tree. | |
|
Essential binary files, such as commands that are needed by both the system administrator and normal users. Usually also contains the shells, such as Bash. | |
|
Static files of the boot loader. | |
|
Files needed to access host-specific devices. | |
|
Host-specific system configuration files. | |
|
Holds the home directories of all users who have an account on the
system. Only | |
|
Essential shared libraries and kernel modules. | |
|
Mount points for removable media. | |
|
Mount point for temporarily mounting a file system. | |
|
Add-on application software packages. | |
|
Home directory for the superuser | |
|
Essential system binaries. | |
|
Data for services provided by the system. | |
|
Temporary files. | |
|
Secondary hierarchy with read-only data. | |
|
Variable data such as log files | |
|
Only available if you have both Microsoft Windows* and Linux installed on your system. Contains the Windows data. |
The following list provides more detailed information and gives some examples which files and subdirectories can be found in the directories:
/bin
Contains the basic shell commands that may be used both by
root and by other users. These commands include ls,
mkdir, cp, mv,
rm, and rmdir.
/bin also contains Bash, the default shell in
openSUSE.
/boot
Contains data required for booting, such as the boot loader, the kernel, and other data that is used before the kernel begins executing user mode programs.
/dev
Holds device files that represent hardware components.
/etc
Contains local configuration files that control the operation of
programs like the X Window System. The
/etc/init.d subdirectory contains scripts that are
executed during the boot process.
/home/username
Holds the private data of every user who has an account on the system.
The files located here can only be modified by their owner or by the system
administrator. By default, your e-mail directory and personal desktop
configuration are located here in form of hidden files and directories. KDE
users find the personal configuration data for their desktop in
.kde, GNOME users find it in
.gconf. For information about hidden files, refer to
Section “Key Features” (Chapter 7, Basic Concepts, ↑Start-Up).
![[Note]](admon/note.png) | Home Directory in a Network Environment |
|---|---|
If you are working in a network environment, your home directory
may be mapped to a directory in the file system other than
| |
/lib
Contains essential shared libraries needed to boot the system and to run the commands in the root file system. The Windows equivalent for shared libraries are DLL files.
/media
Contains mount points for removable media, such as CD-ROMs, USB sticks,
and digital cameras (if they use USB). /media
generally holds any type of drive except the hard drive of your system. As
soon as your removable medium has been inserted or connected to the system
and has been mounted, you can access it from here.
/mnt
This directory provides a mount point for a temporarily mounted file
system. root may mount file systems here.
/opt
Reserved for the installation of additional software. Optional
software and larger add-on program packages can be found there. KDE3 is
located there, whereas KDE4 and GNOME have moved to
/usr now.
/root
Home directory for the root user. Personal data of
root is located here.
/sbin
As the s indicates, this directory holds
utilities for the superuser. /sbin contains binaries
essential for booting, restoring, and recovering the system in addition to
the binaries in /bin.
/srv
Holds data for services provided by the system, such as FTP and HTTP.
/tmp
This directory is used by programs that require temporary storage of files.
/usr
/usr has nothing to do with users, but is
the acronym for UNIX system resources. The data in
/usr is static, read-only data that can be shared
among various hosts compliant to the Filesystem Hierarchy
Standard (FHS). This directory contains all application programs and
establishes a secondary hierarchy in the file system.
/usr holds a number of subdirectories, such as
/usr/bin, /usr/sbin,
/usr/local, and
/usr/share/doc.
/usr/bin
Contains generally accessible programs.
/usr/sbin
Contains programs reserved for the system administrator, such as repair functions.
/usr/local
In this directory, the system administrator can install local, distribution-independent extensions.
/usr/share/doc
Holds various documentation files and the release notes for your
system. In the manual subdirectory, find an online
version of this manual. If more than one language is
installed, this directory may contain versions of the
manuals for different languages.
Under packages, find the documentation included
in the software packages installed on your system. For every package, a
subdirectory
/usr/share/doc/packages/
is created that often holds README files for the package and sometimes
examples, configuration files, or additional scripts.packagename
If HOWTOs are installed on your system
/usr/share/doc also holds the
howto subdirectory in which to find additional
documentation on many tasks relating to the setup and operation of Linux
software.
/var
Whereas /usr holds static, read-only data,
/var is for data which is written during system
operation and thus is variable data, such as log files or spooling data.
For example, the log files of your system are in
/var/log/messages (only accessible for
root).
/windows
Only available if you have both Microsoft Windows and Linux installed on your system. Contains the Windows data available on the Windows partition of your system. Whether you can edit the data in this directory depends on the file system your Windows partition uses. If it is FAT32, you can open and edit the files in this directory. For an NTFS file system, however, you can only read your Windows files from Linux, but not modify them. Learn more in Section “Accessing Files on Different OS on the Same Computer” (Chapter 11, Copying and Sharing Files, ↑Start-Up).
