Glossary of Common UNIX and General Computer Terms

This glossary provides definitions for many of the terms you may see while using the Tru64 UNIX documentation. Although the majority of terms deal with the UNIX environment, you will also find other common terms you will encounter; for example, words related to the Internet.

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Special Characters


See root

. (dot)

A shorthand expression representing the user's working directory.

See also working directory

.. (dot-dot)

A shorthand expression representing the immediate parent of the user's working directory.

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absolute pathname

A pathname that begins at the root directory; a pathname that always begins with a slash (/). For example, /usr/games is an absolute pathname. Also called a full pathname.

See also relative pathname

active user

In an XTI transport connection, the transport user that initiated the connection.

See also client process, passive user, XTI (X/Open Transport Interface)

Address Resolution Protocol

See ARP (Address Resolution Protocol)


A name or symbol used in place of another name, symbol, or group of symbols; usually shorter or easier to use than what it represents. For example, if you often access a certain directory, you could set up an alias so that the word work would be an alias for "cd /share/tomb/tools/tools/work". Thereafter, typing work would put you in the /share/tomb/tools/tools/work directory. For more information see the alias(1) reference page.

API (Application Program Interface)

A method prescribed by a specific program (application) or by the computer operating system by which a programmer writing an application program can make requests of the specific program or the operating system.


A program or set of programs designed to perform a particular useful function or set of functions; for example, the Source Code Control System (SCCS) is an application for managing program source code.

Application Program Interface

See API (Application Program Interface)


A command that displays the reference page names and summary lines that contain a specified word or string of characters. The apropos command is the same as the man -k command.

See also reference page, man


1. To store programs, data files, text files, and other types of files for safekeeping.

2. A repository for such files.

argument count

The number of arguments passed by a command interpreter to a command, or from a routine in a program to a subroutine, procedure, or function.

argument list

The actual information (arguments) passed by a command interpreter to a command, or from a routine in a program to a subroutine, procedure, or function.

ARP (Address Resolution Protocol)

1. The Internet (TCP/IP) Protocol that can dynamically bind a high-level Internet address to a low-level, physical hardware address. ARP can be used only across a single physical network and in networks that support the hardware broadcast feature.

2. The Internet (TCP/IP) Protocol that dynamically maps between Internet addresses, Baseband Adapter addresses, and Token-Ring Adapter addresses on a local area network (LAN).


A collection of data elements (variables) identified by a common name and distinguished from one another by numbers representing their positions in the collection. The distinguishing numbers are called subscripts.

assignment statement

A statement that sets a value for a particular field or parameter. In program source files and scripts, assignment statements often have the form parameter=value.


A standard character set that defines 128 characters (including control and graphic characters). ASCII (American Standard Code for Information Interchange) assigns a 7-bit binary value to each letter, number, and selected control character. The terms ASCII file and text file are used interchangeably.

asynchronous event

See event

asynchronous execution

1. The execution of processes or threads in which each process or thread does not await the completion of the others before starting.

2. In XTI, a mode of execution that notifies the transport user of an event without forcing it to wait.

Asynchronous Transfer Mode

See ATM (Asynchronous Transfer Mode)

ATM (Asynchronous Transfer Mode)

A 25 M/bps to 622 M/bps network standard that uses cell switching. It is connection oriented, providing switched, full-duplex communication circuits between nodes.


The command for executing programs written in the awk programming language. An awk program is a sequence of patterns and corresponding actions that are carried out when a pattern is read. The awk utility is a more powerful tool for pattern matching and text manipulation than either grep or sed.

See also grep, sed

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background job

See background process

background process

A job that runs without interfering with normal command-line entries. A process runs in the background when the command to begin the process is entered with an ampersand (&) character following it. For example, to run the X Window System clock program in background, a user would enter the command xclock &. As a result, the clock would be invoked in one window, while the command line on which the xclock command was entered would be ready to accept new commands.

See also foreground process

Berkeley Internet Name Domain

See BIND (Berkeley Internet Name Domain)

Berkeley Software Distribution

See BSD (Berkeley Software Distribution)

Berkeley UNIX

See BSD (Berkeley Software Distribution)

/bin directory

A directory that contains executable programs and scripts. For example, the /usr/bin directory contains programs that nonprivileged users can run, and the /sbin directory contains programs that only privileged users can run.

See also binary file, path, script


1. Referring to the number 2 or the system of binary numeration.

2. Referring to an executable file created by a compilation process.

3. Referring to a situation that can assume one of two possible states.

binary file

A file created by a compilation process. Binary files contain codes that are not part of the ASCII character set and utilize all 256 possible byte values. Binary files cannot be read using programs such as more, nor can they be edited using editors such as vi.

See also text file

binary operator

1. A symbol that represents an operation to be performed on two arrays, data items, or expressions. The four types of binary operators are character, logical, numeric, and relational.

2. An arithmetic operator that has two terms.

BIND (Berkeley Internet Name Domain)

A name service available on internet networks.

bit bucket

A term for any receptacle into which data is placed without the possibility of retrieval. It is often used to refer to the null device /dev/null.

block device

A data storage or transfer device that manipulates data in groups of a fixed size; for example, a disk, whose data storage size is usually 512 bytes.

See also character device

block device switch table

The method used by the Tru64 UNIX operating system to select the entry points associated with a particular block device.

See also character device switch table

blocking mode

See synchronous execution

block special file

A device special file that provides access to an input or output device and is capable of supporting a file system.

See also device special file


1. An algebra (named for George Boole) that is similar in form to ordinary algebra, but in which the values of the variables are restricted to the two possible values true and false. The logic of Boolean algebra works well with the binary logic of computers, where values are represented by the digits 0 and 1.

2. A term sometimes used to refer to Boolean operators, including AND, OR, NOT, EXCEPT, IF, THEN, TRUE, and FALSE.

Bourne shell

The command interpreter and interpreted programming language originally developed by Steve Bourne.

See also shell


A place in a source code program that stops the debugger during program execution. Breakpoints aid in the testing and debugging of programs.

See also tracepoint

break statement

In a programming language, a statement that causes the program to exit immediately from the current control structure (such as a case statement or a for loop). A break statement is often used to terminate execution of a loop before the programmed number of iterations has been performed.

BSD (Berkeley Software Distribution)

The UNIX software release of the Computer System Research Group of the University of California at Berkeley — the basis for some features of the Tru64 UNIX operating system.

BSD socket interface

A transport-layer interface provided for applications to perform interprocess communication between two unrelated processes on a single system or on multiple connected systems. This interprocess communications facility allows programs to use sockets for communications between other programs, protocols, and devices.


A command that is built into a shell, as opposed to a command that stands alone as a separate executable file and is invoked by a shell.

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A structured, procedural programming language that is widely used both for operating systems and applications and that has a wide following in colleges and universities. The Tru64 UNIX operating system is written in C, which has been standardized as part of the Portable Operating System Interface (POSIX).

See also C++, compiler, Java


An object-oriented programming language that is now generally viewed as the best language for creating large-scale application programs. C++ (pronounced C plus plus) is a superset of the C programming language.

See also compiler, Java


In a programming language, a statement that invokes a subroutine, function, or procedure.

call by reference

In a programming language, a method of passing an argument to a subroutine, a function, or a procedure by supplying the address of the data rather than its actual value.

See also call by value

call by value

In a programming language, a method of passing an argument to a subroutine, a function, or a procedure by supplying the actual value of the data.

See also call by reference

CAM (Common Access Method)

The ANSI standard that defines the software interface between device drivers and the Host Bus Adapters, as well as other means by which SCSI peripherals are attached to a host processor.

See also SCSI (Small Computer System Interface)

CAM Control Block

See CCB (CAM Control Block)

carriage return

A character that forces all following text to the left margin of the next line or that signals the end of user input. The Return key is usually used to produce a carriage return.

case insensitive

Unable to distinguish between uppercase and lowercase letters. A case-insensitive device or program considers A and a to be the same character.

See also case sensitive

case sensitive

Able to distinguish between uppercase and lowercase letters. A case sensitive device or program considers A and a to be different characters. Devices and programs that are part of the Tru64 UNIX operating system are case sensitive.

See also case insensitive

case statement

In a programming language, a control structure that can take any of several possible paths depending on the evaluation of its argument.

cbreak mode

A terminal driver operation mode that allows processes to read input as it is being typed. This mode eliminates the character, mode, and line editing input facilities.

CCB (CAM Control Block)

The data structure provided by SCSI peripheral drivers to the XPT transport level to control the execution of a function by the SCSI Interface Module (SIM).

CDB (Command Description Block)

A data structure that contains the SCSI operation code, parameters, and control bits for a specific operation.

CDE (Common Desktop Environment)

A graphical user interface for interacting with the Tru64 UNIX operating system. The CDE interface was jointly developed and is based on industry standards, including the X Consortium's X Window System and the Open Software Foundation's Motif interface.

character device

A data storage or transfer device that manipulates data in increments of a single character; for example, a terminal.

See also block device

character device switch table

The method used by the Tru64 UNIX operating system to select the entry points associated with a particular character device.

