access permissions

The access permissions of a file determine whether a user or group can read, write, or execute a file or directory. They are set by the system administrator or the owner of a file.


The account is defined by the username or login name and the password. An account corresponds to a user ID (UID).

ACL (Access Control List)

Extension of the conventional permission concept for files and directories. These allow a more fine-grained control of the access permissions.

ADSL (Asymmetric Digital Subscriber Line)

Fast transmission protocol using the telephone network.

AGP (Accelerated Graphics Port)

A high-speed slot for graphics cards, offering a higher bandwidth than PCI. AGP graphics cards can revert directly (without routing around the processor) to the random access memory.

ATAPI (Advanced Technology Attachment Packet Interface)

ATAPI is one of the most frequently used mass storage device interfaces, next to ATA or SCSI. The majority of CD-ROM drives are ATAPI devices.


A backup is a copy of data used to restore data that has been damaged or lost. Backups of all important data should be made regularly.


Maximum transfer rate of a channel for data transmission. Usually used with network connections.

BIOS (Basic Input/Output System)

Small program started after power-on or reboot of a computer. It is responsible for the initialization of hardware components. Most BIOSs allow modifications of low level system parameters via an interactive setup program. The program code resides in a read-only memory (ROM) chip.

bookmark (with browsers)

In bookmarks, save the URL of frequently visited or important Web sites. They can be sorted in folders or renamed.


The sequence of computer operations from power-on until the system is ready for use.


Program that displays the content of local files or Web pages.


A program or computer in a networking environment that connects to and requests information from a server.

command line

Text-based mode of issuing commands to the computer.


Formerly synonymous with terminal. In Linux, the virtual consoles allow the screen to be used for several independent, parallel work sessions without any graphical display running.

CPU (Central Processing Unit)

See processor.


The cursor is a block or underline character that marks the place for text input.

daemon (Disk and Execution Monitor)

A daemon is a program that runs in the background and is activated automatically when required. For example, the HTTP daemon (httpd) answers HTTP requests.

DDC (Direct Display Channel)

Communication standard between the monitor and the graphics card that allows transmission of certain parameters, such as monitor name or resolution, to the graphics card.

directory (in a file system)

A structure containing files or further directories (subdirectories). The directories in a file system build a tree-like structure for organizing files.

DNS (Domain Name System)

A protocol for converting name-based addresses to IP addresses and vice versa.


Part of the operating system that is responsible for the communication to hardware components.

e-mail (electronic mail)

The means of transporting mail electronically between users via a network. An e-mail address has the form

EIDE (Enhanced Integrated Drive Electronics)

Enhanced IDE standard that allows hard disks with a size over 512 MB.


The set of environment variables and their values kept by the shell. The user can alter (or unset) the values of existing environment variables and set new variables. Permanent assignments are made by means of the configuration files of the shell.

environment variable

An element of the environment of the shell.


A standard for data transmission in local computer networks.

EXT2 (Second Extended File System)

A file system supported by Linux.

FAQ (Frequently Asked Questions)

Acronym for documents providing answers to frequently asked questions.


A mechanism for filtering network traffic that protects a local network from unauthorized access from the outside.

FTP (File Transfer Protocol)

A protocol based on TCP/IP for transferring files over a network.

GNOME (GNU Network Object Model Environment)

A graphical desktop environment for Linux.


GNU is a project of the Free Software Foundation (FSF). The aim of the GNU Project is to create a complete and free UNIX-style operating system. It is free not so much in the sense of free of cost, but in the sense of freedom: having the right to obtain, modify, and redistribute the software. The now classic GNU Manifesto ( explains the details. In legal terms, GNU software is protected by the GNU General Public License, or GPL (, and by the GNU Lesser General Public License, or LGPL ( The Linux kernel, which is subject to the GPL, benefits from this project (especially from the tools), but should not be seen as the same thing.

GPL (GNU General Public License)

See GNU.

GRUB (Grand Unified Boot Loader)

Small program installed in the boot sector of the hard disk that starts Linux or another operating system.

home directory

A private directory in the file system that belongs to a specific user (usually in /home/<username>). Except for the superuser root, only the owner has full access rights in the home directory.


Name of a machine. This often is the name by which it can be reached on the network.

HTML (Hypertext Markup Language)

A markup language for text documents used in the World Wide Web. HTML documents are usually viewed with a browser.

HTTP (Hypertext Transfer Protocol)

A network protocol defining how to request and transfer documents in the World Wide Web. The documents are usually HTML pages offered by a server and requested by a user via the browser.

IDE (Integrated Drive Electronics)

Mass storage device interface, mainly used to attach hard disks.


Worldwide computer network based on TCP/IP.

IP address

A unique (32-bit) address of a computer in a TCP/IP network. Often written as four decimal numbers separated by periods (for example,

IRQ (Interrupt Request)

An asynchronous request for some action that can be triggered by hardware or software. Most IRQs are handled by the operating system.

ISDN (Integrated Services Digital Network)

A standard for digital data transfer over a telephone network.

KDE (K Desktop Environment)

A graphical desktop environment for Linux.


The kernel is the core component of the operating system. It manages memory and file systems, contains the drivers for the communication with the hardware devices, and handles processes and networking.

LAN (Local Area Network)

A LAN is a local network that is usually rather small.

LILO (Linux Loader)

Small program installed in the boot sector of the hard disk that starts Linux or another operating system.


A link (in a file system) is a pointer to a file. There are hard links and symbolic links. While hard links refer to the exact position in the file system, the symbolic link only points to the respective name.


High performance UNIX-like operating system core distributed freely under the GPL (GNU). The name is an acronym (Linus' Unix) and refers to its creator, Linus Torvalds. Although the name, in a strict sense, only refers to the kernel itself, the popular understanding of the term Linux usually entails the entire system.


Authentication of a user by username and password to gain access to a computer system or network.


The procedure of closing an interactive Linux session.

main memory

Volatile physical memory that allows random access with virtually no delay. This is often referred to as RAM (Random Access Memory).

man pages

Traditional form of documentation for UNIX systems that can be read using the command man. Man pages are usually written in the style of a reference.

MBR (Master Boot Record)

The first physical sector of the hard disk whose content is loaded to the main memory and executed by the BIOS. This code then either loads the operating system from a hard disk partition or a more sophisticated boot loader, such as LILO or GRUB.


Algorithm for generating hash values (MD5 checksum of a file). These checksums are generated in a way that makes it virtually impossible to create a file that has a given MD5 checksum but a different content than the original file.


The process of attaching a file system into the directory tree of the system.


Compression algorithm for audio files that reduces the data size by about a factor of ten in contrast to the uncompressed audio file. It is called a “lossy” compression because information and quality are lost in the process.


The capability of an operating system to run multiple processes (virtually) in parallel.


The capability of an operating system to let multiple users work in parallel on a computer.


A connection of several computers that allows the transfer of data between them. A computer sending a request over the network is often referred to as a client. The computer answering the request, for example, by delivering a document, is referred to as server.

NFS (Network File System)

A protocol for accessing a file system over a network.

NIS (Network Information Service)

A centralized user administration system in networks. Usernames and passwords can be managed networkwide by NIS.

operating system

See kernel.


A section of a hard disk, containing either a file system or swap space.


Unique description of a file's position in a file system.

plug and play

Automatic hardware detection and configuration protocol.


A running program. Sometimes referred to as a task.


The processor (CPU, for Central Processing Unit) is a microchip that executes machine code stored in the main memory. It is the brain of the computer.


A short (configurable) string that is printed at the start of each command line. It usually contains the current working directory.


A standard defining interfaces and communication methods for hardware, software, or networks. Examples are the HTTP and the FTP protocol.


Typically refers to a computer that serves as intermediate storage for data transferred from the Internet. If the same document is requested more than once, the second request can be served much faster. Computers intended to take advantage of this must be configured to issue their requests via the proxy.

RAM (Random Access Memory)

See main memory.


A file system type that allows for fast repair of potential inconsistencies. Such inconsistencies can occur when a file system is not unmounted before the operating system is shut down, such as in the event of a power failure.


The superuser account. The superuser has all permissions. This account is used for administrative tasks and should not be used for regular work.

root directory

The base directory in the file system hierarchy. In UNIX, the root directory is represented as a /.

SCSI (Small Computer Systems Interface)

A standard for attaching hard disks and other devices, such as scanners and tapes.


A computer or program dedicated to offering services, usually over the network. Examples of services are file delivery, name resolution, and graphical rendering.


A program that allows issuing commands. There are serveral shells, such as Bash, Zsh, and tcsh. Each type of shell has its own specific programming language.

SMTP (Simple Mail Transfer Protocol)

Protocol for transferring electronic mail (e-mails) over a network.

SSH (Secure Shell)

A remote login program that uses encryption. It is a more secure alternative to telnet.

SSL (Secure Socket Layer)

Encryption protocol for transferring HTTP data.


See root.

swap space

A hard disk partition (swap partition) that is used to store memory pages that are currently unused.

system administrator

A person responsible for maintaining a system. This person uses the root account to perform administrative tasks.


See process.


Communication protocol used for the Internet and most local networks.


Telnet is a protocol for the communication with remote hosts. For remote login, telnet is essentially superceded by SSH, which offers encrypted connections.


Formerly, the designation of a keyboard and monitor combination connected to a central computer. Today this term is instead used for programs (like xterm) that emulate a real terminal.


Name of the Linux penguin. See


UNIX is a type of operating system. It is also a trademark.

URL (Uniform Resource Locator)

Specification of a resource in the network consisting of a protocol (for example, http://), the name of the host and domain (such as and a document (for example, /us/company/index.html). The complete URL of this example is

user directory

See home directory.

VESA (Video Electronics Standard Association)

Industrial consortium that defines, among other things, video standards.

wild card

Placeholder for one (symbol: ?) or more (symbol: *) characters. These are parts of regular expressions.

window manager

A program running on top of the X Window System that allows for actions, such as resizing windows or moving them around. The window manager is also responsible for the window decoration like window titles and borders. The behavior and look can be customized by the user.

WWW (World Wide Web)

Based on the HTTP protocol, this is a hyperlinked collection of documents, files, and images that can be viewed with a Web browser.

X Window System

The X Window System is a network-based window system that runs on a wide range of computers. It offers mechanisms for drawing lines and rectangles. It is the middle layer between the hardware and the window manager.


Version 11 of the X Window System.

YaST (Yet another Setup Tool)

The SUSE LINUX administration tool for installing and configuring a system.

YP (Yellow Pages)

See NIS.

SUSE LINUX Administration Guide 9.3