Glossary

/

See root (2).

. (dot)

A shorthand expression representing the user's working directory.

.. (dot-dot)

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

A

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. Contrast with relative pathname.

alias

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.

application

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.

apropos

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 and man.

archive

(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.

array

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.

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

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.

attribute-value pair

In the key file of a software product kit, a line specifying the name and value for a single attribute of the kit. Controls how the kit is built by the kits command and how it is installed by the setld utility.

awk

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

B

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 issued with an ampersand (&) character following it. For example, to run the calculator program in background, a user would issue the command dxcalc &. As a result, the calculator would be invoked in one window, while the command line on which the dxcalc command was issued would be ready to accept new commands. Contrast with foreground process.

Berkeley Internet Name Domain

See BIND.

Berkeley Software Distribution

See BSD.

Berkeley UNIX

See BSD.

/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, path, and script.

binary

(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 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. Contrast with character device.

block device switch table

The method used by the Digital 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.

BOM

A sequence of characters written on a magnetic tape to signify the beginning of medium. See also EOF and file mark.

Boolean

(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.

breakpoint

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

UNIX software release of the Computer System Research Group of the University of California at Berkeley -- the basis for some features of the Digital UNIX version of the UNIX 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.

built-in

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.

C

c89

A command that invokes the C compiler and whose use is recommended for portability among systems that conform to the X/Open UNIX CAE specification for commands and utilities. See also cc.

call

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. Contrast with 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. Contrast with 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.

CAM Control Block

See CCB.

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. Contrast with 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 Digital UNIX operating system are case sensitive. Contrast with 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.

cc

A command commonly used to invoke the C compiler on UNIX systems. See also c89.

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).

CDE (Common Desktop Environment)

A graphical user interface for interacting with the Digital 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.

CDB (Command Description Block)

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

character device

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

character device switch table

The method used by the Digital 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.

client

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.

clist

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

Command Description Block

See CDB.

command history

See history list.

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 Desktop Environment

See CDE.

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.

compile

To process one or more program source files in order to produce an executable binary file (or an intermediate binary file referred to as an object file).

compile time

Refers to actions that are taken by a compiler during the compilation of a program. Contrast with run time.

computer virus

See virus.

computer worm

See worm.

concatenate

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 Digital 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.

configuration

(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.

connection-oriented mode

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

construct

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. Contrast with raw mode.

cron

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.

csh

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.

cursor

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. Compare to 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.

D

daemon

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.

datagram

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.

dbxd

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

DCE (Distributed Computing Environment)

A defacto 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.

delta

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.

dependent

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 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.

directory

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 File System

See DFS.

DMS (Dataless Management Services (DMS)

A service provided by Digital whereby 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). See also 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.

domain

See communication domain, domain name system, Internet 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. Contrast with up time.

E

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."

editor

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 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.

Emacs

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 Digital UNIX operating system.

environment

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. Contrast with 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 BOM, file mark.

EPG (External Gateway Protocol)

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

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.

error

Any condition in which the expected results of an operation are not achieved.

escape

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

/etc

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

Ethernet

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.

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. See also out-of-band data.

expression

(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.

F

field

(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 BOM and EOF.

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.

filter

(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.

flag

See option (1).

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. Contrast with background process.

fork

(1) The command used to create and start a child process. (2) The result of using the fork command. See also parent process.

full pathname

See absolute pathname.

full-screen editor

An editor that displays an entire screen at a time. Contrast with line editor.

G

geometry

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

gid, GID

See group ID.

global

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.

globbing

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.

grep command

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.

group

(1) A collection of users who can share access authorities for protected resources. See also login group. (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.

group ID

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.

H

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 action 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.

hashing

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

HBA (Host Bus Adaptor)

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

head

A command that displays a user-specifiable number of lines from the beginning of a text file. See also tail.

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.

history

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.

$HOME

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

$home

A process variable containing the absolute pathname of the user's home directory. See also $HOME.

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. Contrast with working directory.

host

(1) The primary or controlling computer in the communications network. (2) A computer attached to a network.

Host Bus Adapter

See HBA.

host name

The name given to a computer on the network.

I

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.

#include

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"

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.

init

The command given by a UNIX system as the final step in the boot procedure.

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.

inode

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.

input

Data to be processed.

input redirection

The specification of an input source other than standard input.

instruction

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

International Standards Organization

See ISO.

internet

A collection of connected networks using the Internet Protocol (IP).

Internet

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. The Internet is also known as the TCP/IP Internet.

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 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.

Internet Protocol

See IP.

interrupt

(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.

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.

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.

iterate

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

J

job

(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.

K

kdbx

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.

kernel

The integral part of the operating system that controls processes, system scheduling, memory management, input and output services, device management, network communications, and the organization of the file systems.

keyword

(1) A word that must be matched when retrieving information. (2) A reserved word whose presence is required in a file.

kill

(1) To stop the operation of a process. In most cases, a user can kill a foreground process by pressing Ctrl/c. (2) The Digital 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.

ksh

The command that invokes the Korn shell; the name of the executable file that is the shell.