See also block device switch table

character special file

A file through which processes can access either a character-stream oriented I/O interface or an unstructured (raw) device, such as a communication line or an unbuffered magnetic tape or disk.

child process

See parent process


A computer system that uses resources provided by another computer system called a server.

client process

In the client/server model of communication, a process that requests services from a server process.


A data structure used by a BSD-type of terminal driver to store data coming from, or going to, terminals.

See also STREAMS

Command Description Block

See CDB (Command Description Block)

command history

See history list

command interpreter

A program that understands and executes programs written in a particular source language. Interpreted programs execute more slowly than compiled programs because the interpreter is performing two operations at once.

Perl and JavaScript are examples of popular scripting languages that rely on command interpreters. The UNIX shells are command interpreters.

See also compiler, shell

command interpreter

See shell

command mode

A state of a system or device in which the user can enter commands.

command substitution

The ability to capture the output of any command as an argument to another command by placing that command line within grave accents ( ` ` ). The shell first executes the command or commands enclosed within the grave accents and then replaces the whole expression, including grave accents, with their output. This feature is often used in assignment statements.

comment out

To selectively disable interpretation of a portion of a program or document source file.

Common Access Method

See CAM (Common Access Method)

Common Desktop Environment

See CDE (Common Desktop Environment)

common internet address notation

On internet networks, the decimal for the 32-bit internet address. Also called dotted-decimal notation.

communication domain

An abstraction used by the interprocess communication facility of a system to define the properties of a network. Properties include a set of communication protocols, rules for manipulating and interpreting names, and the ability to transmit access rights.


To process one or more program source files in order to produce an executable binary file or an object file.


A program that translates programs written in a particular source language into executable binary files (or into intermediate binary files referred to as object files). The input can include one or more source-language files together with one or more object files. Compiled programs execute faster than interpreted programs because the compiler has already performed the interpretation. The cc program is a C compiler.

See also binary file, compile, command interpreter, object file

compile time

Refers to actions that are taken by a compiler during the compilation of a program.

See also run time

computer virus

See virus

computer worm

See worm


To place together. Data elements such as strings can be concatenated to produce a string that contains all of the characters of the first original string, followed by the characters of the next original string, and so on. Files can be concatenated by combining their contents in a similar manner, either into a new file or into one of the original files.

conditional compilation

During the compilation of a program, a portion of the process (code block) that is enabled or disabled by a variable or condition external to the code block under consideration. For example, a certain program might contain a block that is to be compiled only if the compilation is performed on a Tru64 UNIX system.

conditional execution

During the execution of a program, a portion of the program's behavior or output that is enabled or disabled by a variable or condition. For example, a certain program might contain code that asks the user questions only if the user initiates the program to run in a menu mode.

conditional statement

In a programming language, a statement (for example, the if statement) that evaluates one or more variables or conditions and uses the result to choose one of several possible paths through the subsequent code.


1. The machines, devices, and programs that make up a data processing system or network.

2. The act of making a subsystem, or a set of subsystems, available for use by a running operating system.

3. The set of configured subsystems in an operating system.

configuration file

A file that specifies the characteristics of a system or subsystem.

connectionless mode

A mode of service supported by a transport endpoint that requires no established connection for transmitting data. Data is delivered in self-contained units, called datagrams.

console firmware

See SRM console firmware

connection-oriented mode

A mode of service supported by a transport endpoint for transmitting data over an established connection.


A data structure used for a particular purpose.

context search

See global search

control statement

In a programming language, a statement that can cause different actions to ensue, depending on the results of an evaluation or test.

cooked mode

The condition of a device driver in which the driver interprets the data passing through it. For example, a UNIX terminal driver operating in cooked mode translates a Return character from the terminal into a Line Feed character to be passed to the system.

See also raw mode


A daemon that executes commands at specified times and dates, according to instructions in the crontab file.

See also daemon

crontab file

A file that specifies the dates and times at which specified commands are to be executed. The cron daemon examines the crontab file at specified intervals, and executes the indicated commands at the specified dates and times.


The command that invokes the C shell.

See also C shell, shell

C shell

A command interpreter and interpreted programming language developed at the University of California at Berkeley; so named because many of its constructs resemble the equivalent C language constructs.

See also shell

current directory

See working directory


For video display screens, a symbol that shows the location of keyboard input. The cursor shows the position at which the next character to be displayed will be placed.

See also pointer

cursor movement keys

A set of keys, usually labeled with arrows pointing up, down, left, and right, that position the cursor on a video display screen.

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A process that performs a system management function that is transparent to the user. A daemon can perform its task automatically or periodically. For example, the cron daemon periodically performs the tasks listed in the crontab file. Daemons can be generated by the system and by applications. Some daemons can also be started manually; for example, the binlogd command starts a daemon that logs binary event records to specified files. The commands that manually start daemons usually end with a d.

data communications

The transmission of information between computers by means of a network such as an Ethernet, a telephone system, or a satellite link.


A unit of data that is transmitted across a network by the connectionless service of a transport provider. In addition to user data, a datagram includes the information needed for its delivery. It is self-contained, in that it has no relationship to any datagrams previously or subsequently transmitted.

datagram socket

A socket that provides datagrams consisting of individual messages for transmission in connectionless mode.

Dataless Management Services

See DMS (Dataless Management Services)


The command that invokes the dbx program, which is used by developers to help debug other programs under development.

DCE (Distributed Computing Environment)

A de facto standard for distributed computing that defines a uniform set of services that share certain global properties for common naming, security, time synchronization, system availability, access to data, and system management. DCE enables applications and data on heterogeneous systems to work together.


In an RCS or SCCS file, the set of changes that constitute a specific version of the file.

dependency file

See dependent

dependency subset

The condition in which a subset may or may not require the presence of other subsets in order to function properly. Evaluated by a subset's software control program (SCP) under control of the setld utility.

See also SCP (Subset Control Program), subset


Also called a dependency file. In the make utility, an entity on which a file to be built (the target) depends. A source file is a dependent of an object module.

detached job

A job that continues processing after the user has logged out.

device driver

The software that controls a peripheral device such as a disk or a printer.

device special file

A file used by processes to access hardware devices. For example, a printer is accessed through a device special file.

See also block special file

DFS (Distributed File System)

A distributed DCE application that provides a unified, globally distributed file system. Under this file system, a DFS file is accessible from any DCE DFS machine using the same name, regardless of the server currently storing the file.

DHCP (Dynamic Host Configuration Protocol)

An Internet (TCP/IP) Protocol that enables the automatic assignment of Internet addresses to clients on the network from a pool of reusable addresses. Address assignment occurs automatically whenever client systems such as portable computers are attached to the network.


A type of file containing the names and controlling information for other files or other directories.

directory hierarchy

The arrangement of directories in a file system. The root directory is at the top of the directory hierarchy and contains pointers to all file systems and all directories on the system.

directory stack

A data structure that stores directories for later recall.

disk label

The disk information, usually located in sector 0 (zero), that includes the disk geometry and partition divisions. This information is used by the system disk driver and the boot program to identify a drive, and to determine how to program a drive and where to find the file systems.

See also geometry, partition

disk partition

See partition

Distributed Computing Environment

See DCE (Distributed Computing Environment)

Distributed File System

See DFS (Distributed File System)

DMS (Dataless Management Services)

A service provided by HPwhereby a server computer system maintains the root, /usr, and /var file systems for client computer systems connected to the server via a local area network (LAN).

DMS area

A reserved disk area that is physically connected to a DMS server and that contains multiple copies of the DMS root area, one for each DMS client.

DMS client

A computer system whose system disk area is physically connected to a DMS server rather than to the client itself and is accessed across the network by the client.


See domain name system

domain name system

A tree-structured system for organizing hosts names for an entire internet.

See also communication domain, Internet domain name system

down time

The period during which a machine is unavailable for use.

See also up time


A utility included in a patch kit that installs, removes, and manages patches for Tru64 UNIX and the TruCluster products. This utility is installed and left on the system through the successful installation of a Tru64 UNIX patch kit.

Dynamic Host Configuration Protocol

See DHCP (Dynamic Host Configuration Protocol)

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ed editor

A line-oriented program for modifying the contents of text files. The program operates by accepting commands from the user; for example, issuing the command s/Unix/UNIX/g would cause the editor to replace each instance of the string "Unix" on the current line with "UNIX."


A program for modifying the contents of text files. Full-screen editors, such as vi, use video display terminals to display several lines of the file being manipulated; they allow the user to move the cursor to a specific location and change the text there. Line editors, such as ed, work on a line-by-line basis. Stream editors, such as sed, work by applying commands from a previously prepared list (called a script) instead of by accepting commands from the user.

effective root directory

The point where a system starts when searching for a file. Its pathname begins with a slash (/).

effective user ID

The current user ID, but not necessarily the user's ID. For example, a user logged in under a login ID may change to another user's ID. The ID to which the user changes becomes the effective user ID until the user switches back to the original login ID.

EGP (External Gateway Protocol)

A type of routing protocol that allows individual networks to communicate with the Internet backbone.

