The system administrator's home directory. See also root and root. 419 scam

A type of spam that violates section 419 of the Nigerian Criminal Code. Such spams purport to be ways to make money by brokering shady funds transfers from Nigeria or other countries. Those who respond actually encounter increasing demands for cash to facilitate the promised funds transfers, which never occur.

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^ previous access control list (ACL)

An access control list (ACL) is an advanced file-access control tool that's growing in popularity. ACLs permit finer-grained control of who may access a file than do the older (and still more popular) Unix-style ownership and permissions. ACL

See access control list (ACL). Advanced Linux Sound Architecture (ALSA)

An alternative sound protocol to the standard Open Sound System. ALSA drivers are being integrated into the 2.5.x kernel series. Advanced Technology Attachment (ATA)

The most common means of connecting hard disks to IA-32 and other small computers. See also ATAPI and SCSI. AGP bus

The Accelerated Graphics Port bus, a standard for interfacing video cards to motherboards. Most video cards sold since 2000 use AGP interfaces. Alpha

The Alpha CPU architecture was moderately popular among Unix workstations in the

1990s, but its future is uncertain.


See Advanced Linux Sound Architecture (ALSA). American Standard Code for Information Interchange (ASCII)

The most common encoding method for plain text. ASCII assigns a single 8-bit number to each symbol (uppercase and lowercase letters, numbers, punctuation, and so on), as well as to some special functions, such as a "bell" (a tone played when the character is displayed on the screen).


See font smoothing. API

See application programming interface (API), application programming interface (API)

A set of functions provided by an operating system, user interface, driver, or the like for the benefit of other programs.


See American Standard Code for Information Interchange (ASCII). ATA

See Advanced Technology Attachment (ATA). ATA Packet Interface (ATAPI)

A software extension to the ATA interface that supports commands for CD-ROM drives, tape drives, and other non-hard-disk devices. ATAPI

See ATA Packet Interface (ATAPI).

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Bayesian spam filters

See statistical spam filters, binary

1: A number system in which only two digits exist: 1 and 0. Computers work on binary numbers at their lowest levels. 2: A file format in which data are encoded in a way that's not readily interpretable by humans. Binary data files may be raw dumps of in-memory representations, compressed data, or otherwise hard to interpret. This contrasts to an ASCII file. 3: A program file generated by a compiler. bitmap

A type of graphic format in which individual pixels are mapped one-to-one onto the computer display. Bitmap graphics formats include GIF, JPEG, TIFF, and PNG. Bitmap fonts are also common, although they're losing ground to outline fonts. block device

A hardware or simulated hardware device that performs input/output operations in multibyte groups, such as 512 bytes or 2,048 bytes at a time. Disk devices are examples of block devices. This contrasts with character devices. boot loader

A small program, often stored in the boot sector, that directs the boot process. Simple boot loaders can boot just one OS, but more complex boot loaders enable you to select which OS to boot. These complex boot loaders often rely on files outside of the boot sector. Sometimes a primary boot loader in the boot sector calls upon a secondary boot loader stored elsewhere to finish the job. boot sector

The first sector of a disk, which contains code that directs the computer's boot process. See also MBR.

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In networking, a type of network packet that's addressed to many or all computers. At a low level, computers use broadcasts to locate each others' hardware addresses. Some protocols, such as DHCP, also rely on broadcasts to provide basic functionality, buffer overflow

A type of programming error in which input data exceeds the space used to store it. The result can be that the excess data ends up in other data's storage space, or even in the space used by executable code. Typically, the result is a program crash; but clever crackers may use buffer overflows as a way of getting their own code to run on a computer, thereby giving them access to the system, bug

1: An error in a program or, less commonly, hardware design. 2: A tool used to track who reads e-mail and when they read it. The sender incorporates a reference to a tiny graphics file as a URI in an HTML-enabled e-mail message and checks server log files to see when that graphics file is accessed, bus

A hardware system for passing data between components. The PCI, AGP, and ISA busses are common internal busses. The ATA and SCSI busses connect computers to hard disks; and the USB bus connects computers to some external devices.

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central processing unit (CPU)

The computer component that runs the OS and most programs.

See Compact Flash (CF). CGI script

A Common Gateway Interface script is a program that a web server runs to generate a web page to be delivered to the client. CGI scripts enable web servers to deliver dynamic content based on user input, character device

A hardware or simulated hardware device that performs input/output operations a byte at a time. Examples include serial ports, parallel ports, and the keyboard. This contrasts with block devices. child

In reference to Linux processes, the process that was launched from a specific parent process.


