Glossary of Terms

This list contains the complete list of terms assumed by LPI tests. Knowledge of these terms will be important in preparing for LPI exams, but no exam question should depend on knowledge to be found solely within this list.


A term for any operating system resembling UNIX(R)(TM), including Linux and a large number of free and commercial systems; also UN*X.


So-called Thin Ethernet, using RG-58 coax cables and BNC connectors to construct a chain of cables, which must be terminated by resistors; supports a maximum (theoretical) transmission of 10 Mbit/s.


The older Thick Ethernet, which used vampire taps into a single cable; supports a maximum (theoretical) transmission of 10 Mbit/s.


Ethernet over UTP cables, using hubs to produce a star topology; supports a maximum (theoretical) transmission of 10 Mbit/s.


Ethernet over UTP cables, using hubs to produce a star topology; supports a maximum (theoretical) transmission of 100 Mbit/s.


Ethernet over UTP cables, using hubs to produce a star topology; supports a maximum (theoretical) transmission of 1Gbit/s.


To connect to and utilize a device (computer, printer) or file.


The symbol or number that refers to a user for accounting purposes.

address [1]

A location in memory; specifically, the I/O-port used by a device to communicate with the processor.

address [2]

A unique identifier assigned to an interface on a network-attached device such as a network interface card. Notice: a host can have multiple interfaces, hence multiple addresses.

address [3]

The name|number|both given to a computer, device or resource so it can be identified, found and accessed on a network.


To make it work. ;-) To control the operation and use of a computer or other device; the task of a system administrator.


A formal description of a procedure that, when suitable input is entered, will generate output as a result that satisfies specific requirements.

alias [1]

Within a shell, a substitute word for a command string (e.g.: alias dir = “ls –color”).

alias [2]

An additional IP address on an interface.

alias [3]

Refers to another name given to an e-mail account, in order to accept mail for one e-mail address and forward it to another.


The Alternative key on a keyboard


Refers to a physical measure that can take any value within a continuous range; e.g., the voltage used to encode loudness when transmitting a signal over a conventional copper telephone line. cf. digital.


A standards body responsible for many protocols.


A specification which allows simple access to functionality of a library or other system resources when writing a program; operating system functionality is made available through an API.


A program that runs on top of an operating system.

application layer

The name of the top layer of both the seven-layer ISO/OSI model, and the four-layer TCP/IP protocol stack; although some of the functionality of the session and presentation layers of the former may be assigned to the latter. It includes protocols such as telnet, FTP, HTTP, SMTP, etc.

archive [1]

A backup of data to be preserved.

archive [2]

A file that contains one or more components and an index (e.g. in tar, cpio, rpm or deb format).


A piece of information passed to a command or function (usually typed in behind it), that modifies its behavior, or that is operated upon by the command or function. e.g. in `cat motd`, “motd” is the argument. cf. parameter.


A low-level protocol which, given an IP address on the local network, returns the Ethernet MAC address of the corresponding interface. cf. RARP.


A specification of characters widely used in the UNIX world and beyond.

aspect ratio

The ratio between the width and the height of a pixel on a computer display.


A program that compiles programs written in assembly language into object code.

assembly language

A low-level computer language that can be translated directly to the object code of the computer processor.


A popular 16-bit interface standard that extends the ISA bus of the IBM PC-AT to attach peripherals; it has evolved through over 5 generations; the original ATA is better known as IDE.


An enhancement of the ATA protocol to be able to connect CD drives etc.


This list was compiled by (in alpha order): Les Bell, David DeLano, Alan Mead, Tom Peters, Richard Rager.

background [1]

A state of process execution which does not produce output to the terminal (execution may stop if the process tries to write to the terminal); it is common to run system processes and long running user applications in the background; cf. foreground [1].

backup [1] (noun)

A copy of essential data stored on- or off-site as insurance against failures of system hardware, software or user.

backup [2] (verb)

To make a backup.

binary [1] (adj)

Taking two discrete values (e.g. bits), as opposed to decimal (= taking ten discrete values).

binary [2] (noun)

A file that is not intended to be read by humans but by applications or the operating system; especially in plural (“binaries”) for compiled sources; cf. text.


A simple, low-level operating system which supplies a uniform API to higher-level operating systems; BIOS is generally implemented in ROM of some sort.


The smallest entity of information: can have one of two states (0-1, on-off, open-closed, etc.).


The number of bits available for each display pixel to code for visual appearance (color, proximity, etc.).

block device

A device that exchanges data with the operating system in sizable blocks (e.g., 512 bytes) at a time.

boot loader

Software, usually installed on the MBR of Intel machines, which exists to load the operating system kernel and begin its functioning.


To cause the operating system to begin to function. Takes its name from “pulling oneself up by the bootstraps”, a whimsical analogy applied to the BIOS loading itself and then running the “boot loader”. (Also reboot).


See RFC951; cf. DHCP.


A device that propagates packets between two computer networks; it operates at the second, data link layer within the ISO/OSI model, and broadcasts packets based on the address, but does not do routing. cf. repeater, router.

broadcast (noun)

A frame or datagram addressed to all interfaces on a network.


A variant of UNIX originally developed at the University of California, Berkeley. The BSD TCP/IP stack is the model for most subsequent TCP/IP implementations.