See also Internet


A text editor developed by the Free Software Foundation that is available for all UNIX systems, although it is not a standard part of Berkeley UNIX or System V. It is included with the Tru64 UNIX operating system.

email (electronic mail)

A system that allows the exchange of written messages with other users over a network.


The set of conditions under which a user is working on the computer. The environment includes such information as the name of the working directory, the name of the command interpreter, the identity of the user's terminal, and so on.

environment variable

A symbol containing information that can be used by shells or commands. Environment variables are available to all processes in a given process group; they are propagated by the creation of a child process.

See also process variable

EOF (end of file)

1. A condition indicating that the end of a data file has been reached by a program reading the file.

2. A specific sequence of characters written on a magnetic tape.

See also file mark

equivalence class

A grouping of characters or character strings that are considered equal for purposes of collation. For example, many languages place an uppercase character in the same equivalence class as its lowercase form, but some languages distinguish between accented and unaccented character forms for the purpose of collation.


Any condition in which the expected results of an operation are not achieved. In XTI, an indicator that is returned by a function when it encounters a system or library error in the process of executing. The object is to allow applications to take an action based on the returned error code.


1. To protect a character from interpretation by a program by preceding it with a backslash (\).

2. An ASCII character that is usually interpreted as a command to cease a certain activity or as the initial character of a sequence that performs a special function. Cursor control sequences for many terminals and workstations use the escape character.

See also quote


A catchall directory, which usually contains miscellaneous system data files (such as termcap, the terminal capabilities database).


A communications concept for local communication networks that interconnects different kinds of computers, information processing products, and office equipment. It is a 10-megabit-per-second baseband local area network (LAN) using carrier sense multiple access with collision detection (CSMA/CD). The network allows multiple stations to access the medium at will without prior coordination, and avoids contention by using carrier sense and deference, and detection and transmission.


An occurrence, or happening, that is significant to a transport user. Events are asynchronous, in that they do not happen as a result of an action taken by the user.

event executable image

An executable image located in physical memory.

event management

A mechanism by which transport providers notify transport users of the occurrence of significant events.

executable file

A data file created by a compiler that contains program information a computer can read, interpret, and execute. Also called an image or a binary file.

ex editor

A line-oriented program for modifying the contents of text files. The ex editor is an extended version of the ed editor.

expedited data

Data that is considered urgent. The semantics of this data are defined by the transport provider.


1. A representation of a value; for example, variables and constants appearing alone or in combination with operators.

2. In programming languages, a language construct for computing a value from one or more operands, such as literals, identifiers, array references, and function calls.

3. A configuration of signs.

extended character

A character other than a 7-bit ASCII character. An extended character can be a 1-byte code point with the eighth bit set (ordinal 128-255).

External Gateway Protocol

See EGP (External Gateway Protocol)

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Fibre Channel

A technology that provides the means for moving data between computer devices at as much as three times the speed of SCSI (currently up to a billion bits per second, with even faster speeds expected). Fibre Channel, which works using optical fiber, coaxial cable, and twisted pair, is specified by a set of standards, specifically the Fibre Channel Physical and Signalling standard, ANSI X3.230-1994, which is also ISO 14165-1.


1. The basic unit of information in a record.

2. In awk, one element of an input record.

See also record

field separator

One or more characters used to separate fields in a record.

file descriptor

A small unsigned integer that a UNIX system uses to identify a file. A file descriptor is created by a process through issuing an open system call for the file name. A file descriptor ceases to exist when it is no longer held by any process.

file mark

A sequence of characters written on a magnetic tape to signify the end of a data file.

See also EOF (end of file)

file name expansion

See globbing

file pointer

An identifier that indicates a structure containing the file name.

file system

The collection of files and file management structures on a physical or logical mass storage device.


1. A command that reads standard input data, modifies the data, and sends it to standard output.

2. A device or program that separates data, signals, or materials in accordance with specific criteria.


Software provided as an integral part of a hardware system, such as a server, an I/O controller, or a storage subsystem. Alpha based servers and workstations provide the SRM console firmware.


See option

foreground job

See foreground process

foreground process

A job that must be completed or interrupted before the shell will accept more commands; a job receiving input from a workstation or terminal.

See also background process


1. The command used to create and start a child process.

2. The result of using the fork command.

See also parent process

full installation

A Tru64 UNIX installation that creates new file systems and loads a full copy of the operating system from the kit onto a system. Any other version of the operating system, any layered products, and any patches that previously existed on the system are overwritten. A full installation does not preserve system customizations (for example, user or data files) because the root (/), /usr, and /var file systems are re-created during the process.

See also update installation

full pathname

See absolute pathname

full-screen editor

An editor that displays an entire screen at a time. Also called a visual editor.

See also line editor

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The sizes (in bytes) of cylinders, tracks, and sectors for a particular disk device.

See also disk label

gid, GID

See group ID (GID)


In programming languages, pertaining to information defined in one subdivision of a program and used in at least one other subdivision of the program; pertaining to information available to more than one program or subroutine.

global character

See wildcard character

global search

In an editing environment, the process of having the system look through a document for specific characters, words, or groups of characters.


A UNIX term for the shell's process of wildcard file name expansion to develop a list of literal file names that the shell then passes to a command. The C shell permits the user to disable globbing by default; the Bourne, Korn, and POSIX shells require the user to quote or escape metacharacters in file names if globbing is not desired.


The command that invokes the grep program, which is used to search specified files for lines containing characters that match specified patterns, and then writes those matching lines to standard output. The name means Global Regular Expression Printer.

See also regular expression


1. A collection of users who can share access authorities for protected resources.

2. A list of names that are known together by a single name.

3. A set of related records that have the same value for a particular field in all records.

4. A series of records logically joined together.

See also login group

group ID (GID)

A unique number assigned to a group of related users. The group number can often be substituted in commands that take a group name as an argument.

See also user ID (UID), process ID (PID)

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hard link

1. A mechanism that allows the ln command to assign more than one name to a file. Both the new name and the file being linked must be in the same file system.

2. The default result of using the ln command.

See also symbolic link

hashed passwd database

An indexed database containing the contents of the passwd file. The indexed database minimizes the search time needed to retrieve information.


A method of transforming a search key into an address for the purpose of storing and retrieving items of data.

HBA (host bus adapter)

The hardware and microcode that provides the interface between system memory and a Small Computer System Interface (SCSI) bus.

header file

See include file

hidden character

A character in the ASCII character set that is not printable; for example, the DEL and ESC characters.

hidden file

A file whose name begins with a period. by default, the ls command omits such files from its listings.


In the C shell and the Korn shell, a command that displays the user's history list.

history list

In the C shell and the Korn shell, a listing of the most recent commands entered by the user. Commands in the history list are available for recall, modification, and reexecution.


An environment variable containing the absolute pathname of the user's home directory.

See also $home, environment variable


A process variable containing the absolute pathname of the user's home directory.

See also $HOME, process variable

home directory

A directory that is owned by a specific user and from which that user's other directories descend in a hierarchy. Also known as a login directory.

See also working directory


1. The primary or controlling computer in a communications network.

2. A computer attached to a network.

Host Bus Adapter

See HBA (host bus adapter)

host name

The name given to a computer on the network.

HTML (HyperText Markup Language)

The coding (markup) inserted in a file intended for display on a World Wide Web browser that tells the browser how to display a Web page's words. The markup is done with tags, which are command words enclosed in angle brackets. For example, the tag <P> creates a new paragraph; the tag <TABLE> begins the formatting of a table. Although the World Wide Web Consortium (W3C) promotes the standardization of HTML, both Netscape and Microsoft browsers currently implement some features differently and provide nonstandard extensions.

See also PDF file

HyperText Markup Language

See HTML (HyperText Markup Language)

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See internationalization

ICMP (Internet Control Message Protocol)

A host-to-host protocol from the Internet Protocol suite that controls errors and the operations of the Internet Protocol (IP).

See also IP (Internet Protocol)


A C language precompiler directive specifying interpolation of a named file into the file being compiled. The interpolated file is a standard header file (indicated by placing its name in angle brackets) or any other file containing C language code (indicated by placing its name in double quotation marks). For example:

#include <header_file.h>
#include "myfile.c"

The absolute pathname of header files whose names are placed in angle brackets (<>) is /usr/include/file.h.

See also include file

include file

A text file that contains declarations used by a group of functions, programs, or users. Also known as a header file.

See also #include

incremental backup

The process of copying files that have been opened for reasons other than read-only access since the last backup was created and that meet the backup frequency criteria.

infinite loop

A source code error that causes the program to continually repeat the same set of instructions. For example, Instruction A sends the program execution to Instruction B, which in turn sends the program execution back to instruction A. Such a loop can only be interrupted by intervention from outside the program.


The command given by a UNIX system as the final step in the boot procedure after the root file system is mounted. The init program initializes the system by creating and controlling processes, which are defined in the inittab file.

init process

A process created by the system that performs system administration tasks, such as spawning login processes and handling the orderly shutdown from multiuser to single-user mode.

inline editing

A feature of some shells that allows users to edit a current or previously entered command line.