A set of one or more chips that together provide the core functionality of a circuit board. Linux drivers are typically written for chipsets, because one chipset may be used in dozens of boards sold by different manufacturers. CHS geometry

The cylinder/head/sector geometry is a way of addressing a specific cylinder on a hard disk by using three numbers. This contrasts with LBA mode. The IA-32 BIOS uses CHS geometry in its oldest modes, and this method is used for some low-level disk data structures. See also head and sector.


See complex instruction set computer (CISC), client

A network program that initiates a data transfer with a server. People often run and directly control network clients, such as web browsers and e-mail readers. CMYK

See cyan/magenta/yellow/black (CMYK). Common Unix Printing System (CUPS)

The printing software that's emerging as the new printing standard in the Linux world, pushing aside the older LPD systems. CUPS uses the /PP standard for network printing.

Compact Flash (CF)

A hardware format for solid-state data storage. It's commonly used by MP3 players, digital cameras, and other portable consumer electronics that may or may not interface with a computer. CF readers for computers are available, and Linux can treat them like hard disks, compiled program

A program that's transformed from its original human-readable source code form into instructions that can be executed directly by the CPU. Compiled programs run quickly, but are more tedious to develop than interpreted programs. compiler

A program that converts source code into a compiled program (aka object code or a binary file).

complex instruction set computer (CISC)

A CPU that can perform a wide range of operations using a single CPU command for each operation. CISC CPUs tend to be large and complex compared to RISC CPUs. The IA-32 architecture is a CISC architecture. CPU

See central processing unit (CPU), cracker

A computer miscreant. Crackers break into computers they're not authorized to access. Often referred to as hackers by the general media.


See Common Unix Printing System (CUPS), cyan/magenta/yellow/black (CMYK)

A color encoding scheme that describes every color as a combination of the four colors cyan, magenta, yellow, and black. CMYK color encoding is common on printers. This contrasts with RGB color encoding, cylinder

In disk technology, a cylinder is a collection of matching tracks from multiple disk platters. Each track in a cylinder lies directly atop or below others in a collection of platters. See also sector and head.

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A program that runs in the background to perform some helpful task. (The word daemon is derived from the Greek for "helper.") Most servers run as daemons. DDoS attack

A distributed denial-of-service attack is a type of network attack that uses many computers to saturate your network's bandwidth, effectively shutting down your Internet access. Debian package

A package format used by Debian GNU/Linux and its derivatives. Debian packages are roughly comparable to RPM files, but the two file formats aren't directly compatible, default policy

In firewall configuration, this is what the firewall does with packets that don't match any explicit rules, desktop environment

An integrated software package that includes a window manager, file manager, and assorted small utilities such as calculators, image viewers, text editors, and so on. GNOME and KDE are the two most popular desktop environments for Linux. DHCP

See Dynamic Host Configuration Protocol (DHCP), direct memory access (DMA)

A method of transferring data between memory and peripherals such as hard disk interfaces, Ethernet cards, and sound cards. DMA uses little CPU overhead, so it's better for multitasking OSs such as Linux than the competing PIO mode.

dirty bit

A flag on a disk filesystem that indicates whether the filesystem is currently in use (that is to say, it's "dirty"). When a computer unmounts the filesystem, it clears the dirty bit flag; when it mounts the filesystem, it sets the flag. If the computer detects the dirty bit when mounting a filesystem, that's an indication that a system crash or other problem happened, and that the filesystem may be in an unstable state. DMA

See direct memory access (DMA). DNS

See Domain Name System (DNS). Domain Name System (DNS)

A method of converting hostnames to IP addresses and vice versa. DNS relies on a series of distributed DNS server computers, which know the mappings for their own subset of the Internet. DoS attack

A denial-of-service attack is a type of cracker activity designed to prevent you from using your computer or network. See also DDoS attack.


A software component that manages a hardware device or filesystem. Using drivers enables user software to access hardware with differing designs using the same commands. For instance, a CD-R package doesn't need to know whether you've got an Adaptec or Initio SCSI adapter. Dynamic Host Configuration Protocol (DHCP)

A popular method of assigning IP addresses and related information to clients on a network.

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See enhanced capabilities port (ECP). emulator

A program that runs one operating system's programs inside another OS. Some emulators run an entire OS within another OS, and a few even emulate the target OS's hardware, enabling you to run, say, Microsoft Windows on a Macintosh, enhanced capabilities port (ECP)

The most recent standard for parallel printer ports. See also SPP and EPP. EPP

See enhanced parallel port (EPP). enhanced parallel port (EPP)

An improved parallel printer port design capable of higher speeds than the original

SPP design. See also ECP.


Used as a noun, refers to directories served to other computers via an NFS server. ext2fs

See Second Extended Filesystem (ext2 or ext2fs). ext3fs

See Third Extended Filesystem (ext3 or ext3fs).