Temporary storage; cf. cache


A mailing list for discussions regarding network security (daemons, programs, operating systems, routers).


To run a sequence of compile and link steps to produce a new version of an executable program.


A cable for transmitting signals between various components within one computer system.


A data type of 8 bits.


A compiled computer language closely associated with UNIX.


An object-oriented computer language derived from C, that needs a compiler.


Any readily accessible storage area used to keep data handy which is (somehow) indicated to be needed again shortly; the purpose being to speed up the access of that data and improve system performance.

Specifically: the fast computer memory that is used as a buffer for data and program instructions between the CPU and the slower main memory (cf. RAM).

caching-only DNS

A domain name server that does not have any domains files.


Any device that can be plugged into a computer expansion slot.


A removable medium of considerable popularity which comes in several variations, the most popular being ISO9660.


A team of people that study Internet security, and provide incident response services; see


“confer”, which means “consult” in the meaning of “also see” or “compare”. N.B.: Avoid this. Use only in parenthetical examples (cf. e.g., i.e.) but avoid “cf.” by putting examples in text like this. Also see “e.g.”, “i.e.”.


A standard for allowing server applications to be executed as part of a HTTP request.


C data type (usually one byte) used to store letters (cf. character).


A letter or sign usually represented by 1 byte in ASCII code.

character device

A device which exchanges data with the operating system in one character (or byte or even word) at a time.

child process

Any process created by another, so-called parent process; usually used in reference to a particular parent process.


See RFC1519; cf. variable length subnet mask


Microsoft’s successor to SMB, a suite of protocols for sharing file and print services (among Windows machines or UN*X machines running CIFS servers like Samba).


In reference to a drive being mounted, clean means that the drive was unmounted properly and thus (theoretically) does not need to be checked; otherwise a drive is dirty.


A computer or process which connects to and receives a service from a server computer or process.


Cable with inner and outer conductors used for TV cables and for Ethernet LANs, where the computers usually have T-joints to attach to a single chain of cables which needs to be terminated by resistors.


A table used to encode a palette of colors for images.

command line interface

An interactive user interface which allows commands to be given to a computer program or shell through a text-based terminal (or terminal emulator in a window within a graphical user interface).


A program which examines program source code and translates it into an equivalent object code file; cf. interpreter.


Removal of redundant information from a file or data stream, to reduce its size, the storage space it needs, or the time needed for transmission. Lossy compression actually discards information that is considered not essential, and is only appropriate for data like images or sound.


A digital, electronic, general-purpose, programmable, information processing automate.


The primary, directly attached, user interface of a computer. Some system administration functions may only be performed at a console.

control panel

A collection of buttons, switches, lights or display used to configure and control a router, printer, computer or other device.

core dump

The content of memory written to a file on disk (usually called “core”) when a program crashes.


Damaged (said of a file or disk contents)


The main component that makes a computer work; these days usually a “micro-processor” on a single silicon chip (cf. processor).


To gain access to a computer system without proper authorization (e.g. by guessing a legitimate user’s password), and possibly interfere with its normal operation or integrity.

cracker [1]

Someone who tries to crack; cf. hacker.

cracker [2]

A software program used to crack, for instance by guessing passwords.


A sudden stop of normal operation. Supposedly, the original hard drives would sometimes experience a catastrophic failure in which the read/write heads would crash into the media, possibly sending the media flying; hence a crash is a unintentional termination of software or hardware due to some failure or error – especially a termination in a final, catastrophic, or unpleasant way.

data link layer

Layer two of the ISO/OSI seven-layer model. Responsible for establishing an error-free communication path between network nodes over the physical link layer, it frames messages for transmission, checks the integrity of received messages, manages access to and use of the media, and ensures proper sequencing of transmitted data. These functions are generally provided by a network card driver. The IEEE in its 802.x series of standards splits this layer in two: the LLC layer and the underlying MAC layer.

database [1]

A usually large collection of ordered and readily accessible data.

database [2]

A program to manage a database and extract information from it.


Packet, especially as used in UDP (Note: not IP-specific – other protocols use the term datagram in their documentation).


A GNU/Linux distribution built by a volunteer organization.


The value of a parameter that a program uses if it is not explicitly given a value.


The Delete key on a keyboard


Remove or erase a file|character|directory .


A state in which other libraries|programs|packages are required to make a program work.


A USA government-sanctioned standard for the encryption of data now considered insecure to high-end brute force attacks.


The screen from which all programs are started and run on X.

device [1]

A “peripheral” piece of hardware that is an optional part or can be attached to a computer (even one that is actually housed within the computer’s casing): interface cards, drives, printers etc.

device [2]

The software interface used within Unix (Linux) to represent a computer peripheral: interface cards, drives, printers, etc.; see the /dev/ directory .


Provides for automatic downloading of IP address and other configuration data from a server to a client. Allows for reuse of IP addresses so that the number of hosts can exceed the number of available IP addresses. See RFC2131, cf. BOOTP.

dial-in, dial-up, dial-out (adj)

Refers to a connection made over the Public Switched Telephone Network (PSTN), as opposed to a permanent, or leased-line, connection.


To cease execution, especially in a final or complete manner.