The internal structure that describes the individual files in the operating system. There is one inode for each file. An inode contains the node, type, owner, and location of a file. A table of inodes is stored near the beginning of a file system.

inode number

A number specifying a particular inode file in the file system.


Data to be processed.

input redirection

The specification of an input source other than standard input.


The part of a computer program that tells the computer what function to perform at that stage.


The capability of a computer program of making itself adaptable to the requirements of different native languages, local customs, and coded character sets, which means, essentially, that internationalized programs can run in any supported locale without having to be modified.

The term internationalization is often represented by the abbreviation I18N, with 18 representing the number of letters between the first and last letters of the word.

International Standards Organization

See ISO (International Standards Organization)


1. A collection of computing networks consisting of participants from major research institutions, universities, and government labs, including the National Science Foundation (NSF) and the NFSnet regional organizations. The Internet is not a commercial product, but rather a large project in support of research.

2. A collection of connected networks using the TCP/IP protocols.

internet address

A unique 32-bit number that identifies a host's connection to an internet network. An internet address consists of a network number and a host number.

Internet Control Message Protocol

See ICMP (Internet Control Message Protocol)

Internet domain name system

The domain name system of the Internet, which consists of the following categories of hosts: COM, EDU, GOV, MIL, NET, ORG, and ARPA.

See also communication domain, domain name system, Internet

Internet Protocol

See IP (Internet Protocol)


1. An event that causes a computer to digress from its normal processing stream in order to respond to the condition that triggered the digression. Upon completion of the digression, the normal processing stream is resumed at the point of interruption. Interrupts can be caused either by software instructions or by hardware events such as the completion of an I/O operation.

2. To trigger an interrupt.

interrupt handler

Code in a program or operating system that performs actions in response to an interrupt.

IP (Internet Protocol)

The network layer protocol for the Internet protocol suite that provides the basis for the connectionless, best-effort packet delivery service. IP includes the Internet Control Message Protocol (ICMP) as an integral part. The Internet protocol suite is referred to as TCP/IP because IP is one of the two most fundamental protocols.

IP gateway

See IP router

IP router

A host that connects two or more internet networks. The IP router knows how to reach all the hosts on the networks to which it is attached. Also known as an IP gateway.

ISO (International Standards Organization)

An international body composed of the national standards organizations of 89 countries. ISO issues standards on a vast number of goods and services, including networking software.


To perform the same function repeatedly on different data, often with the object of arriving at a result by successively closer approximation.

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A programming language developed by Sun Microsystems that is based on C++ but optimized for the distribution of program objects in a network such as the Internet. Java is somewhat simpler and easier to learn than C++ and has characteristics that give it other advantages over C++.

A Java applet is a small program, such as a window or a pull-down menu, written in Java.


An interpreted programming (script language) from Netscape. It is somewhat similar in capability to Microsoft's Visual Basic, Sun's Tcl, the UNIX-derived Perl, and IBM's REXX. In general, script languages are easier and faster to code in than the more structured and compiled languages such as C and C++. Script languages generally take longer to process than compiled languages, but are very useful for shorter programs.


1. A unit of work defined by a user to be done by a system. The term job sometimes refers to a representation of the job, such as a set of programs, files, and control statements to the operating system.

2. One or more related procedures or programs grouped into a procedure, identified by appropriate job control statements.

job control

Facilities for monitoring and accessing background processes.

job number

A number assigned to a job as it enters the system to distinguish the job from other jobs.

job queue

A list of the jobs that are waiting to be processed by the system.

job state

The status of the work being done by a system.

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The command that invokes the kdbx program, an interactive crash analysis and kernel debugging tool. The kdbx program serves as a front end to the dbx debugger.

kdebug program

A program that lets programmers control the execution of a running kernel.


The integral part of the operating system that provides fundamental services to users and applications. Traditional kernels do the following:

The kernel has specialized knowledge of the hardware on which it runs.

See also shell, microkernel


1. A word that must be matched when retrieving information.

2. A reserved word whose presence is required in a file.


1. To stop the operation of a process. In most cases, a user can kill a foreground process by pressing Ctrl/c.

2. The Tru64 UNIX command that a user can issue to stop a background or suspended process. A superuser can use this command to stop any process on the system.

Korn shell

A command interpreter and interpreted programming language developed by David Korn. The Korn shell (ksh) is semantically an extended version of the Bourne shell, with constructs and commands to implement enhanced features, including job control and command history recall. The POSIX shell is a superset of the Korn shell.

See also shell

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See localization


See disk label

LAN (Local Area Network)

A device communications system that operates over a limited physical distance, offering high-speed communications channels optimized for connecting information-processing equipment.

LAPD (Lightweight Directory Access Protocol)

An Internet standard directory service protocol that runs over TCP/IP. An LDAP server manages entries in a directory, and makes the information available to users and applications across the network; it can be used as a central repository of user information to identify and authenticate individuals. When used in this way, an LDAP server is similar to Network Information Services (NIS).

See also LAN (Local Area Network)

LAT (Local Area Transport)

A protocol that supports communications between host computer systems and terminal servers with terminals, PCs, printers, modems, and other devices over local area networks (LANs).

See also LAN (Local Area Network)

layered product

An optional software product designed to be installed as an added feature of the Tru64 UNIX system.


The command that invokes the Lexical Analyzer Generator, a program for generating other programs that can organize input into units of meaning (symbols) called lexemes.

See also lexical analyzer, parser, yacc (Yet Another Compiler-Compiler)

lexical analyzer

A program or program fragment for analyzing input and assigning elements of it to categories to assist in parsing the input. The lex program assists in the creation of lexical analyzers.

See also parser

Lexical Analyzer Generator

See lex

line editor

An interactive or noninteractive text editor that works on one line of text at a time.

See also full-screen editor


A directory entry referring to a file.

See also hard link, symbolic link

linking loader

A single program that loads, relocates, and links compiled and assembled programs, routines, and subroutines to create an executable file. Also known as link loader and linker loader.


A program that checks C code for bugs, portability problems, and errors, such as mismatched argument types and uninitialized variables.


1. A value expression representing a constant.

2. A specific symbol that cannot be modified during the translation of a program.

local area network

See LAN (Local Area Network)

local area transport

See LAT (Local Area Transport)


A software environment that correctly handles the cultural conventions of a particular geographic area, such as China or France, and a language as it is used in that area. So by selecting a Chinese locale, for example, all commands, system messages, and keystrokes can be in Chinese characters and displayed in a way appropriate for Chinese.

See also internationalization

local host

The computer system to which a user's terminal is directly connected.


The process of implementing local requirements within a computer system. Some of these requirements are addressed by locales. Each locale is a set of data that supports a particular combination of native language, cultural data, and codeset. The type of information a locale can contain and the interfaces that use a locale are subject to standardization.

The term "localization" is sometimes abbreviated as L10N, with 10 representing the number of letters between the first and last letters of the word.

See also internationalization

lock file

A file that indicates that operations on one or more other files are restricted or prohibited. The presence of the lock file can be used as the indication, or the lock file can contain information describing the nature of the restrictions. For example, the Tru64 UNIX setld utility creates a lock file for each product kit subset that it installs. If a given product includes subsets that require the presence of a previously installed subset, setld places in the earlier subset's lock file the names of the later subsets to prevent inadvertent deletion of the earlier subset.

logical unit number

See LUN (Logical Unit Number)

log in

To begin using a computer system, usually by entering one's login name and a password to gain access to and communicate with the operating system as an authorized user.

login directory

See home directory

login group

The primary classification that establishes the access permission for the files created by the user.

See also group

login name

The name that identifies a user to a computer system and to other users of the system. When logging in to the system, the user enters this name and (usually) a password. Also known as user name.

login shell

The shell that a user uses by default upon logging in to the system. It is specified by the user's entry in the passwd file.

log out, log off

To stop using a computer system, usually by entering a command that tells the operating system that the user is ending the current session.


1. A sequence of instructions that is executed repeatedly until a specified condition is satisfied.

2. In the Tru64 UNIX virtual memory system, the page clusters in main memory that are repeatedly scanned for replacement.

See also infinite loop

LUN (Logical Unit Number)

The number assigned to a SCSI device to identify it to the SCSI driver.

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An instruction written as part of a source language, which when compiled into machine code will generate several machine code instructions.

See also instruction


A file that contains new and unread mail messages. The mailbox file is usually in the /usr/spool/mail directory.


A script that creates device special files for the devices on a Tru64 UNIX system. This script resides in the /dev directory.


A tool that builds programs and applications by testing to see whether the source files that produce a given application are newer than the target files produced from them. If any source or intermediate file is newer than its target, make performs the actions necessary to rebuild the target file by following a set of rules. The rules can be standard (specified by default) or they can be explicit descriptions of the steps required.


The specification file used by the make tool. The makefile specifies the names of target programs and describes rules for their creation.

See also make


The command that displays reference pages on line; the name is a short form of manual.