L

label

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.

LAT (local area transport)

A Digital protocol that supports communications between host computer systems and terminal servers with terminals, PCs, printers, modems, and other devices over LANs. See also LAN.

layered product

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

lex

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.

lexical analyzer

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

Lexical Analyzer Generator

See lex.

line editor

An interactive or noninteractive text editor that works on one line of text at a time. Contrast with full-screen editor.

link

A directory entry referring to a file. See also hard link and 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.

lint

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

literal

(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 transport

See LAT.

local host

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

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 Digital 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.

locking

(1) In software installation by the setld utility, the act of inserting a new subset's name in the lock file of an existing subset so that an attempt to remove the latter subset will flag the user with a dependency warning. (2) In a version control system, the creation and use of information flagging a version control file as being checked out for editing.

locking mechanism

In a version control system, a way to prevent overlapping and concurrent changes to a file. SCCS uses p-files to indicate which files are currently out for editing; RCS creates locks by editing the RCS file to insert lock information.

log in

To begin using a computer system, usually by entering one's login name and a secret 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 into the system, the user enters this name and (usually) a secret password. Also known as user name.

login shell

The shell that a user uses by default upon logging into 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.

loop

(1) A sequence of instructions that is executed repeatedly until a specified condition is satisfied. (2) In the UNIX virtual memory system, the page clusters in main memory that are repeatedly scanned for replacement. See also infinite loop.

M

macro

A shortened form of macro instruction.

macro instruction

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

mail

A system that allows the exchange of written messages with other users. Also known as E-mail (for electronic mail).

mailbox

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

make

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.

MAKDEV

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

makefile

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

man

The command that displays reference pages on line; the name is a short form of manual. See also apropos and reference page.

man page, manpage, manual page

See reference page.

MANPATH

An environment variable whose value provides the default directory search path use buy the man, catman, and xman commands. See also search path.

metacharacter

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.

mode

The set of permissions for a file.

Motif

See OSF/Motif

mount

A command used to make a file system available. Contrast with unmount.

mount point

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

multiprocessor

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

N

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.

neqn

The command for invoking the neqn program, which is used with the nroff program to format mathematical expressions. See also nroff.

network

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

nonblocking mode

See asynchronous execution.

nroff

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.

O

octal

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.

open system

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

Open Systems Interconnection

See OSI.

operator

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.

optimization

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.

option

(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. (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.

OSF/Motif

A graphical user interface developed and licensed by the Open Software Foundation, Inc. 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.

owner

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.

P

package

For the Digital 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.

page

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.

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 UNIX system, every command that is not a shell built-in command creates a child process. See also fork.

parser

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

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.

partition

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.

passwd

(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.

$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.

$PATH

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

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.

pathname

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.

pattern space

In the sed editor, the range of lines currently being edited; the pattern space is selected by an address or pair of addresses.

permission code

See permissions.

permission field

See permissions.

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."

pid, also PID

See process ID.

pipe

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 (the lpr command). See also pipeline.

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.

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.

pointer

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 position. Compare to cursor.

POSIX (Portable Operating System Interface for Computer Environments)

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. Contrast with SVID.

POSIX shell

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

PostScript

The registered trademark for a language developed by Adobe Systems, Inc., for specifying the formatting of typeset documents or displays. An encapsulated PostScript file is a file that follows a standard for embedding PostScript files into other PostScript files.

predefined variable

A shell variable defined and maintained by the C shell.

preprocessor

A program that translates some portion of its 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

A unique number assigned to a process that is running.

process identification

See process ID.

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. Contrast with environment variable.

profile data

Information about how a program is spending its execution time. See also profiling.

profiling

The monitoring of how system resources are utilized in a given program. Profiling helps programmers improve the efficiency of their program code. Different versions of the UNIX operating system provide different profiling utilities that work in different ways.

pseudodevice

A device that consists of a software simulation, rather than hardware; for example, a pty (pseudo-tty) device.

pseudoterminal

A special file that effectively functions as a keyboard and display device. See also pseudodevice.

pseudo-tty

See pseudoterminal.

pty

See pseudoterminal.

pwd

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

Q

query

(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 for information from a file based on specific conditions.

queue

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 job, daemon.

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.

quote

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.

R

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. Contrast with cooked mode.

raw socket

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

rc

An element of the name applied to files containing command scripts that control the process of booting a computer. The rc characters are also used in the names of files that contain user-customized startup information, such as the BSD mail utility .mailrc and the Motif window manager .mwmrc.

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 a single user can apply changes to a given file at any one time.

RCS file

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

RCS library

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

record

(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.

recursive

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.

redirection

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

reference page

One of a collection of files containing documentation on all commands, system calls, library routines, and so forth. Often called manual pages or manpages, this online documentation is viewed by using the man and xman commands. For example, to view documentation on the mkdir (make directory) command, a user would type man mkdir.

When the reference page subset is installed, the reference pages are located in the /usr/share/man and /usr/dt/share/man directories. By default, the man and xman commands search both of these directories for reference 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; they are written without the initial slash. For example, docs/myfile.txt is a relative pathname. Contrast with absolute pathname.

restricted shell

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

Revision Control System

See RCS.