Refers to an entity that can assume only a limited number of discrete states and not an arbitrary value; e.g. binary. cf. analog.


A special type of file which contains information about other files, such as file name, location, permissions, size etc.


Not clean


Rotating magnetic media which supports direct or random access; cf. floppy disk, hard disk.


A human readable device to display text, graphics or other data.


A (usually) complete collection of software needed to operate a computer including the Linux kernel and various utilities and applications.


A hardware protocol which allows a special controller circuit (DMA controller) to transfer a block of data from a peripheral device’s buffer memory directly to main memory without CPU involvement; cf. PIO.


Western Digitals proprietary extension of the IDE interface standard with ATA-2 and ATAPI features, used to connect hard drives and CD-ROMS to a PC.


To simulate the actions of a device or program so that the simulation can actually perform the same functions as the original.


A program that emulates the functions of some device or other program.


A collection of variables associated with a process so that it knows about the user preferences and configuration of the system; they are inherited by a child process.

environment variables

The variables that define an environment.


Easy to use by humans


The Escape key on a keyboard


A type of LAN computer network interface using coax (10Base2 or 10Base5) or UTP cables (10BaseT, 100BaseT or 1000BaseT). The specifications are described in IEEE standard 802.2 . cf. MAC.


To set to work (a program); cf. run

execute permission

Permission set on a file on a Unix filesystem so that it may be run as a program by the operating system.


A file that is a binary or a script that can be run as a program (may assume execute permission).


A simple filesystem using a table to index files on a block device (floppy or hard disk). It comes in the varieties of FAT-12 (MS-DOS), FAT-16 (MS-DOS, MS-Windows 3.x) and “FAT-32” (MS-Windows 9x).


A proposed standard for the location of files on a Unix system. See


A named sequence or stream of bytes at a known location in storage.


The data structures placed on a logical disk or partition (by mkfs) which allow the operating system to record information about files stored there.


To remove unwanted data.


A gateway that restricts data communication between the “inside” network and the Internet “outside” the firewall.

floating-point (adj)

Used with numbers that may represent a fraction; cf. integer

floppy disk

A magnetic storage medium with a flexible disk inside; cf. hard disk.

floppy drive

A device that can read and write floppy disks.


The shape of each of the letters in a character set.

foreground [1]

The context in which a process is having access to a terminal for output, i.e. is not running in the background.

foreground [2]

The color of text on a computer display (as opposed to the text’s background).

foreground [3]

Refers to the window ‘in front of’ all others and with which the user is interacting.

fork (verb)

When an executing process creates an exact executing duplicate (except for the different PID) of itself; see child process, spawn.

format [1] (noun)

Specification regarding how data are stored.

format [2] (verb)

To apply the requisite format to storage media in preparation to making a filesystem.


The act of receiving an e-mail and then resending it to another destination.


A packet as assembled and transmitted over the physical layer of a network (e.g. Ethernet, Token Ring, etc.).

free [1]

Not costing anything.

free [2]

Not inhibited. As applied to source code it allows modification, study and adaptation, not inhibited by excessively restrictive commercial license terms. cf. GPL, Free Software Foundation.


Free Software Foundation: a tax-exempt charity that raises funds for work on the GNU project; see


A standard for the location of files on a Linux system; replaced by the FHS.


A protocol for transferring files over the Internet and the software to accomplish the transfer. See RFC959.


A device or relay mechanism that connects two or more computer networks and which directs packets between the networks in an internet. In common usage today, a gateway is a general-purpose computer with a general-purpose operating system [e.g. Linux] which *may* be performing other functions, and in that role it operates at the third, network layer in the ISO/OSI model; while a router is a special-purpose computer with a special purpose operating system [e.g. IOS], generally from a specialist supplier [e.g. Cisco]). cf. bridge.


A license for distribution of free software which permits copying, modification and redistribution. It was created by the Free Software Foundation for its projects like GNU, and has been applied to Linux as well. See


Images, pictures; in contrast to text

graphical user interface

An interactive interface using a graphics display. N.B.: refer to a “graphical user interface” only if there actually is a graphical interface (like X), and do not use it for interactive programs on text terminals (based on ncurses or slang). Use “interactive interface” as a catch-all. cf. command line interface.


Refers to a list of one or more users having the same access rights; see /etc/groups .


A boot loader: a program that loads the kernel so Linux can boot; can also boot other operating systems.


To accomplish a result in an unorthodox way.


Someone who hacks: a title assigned to people with remarkable computing skills; cf. cracker.


cf. crash

hard disk

A computer device that uses solid disks as magnetic medium to store data. cf. floppy disk.

hard link

In Unix filesystems, an entry in a directory that points to a file in another directory on the same disk or partition, and shares the inode of that file; cf. symbolic link.


All physical parts making up the computer (“the parts that can be kicked” ;-)


ISO/IEC 3309 standard; relevant in PPP.

high-level (adj)

Refers to a computer language with a higher level of abstraction from the computer architecture than a low-level language.


Any computer attached to an IP-based internet, especially computers that can act as a server to a client program or computer.


A series of documents, each on a particular topic, which form a significant portion of the documentation for Linux. HOWTO’s originated with, and are generally published by, the Linux Documentation Project.