See also apropos, reference page

Management Information Base

See MIB (Management Information Base)

manpage, manual page

See reference page


An environment variable whose value provides the default directory search path used by the man, catman, and xman commands.

See also search path

Memory File System

See MFS (Memory File System)

memory trolling

A process of reading a system's memory to proactively discover and handle memory errors.


A character that is interpreted by a computer system to mean something other than its obvious meaning. For example, the asterisk is often used to allow wildcard matching in file names.

MFS (Memory File System)

A UFS file system that resides only in memory. No permanent data or file structures are written to disk. An MFS can improve read/write performance, but it is a volatile cache. The contents of an MFS are lost after a reboot, unmount operation, or power failure.

MIB (Management Information Base)

The Management Information Base defines a set of data elements that relate to network management. Many of these are standardized in the RFCs that are produced as a result of the Internet Engineering Task Force working group standardization effort of the Internet Society.


A type of kernel that delegates much of the work of memory management, task scheduling, and other services to nonkernel code. A microkernel provides only the basic primitives that control such operations on a specific processor architectures.


A term used to describe software that enables two other programs to work together.


A way of duplicating information on a disk to ensure that the information is still available in the event of a disk failure.

See also RAID (redundant array of independent disks), striping


The set of permissions for a file. These permissions are often expressed as three numbers, which represent an octal notation to set each bit in the permission code. Users who are given or denied permissions are "owner," "group," and "other"; the most common permissions given are read, write, and execute. The command used to change permissions is chmod.


See OSF/Motif


A command used to make a file system available.

See also unmount

mount point

A directory file that is the name of a mounted file system.


A system with two or more processors sharing common physical memory.

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name service

The service provided to client processes for identifying peer processes for communications purposes.

native software

Software that is written in a language that compiles either to assembly language or directly to the computer's standard machine representation (object files). Native software is more efficient and runs much faster than translated or interpreted software; in addition, it can be tailored to make the most effective use of the machine's resources.

NetRAIN (Redundant Array of Network Adaptors)

An interface that provides a mechanism to protect against certain kinds of network connectivity failures. NetRAIN integrates multiple network interfaces on the same local area network (LAN) segment into a single virtual interface called a NetRAIN set. One network interface in the set is always active while the others remain idle. If the active interface fails, one of the idle set members comes on line with the same IP address within an adjustable failover time period.


Two or more computing systems that are linked for the purpose of exchanging information and sharing resources.


A connection point, such as the interface between a system's CPU , memory, and I/O buses.

NFS (Network File System)

A service that allows a system (the server) to make file systems available across a network for mounting on other systems (clients). When a client mounts an NFS file system, the client's users see the file system as if it were local to the client.


Refers to a file system that is mounted over a network via NFS rather than being physically connected (local) to the system on which it is mounted.

See also NFS (Network File System)

NIS (Network Information Service)

A distributed data lookup service for sharing information on a local area network (LAN). NIS allows you to coordinate the distribution of database information throughout your networked environment. NIS was formerly known as Yellow Pages.

See also NFS (Network File System)

nonblocking mode

See asynchronous execution

NUMA (non-uniform memory access)

One of the two supported architectures for multiprocessor systems, the other being symmetric multiprocessors (SMP). The NUMA architecture overcomes a drawback of traditional SMP systems that provide one interconnect, either a bus or a switch, that links all system resources. With NUMA, systems can be scaled to large numbers of CPUs without the system switch or bus becomming a performance bottleneck.


The command that calls the nroff program, a member of the roff family of text formatters. The nroff program produces ASCII output suitable for display or printing on character-cell devices such as terminals and printers.

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object file

A nonexecutable intermediate binary file created by a compiler. Object files are frequently used as libraries, to provide precompiled program elements for use in compiling a complete executable binary.

See also binary file, compiler


A number system that uses 8 as a base (radix). The octal system uses the digits 0 through 7, and each digit position represents a power of 8.

OLAR (online addition and replacement)

A system management process that is used to expand capacity, upgrade components, and replace failed components, while the operating system services and applications continue to run. This functionality (sometimes referred to as "hot-swap") provides the benefits of increased system uptime and availability during both scheduled and unscheduled maintenance.

open system

A system that supports the International Organization for Standardization (ISO) Reference Model for Open System Interconnection (OSI).

Open Systems Interconnection

See OSI (Open Systems Interconnection)


In regular expressions, a character that is interpreted to mean something other than its literal meaning. For example, a pair of brackets ( [ ] ) form an operator that enables a single-character match on any one of the characters enclosed by the brackets.


The process of selecting the specific method by which a program is to perform a given task such that the most effective use is made of time, I/O, or other resources.


1. An argument that controls how the shell executes a command. Options are usually preceded by a hyphen and appear with the command name on a command line; for example, ls -a. An option is often referred to as a flag or a switch.

2. An indicator or parameter that shows the setting of a switch.

3. A character that signals the occurrence of some condition, such as the end of a word.

4. An internal indicator that describes a condition to the CPU.

OSF (Open Software Foundation)

A consortium of software vendors formed for the purpose of developing and marketing widely compatible UNIX systems based on a common set of features.


A graphical user interface developed and licensed by the Open Group (originally by the Open Software Foundation). OSF/Motif is based on the X Window System. Also called Motif.

OSI (Open Systems Interconnection)

A set of international standards developed by the International Organization for Standardization. The goal of the OSI is that different vendors' computer systems can interconnect.


Usually, the user who creates a file. The owner has the right to change the list of users or groups who are permitted access to the file and the ways in which those users or groups may access the file. Ownership of a file can be reassigned by the system manager or superuser.

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For the Tru64 UNIX operating system loader, a collection of object entities that share a common name space. Symbol names are unique within a package. Symbols from different packages may bear identical symbol names, because they are distinguished by their package names.


A fixed-size unit of physical memory.

PALcode (Privileged Architecture Library)

A set of subroutines that are specific to a particular Alpha operating system implementation. These subroutines provide operating-system primitives for context-switching interrupts, exceptions, and memory management. They are implemented in low-level code and delivered by the SRM console firmware as part of the hardware system.

parent directory

The directory in which another directory resides. The directory that is contained in the parent is called a subdirectory.

parent process

A process that has created other processes, called its children. In the Tru64 UNIX system, every command that is not a shell built-in command creates a child process.

See also fork


A program or program fragment for interpreting input and determining how to act upon it. The yacc program assists in the creation of parsers.

See also lexical analyzer

parsing order

The sequence in which a program interprets information that is input to it. For example, a program using left-to-right parsing order interprets input reading "create a number; write the number" so that the number created by the first step is written. A program with right-to-left parsing order interprets the same input to mean that the program is to write a number that it created in some previous step and then to create a new number.


A physical portion of a disk. Disks are divided into partitions that are then assigned to hold various file systems. For example, the root file system is usually on the first partition, named a. The /usr file system is on a different partition, often the g partition. The use of partitions provides flexibility and control of disk usage, but it is restricted in that it denies unlimited use of all the available space on a given disk for a given file.

See also disk label, geometry

passive user

In an XTI transport connection, the transport user that did not initiate the connection.

See also client process, active user, XTI (X/Open Transport Interface)


1. The command by which users change their login password.

2. The UNIX file in which user passwords and associated information are stored; the file's pathname is /etc/passwd.


A file or a collection of files that contain fixes to problems. A patch may correct one or more problems. A collection of patches for a software product is sometimes referred to as a patch kit.

See also dupatch


An environment variable containing the user's search path for commands. Directory names in the $PATH variable are separated with colons.

See also $path


A process variable containing the user's search path for commands. Directory names in the $path variable are separated with spaces.

See also $PATH


An ordered list of the directories in which the shell searches for the executable files named by commands that are not entered with a pathname and are not shell built-in commands.

See also $PATH, $path


The name of a file, concatenated onto a list of the directories through which access to that file is achieved; hence, the complete name of the file. Absolute pathnames begin at the root directory and are written with an initial slash (for example, /usr/users/rolf/myfile.txt). Relative pathnames begin at the user's working directory and are written without the initial slash (for example, rolf/myfile.txt).

pathname qualifier

See variable modifier

pattern matching

The process of comparing input information (usually text) against a specified set of symbols (usually regular expressions) to find correspondences.

See also regular expression


A versatile scripting language that is often used to develop CGI (common gateway interface) programs for the World Wide Web, such as the forms you would use to order merchandise. Perl is similar in syntax to the C language and includes a number of popular UNIX facilities such as sed and awk. Perl is an interpreted language that can be compiled just before execution into either C code or cross-platform byte code. When compiled, a Perl program executes almost as fast as a fully precompiled C language program.

See also script

permission code

See permissions

permission field

See permissions


The constraints a user places on a file to control what other users or groups may read, write, or execute the file. There are three sets of permissions: those applied to the user, those applied to the user's group, and those applied to everyone else, called "other."