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 operating system software 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.

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 clients.

roff

A family of text formatting programs designed to prepare output for different types of display devices.

root

(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 (2).

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 (1).

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

Pertaining to actions that are taken by a program or system during execution. Contrast with compile time.

S

SCCS library

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

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 a single user can apply changes to a given file at any one time. See also RCS.

SCP (software control program)

A program that contains path specifications for all of the files related to a product kit. The SCP is written by the kit's developer and is invoked by the setld utility during the installation of the kit.

script

(1)A nonbinary program that is interpreted and executed by a specified shell. (2) In the sed editor, a list of editing commands to be applied to the input file.

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.

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.

security

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

sed

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.

server

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 also passive user.

session

See terminal session.

setld

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

sh

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

shell

A program that interprets commands entered by the user, invoking programs and calling for system resources as needed. See also C shell, Korn shell, POSIX shell, and Bourne shell.

shell variable

See process variable and environment variable.

sign-extend

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 zeroes. 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 Network Management Protocol

See SNMP.

SLIP (Serial Line Internet Protocol)

A transmission line protocol that encapsulates and transfers IP datagrams over asynchronous serial lines.

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.

socket

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

socketpair

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.

sort

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

Source Code Control System

See SCCS.

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.

special file

See device special file.

spooling

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.

standard error

The file to which programs write error messages. The standard error file (commonly called stderr) 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.

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.

statement

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

stderr

See standard error.

stdin

See standard input.

stdout

See standard output.

store-and-forward

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

stream

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 the UNIX system's sed, can perform any operation available to a full-function interactive line editor.

STREAMS

A kernel mechanism developed by AT&T that supports the implementation of device drivers and networking protocol stacks. Compare to clist. See also 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.

stty

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

su

A command that substitutes another user's login for that of the user who invoked the command, logging the invoking user in under the substituted login. The invoking user must know the login password for the user whose login is being substituted. If no other user's login is specified, the command substitutes the root login.

subdirectory

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

subset

A software kit module that is installed or removed with the Digital 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 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.

superuser

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 into the system as root.

suspended

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.

SVID (System V Interface Definition)

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

SVVS (System V Verification Suite)

A program used to test adherence to the System V Interface Definition.

switch

Another name for an option. See option (1).

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.

synchronous execution

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

system call

Functions that access 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 (SVID)

See SVID.

System V Verification Suite

See SVVS.

T

tail

A command that displays a user-specifiable number of lines at the end of a text file. See also head.

tar program

A program that makes portable copies of files for archiving or transfer to another system. By default, the tar program writes its archive files on the system's primary magnetic tape unit.

target

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.

task

(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.

TCP/IP

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 and Internet Protocol.

$TERM

An environment variable containing the user's terminal type.

termcap database

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

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.

terminal session

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

terminated job

A process that is permanently stopped. Contrast with suspended job.

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.

tool

A command or utility designed to help get a job done; for example make or dbx.

tracepoint

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

Transmission Control Protocol

See TCP.

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.

trap

(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.

trusted host

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

tty

A shorthand term for a terminal.

U

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, also UID

See user ID.

ULTRIX

One of two UNIX operating system products available from Digital Equipment Corporation. The ULTRIX operating system runs on VAX and RISC computers, whereas Digital UNIX runs on Alpha systems.

umask

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.

UNIX

A trademark of X-Open Company, Ltd., that can be used in names of operating systems that conform to X/Open UNIX CAE specifications and meet other X/Open UNIX branding requirements. The UNIX operating system 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.

unlink

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

unmount

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.

up time

The period during which a machine is available for use. Contrast with down time.

upward compatible

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

User Datagram Protocol

See UDP.

user ID

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

user name

See login name.

/usr

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 developed at the Bell Laboratories of AT&T for the purpose of 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.

V

variable

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.

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.

virus

A computer program designed to insinuate itself into other programs or files in a system and then to replicate itself through any available means (disk file, network, and so forth) into other similar computers, from which it can attack yet more systems. Viruses are designed with the object of damaging or destroying the "infected" programs or systems and are often programmed to become destructive at a specific time, such as the birthday of the virus's programmer. Contrast with worm.

visual editor

See full-screen editor and line editor.

W

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.

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. Contrast with home directory.

worm

A computer program designed to insinuate itself into other programs or files in a system and then to replicate itself through any available means (disk file, network, and so forth) into other similar computers, from which it can attack yet more systems. Worms are designed with no serious intent to do damage, but they are harmful because they occupy resources intended for legitimate use. Contrast with virus.

WORM

Refers to a write-once, read-many-times device.

X

X/Open Transport Interface (XTI)

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.

XPT

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

XTI

See X/Open Transport Interface.

X Window System

A network-based windowing interface developed by the Massachusetts Institute of Technology (MIT). The X Window System has been adopted by many major computer manufacturers.

Y

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 parser.

younger file

For the make utility, a dependency file that has changed more recently than its target.