A standard for specifying the structure of a document indicated by tags in the document text; used on the World Wide Web with HTTP.


The succession of application layer protocols used for communication between a WWW browser and a WWW server. See RFC2616.


Generally, a device connected to several other devices; specifically in computer networks, a repeater in the center of a network with star topology, usually with 10BaseT or 100BaseT or 1000BaseT Ethernet.


“that is” (Latin: “id est”). N.B.: Avoid this. Use it only in parenthetical asides (i.e., asides like this one) and then only to clarify a point. Do not confuse with “e.g.”. Also see “cf.”.




A required protocol (RFC792) for the notification of errors between gateways and hosts on IP-based internets. It operates at the level of the IP protocol in the internet layer. Interestingly, although ICMP is required (*must* be implemented), hosts and gateways are not required to generate ICMP messages, and hosts are not required to respond or react to incoming ICMP messages (in fact, mostly, they don’t, relying on higher-level protocols like TCP to simply time-out and retransmit, so you can’t say that ICMP _handles_ errors). Also, because IP is a packet-oriented connectionless protocol, there’s no concept of duration of transmissions.




A popular interface to attach hard drives to PC’s, where the electronics of the controller are integrated with the drive instead of on a separate PC card; also see ATA.

Integrated Development Environment

A programming environment integrated into an application; rare on Linux.


Inactive; waiting for a task or a wake up call


USA based, international organization of professional engineers; also an important standards body

IMAP [1]

See RFC1203

IMAP [2]

See RFC2060 on IMAP4 (beats me why there’s two names for the same thing, with the same acronym yet).


To create an actual object (program, device) that conforms to abstract specifications.

include file

A file which contains constants and parameters, possibly shared between two or more programs, and included into the source code when these programs are compiled.


Something worth knowing, in contrast to just plain data.


In Unix filesystems, a block of administrative data for a file on the disk partition.


Any data that are entered into a running program, or into a file.


Transferring a new program to a computer’s permanent storage (e.g., hard disk) and performing any necessary configuration or administration.


A data type used to represent a whole (integer, non-fraction) number within a limited range.




Adjective, meaning: having the property to be able to interact, i.e. respond to stimulation from the outside. Used in the context of programs or interfaces.

interactive interface

An interface between a computer and a user which allows them to interact and exchange input and output (commands and data).


A connection (through a hardware device or through a software program) between different components of a computer system (usually performing some kind of translation between protocols internal to the components); used especially in the contexts of network communication, or communication between computer systems and their users.


The worldwide distributed network of computers linked by the Internet Protocol.

internet layer

The network layer in the TCP/IP protocol stack: this alternative name may be used to distinguish it from the underlying network access (physical) layer. cf. Internet Protocol.

Internet service provider

A company which provides connections to the Internet.


A program which examines a script or program source code and executes it, line by line; cf. compiler.


A network (usually a LAN) based on IP but, unlike the Internet, allows only restricted access.


Induce execution of; call


The memory address peripheral devices use to communicate with the CPU; see /proc/ioports.


The network layer protocol used on IP-based internets. See RFC791.


An increasingly obsolete PC bus standard.


A baseband protocol used by telephone companies to offer one, two or more B-channel (Bearer channel) lines of 64 Kbit/s each on a single copper pair of up to 5.5 km length. Each B-channel can be used to provide a high-quality voice line, or fax or data services.


One of several bodies which exist to promote standards, including computer standards.


A task which has been sent to the background or has been submitted for later execution.


A factor of 1000, but with computers usually 1024 (2^10)


1024 bytes


Data transfer rate in units of 1000 bits per second.


Data transfer rate in units of 1024 bytes per second.


The core of an operating system, which provides multitasking (process creation, interprocess protection, interprocess communication), memory management, and basic I/O management.

key [1]

A token which is used to encrypt plain text or decrypt cipher text in an encryption system.

key [2]

A database field which may be used as the basis of a query.

key [3]

A marked switch on a keyboard which used to be a common computer input device before they were eaten by mice ;-).


An input device having many keys marked with letters and other symbols.


A small network, usually with one or a few segments, which supports broadcasting and direct connections between hosts; e.g. Ethernet, Token Ring, Appletalk and ARCNet; cf. WAN.


A collection of (often related) subroutines to be linked to a program.


A boot loader: a program that loads the kernel so Linux can boot; can also boot other operating systems.


To bind a program to the subroutines it references (calls). These are typically located in object modules or libraries.


A Unix-like operating system first developed, still maintained by, and named after Linus Torvalds. It is freely available under the General Public License.


An IEEE network standard (#802.2) that fits within the ISO/OSI Layer 2: data link layer, on top of the MAC sub-layer. It deals with error detection, flow control, and frame formats.


To transfer from disk into memory.


within easy reach, on the local area network, not remote.


record of activities


In the jargon of electronics engineers: the electronic components and circuitry of a device. This use of the term should be avoided because of the confusion with the conventional meaning of: abstract formal reasoning, which is involved in computer programming.

low-level (adj)

Refers to a computer language in which statements are similar to instructions for the processor (or: in which statements are more like object code than in a high-level language).


Linux Professional Institute, a non-profit organization founded to create a widely supported certification program for Linux.