PDF file

A file type recognized by the Adobe Acrobat Reader, which provides an easy way to view and print documentation. PDF files have become a standard way of distributing documentation, especially on CD-ROM and over the Internet. Most Tru64 UNIX documentation is provided in PDF and HTML formats. The Acrobat Reader is provided on the Tru64 UNIX Documentation CD-ROM. It is also available at the Adobe Web site:

pid, PID

See process ID (PID)


The construct that couples the output of one program directory to the input of another. Pipes are created by the use of a vertical bar ( | ) between commands on the command line. For example:

% nroff inputfile -ms | lpr

This pipeline processes the input file with the nroff command and sends the processed file directly to the printer with the lpr command.

See also pipeline


A series of commands connected by pipes. The process of coupling the output of one command directly to the input of another with a pipe is called "pipelining" or "piping".


See pipeline

pixel (picture element)

The smallest element of a display in a graphics application. On a video screen, pixels are the dots that produce the visual image. The number of pixels usually determines the resolution of the image; the more pixels, the better the resolution.

Point-to-Point Protocol

See PPP (Point-to-Point Protocol)


A symbol that specifies position by reflecting the motion of the mouse. The pointer can change shape to indicate the function of the area in which the pointer is positioned.

See also cursor

POSIX (Portable Operating System Interface)

A collection of standards proposed by the POSIX working groups of the Institute of Electrical and Electronics Engineers (IEEE). POSIX standards define system interfaces to support the source portability of applications.

See also C, SVID (System V Interface Definition)

POSIX shell

The shell that conforms to the POSIX standard. The POSIX shell (sh) is a subset of the Korn shell.

See also shell


A language developed by Adobe Systems, Inc., for specifying the formatting of typeset documents or displays.

See also PDF file

PPP (Point-to-Point Protocol)

A transmission line protocol that encapsulates and transfers IP datagrams over asynchronous serial lines. PPP is more efficient than SLIP.

See also SLIP (Serial Line Internet Protocol)

predefined variable

A shell variable defined and maintained by the C shell.


A program that translates some portion of information in a file into a form understandable to another program. For example, the tbl program is a preprocessor for the nroff text formatter.

printcap database

A file (/etc/printcap) containing descriptions of all the printers known to the system.

process ID (PID)

A unique number assigned to a process that is running.

See also group ID (GID), user ID (UID)

process identification

See process ID (PID)

process table

A kernel data structure that contains relevant information about all processes in the system.

process variable

A symbol containing information that can be used by the current process only. Process variables are not automatically propagated to child processes.

See also environment variable

profile data

Information about how a program is spending its execution time.

See also profiling


The monitoring of how system resources are used in a given program. Profiling helps programmers improve the efficiency of their program code.


A device that consists of a software simulation, rather than hardware; for example, a pseudoterminal.


A special file that effectively functions as a keyboard and display device. Also called a pty or pseudo-tty.

See also pseudodevice


See pseudoterminal


See pseudoterminal


The command that causes the system to display the absolute pathname of the user's working directory.

See also working directory

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1. The action of searching data for desired information.

2. In data communications, the process by which a master station asks a slave station to identify itself and to give its status.

3. In interactive systems, an operation at a terminal or workstation that elicits a response from the system.

4. A request, based on specific conditions, for information from a file .


A line of items waiting to be processed. For example, a print queue consists of jobs waiting to be printed.

queue daemon

The process that maintains a list of outstanding jobs and sends them to the specified device at the appropriate time.

See also queue, daemon, job

queued message

A system message that is added to a list of messages stored in a file for user viewing at a later time. Background processes usually produce queued messages. Programs interacting directly with users typically send messages to the screen for immediate user viewing.

queue element

An item in a queue.


To protect a character from interpretation by a program by enclosing it in quotation marks or by preceding it with a backslash character (\); to mask the special meaning of certain characters, causing them to be taken literally.

See also escape

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RAID (redundant array of independent disks)

A way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O operations can overlap in a balanced way, thereby improving performance.

RAID technology is most used in storage configurations for high performance and high data availability, using the Logical Storage Manager (LSM) or a hardware-based RAID subsystem.

The four primary RAID levels are RAID 0, also known as data or disk striping; RAID 1, also known as data or disk mirroring; and RAID 3 and RAID 5, which are types of parity RAID.

raw mode

The condition of a device driver in which the driver does not interpret the data passing through it. For example, a UNIX terminal driver operating in raw mode passes a Return character from the terminal directly to the system.

See also cooked mode

raw socket

A socket that provides privileged users access to internal network protocols and interfaces. These sockets can be used to take advantage of protocol features not available through more normal interfaces or to communicate with hardware interfaces.

RCS (Revision Control System)

A set of programs for managing program and documentation source files so that any revision of a given file can be retrieved. Revisions to a file are stored as a series of incremental changes (deltas) applied to the original version instead of as complete copies of all the versions. The system provides locking mechanisms so that only one user can apply changes to a given file at any one time.

See also SCCS (Source Code Control System)

RCS file

A file stored in the Revision Control System (RCS) library containing the text of the original file and the list of changes that have been applied to it.

RCS library

The directory in which Revision Control System (RCS) files are stored.


1. A collection of related data items treated as a unit. A record contains one or more fields.

2. In awk, the information between two consecutive occurrences of the record separator. For most purposes, a record in awk can be thought of as a line from the input file.


In programming, pertaining to a procedure or function that accomplishes its task by repeatedly calling itself until a specified condition is reached. The process of using a recursive procedure or function is called recursion.


The specifying of one or more devices with which standard input, standard output, and standard error virtual files are to be associated during the execution of a given command.

Redundant Array of Network Adaptors

See NetRAIN (Redundant Array of Network Adaptors)

reference page

One of a collection of files containing documentation on commands, system calls, library routines, and so forth. Reference pages are often called man pages (short for manual pages).

regular expression

A pattern of one or more characters used to find text information and formed according to a set of rules that define how the characters are to be interpreted. For example, a period is interpreted as a valid match for any character in the input. The regular expression a.c matches any string containing the letter a and the letter c separated by a single intervening character, such as abc, a?c, a9c, and so on.

See also pattern matching

relative pathname

A pathname that begins at the user's working directory. A relative pathname is written without the initial slash; for example, docs/myfile.txt is a relative pathname.

See also absolute pathname

Request For Comments

See RFC (Request For Comments)

restricted shell

A security feature that provides a controlled shell environment with limited features.

Revision Control System

See RCS (Revision Control System)

RFC (Request For Comments)

A formal specification or document that describes a component of the Internet. RFCs are drafted by groups of engineers and submitted for review by their peers. Once approved, an RFC is numbered and is then considered to be a definitive specification. Although numbered RFCs cannot be changed, subsequent RFCs can supersede or elaborate on all or parts of previous RFCs.

RIS (Remote Installation Services)

A utility for installing software kits across a network instead of by using locally mounted distribution media.

RIS area

A reserved disk area physically connected to a RIS server, containing one or more product environments in which are stored installable software kits.

RIS client

A computer system that has permission to install software across the network by accessing kits stored in the server's RIS area.

RIS server

A computer system that serves other computers by providing software kits for them to install. The software is stored on disks belonging to the server and is accessed across the network by the RIS clients.

RISC (Reduced Instruction Set Computing)

A computer architecture that is based on a limited set of simple instructions instead of a larger and more varied set of more complex instructions.

rolling upgrade

A software upgrade of a cluster that is performed while the cluster is in operation. One member at a time is "rolled" and returned to operation while the cluster transparently maintains a mixed-version environment for the base operating system, cluster, and Worldwide Language Support (WSL) software. Clients accessing services are not aware that a rolling upgrade is in progress.

On clustered Tru64 UNIX Version 5.0A and higher systems, you perform a rolling upgrade to update the Tru64 UNIX operating system or TruCluster Server software or to patch the system.


1. The login name for the superuser (system administrator).

2. The name applied to the topmost directory in the UNIX system's tree-like file structure; hence, the beginning of an absolute pathname. The root directory is represented in pathnames by an initial slash (/); a reference to the root directory itself consists of a single slash.

See also pathname

root directory

See root

root file system

The basic file system, onto which all other file systems can be mounted. The root file system contains the operating system files that get the rest of the system running.

root login

See root

routing daemon

A program that provides a routing-management service. The routing daemon, routed, is invoked when the system is booted to manage the network routing tables.

See also daemon

run time

Refers to actions that are taken by a program or system during execution.

See also compile time

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SCCS (Source Code Control System)

A set of programs for managing program and documentation source files so that any revision of a given file can be retrieved. Revisions to a file are stored as a series of incremental changes (deltas) applied to the original version instead of as complete copies of all the versions. The system provides locking mechanisms so that only one user can apply changes to a given file at any one time.

See also RCS (Revision Control System)

SCCS library

The directory in which Source Code Control System (SCCS) s-files and p-files are stored.

SCP (Subset Control Program)

Files included in software kits to control the installation of the product. The SCP is written by the kit's developer and is invoked by the setld utility during the installation of the kit. System control program files have the extension .scp.


A program that is interpreted (as opposed to compiled) and executed by a specified shell. In general, script languages are easier and faster to code in than the more structured and compiled languages such as C and C++. Script languages generally take longer to process than compiled languages, but are useful for shorter programs.