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Fast File System (FFS)

A filesystem used by FreeBSD and related OSs. It's supported in Linux through the ufs driver. See also UFS.

See File Allocation Table (FAT). FFS

See Fast File System (FFS). File Allocation Table (FAT)

The filesystem used by DOS and Windows 9x/Me. It can also be used by many other OSs, including Windows NT/2000/XP, OS/2, BeOS, Mac OS, Linux, and most other Unix-like OSs. The filesystem is named after an important data structure it uses internally, file manager

A program that provides a GUI or menu-based interface for manipulating files. A file manager is an important component of most desktop environments, but stand-alone file managers are also available, filesystem

1: A set of data structures written to a disk to support accessing files by name. Common Linux filesystems include ext2fs, ext3fs, ReiserFS, JFS, and XFS. FAT is a common filesystem from the Windows world. 2: A directory tree, such as/usr and all the directories and subdirectories it contains. File Transfer Protocol (FTP)

An old but popular protocol for transferring files across TCP/IP networks, firewall

A router that's configured to restrict access between two networks as a security measure. The word can also be applied to software that protects a single computer from the outside world.

A collection of characters rendered in a particular style; a typeface, font server

A network server that delivers font data to the same or other computers. Font servers can simplify font configuration on large networks, font smoothing

A technique for font display in which some pixels are gray rather than black or white. The result is an illusion of higher resolution than the monitor can deliver. Some people like this effect, but others say that it makes characters look blurry. Also called anti-aliasing, fork

The act of creating a new process. One process forks another one, enabling one program to start another one running. See also spawn.


Applied to disks, refers to the data structures written on the disk to support holding and accessing data. The word format may be used as a verb to refer to the process of writing this data to the disk. See also low-level format and high-level format. FPU

A floating-point unit. See math co-processor. Free Software Foundation (FSF)

An organization devoted to developing and promoting free software. In this context, free refers to freedom (as in "freedom of speech") more than to price. Free software is a specific type of open source software, frame buffer

1: A buffer that holds a single image, as in a video processing system. 2: A method of abstracting video hardware, allowing a single XFree86 driver, fbdev, to handle many video cards.

See Free Software Foundation (FSF). FTP

See File Transfer Protocol (FTP).

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A router computer. Ghostscript

A program that converts PostScript into various other formats, including bitmap formats useable by many non-PostScript printers, common bitmap graphics file formats, and Adobe's Portable Document Format (PDF). Ghostscript is an integral part of many Linux systems' printer queues. GNU's Not Unix (GNU)

A recursive acronym referring to a software project sponsored by the FSF to develop a free Unix-like OS. Many Linux components derive from the GNU project, but the Linux kernel was developed independently. Grand Unified Boot Loader (GRUB)

One of two common boot loaders for Linux. GRUB

See Grand Unified Boot Loader (GRUB).

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1: A person who's skilled with computers, and especially with computer programming, and who uses that skill for productive and legal purposes. 2: A computer miscreant; a cracker. The media generally uses this second definition, but the first is more common in the Linux community, head

In disk technology, a head is a device that reads data from and writes data to a disk. Heads rest at the ends of pivoting arms so that they can be moved over any track on a hard disk. On most disks, heads are stacked so that they mark out cylinders built from tracks. See also sector, high-level format

A type of disk format that holds filesystem data, hostname

A name assigned to a computer, such as Hostnames consist of a machine portion (the part before the first dot—www in this example) and a network portion ( in this case). HTML

See Hypertext Markup Language (HTML). HTTP

See Hypertext Transfer Protocol (HTTP). Hypertext Markup Language (HTML)

A file format used by most web pages. HTML is plain ASCII text with certain characters and character groups assigned special meanings. Hypertext Transfer Protocol (HTTP)

The protocol upon which the Web is based. Its most common use is in transferring files from a web server to a web browser.

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See Intel Architecture 32 (IA-32). IA-64

See Intel Architecture 64 (IA-64). I MAP

See Internet Message Access Protocol (IMAP). ¡node

A low-level data structure in a filesystem. The inode points to a specific file and holds information such as the file's creation time, owner, and permissions. Intel Architecture 32 (IA-32)

A 32-bit CPU architecture designed by Intel. IA-32 CPUs have dominated the market from the late 1980s through the early 2000s. Also known as x86. Intel Architecture 64 (IA-64)

A 64-bit CPU architecture designed by Intel. In 2003, its market penetration is slim, but Intel aims to wean consumers from the older IA-32 architecture onto IA-64. Internet Message Access Protocol (IMAP)

A popular pull protocol for mail transfer. IMAP transfers are initiated by mail readers so that users can retrieve their mail from mail servers. IMAP is more complex than the competing POP. Internet Printing Protocol (IPP)

The printing protocol used by CUPS, the printing system that's becoming the Linux standard.