A layer of IEEE network standards (#802.x) that fits within the ISO/OSI Layer 2: data link layer, below the LLC sub-layer. It deals with access methods, error detection, and transmission unit formats. Well-known IEEE MAC specifications are Ethernet in its various incarnations (#802.2) and Token Ring (#802.5?).

Mail User Agent

An end-user program used to access, process, read, archive, compose and send e-mail messages. See RFC1711. Such e-mail programs often include some “MTA” functionality, in particular the ability to use SMTP to send e-mail to an outgoing mail server, and POP3 or IMAP4 protocol to download mail from an inbound mail server. cf. Message Transfer Agent.

manual [1] (noun)

A document, often of book-length, discussing the design or operation of a software package or device.

manual [2] (adj)

By hand (as opposed to some more automated means)

man page

Standard Unix manual page (usually available on the computer system in nroff format, called with the command `man`).


To pretend to be another host for the purposes of sharing one IP address among several local hosts hidden to the outside world for reasons of resource shortages or security. cf. NAT


1000 (or sometimes 1024) KB (1,000,000 or 1,024,000 or 1,048,576 bytes).


Data transfer rate in units of 1,000,000 bits per second.


An area of the outermost cylinder of a PC hard disk which contains the partition table. This contains four entries identifying the types, starting cylinder and sizes of up to four partitions on the hard disk. One of the entries is flagged as ‘active’; this marks the partition from which the machine will boot. (Floppy disks don’t have an MBR, since they don’t have a partition table. Instead, they just have a boot sector (same as a logical disk), which contains a Media Descriptor Table (MDT) and bootstrap loader. The MDT describes the format of a floppy disk or logical disk).


The physical device by which data are transmitted or (more commonly) stored.


The place where a computer stores data and|or programs for direct access by the CPU: RAM or ROM (and also cache memory), not disks.

Message Transfer Agent

A program which routes e-mail based on the RFC822 header and invokes the correct delivery agent, especially SMTP (RFC821) in order to route the mail towards its ultimate destination. For example: exim, qmail, sendmail, smail. Also see RFC1711 and Mail User Agent.The term “Mail Transport Agent” is used in the online “Network Administrator’s Guide” to refer to rmail, which, of course, is used to process incoming mail from UUCP before passing it onto sendmail. This usage is at least confusing, if not incorrect.

On MDA (Message Delivery Agent): This one really has me going. I’m not sure whether it is “A protocol, or its implementing program, responsible for transferring messages from one host to another. For example, SMTP.”; or “A program responsible for delivering mail to the correct user mailbox on a host. For example, sendmail.”I’ve been researching this in my paper library and on the net for the last half hour, and have not come up with any consistent or reasonably definitive examples. Personally, but based on what evidence I can’t remember, I lean to the first definition, but Aileen Frisch uses the second in her “Essential System Administration” book. Hold on – after a search at , I’ve discovered RFC 1711, which defines MTA and UA, but has no mention of (M)DA. I think this one is what we in Australia would call “a furphy”. – Hence the use of “MDA” is to be AVOIDED.


A slimmer, more focused document otherwise like a HOWTO.


A device that converts between digital signals from the computer and analog signals for communication over a telephone line.


An input device which allows pointing to, selecting and activating objects, usually displayed in a graphical user interface.

MS-Windows NT

A 32-bit operating system from Microsoft(C)(R)(TM).


Maximum size of an IP packet that will be accepted for transmission without fragmenting it into smaller datagrams. Usually an optimal size is determined automatically; typical sizes are 296 bytes (40 header + 256 data for phone lines), and 1500 bytes (the maximum for ethernet connections).


A generic description of the process whereby the IP address of a host on a private internet is translated into an IANA-assigned unique address on the wider Public Internet. This can be accomplished by several techniques: masquerading, circuit-level gateways such as SOCKS, transparent proxying or application-level gateways.


“take good notice” (Latin: “nota bene”).


The current implementation of the NetBIOS protocol used in MS-DOS, MS-Windows and OS/2.


A layer of code which implements the NetBIOS API, but utilizing TCP and UDP datagrams, which are of course encapsulated in IP datagrams. Since IP is routable, this overcomes the most significant limitation of NetBIOS. See RFC’s1001, 1002, 1088.


A lightweight transport protocol developed by Sytek, IBM and Microsoft for use on personal computers. NetBIOS defines three things: the protocol on the wire (datagram formats); the code which implements the protocol; the API used to employ the protocol. The major example of an application which uses the NetBIOS API is Microsoft Networks, the workstation and server code implemented in MS-DOS 3.0 and later, OS/2 and various Windows incarnations – though other applications do exist. NetBIOS employs name registration and broadcast discovery, rather than addressing, and is consequently a non-routable protocol. cf. SMB, NetBIOS over TCP/IP.


network mask: the network part of an IP address; cf. variable length subnet mask


An interconnected set of hosts and other network devices which share a common physical layer such as Ethernet, X.25, etc.; cf. LAN, WAN.

network access layer

The lowest layer of the TCP/IP protocol stack, also known as the “physical” or “hardware” layer. Consists of the cables, connectors and associated hardware such as driver chips to implement a network such as Ethernet or Token Ring, as well as the drivers for the hardware. It approximately spans the lowest two layers of the theoretical ISO/OSI network protocol stack: the physical and data link layers.

network interface card

An expansion board allowing a computer to access a network.

network layer

The layer of a network protocol stack that is concerned with addressing and delivery of datagrams across a network or internet. It is layer three in the ISO/OSI seven-layer model. In the TCP/IP protocol stack, the main network layer protocol is the Internet Protocol (IP); therefore this layer is also known as internet layer.