SCSI (Small Computer System Interface)

An industry-standard bus for small systems such as personal computers, small multiuser systems, or workstations. SCSI-based devices can be configured in a series, with multiple devices on the same bus. SCSI is pronounced "scuzzy."

SCSI Interface Module

See SIM (SCSI Interface Module)

search path

A list of full pathnames (usually separated by colons) of directories to be searched for executable files and other kinds of files. Users can create search paths by defining variables, such as path, $PATH, and MANPATH.


The protection of data, system operations, and devices from accidental or intentional ruin, damage, or exposure.


The command that invokes the sed utility, the standard stream editor. The sed editor reads one or more text files, makes editing changes according to a script of editing commands, and writes the results to standard output.

Serial Line Internet Protocol

See SLIP (Serial Line Internet Protocol)


A computer system that serves one or more other computers, called clients, by providing a resource to them.

server process

In the client/server model of communication, a process that provides services to client processes.


See terminal session


A utility for installing, managing, updating, and removing software subsets.

See also subset


The command that invokes either the Bourne shell or the POSIX shell, depending on the user set up in the passwd file.


A component of the operating system that understands and executes commands entered by the user or by another program. The most popular UNIX shells (all of which are included in the Tru64 UNIX operating system) are the Bourne, C, Korn, and POSIX shells.

See also script


To increase the data size of an operand smaller than the computer's data path by appending high-order bits to the operand. If the sign bit of the operand is a one, the added bits are ones; if a zero, they are zeros. This operation preserves the twos-complement numerical value of the operand.

silent character

See hidden character

SIM (SCSI Interface Module)

A subprogram designed to accept CAM Control Blocks routed through the XPT transport layer in order to execute SCSI commands.

Simple Mail Transfer Protocol

See SMTP (Simple Mail Transfer Protocol)

Simple Network Management Protocol

See SNMP (Simple Network Management Protocol)

SLIP (Serial Line Internet Protocol)

A transmission line protocol that encapsulates and transfers IP datagrams over asynchronous serial lines. SLIP is less efficient than PPP.

See also PPP (Point-to-Point Protocol)

SMTP (Simple Mail Transfer Protocol)

The Internet standard protocol for exchanging electronic mail.

SNMP (Simple Network Management Protocol)

The Internet standard protocol for exchanging network management information.


In interprocess communications, an endpoint of communication. Also, the system call that creates a socket and the associated data structure.


A pair of sockets that can be created in the UNIX domain for two-way communication. Like pipes, socketpairs require communicating processes to be related.

See also pipe

soft link

See symbolic link


To organize the information in a file into the desired order based on specifiable criteria.

Source Code Control System

See SCCS (Source Code Control System)

source hierarchy

For building software kits, the directory tree and files that are to be compiled by the kits command into subsets for a kit.

See also target hierarchy

special file

See device special file


The process of copying files into a reserved disk area and then delivering the temporary copies to a serially accessed device as the device becomes ready to receive each new file. The temporary copies are delivered to the device in the order of their creation and are deleted as their delivery is completed; hence, spooling is a form of FIFO (first in, first out) buffering. The most common use of spooling is for printing. Rather than require a user to wait until the printer becomes available, the system spools the file to be printed. The user can then edit or delete the original copy.

SRM console firmware

Software provided as part of an Alpha system that is responsible for initial system testing and loading the operating system. The Alpha System Reference Manual (SRM) defines the console functions and interfaces.

standard error

The file to which programs write error messages. The standard error file (commonly called stderr) is a virtual file that by default is assigned to the user's screen but can be reassigned (redirected) to any device or file available to the user.

standard input

The file from which most programs receive input data or commands. The standard input file (commonly called stdin) is a virtual file that is by default assigned to the user's keyboard but can be reassigned (redirected) to any device or file available to the user.

standard output

The file to which programs write output data. The standard output file (commonly called stdout) is a virtual file that is by default assigned to the user's screen but can be reassigned (redirected) to any device or file available to the user.


An instruction in a source language, shell script, command language, and the like.


The state in which a program exists.


See standard error


See standard input


See standard output


A type of network connection in which a complete transmission is passed to one intermediate host before transmission to the next intermediate host begins.


The TCP/IP definition developed for System V systems and now in wide use across UNIX systems.

stream editor

A program that manipulates the data in a text file by applying commands from a previously prepared list called a script instead of by accepting commands from the user. Powerful stream editors, such as sed, can perform any operation available to a full-function interactive line editor.


A kernel mechanism that supports the implementation of device drivers and networking protocol stacks.

See also clist, STREAMS framework

STREAMS framework

STREAMS components that define the interface standards for character I/O within the kernel and between the kernel and user levels. These components include functions, utility routines, kernel facilities, and data structures.

stream socket

A socket that provides two-way byte streams across a transport connection.


A way of distributing disk I/O and to improve throughput. The striped data is divided into blocks (sometimes called chunks or stripes) and distributed across multiple disks in an array. Striping enables parallel I/O streams to operate concurrently on different devices, so that I/O operations can be handled simultaneously by multiple devices.

See also RAID (redundant array of independent disks), mirroring


A command that sets or reports certain characteristics of the user's terminal.


See superuser


A directory that is contained (nested) in another directory. The containing directory is called the parent directory.


A software kit module that is installed or removed with the Tru64 UNIX setld utility. A subset usually consists of a collection of related files, such as an application and its support files.

subset control program

See SCP (Subset Control Program)

subset dependency

The condition in which a given subset requires the presence, or lack thereof, of other subsets in order to function properly. Evaluated by a subset's subset control program (SCP) under control of the setld utility.


A user possessing privileges to override the normal restrictions on file access, process control, and so forth. A user who possesses these privileges becomes a superuser by issuing the su command or by logging in to the system as root.


The condition of a process that is stopped but not killed. C shell, Korn shell, and POSIX shell users have the ability to suspend and reactivate processes by using the fg and bg commands, or by pressing Ctrl/z. A process that is suspended is called a "suspended job."

See also terminate

SVID (System V Interface Definition)

The specification that defines subroutine calls, system calls, commands, utilities, and services under System V.

See also POSIX (Portable Operating System Interface)

SVVS (System V Verification Suite)

A set of programs used to test adherence to the System V Interface Definition.


Another name for an option.

symbolic link

A file that contains the pathname of another file or directory and acts as a pointer to that file or directory. The symbolic link can occur within the same file system or across file systems; also called a soft link.

See also hard link


A command that forces all cached disk write operations to be completed before the system is halted.

synchronous execution

A mode of execution that forces transport primitives to wait for specific events before returning control to the transport user.

system call

A function that accesses the file system and communication facilities of the kernel.

system load

The demand that all processes place on the computer. System load is usually expressed as a number, with 1.0 representing 100 percent utilization and 0.1 representing 10 percent utilization of system resources.

System V

A version of the UNIX system developed by AT&T.

System V Interface Definition

See SVID (System V Interface Definition)

System V Verification Suite

See SVVS (System V Verification Suite)

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tar file

A file created with the tar command that saves and restores multiple files in a single file. Tru64 UNIX patch kits are provided as tar files (except for kits included on the Tru64 UNIX CD-ROM).


In the make utility, an entity to be built from its dependents. An executable program is a target that is built from one or more object modules. Also called a target file.

target hierarchy

For building software kits, the directory tree into which a software kit is placed by the kits command.

See also source hierarchy


1. A defined activity; a unit of work to be performed, for example, a user task, a server task, and a processor task.

2. A process and the procedures that run the process.

TCP (Transmission Control Protocol)

The Internet transport-layer protocol that provides a reliable, full-duplex, connection-oriented service for applications. TCP uses the IP protocol to transmit information through the network.


The two fundamental protocols of the Internet Protocol suite, and an acronym that is frequently used to refer to the Internet Protocol suite. TCP provides for the reliable transfer of data, while IP transmits the data through the network in the form of datagrams.

See also TCP (Transmission Control Protocol), IP (Internet Protocol)

termcap database

A file containing descriptions of terminal types and capabilities; used by the tset command and BSD Curses library routines to determine how a given physical terminal is to be controlled.

See also terminfo database

terminal session

A user's interaction with a computer between the time the user logs in and logs out.


1. To place special electrical resistors (terminators) at the endpoints of a SCSI bus. With some SCSI devices you must manually insert or remove the terminators. Other devices have built-in terminators that are enabled or disabled with switches or software commands. A SCSI host adapter and the SCSI devices attached to it must be properly terminated or they will not work reliably.

2. To permanently end (kill) a process. A process that is terminated is called a "terminated job."

See also suspended

terminfo database

A file containing descriptions of terminal types and capabilities; used by the system and X/Open Curses library routines to determine how a given terminal is to be controlled.

See also termcap database

text file

A file that can be read using a command such as more and edited using a program such as vi. Text files are comprised of the ASCII character set.

See also binary file

tilde substitution

In the POSIX, Korn, and C shells, use of a tilde ( ~ ) as the first character in a pathname. By default, the shell interprets the tilde as the pathname of the user's home directory; for example, if a user whose login name is rolf enters ~/docs/figure_1 as a pathname, the system might expand the entry to be /usr/users/rolf/docs/figure_1. If the tilde is followed immediately by a user's login name, the shell interprets the combination as a reference to the named user's home directory; for example, ~willy represents the path to Willy's home directory when entered by any user on the system.


A specific place in a source code program where the value of a variable is printed, without pausing the program's execution. Used to test and debug a program.

See also breakpoint

Transmission Control Protocol

See TCP (Transmission Control Protocol)

transport endpoint

A communication path over which a transport user can exchange data with a transport provider.

transport provider

A transport protocol that offers transport layer services in a network.

transport services

The support given by the transport layer in a network to the session layer for the transfer of data between user processes. The two types of services provided are connection oriented and connectionless.

transport user

A program needing the services of a transport protocol to send data to or receive data from another program or point in a network.


1. In data communications, an unprogrammed, hardware-initiated, conditional jump to a specific address. Similar to an interrupt, but triggered by direct action of an executing program rather than by an external event.

2. In programming languages, the process of branching or jumping to a subroutine that provides the desirable operation when a specific condition occurs.

3. In the UNIX system, a special statement used to catch signals in a shell script and transfer control to a handler routine within the script.

trap handler

A system-defined routine used when an abnormal situation arises during a program's execution.

tree structure

1. The organization of disk directories in most operating systems. Any given directory can contain files or other directories (called subdirectories), or both. By extension, any subdirectory can contain subdirectories of its own; when diagrammed, the resulting structure resembles the branching of a tree.

2. The organization of data in a manner similar to that described for disk directories. Common tree structures in files are the binary tree, in which each data element has zero, one, or two elements beneath it (called children); and the B+ tree, in which each data element can have more than two children, with the distribution of elements in the tree being balanced so that all of the elements at a given level have the same or similar numbers of children.

Trojan Horse

A computer program that appears to do something useful but is also designed to damage or destroy other files or programs or the system itself, without the user's knowledge. An example of a Trojan Horse would be a game program that secretly erased disk files while the game was being played.

See also virus, worm

trusted host

A computer within a network that permits access without the need to supply password information.


A shorthand term for a terminal.

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UBC (Unified Buffer Cache)

Functions as a layer between the operating system and a storage disk by temporarily holding recently accessed file system data for reads and writes from conventional file activity and holding page faults from mapped file sections.

Processes and the UBC compete for a limited amount of physical memory, and the virtual memory subsystem allocates physical pages according to the process and file system demand. To be able to meet the demands of competing claims on memory resources, the virtual memory subsystem periodically reclaims the oldest pages by writing their contents to swap space. Under heavy loads, entire processes may be suspended (swapped out) to free memory.

See also VFS (Virtual File System)

UDP (User Datagram Protocol)

The Internet protocol that allows application programs on remote machines to send datagrams to one another. UDP uses IP to deliver the datagrams.

uid, UID

See user ID (UID)


A forerunner to the Tru64 UNIX operating system. Originally produced by Digital Equipment Corporation, the ULTRIX operating system ran on VAX and RISC computers, whereas HP Tru64 UNIX runs on Alpha systems.


A three-digit octal number that specifies the default permissions given to a file when it is created. The umask command sets or changes this number.

unified buffer cache

See UBC (Unified Buffer Cache)


An operating system that was originally developed at the Bell Laboratories of AT&T in the late 1960s and early 1970s and subsequently enhanced by the University of California at Berkeley, AT&T, the Open Software Foundation (OSF), and others.

UNIX-to-UNIX Copy Program

See UUCP (UNIX-to-UNIX Copy Program)


The system call used to sever the connection between files that had been created with the link system call.


To announce to the system that a file system previously mounted on a specified directory is to be removed. Only the person who mounted the particular file system or a superuser can unmount it. A file system is unmounted with the umount command.

update installation

A type of installation that preserves disk partitions; file systems; file customizations; the network, print, and mail environments; user accounts; user created files; and any other system setup you may have done.

See also full installation

up time

The period during which a machine is available for use.

See also down time

upward compatible

Pertaining to that which is designed for use on small machines but capable of running without change on larger machines.

URL (Uniform Resource Locator)

The address of a file or other resource accessible on the Internet. The type of file or resource depends on the Internet application protocol. For example, using the HyperText Transfer Protocol (HTTP), the file can be an HTML page, an image file, or a program such as a CGI application or Java applet. Such an address would look like this:, which is the URL for the HP Tru64 UNIX Web site.

User Datagram Protocol

See UDP (User Datagram Protocol)

user ID (UID)

The number associated with each login name. This number is stored in the /etc/passwd file.

See also group ID (GID), process ID (PID)

user name

See login name


A read-only file system in which some components of the operating system and of applications are stored. Users' home directories are sometimes also located in a subdirectory of /usr.

UUCP (UNIX-to-UNIX Copy Program)

A set of programs and protocols for connecting computers by means of dial-up lines. The programs include facilities for copying files, logging in to remote computers, and encoding binary files for transmission of 7-bit ASCII data lines. The ease of connection and low cost have made UUCP one of the most popular information networks in the world.

UUCP network

A term applied to any grouping of computers connected by means of the UUCP programs.

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In programming languages, shell scripts, command procedures, and the like, a symbol whose value is allowed to change.

variable expansion

The replacement of the variable identifier with its associated strings in a shell command line.

variable modifier

A symbol referring to part of a variable, usually under the assumption that its value is a pathname.

version control file

In a version control system, a file that consists of original text and a set of revisions (deltas) that have been made to it. In RCS, this file is called an "RCS file"; in SCCS, an "s-file."

version control library

A directory that contains files that are organized and maintained under a version control system, such as RCS or SCCS.

version control system

A software tool that aids in the organization and maintenance of file revisions and configurations. In particular, it automates the storing, logging, retrieval, and identification of revisions to source programs, documentation, and data files.

See also version control library

VFS (Virtual File System)

A uniform interface that allows common access to files, regardless of the file system on which the files reside.

vi editor

A full-screen text editor. The vi editor is a modal editor. In command mode, it accepts commands for cursor movement, text deletion, and so forth. To insert text into the file, the user gives the editor a command that places the editor in input mode, and all keystrokes thereafter are interpreted as input data until the Escape key is pressed.

See also full-screen editor

Virtual File System

See VFS (Virtual File System)

virtual memory

Because processes and file systems compete for a limited amount of physical memory, the virtual memory subsystem periodically reclaims the oldest pages by writing their contents to swap space or disk (paging). Under heavy loads, entire processes may be suspended to free memory (swapping).


A piece of software designed to attach itself to other computer programs or files in a system and then to replicate itself indefinitely through any available means (disk file, network, and so forth) into other computers. Viruses are usually designed to damage or destroy "infected" programs or systems and are often programmed to become destructive at a specific time, such as the birthday of the virus's programmer.

See also Trojan Horse, worm

visual editor

See full-screen editor

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WEBES (Web-Based Enterprise Services )

A common architecture implemented by HP for many of its service tools. For example Compaq Analyze and HP Insight Manager utilize the common components of WEBES and add their own functions. Other service tools can be added to the same machine utilizing the same common WEBES components. Each WEBES-based service tool adds functionality to the Director, a process that executes continuously on the machine.

wildcard character

A metacharacter that is used to allow wildcard matching in file names or regular expressions.

See also metacharacter, regular expression

wired memory

Physical memory that is allocated to the operating system, usually at boot time, and cannot be used for paging. Wired memory is either static or dynamic:

word identifier

A piece of a command line delimited by blanks and recognized as a unique entity by the shell. Used to save keystrokes. By using word identifiers, a user can select part of a previous command line for use in the current command line.


A C shell variable consisting of more than one word.

working directory

1. The directory from which a file is read or into which a file is written when a program does not include a directory path in the name of the file when operating on it.

2. The user's current directory.

See also home directory


A computer program designed to replicate itself and spread through a network into other computers. Worms are not attached to other programs or files. Worms are usually designed to damage or destroy "infected" systems and are often programmed to become destructive at a specific time, such as the birthday of the worm's programmer. Some worms are not designed to cause damage, but they are still harmful because they occupy resources intended for legitimate use.

See also Trojan Horse, virus


Refers to storage media that can be written once and read many times, such as a recordable compact disc (CD-R).

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X/Open Transport Interface

See XTI (X/Open Transport Interface)


A transport layer of software that SCSI peripheral drivers use to originate the execution of CAM (Common Access Method) functions.

XTI (X/Open Transport Interface)

Protocol-independent, transport-layer interface for applications. XTI consists of a series of C language functions based on the Transport Layer Interface (TLI), which in turn was based on the transport service definition for the OSI model.

X Window System

A network-based windowing interface. The X Window System has been adopted by many major computer manufacturers.

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yacc (Yet Another Compiler-Compiler)

A program for generating parsers (programs that can interpret their input in a rational manner). The output from yacc is a C language program. The yacc program is usually used to generate parsers for interpreting the output of a lex-generated front end.

See also lex, parser