Internet Protocol (IP)

A key component of TCP/IP networking, interpreted program

A program that's run by an interpreter, which reads the program file as created by the programmer and interprets it line-by-line. Interpreted programs run slowly, but they are relatively easy to develop. This approach contrasts with compiled programs. interpreter

A program that runs interpreted programs.

See Internet Protocol (IP). IP address

A4-byte address, such as, assigned to a computer on a TCP/IP network.

See Internet Printing Protocol. IPv4

See Internet Protocol version 4. IPv6

See Internet Protocol version 6. Internet Protocol version 4 (IPv4)

Currently the most common version of IP. It is the basis for most of the Internet as it's implemented in 2003. IPv4 supports 32-bit addressing, for a theoretical maximum of 4,294,967,296 addresses. Internet Protocol version 6 (IPv6)

The next-generation version of IP. The Internet will most likely shift to IPv6 sometime this decade. IPv6 supports 128-bit addressing, for a theoretical maximum of 3.4 x

10 addresses. ISA bus

The Industry Standard Architecture bus is a standard for connecting components such as parallel ports, sound cards, and modems to computers. In 2003, the ISA bus has been largely abandoned in favor of the PCI bus and AGP bus, but you may still have ISA devices on older computers. ISO-9660

Named after the International Standards Organization document that defines it, this filesystem is the standard cross-platform lowest-common-denominator filesystem for CD-ROM, CD-R, and similar media. The Linux mkisofs program can create an ISO-966Q filesystem.

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See Journaled File System, journal

A data structure used by a journaling filesystem. Journaled File System (JFS)

One of four journaling filesystems that are available for Linux. JFS was originally developed by IBM, has been added to the 2.4.20 kernel, and it can be added after the fact to older kernels. Some distributions, such as SuSE, ship with it and make it available as an install-time option, journaling filesystem

A type of filesystem that maintains a journal, or a data file that holds information on pending operations. After a power outage or crash, the computer can use the journal to speed up checking the disk contents, thereby greatly reducing the startup time after a crash. Linux supports four journaling filesystems: ext3fs, ReiserFS, JFS, and XFS.

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The core of an OS. The kernel assigns memory to programs, dishes out CPU time, provides an interface between programs and hardware, and manages filesystems. Technically, Linux is just a kernel; everything else, including X, user programs, and so on, runs atop the kernel. See also module.

In cryptography, a number that's used along with a precisely defined algorithm to encrypt or decrypt data.

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1: The time required for a data packet to pass from a sender to its recipient on a network. In practice, round-trip latency—the time for a packet to travel to its destination and a reply to be received by the original sender—is frequently measured. 2: The time required for a data block to rotate under a read/write head on a disk device. LBA mode

Logical (or Linear) Block Addressing is a method of specifying an individual sector to be read from a hard disk by using a single number. This method contrasts with CHS geometry. Most systems favor LBA mode once booted, but CHS mode is still required for some operations. LILO

See Linux Loader (LILO). Line Printer Daemon (LPD)

A printing system that's long been dominant in the Linux world, but that's losing ground. Two common LPD systems for Linux are the original BSD LPD and LPRng. Both are still available, but most distributions have switched to CUPS and its IPP. Linux Loader (LILO)

One of two boot loaders for Linux, load average

A measure of the demand for CPU time placed on a system. A load average of 0.0 means few or no programs are actively using the CPU. A load average of 1.0 means the demand for CPU time is exactly equal to the available CPU time. Load averages above 1.0 mean that the kernel must ration CPU time delivered to individual programs.

This document was created by an unregistered ChmMagic, please go to to regist* lossy compression

A compression scheme in which the decompressed data doesn't exactly match the input data. Lossy compression is useless for storing program files, databases, and so on, but it is often useful for audio, graphics, and video files. In these applications, humans are unlikely to notice the lost data, assuming the compression ratio isn't set too high, low-level format

A type of disk format that defines low-level data structures such as sectors and tracks. Hard disks are low-level formatted at the factory, but floppy disks may need to be low-level formatted with fdformat before they can be used. LPD

See Line Printer Daemon (LPD).

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MAC address

The Media Access Control address is a low-level address associated with network hardware. Network hardware responds to packets addressed to its MAC address or to broadcast packets. The network stack converts an IP address into a MAC address when sending data. Master Boot Record (MBR)

The MBR is closely related to the boot sector; it's the code in the boot sector that directs the boot process. The MBR frequently holds the primary boot loader. math co-processor

A chip or part of a CPU that handles floating-point arithmetic—arithmetic that involves numbers that might not be integers, such as 208.3 or-0.00005. Also known as an FPU. MBR

See Master Boot Record (MBR). MIME

See Multipurpose Internet Mail Extension (MIME), mixer

A program that adjusts the volume levels of various sound inputs and outputs. You can use a mixer to get good sound levels from such varied audio sources as audio CDs and MP3 file playback, module

A software component that can be loaded into another one. The word is frequently applied to kernel modules, which contain hardware drivers or other components of the Linux kernel.

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The process of making a removable disk or partition available as a directory in the Linux directory tree. A command of the same name accomplishes this task. See also mount point, mount point

A directory that serves as an access point for a partition or removable disk. For instance, if /mnt/cdrom is the CD-ROM mount point, then files on the CD-ROM are available in /mnt/cdrom or its subdirectories, once the CD-ROM is mounted. Multipurpose Internet Mail Extension (MIME)

A code that identifies the type of data a file contains. File managers, Web browsers, e-mail clients, and other tools all rely on MIME types to tell them what application should handle particular file types. MX record

A mail exchanger record is a type of entry in a DNS server that points to a domain's mail server.

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See Network Address Translation, netmask

See network mask. Network Address Translation (NAT)

A technique used by some routers that enables an entire network to "share" a single external IP address. NAT is particularly popular among home broadband users and to stretch a limited supply of IP addresses in businesses that don't want to pay for more than they must. Network File System (NFS)

A popular protocol for sharing files among Unix-like OSs. NFS exports can be mounted like local filesystems, giving remote systems convenient access to a server's files.

network mask

A numeric code that separates the network and machine portions of an IP address. network stack

A set of kernel routines that interface between programs and a network. To communicate on a network, two computers require compatible network stacks to pack and unpack data. The most common network stack today is TCP/IP. Network Time Protocol (NTP)

A network protocol for synchronizing two or more computers' clocks. NFS

See Network File System (NFS).

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See Network Time Protocol (NTP).

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A type of computer program file consisting of code that's been compiled by a compiler, usually into binary format for the target CPU. open relay

A mail server that's configured to relay mail from any site to any other site. Open relays were once common, but in the past decade, their abuse as a tool for sending spam has driven all responsible mail server administrators to close their mail servers. Open Sound System (OSS)

The primary sound standard for Linux. Two sets of OSS drivers are available: standard drivers that come with the kernel and an expanded commercial set available from 4Front Technologies, open source software

Software for which the source code is readily available and for which users have the right to modify and redistribute both the source code and compiled binaries. The Linux kernel and most or all programs that ship with Linux distributions are open source, orphan

A process whose parent has terminated. Orphans are "adopted" by init, the first regular process.

See Open Sound System (OSS).

See open source software. (Microsoft frequently uses the OSS acronym in this way, but its use elsewhere is rare.) outline font

A font that's described in terms of lines and curves. To display such a font on the screen, the system must rasterize it into a bitmap font, format.

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A collection of files that provides a logically related set of features, such as a family of related fonts or a program file along with its documentation, configuration, and other support files. Linux packages are often distributed as tarballs, RPM files, or Debian packages. packet-filter firewall

A type of firewall ihai operates by examining and passing or discarding individual

TCP/IP packets.


A tool that enables you to switch between virtual desktops, typically by clicking one square in a line or array of squares representing the different virtual desktops, parallel port

A type of port that uses several signal lines, enabling transmission of an entire byte (or more) at one time. The term may be used generically to refer to any type of parallel interface or specifically to the port that's present on most IA-32 computers as a printer interface, parent

In terms of Linux processes, a relative term describing the process that launched another process. See also child.


A short file that can be merged with a larger file or set of files to modify the larger file or files. Patches are a common way of distributing changes to source code. PC Card

A hardware interface standard most commonly used by laptop computers. PC Card devices plug into the computer and provide functionality such as network interfaces, modems, or external hard disk interfaces. Also known as PCMCIA. PCI bus

The Peripheral Component Interconnect bus, a hardware standard for plug-in cards such as video cards, EIDE controllers, and Ethernet adapters. PCI is the dominant bus type on IA-32 systems in 2003, except for video cards, which generally use the AGP bus. See also ISA bus. PCMCIA

See Personal Computer Memory Card International Association (PCMCIA). Personal Computer Memory Card International Association (PCMCIA)

An industry association that developed a hardware standard, which is also sometimes referred to by the same acronym. See PC Card.

See process ID (PIP).

See Programmed Input/Output (PIO). pipe

A tool for linking programs together. The first program's standard output (see stdout) is directed to the second program's standard input (see stdin). In a shell, you create a pipe by separating the program names with a vertical bar (|). POP

See Post Office Protocol (POP), pop-up ad

A type of ad delivered via web pages or HTML-enabled e-mail. Pop-up ads create new browser windows that display advertisements, requiring you to close the window to get rid of the ad.

1: A hardware interface, frequently to an external device, such as a USB port or an

RS-232 serial port. 2: A number associated with a specific network-enabled program. Servers run on specific well-known ports, and clients also use ports for outgoing connections.

Post Office Protocol (POP)

A popular pull protocol for mail transfer. POP transfers are initiated by mail readers so that users can retrieve their mail from mail servers. POP is simpler than the competing IMAP. PowerPC

A CPU architecture used primarily in Apple Macintoshes, some IBM workstations, and some embedded systems. Linux support for PowerPC (or PPC) is good, but not as good as for IA-32. PPD file

A PostScript Printer Description file is a standardized file that describes a PostScript printer's capabilities—its page size, margins, resolution, and so on. Some applications can use PPD files to optimize their output for specific printers, print filter

A program that processes printed files as part of a Linux print queue. A print filter may convert text to PostScript, PostScript to another format, or perform other transformations, process

A running program, identified by a PID number, process ID(PID)

A number that uniquely identifies a process. Programmed Input/Output (PIO)

A method of transferring data between peripherals such as disk interfaces, Ethernet adapters, and sound cards. PIO mode requires extensive CPU intervention, and so slows down normal programs during I/O operations, proxy server

A server that functions as a stand-in for another server. Typically, a proxy server partially processes a data-transfer request, sends a copy of the request to the true destination, receives a reply, partially processes the reply, and forwards it to the original client. Proxy servers can function as security filters or can improve network performance by caching replies from popular servers, pull protocol

A protocol in which the recipient of data initiates the transfer. This term is often applied to the POP and IMAP mail protocols, push protocol

A protocol in which the sender of data initiates the transfer. This term is often applied to the SMTP mail protocol.

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RAM disk

A technique whereby a section of random access memory (RAM) is set aside and treated like a disk device. Many Linux distributions use RAM disks during system installation and even as part of the normal boot process, random access

A method of data storage that enables reading or (if supported) writing any stored data without reading intervening data. Hard disks, floppy disks, and memory are all random access devices. This contrasts with sequential access devices, rasterize

The process of converting an image into a format that can appear on a bitmapped computer display. This term is often applied to converting outline fonts into a bitmap format.

red/green/blue (RGB)

A color encoding system that describes every color as a combination of the three colors red, green, and blue. Computer monitors use RGB encoding. This contrasts with CMYK color encoding, reduced instruction set computer (RISC)

A CPU that provides a limited set of operations. This reduces CPU complexity, allowing the CPU to perform tasks more quickly; but multiple commands may be required to perform some tasks that can be performed with a single command in a CISC CPU. The PowerPC and Alpha are both RISC CPUs. ReiserFS

A journaling filesystem that's been included in the Linux kernel since early in the 2.4.x kernel series. Most distributions make ReiserFS an option for the default filesystem at install time.

See red/green/blue (RGB). RISC

See reduced instruction set computer (RISC).

The system administrator's username. In this book, the name always appears in a monospaced font, or italicized in some headings. See also root and /root, root

1: The lowest-level directory on a Linux system, referred to in shell commands or directory specifications with a single slash (/) character, as in cd /. All directories and files can be referred to relative to the root directory. 2: The lowest-level directory in a specific directory tree or on a removable media, as in "you'll find the file in the CD-ROM's root directory." See also /root and root, root kit

A software package that crackers use to acquire root privileges on a computer to which they have access as ordinary users.


A computer that links two or more networks together, passing network packets between the networks. The Internet is a collection of a very large number of networks tied together through a series of routers. RPM Package Manager (RPM)

A recursive acronym referring to a file format and tool for distributing software packages. RPM files provide dependency and summary information that the RPM utilities store in a local database, enabling easy upgrades or removal of the package at a later date. RS-232 serial port

A type of interface with external devices, such as modems, printers, or mice. Most RS-232 serial ports are limited to speeds of 115,200 bits per second, which is very slow by today's standards but still adequate for low-speed devices such as mice and telephone modems

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A popular Linux server for the SMB/CIFS protocol. Samba enables Windows (and other operating systems') clients to use a Linux server for storing files and as a print server. SANE

See Scanner Access Now Easy (SANE), scan code

A numeric code sent from a keyboard to the computer to represent the key that a user has pressed.

Scanner Access Now Easy (SANE)

The primary scanner software for Linux. SCSI

See Small Computer System Interface (SCSI). Second Extended Filesystem (ext2 or ext2fs)

Linux's primary native filesystem through the late 1990s. Since then, development of several journaling filesystems has reached a point where they're taking over as the standard Linux filesystem. sector

A discrete unit of data storage on hard disks and similar devices. Most hard disk sectors are 512 bytes in size, but some devices use other sector sizes. CD-ROM sectors are 2,048 bytes. See also track, cylinder, and head. Secure Shell (SSH)

An increasingly popular means of establishing a secure data transfer connection between two systems. SSH is commonly used as an encrypted remote text-based login tool, but it can also tunnel other protocols. Used in this way, SSH can add encryption to just about any network protocol. Secure Sockets Layer (SSL)

An encryption protocol that's used by secure websites, SSH, and other secure Internet protocols, sequential access

A type of data storage device in which data are read in sequence from start to end. These devices don't allow quick access to most data, so they're best used for backups or archival storage. Tape drives are the most common sequential access devices. See also random access, server

1: A network program that responds to network data transfer requests from clients. Examples include web servers and e-mail servers. Servers usually run in the background, without direct human intervention, as daemons. 2: A computer that exists mainly to run server programs.

Server Message Block/Common Internet File System (SMB/CIFS)

The protocol upon which Windows' file- and printer-sharing tools are built. Linux supports SMB/CIFS through the Samba package. SGID bit

The set group ID bit is a special permission bit that tells the system to run a program with the group permissions associated with the file rather than those of the user who runs the program, shell

A program that accepts commands and that performs actions or launches programs in response to those commands. The most common shell on Linux systems is bash. Simple Mail Transfer Protocol (SMTP)

The protocol that dominates mail delivery on the Internet today. SMTP is a push protocol for mail delivery, and it is used by common mail servers such as sendmail, Postfix, Exim, and qmail.

Small Computer System Interface (SCSI)

A method of connecting hard disks and similar devices to computers. SCSI supports more devices per chain than does the more common ATA interface, and it has some other technical advantages, but SCSI is also more expensive than ATA. SMB/CIFS

See Server Message Block/Common Internet File System (SMB/CIFS). SMTP

See Simple Mail Transfer Protocol (SMTP), social engineering

The process of tricking users into divulging their passwords or other sensitive computer data. Some crackers engage in social engineering as a method of breaking into computers, source code

The original form of a computer program, before it's compiled by a compiler. Source code is relatively easily interpreted by humans, compared to the binary format into which it's ultimately converted. (Some programs are interpreted, meaning that they're never changed from their original source code form.) spam

"Junk" e-mail, sent in bulk to recipients who, by and large, don't want it. Also called



The mechanism one process uses to start a thread running. See also fork. SPP

See standard parallel port (SPP). SSH

See Secure Shell (SSH). SSL

See Secure Sockets Layer (SSL), standard parallel port (SPP)

A term that applies to old-style parallel printer ports. This hardware is limited in speed, but remains adequate for many purposes. See also EPP and ECP. statistical spam filters

Spam filters based on a statistical analysis of the words or other components of a message. A message with too many words that appear mostly in other spams is flagged as a probable spam message. stderr

Standard error is an output stream used for high-priority messages from programs—frequently error messages. It's normally sent to your text-mode console, but it can be redirected. stdin

Standard input is an input stream that text-mode programs use to accept input. It's normally linked to your keyboard, but it can be redirected.


Standard output is an output stream used for normal output from text-mode programs. It's normally sent to your text-mode console, but it can be redirected, sticky bit

A special permission bit that alters the way Linux treats permissions within a directory. Without the sticky bit set, users can delete any files in a directory so long as they have write permission to the directory. Wth the sticky bit set, users need to own the files in a directory before they can delete them, subnet mask

See network mask. SUID bit

The set user ID bit is a special permission bit that tells the system to run a program with the permissions associated with the program's owner rather than the user who runs the program. See also SGID.

SysV startup scripts

A method of starting a Unix-like OS via many small startup scripts, one for each server or subsystem. Most Linux distributions use a SysV startup script system.

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A file created by the tar program, and typically compressed with gzip or bzip2. Tarballs are commonly used for distributing source code or distribution-neutral binary programs. TCP/IP

See Transmission Control Protocol/Internet Protocol (TCP/IP). Telnet

An old but popular text-based remote-access protocol. Telnet doesn't encrypt data, unlike SSH, so Telnet is a poor choice on the Internet at large, on wireless local networks, or even on wired local networks where security is important, terminal

A hardware device consisting of a keyboard, monitor, and perhaps a mouse, which enables access to a computer. Terminals have little memory, storage space, and CPU power. Unix (and hence Linux) systems support many terminals and hence many simultaneous users. Software (a terminal program or terminal emulator) can make a computer function as a terminal. Third Extended Filesystem (ext3 or ext3fs)

A journaling filesystem derived from ext2fs. It's now the default filesystem for many distributions' standard Linux installations.


A subprocess of a main process. Threading can improve an interactive program's apparent performance by placing lengthy noninteractive actions, such as formatting a print job, in the background, throughput

Overall data transfer rate, time-to-live (TTL)

A number that corresponds to how long a data structure should survive. TTL values are used in several protocols, including low-level TCP/IP packet transport and DNS server caches, track

A ring-shaped collection of sectors on a hard disk platter. Disks contain multiple tracks in concentric rings. See also cylinder and head. Transmission Control Protocol/Internet Protocol (TCP/IP)

The most common network stack. The Internet is built atop TCP/IP, as are most Linux networking tools.

See time-to-live (TTL). tunnel

1: (noun) A network protocol implemented inside another network protocol. Tunnels may exist to pass protocols over otherwise incompatible network types (for example, to pass NetBEUI traffic over the Internet) or to add features to a protocol (for example, using SSH to add encryption to otherwise unencrypted protocols). 2: (verb) The process of creating and using a tunnel.

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See universal asynchronous receiver/transmitter (UART). UBE

Unsolicited bulk e-mail. See spam. UCE

Unsolicited commercial e-mail. A variety of spam that contains a commercial message. See spam.

See Unix File System (UFS). uniform resource identifier (URI)

A method of describing an Internet resource. URIs include a protocol definition, a hostname, a filename, and additional information. In some instances, some of these components may be omitted. The most common type of URI is for a site on the Web. These URIs begin with http://, as in universal asynchronous receiver/transmitter (UART)

A key component of an RS-232 serial port. Several different models of UARTs exist, the 16550A being the most common on IA-32 hardware. Universal Serial Bus (USB)

A hardware standard for connecting a wide array of external devices, such as keyboards, mice, modems, scanners, and removable disk drives, to computers. Unix File System (UFS)

An early filesystem for Unix systems. It is still supported by some Unix variants. Linux supports it with the ufs driver. See also FFS.

This document was created by an unregistered ChmMagic, please go to to regist* URI

See uniform resource identifier (URI). URL

A uniform resource locator. See URI. USB

See Universal Serial Bus (USB).

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Virtual Network Computing (VNC)

A program and protocol for remote GUI access. VNC clients and servers are available for Linux, other Unix-like OSs, Windows, Mac OS, OS/2, and other platforms, virtual terminal

A display that Linux manages, supporting input/output streams independent of other displays. Linux supports multiple virtual terminals using a single keyboard and monitor; you use Alt+F/7 keystrokes to switch between them. VNC

See Virtual Network Computing (VNC).

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The World Wide Web (WWW or Web for short) has been the most visible part of the Internet since the mid-1990s. It's built largely upon HTTP and is accessed using a web browser program such as Netscape, Mozilla, or Konqueror. web form

A type of web page that includes text entry fields, buttons, or other elements that users can manipulate. CGI scripts often use web forms as a method of acquiring user input, widget set

A programming toolkit that enables programmers to easily create buttons, menu bars, dialog boxes, and so on for GUI applications, window manager

A program that controls the outer edges of windows and provides window sizing and moving functions. There are literally dozens of window managers available for Linux, each with its own unique features. WWW

The World Wide Web. See Web. WYSIWYG display

A what-you-see-is-what-you-get display creates printed output that's identical to the on-screen display—or at least, as near to identical as can be achieved given differing resolutions, aspect ratios, and so on. Most word processors released since about 1990 have been WYSIWYG.

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SeeX Window System. X86-64

This CPU architecture is AMD's entry into the 64-bit CPU arena. It competes with

Intel's IA-64, but it is more closely related to the IA-32 architecture.

One of four journaling filesystems available for Linux. XFS was originally developed by Silicon Graphics. It isn't a standard part of the 2.4.19 kernel, but it is available as an add-on. XFS is arguably the most technically advanced Linux filesystem. XLFD

See X Logical Font Descriptor (XLFD). X Logical Font Descriptor (XLFD)

A string that describes a font—its name, its size, and so on. Programs use XLFDs to specify fonts to display, and you must provide an XLFD when installing a font in X. X server

A program that mediates the interaction between X-based GUI programs and the screen, keyboard, and mouse used by the user. The X server includes or accesses a video driver and responds to local or network-based accesses from programs to display windows, accept keyboard input, and so on. X Window System

Linux's primary GUI environment, called Xfor short. X is a network-enabled GUI, and in Linux it's usually implemented by a program called XFree86.

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A process that's been killed but not removed from the process table by its parent. Zombies can only be killed by killing their parents; init should then automatically do away with the zombie.

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