A protocol (developed by Sun Microsystems) enabling a UN*X machine to mount a remote disk area as part of its local filesystem; widely considered of questionable security.


Protocols to provide network services (such as authentication) for NFS.

object code

Instructions that can be executed by the computer processor.


Not connected to a computer system or network; cf. online

online [1]

Connected to a computer system or network; cf. offline

online [2]

Stored on and accessible through a computer system or network

operating system

Central set of programs that manage the various components and devices of the computer, and its interaction with application programs and users; e.g. MS-DOS, MS-Windows NT, MacOS, Unix, Linux.


The concept of a “stack” of protocols (hence “TCP/IP stack” as in “This damn Microsoft TCP/IP stack is so broken…”) is due to the OSI seven-layer model, even though TCP/IP has only about four distinct layers (certain layers are combined). See physical, data link, network, transport, session, presentation, and application layers (OSI model); network access, internet, transport, and application layers (TCP/IP stack).


Any data that are generated by a process.


The account that has its UID number associated with a file.


A set of related files and programs; especially a single archive file (tar, rpm) that contains them.


A quantum of data transmitted over a network; specifically: a unit of TCP traffic carrying the information necessary to deliver itself, especially using the UDP protocol (datagram).


Several bits at the same time, over time (over multiple wires).


A variable with a specific value that has a meaning or function, which belongs to a program function or command; cf. argument.

parent process

A process that started one or more other, so-called child processes.

partition [1] (noun)

An arbitrary region of a storage device (almost always a hard drive) created by partitioning software before data were stored. Specifically on IBM PC-compatibles: one of up to four distinct areas on a hard drive which can be dedicated to different operating systems. One of the partition types, “extended”, supports further “partitioning” into a maximum of four logical disks.

partition [2] (verb)

To make a partition.


A token which authenticates a user at login time.


A computer designed to be used by one individual at a time; specifically, one compatible with the architecture of the original IBM microcomputer.


A PC bus to connect cards to the processor, replacing the original ISA bus.


A device that is an optional attachment to the core components of a computer (CPU and memory).

physical layer

The lowest layer of the seven-layer ISO/OSI network protocol stack. Consists of the cables, connectors and associated hardware such as driver chips to implement a network such as Ethernet or Token Ring. The corresponding layer of the TCP/IP protocol stack is also known as “hardware” or network access layer and has a wider scope.


A numerical identifier used to track processes by the kernel.


A technique whereby the CPU executes a tightly coded loop in which it copies data from a peripheral device’s buffer memory and writes it back out to main memory; used with earlier versions of ATA, but replaced by DMA.


A data structure which connects a file handle in one process to a file handle in another; by convention stdout of one process to stdin of the next. Established on the shell command line by the ‘|’ symbol.


Picture element: a dot, a grid point on a computer display, the smallest entity that can be drawn on a computer display


IP protocol over a parallel cable (between two machines physically connected and not too distant).


A historical set of Python scripts to offer a web-interface to manage the LPI test objectives.


Protocol to retrieve mail from a mail server. See RFC1939 (POP3). Various software servers typically have names derived from ‘pop’ like ipop3d, ipop2d, and popper.

port [1] (noun)

The name given to an individual, numbered “slot” which is available to Internetworking software. For example, HTTP servers generally listen to port 80. See /etc/services ; also see ioport.

port [2] (verb)

To adapt a computer program to operate in a new computing environment and|or in a new programming language.


A page description language developed and marketed by Adobe Inc. Widely implemented in laser printers, especially where high-quality output is required (e.g. photo typesetters) and, under Linux, widely emulated in software for non-Postcript printers.


The PID of a process’ parent process (cf. PID, parent , child process).


A physical layer protocol (RFC1661) which can be used to encapsulate IP and other network protocols, making it an excellent way of extending LAN protocols to dial-in users. PPP comprises an HDLC-like framing protocol (RFC1662), a link control protocol, and a family of network control protocols, each of which corresponds to a network protocol which PPP can encapsulate. PPP can also use PAP or CHAP (RFC1994) for authentication.

presentation layer

The sixth layer of the ISO/OSI seven-layer model, which specifies character representation (e.g. ASCII) and graphics formats, such as NAPLPS (North American Presentation Layer Protocols). In TCP/IP, the presentation layer is subsumed into the application layer, but perhaps the closest equivalent standards are ASN.1, ANSI and HTML/XML.


A running program; an instance of program execution.


The main component that makes a computer work; these days usually a “micro-processor” on a single silicon chip (cf. CPU)


A sequence of instructions for the computer that implements an algorithm, especially when stored in a file in the form of either directly-executable object code, or source code for an interpreter or compiler. When loaded into memory and executed, the object-code program typically becomes a process.


An indication produced by a shell or application program that it is ready for further user commands or input.


A definition of data structures and formats to be exchanged by two programs over a network.

proxy server

A computer process, usually as part of a firewall, that relays a protocol between client and server computer systems, by appearing to the client to be the server and appearing to the server to be the client (adapted from RFC2828).


A data structure which implements a first-in, first-out list; e.g. print queue, which contains a list of jobs to be printed in order.


Volatile, writable memory that a computer uses as its main memory. Comes in flavors like EDO, ECC, SDRAM, etc. which are not equivalent but from the perspective of a sysadmin are very similar under normal use. cf. ROM.


A low-level protocol which, given a hardware (Ethernet MAC) address on the local network, returns the corresponding IP address. cf. ARP.


An important document that usually comes with a software package to call attention to important issues; usually has its name in capitals, so that it appears at the top of a directory listing.


superfluous; said of information in the contexts of compression, or the preservation of data integrity.

regular expression

A formal expression of a string pattern which can be searched for and processed by a pattern-matching program such as vi, grep, awk or perl.


A device that propagates signals between cables; in case of computer networks it operates at the first, physical layer within the ISO/OSI model, and does not do packet filtering or makes routing decisions. cf. hub, bridge, router.


Despite the name, a “de facto” official specification of Internet protocols and standards. See or /hypertext/information/rfc.html .


Computer memory, usually involving some enduring medium like a silicon chip or a burnt laser disc which can be read but not altered; this is inconvenient when the data can change and, just to be confusing, some special ROMs can be modified under certain circumstances. cf. RAM.

root [1]

The administrative account (UID 0) on a *nix system that has all privileges; cf. superuser.

root [2]

The top-most or first or originating node or object (e.g.: root directory, “/”).

route [1] (noun)

The path across one or more networks from one host to another.

route [2] (verb)

To examine the destination network IP address in a datagram, and by consulting a table, direct the datagram to the next router along the path to the destination, or to the destination itself.


A gateway which directs IP datagrams between networks in an internet; it operates at the third, network layer in the ISO/OSI model, and assumes that the address implies a particular path (the route) to reach the destination. In common usage today, a gateway is a general-purpose computer with a general-purpose operating system [e.g. Linux] which *may* be performing other functions; while a router is a special-purpose computer with a special purpose operating system [e.g. IOS], generally from a specialist supplier [e.g. Cisco]). cf. bridge.


A system which eases installation, verification, upgrading, and uninstalling Linux packages. See the HOWTO for more information.


To let it work (a program); cf. execute.


Mode of operation of a Unix system, offering different services on each level; see /etc/inittab .


A computer program that is written in an interpreted programming language, and therefore stays in human-readable text format; cf. executable, binary.


A multi-drop bus cable architecture particularly suitable for both internal and external attachment of mass storage devices such as hard drives, tape drives and CD-ROMS.


A (limited) length of cable – segments can be joined by repeaters (rare), bridges (common), routers or switches (which are hardware logic bridges and routers).


One bit after another, over time (over a single wire).


A process, or a host computer, which provides a particular service to client processes; e.g. web server, print server.


A process which accepts requests and returns responses in an almost endless loop; a daemon.

session layer

The fifth ISO/OSI layer is the session control layer. It establishes and controls system-dependent aspects of communications sessions between specific nodes in the network. It bridges the gap between the services provided by the transport layer and the logical functions running on the operating system in a participating node. In the TCP/IP network stack, there is no session control layer, and its functions are partially implemented in the transport layer and partially in the application layer.


A program which mediates between the user and the operating system, typically accepting commands and invoking the corresponding programs. In the UNIX world, the term shell is conventionally applied to command-line driven interfaces with scripting capabilities, such as bash, csh and zsh; however, graphical shells exist, such as Windowmaker, KDE and GNOME.


A logical interrupt to a process, which the process must generally deal with synchronously. A form of interprocess communications.

single mode

single user mode, runlevel 1


A way of encapsulating IP datagrams for transmission over asynchronous modem connections. See RFC1055, “A Non-Standard for Transmission of IP Datagrams over Serial Lines”; cf. PPP


A Microsoft protocol developed to transport originally MS-DOS, later OS/2 and MS-Windows, API calls and their arguments across a NetBIOS LAN; primarily used under Linux as a protocol for file and print sharing with Windows machines


A conversational protocol used by mail servers for delivery of e-mail over the Internet. See RFC821.


The relative amount of useful information in a signal, as compared to the noise it carries.


A TCP application layer connection.


computer programs

source code

The plain text (usually typed in by a human) specifying the detailed operation of a program, written in a programming language. It needs to be processed by a compiler to produce a program that can be run (executed) by the computer.


The files containing the source code for a program or program system, from which the executable program or library can be built or ported to another computer platform.


To create a child process by means of a fork() and an exec().


The standard Unix error output device (by default to the terminal display).


The standard Unix input device (by default the terminal keyboard).


The standard Unix output device (by default the terminal display).

sticky bit

A permission bit on an executable file which causes the kernel to keep the memory image of the process after it has terminated, in order to avoid the overhead of reloading it when it is re-invoked.


A sequence of data bytes with sequencing and flow control. The TCP/IP stream protocol is TCP.

subnet mask

A value used in configuring the TCP/IP stack which specifies which part of a 32-bit IP address is the network address and which part the host address.


A permission bit for files in Unix-compatible filesystems which causes the resultant process (i.e., assuming the file is executable) to enjoy access rights to other resources based on the UID of the user who owns the file, rather than the user who created the process.


The user of the root account.

swap space

Virtual memory; called swap space because processes swap location between fast RAM and slow virtual memory if their priority changes.

switch [1]

A two-state (on|off) input device

switch [2]

In computer networks, a bridge or router that uses dedicated hardware to quickly shunt packets through the network.


Symbolic link: in Unix filesystems, an entry in a directory that points to another file name in the filesystem; cf. hard link.

synchronize [1]

To make the events in two separate sequences happen at the same time (used in communications).

synchronize [2]

To make the content and state of data stored in two separate locations identical (e.g. cache, FTP sites).


The formal rules which determine how keywords or commands and their components need to be combined when writing the source code of a computer program or forming shell commands.


System administrator: a person who administers a computer system and keeps it working.


A computer system; a term loosely used to refer to hardware and | or software: cf. operating system.


A session-oriented streaming transport protocol which provides sequencing, error detection and correction, flow control, congestion control and multiplexing; cf. UDP. See RFC793.


A suite of protocols basic to Internet transmissions.


The outlet of a computer, usually consisting of a display for output of text (or possibly graphics), and a keyboard (and possibly a mouse) for input, used as a device for interaction between the computer and a user. cf. workstation.


To disconnect, end, finish, quit, stop, etc.


A resistive load to indicate the end a chain of devices, usually a SCSI chain or a coax network chain.


A series of characters that can be displayed on a terminal display or printed on paper for human reading.


Set of Python scripts to offer a web-interface to manage the LPI test items. See


A protocol like FTP but much simpler and even less secure; used mainly for cracking computers and booting diskless network clients. See RFC1350.


As used with computer networks: the schematic shape formed by the connections between the hosts.

transport layer

The transport layer is the central layer (#4) in the ISO/OSI seven-layer model. It provides end-to-end control of a communication session once the path has been established, allowing processes to exchange data reliably and sequentially, independent of which systems are communicating and their locations in the network. The transport layer in the TCP/IP stack is not defined in the same way; although TCP provides sequencing and error correction, UDP – which is also a transport layer protocol – does not have a session concept and is unreliable. The TCP/IP transport layer primarily provides multiplexing through the use of ports.


The process of finding the reason(s) of the problem(s) with networking, programming, or hardware.


To make small changes to configuration in order to produce more efficient operation.


A connection-less, unreliable, transport protocol which provides multiplexing and error detection for applications which require a low-cost protocol for one-shot transactions; cf. datagram, packet, TCP. See RFC768.


User ID


A term for any variant of the UNIX(R)(TM) operating system, including Linux and a large number of free and commercial systems; also *NIX.


Remove hardware or software from a computer system.


Remove services or software from a server so that more resources (CPU time, disk space, etc.) become available.


In the TCP/IP sense of the term, a protocol which does not perform error correction (relying on “upper” layers to detect and correct errors, usually through retransmission).


To update hardware or software to a better state.


An identifier for an address on the Internet, preceded by the name of the protocol that must be used to reach that address (e.g.: ).


A recently developed bus standard for connecting peripheral devices in a chain.

user [1]

The person that is using the resources of a computer.

user [2]

A person’s account or process; identification listed in /etc/passwd .

user interface

See interactive interface


Official world time.


A program to help you to do a task easier.


Type of network cables with several parallel wires used for Ethernet. The network usually has a star topology with hubs and does not need terminators.

variable length subnet mask

cf. CIDR


A company that provides a service or a product.


Functionality provided without additional hardware|software, often without the user needing to realize this economy; e.g.: virtual memory, virtual console or virtual web server.

virtual memory

Extra memory available on a system that is stored on a hard disk and is therefore essentially unlimited, although much slower than genuine RAM. Usually it is called swap space.


A network which links geographically widespread facilities (and often LANs at those locations) using point-to-point (leased line, SLIP, PPP) or packet-switched network (X.25, frame relay) links and which does not support the broadcast and direct connection capabilities of LANs.


An placeholder used to represent any character or group of characters.


A region on a graphical desktop, the user interface for I/O with a child process of the desktop.


A modem that only has a Digital Signal Processor and uses MS-Windows-specific software running on the CPU of the host computer to encode and decode data.


An automatic NetBIOS name database to resolve NetBIOS names to IP addresses.


A data type consisting of two or four (or a different number – you cannot tell) of bytes; on i386 architectures, a word is four bytes (32 bits) in size.


Computer resources that are assigned to a computer user.


A computer, usually with a graphical display, for interactive use by an individual; cf. server.


Global distributed archive of HTML documents linked through HTTP.


The X Window System: a graphical user interface originating at MIT and having several variations.


cf. workstation

Yellow Pages


Other useful and authoritative glossaries of terms can be found in these RFC’s:

  • RFC1208: A Glossary of Networking Terms
  • RFC1983: Internet User’s Glossary
  • RFC2828: Internet Security Glossary

For an explanation of PC hardware components, see: