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UNIX Unleashed, System Administrator's Edition

Glossary

by David B. Horvath, CCP

This section contains a fairly extensive glossary. This is a selection of words that are related to the UNIX environment and their definitions. The authors of this book contributed words pertinent to their chapters to this section.


NOTE: The language of the computer field is constantly expanding. If you cannot find a word in this section, it is because either it is newer than anything the authors knew about or the authors decided it was so obvious that "everyone should already know it."

Glossary of Terms

$HOME

Environment variable that points to your login directory.

$PATH

The shell environment variable that contains a set of directories to be searched for UNIX commands.

/dev/null file

The place to send output that you are not interesting in seeing; also the place to get input from when you have none (but the program or command requires something). This is also known as the bit bucket, which is where old bits go to die.

/etc/cshrc file

The file containing shell environment characteristics common to all users that use the C Shell.

/etc/group file

This file contains information about groups, the users they contain, and passwords required for access by other users. The password may actually be in another file--the shadow group file--to protect it from attacks.

/etc/inittab file

The file that contains a list of active terminal ports for which UNIX will issue the login prompt. This also contains a list of background processes for UNIX to initialize. Some versions of UNIX use other files like /etc/tty.

/etc/motd file

Message Of The Day file usually contains information the system administrator feels is important for you to know. This file is displayed when the user signs on the system.

/etc/passwd file

Contains user information and password. The password may actually be in another file--the shadow password file--to protect it from attacks.

/etc/profile

The file containing shell environment characteristics common to all users that use the Bourne and Korn shells.

abbreviation

(vi) User-defined character sequences that are expanded into the defined text string when typed during insert mode.

absolute pathname

The means used to represent the location of a file in a directory by specifying the exact location including all directories in the chain including the root.

API (Application Program Interface)

The specific method prescribed by a computer operating system, application, or third-party tool by which a programmer writing an application program can make requests of the operating system.

arguments

See parameters.

ARPA

See DARPA.

ASCII (American Standard Code for Information Interchange)

Used to represent characters in memory for most computers.

AT&T UNIX

Original version of UNIX developed at AT&T Bell Labs, which was later known as UNIX Systems Laboratories. Many current versions of UNIX are descendants; even BSD UNIX was derived from early AT&T UNIX.

attribute

The means of describing objects. The attributes for a ball might be: rubber, red, 3 cm in diameter. The behavior of the ball might be how high it bounces when thrown. Attribute is another name for the data contained within an object (class).

AWK

Programming language developed by A.V. Aho, P.J. Weinberger, and Brian W. Kernighan. The language is built on C syntax, includes the regular expression search facilities of grep, and adds in the advanced string and array handling features that are missing from the C language. nawk, gawk, and POSIX awk are versions of this language.

background

Processes usually running at a lower priority and with their input disconnected from the interactive session. Any input and output are usually directed to a file or other process.

background process

An autonomous process that runs under UNIX without requiring user interaction.

backup

The process of storing the UNIX system, applications, and data files on removable media for future retrieval.

BASH

BASH stands for GNU Bourne Again Shell, and is based on the Bourne shell, sh, the original command interpreter.

beep

Usually referred to in UNIX documentation as the bell (see bell).

bell

The character sent by a program to a terminal to indicate some kind of "error" condition; for example, in vi pressing Esc to exit insert mode when you are already in command mode; actually the ^G character which rather than displaying on the terminal instead causes it to sound an "alarm," which on ancient teletype terminals was implemented as a bell. Different terminals produce different sounds for their bells including one old video terminal that sounded like someone shifting gears without benefit of clutch.

binding

(emacs) The assignment of a shift-key sequence to an Emacs editing command.

block-special

A device file that is used to communicate with a block oriented I/O device. Disk and tape drives are examples of block devices. The block-special file refers to the entire device. You should not use this file unless you want to ignore the directory structure of the device (that is, if you are coding a device driver).

boot or boot up

The process of starting the operating system (UNIX).

Bourne Shell

The original standard user interface to UNIX that supported limited programming capability.

BSD UNIX

Version of UNIX developed by Berkeley Software Distribution and written at UC Berkeley

buffer

(vi) The working version of the file you are editing is usually called the buffer; the buffer is actually an image of the file kept in random access memory during editing; changes are made in this image and only written out to disk upon user command (or when the vi autowrite setting is in effect); see also named buffer and undo buffer.

buffer list

(emacs) A special window which shows all of the buffers currently open; allows you to manipulate buffers using buffer list commands.

C

Programming language developed by Brian W. Kernighan and Dennis M. Ritchie. The C language is highly portable and available on many platforms including mainframes, PCs, and, of course, UNIX systems.

C Shell

A user interface for UNIX written by Bill Joy at Berkeley. It also features C programming-like syntax.

CD-ROM (Compact Disk-Read Only Memory)

Computer-readable data stored on the same physical form as a musical CD. Large capacity, inexpensive, slower than a hard disk, and limited to reading. There are versions that are writable (CD-R, CD Recordable) and other formats that can be written to once or many times.

CGI (Common Gateway Interface)

A means of transmitting data between Web pages and programs or scripts executing on the server. Those programs can then process the data and send the results back to the users browser through dynamically creating HTML.

character-special

A device file that is used to communicate with character-oriented I/O devices such as terminals, printers, or network communications lines. All I/O access is treated as a series of bytes (characters).

characters

1. alphabetic

The letters A through Z and a through z.

2. alphanumeric

The letters A through Z and a through z, and the numbers 0 through 9.

3. control

Any non-printable characters. The characters are used to control devices, separate records, and eject pages on printers.

4. numeric

The numbers 0 through 9.

5. special

Any of the punctuation characters or printable characters that are not alphanumeric. Include the space, comma, period, and many others.

child-process

See sub-process.

child-shell

See sub-shell.

class

A model of objects that have attributes (data) and behavior (code or functions). It is also viewed as a collection of objects in their abstracted form.

command line

(1) The shell command line from which the current vi or Emacs session was started; (2) the ex command line, where ex commands are entered.

command line editing

UNIX shells support the ability to recall a previously entered command, modify it, and then execute the new version. The command history can remain between sessions (the commands you did yesterday can be available for you when you log in today). Some shells support a command line editing mode that uses a subset of the vi, emacs, or gmacs editor commands for command recall and modification.

command line history

See command line editing.

command line parameters

Used to specify parameters to pass to the execute program or procedure. Also known as command line arguments.

command prompt

See shell prompt.

completion

(emacs) The automatic provision of the rest of a command or a file name; when the command or file name cannot be resolved to a single entity, a menu of choices is provided (type a few characters of the name and press TAB; Emacs will either complete the name or give you a menu of choices).

configuration files

Collections of information used to initialize and set up the environment for specific commands and programs. Shell configuration files set up the user's environment.

configuration files, shell

For Bourne shell: /etc/profile and $HOME/.profile.

For Korn shell: /etc/profile, $HOME/.profile, and ENV= file.

For C shell: /etc/.login, /etc/cshrc, $HOME/.login, $HOME/.cshrc, and $HOME/.logout. Older versions may not support the first two files listed.

For BASH: /etc/profile/, $HOME/.bash_profile, $HOME/.bash_login, $HOME/.profile, $HOME/.bashrc, ~/.bash_logout.

control keys

These are keys that cause some function to be performed instead of displaying a character. These functions have names, for instance, the end-of-file key tells the UNIX that there is no more input. The typical end-of-file key is the <^D> (control-d) key.

CPU (Central Processing Unit)

The primary "brain" of the computer; the calculation engine and logic controller.

current macro

(emacs) The most recently recorded macro; it is executed by the call-last-kbd-macro function.

cursor

The specific point on the screen where the next editing action will take place; the cursor is usually indicated on the screen by some sort of highlighting, such as a underscore or a solid block, which may or may not be blinking.

daemon

A system related background process that often runs with the permissions of root and services requests from other processes.

DARPA (U.S. Department of Defense Advanced Research Projects Agency)

Funded development of TCP/IP and ARPAnet (predecessor of the Internet).

database server

See server, database.

default settings

Most tools and systems are governed by a number of settings; those that are in effect when the tool is started is known as the default. vi is governed by a number of settings; the default settings are those in effect when vi is first started and no automatic overrides of settings are in effect through .exrc files or EXINIT environment variables.

device file

File used to implement access to a physical device. This provides a consistent approach to access of storage media under UNIX--data files and devices (such as tapes and communication facilities) are implemented as files. To the programmer, there is no real difference.

directory

A means of organizing and collecting files together. The directory itself is a file that consists of a list of files contained within it. The root (/) directory is the top level and every other directory is contained in it (directly or indirectly). A directory might contain other directories, which are known as sub-directories.

directory navigation

The process of moving through directories is known as navigation. Your current directory is known as the current working directory. Your login directory is known as the default or home directory. Using the cd command, you can move up and down through the tree structure of directories.

DNS (Domain Name Server)

Used to convert the name of a machine on the Internet (name.domain.com) to the numeric address (123.45.111.123).

DOS (Disk Operating System)

Operating system that is based on the use of disks for the storage of commands. It is also a generic name for MS-DOS and PC-DOS on the Personal Computer. MS-DOS is the version Microsoft sells and PC-DOS is the version IBM sells. Both are based on Microsoft code.

EBCDIC (Extended Binary Coded Decimal Interchange Code)

The code used to represent characters in memory for mainframe computers.

echo

The display on the screen of characters you type is sometimes called the echo of characters; it is called this because usually your terminal is set up not to display the characters directly as typed, but rather to wait for them to be sent to the computer, which then echoes (sends) them back to your terminal.

ed

A common tool used for line-oriented text editing.

e-mail

Messages sent through an electronic medium instead of through the local postal service. There are many proprietary e-mail systems that are designed to handle mail within a LAN environment; most of these are also able to send over the Internet. Most Internet (open) e-mail systems make use of MIME to handle attached data (which can be binary).

emacs

A freely available editor now part of the GNU software distribution. Originally written by Richard M. Stallman at MIT in the late 1970's, it is available for many platforms. It is extremely extensible and has its own programming language; the name stands for Editing with MACroS.encapsulation. The process of combining data (attributes) and functions (behavior in the form of code) into an object. The data and functions are closely coupled within an object. Instead of every programmer being able to access the data in a structure his own way, programmers have to use the code connected with that data. This promotes code reuse and standardized methods of working with the data.

environment variables

See variables, environmental.

escape

(1) (vi) The Esc key, used to terminate insert mode, or an incomplete vi command; (2) To prevent a character from having its normal interpretation by a program by preceding it with the escape character (usually \, the backslash); for example in a regular expression, to search for a literal character that has a special meaning in a regular expression, it must be escaped; as a specific example, to search for a period (.), you must type it escaped as \.

ethernet

A networking method where the systems are connected to a single shared bus and all traffic is available to every machine. The data packets contain an identifier of the recipient, which is the only machine that should process that packet.

expression

A constant, variable, or operands and operators combined. Used to set a value, perform a calculation, or set the pattern for a comparison (regular expressions).

fifo

First In, First Out. See named pipe.

file

Collection of bytes stored on a device (typically a disk or tape). Can be source code, executable binaries or scripts, or data.

1. indexed

A file based on a file structure where data can be retrieved based on specific keys (name, employee number, and so on) or sequentially. The keys are stored in an index. This is not directly supported by the UNIX operating system; usually implemented by the programmer or by using tools from an ISV. A typical form is known as ISAM.

2. line sequential

See file, text.

3. sequential

a. A file that can only be accessed sequentially (not randomly).
b. A file without record separators. Typically fixed length but UNIX does not know what that length is and does not care.

4. text

A file with record separators. May be fixed or variable length; UNIX tools can handle these files because it can tell when the record ends (by the separator).

file compression

The process of applying mathematical formula to data typically resulting in a form of the data that occupies less space. A compressed file can be uncompressed (lossless) resulting in the original file. When the compression/uncompress process results in exactly the same file as was originally compressed, it is known as lossless. If information about the original file is lost, the compression method is know as lossy. Data and programs need lossless compression; images and sounds can stand lossy compression.

filename

The name used to identify a collection of data (a file). Without a pathname, it is assumed to be in the current directory.

filename generation

The process of the shell interpreting meta-characters (wild cards) to produce a list of matching files. This is referred to as filename expansion or globbing.

filename, fully qualified

The name used to identify a collection of data (a file) and its location. It includes both the path and name of the file; typically, the pathname is fully specified (absolute). See also pathname and pathname, absolute.

filesystem

A collection of disk storage that is connected (mounted) to the directory structure at some point (sometimes at the root). Filesystems are stored in a disk partition and are also referred to as disk partitions.

firewall

A system used to provide a controlled entry point to the internal network from the outside (usually the Internet). This is used to prevent outside or unauthorized systems from accessing systems on your internal network. The capability depends on the individual software package, but the features typically include: filter packets, filter datagrams, provide system (name or IP address) aliasing, and rejecting packets from certain IP addresses. It can also prevent internal systems from accessing the Internet on the outside. In theory, it provides protection from malicious programs or people on the outside. The name comes from the physical barrier between connected buildings or within a single building that is supposed to prevent fire from spreading from one to another.

flags

See options.

foreground

Programs running while connected to the interactive session.

fseek

Internal function used by UNIX to locate data inside a file or filesystem. ANSI standard fseek accepts a parameter that can hold a value of +2 to -2 billion. This function, used by the operating system, system tools, and application programs, is the cause of the 2 GB file and filesystem size limitation on most systems. With 64 bit operating systems, this limit is going away.

FTP (File Transfer Protocol, or File Transfer Program)

A system-independent means of transferring files between systems connected via TCP/IP. Ensures that the file is transferred correctly, even if there are errors during transmission. Can usually handle character set conversions (ASCII/EBCDIC) and record terminator resolution (<lf> for UNIX, <cr> and <lf> for MS/PC-DOS).

gateway

A combination of hardware, software, and network connections that provides a link between one architecture and another. Typically, a gateway is used to connect a LAN or UNIX server with a mainframe (that uses SNA for networking resulting in the name: SNA gateway). A gateway can also be the connection between the internal and external network (often referred to as a firewall). See also firewall.

globbing

See filename generation.

GNU

GNU stands for GNU's Not Unix, and is the name of free useful software packages commonly found in UNIX environments that are being distributed by the GNU project at MIT, largely through the efforts of Richard Stallman.

grep

A common tool used to search a file for a pattern. egrep and fgrep are newer versions. Egrep allows the use of extended (hence the "e" prefix) regular expressions, fgrep uses limited expressions for a faster (hence the "f" prefix) searches.

here document

The << redirection operator, known as here document, allows keyboard input (stdin) for the program to be included in the script.

HTML (HyperText Markup Language)

Describes World Wide Web pages. It is the document language that is used to define the pages available on the Internet through the use of tags. A browser interprets the HTML to display the desired information.

i-node

Used to describes a file and its storage. The directory contains a cross reference between the i-node and pathname/filename combination. Also known as inode.

I-Phone (Internet Phone)

A method of transmitting speech long distances over the Internet in near real-time allowing the participants to avoid paying long distance telephone charges. They still pay for the call to their ISP and the ISP's service charges.

ICMP (Internet Control Message Protocol)

Part of TCP/IP that provides network layer management and control.

inheritance

A method of object-oriented software reuse in which new classes are developed based on existing ones by using the existing attributes and behavior and adding on to them. For example, if the base object is automobile with attributes of an engine, four wheels, and tires, and behavior of acceleration, turning, and deceleration, then a sports car would modify the attributes so the engine would be larger or have more horsepower than the default, the four wheels would include alloy wheels and high speed rated tires, and the behavior would also be modified for faster acceleration, tighter turning radius, and faster deceleration.

inode

See i-node.

Internet

A collection of different networks that provide the ability to move data between them. It is built on the TCP/IP communications protocol. Originally developed by DARPA, it was taken over by NSF, and has now been released from governmental control.

Internet Service Provider

The people who connect you to the Internet.

IRC (Internet Relay Chat)

A server-based application that allows groups of people to communicate simultaneously through text-based conversations. IRC is similar to Citizen Band radio or the "chat rooms" on some bulletin boards. Some chats can be private (between invited people only) or public (where anyone can join in). IRC now also supports sound files as well as text
it can also be useful for file exchange.

ISAM (Indexed Sequential Access Method)

On UNIX and other systems, ISAM refers to a method for accessing data in a keyed or sequential way. The UNIX operating system does not directly support ISAM files; they are typically add on products.

ISP

See Internet Service Provider.

ISV (Independent Software Vendor)

Generic name for software vendors other than your hardware vendor.

kernel

The core of the operating system that handles tasks such as memory allocation, device input and output, process allocation, security, and user access. UNIX tends to have a small kernel when compared to other operating systems.

keyboard macros

A feature which allows a special key sequence to stand for another, usually more complex sequence; in vi, keyboard macros are implemented via the :map command.

kill ring

(emacs) A set of buffers where killed text is kept; the buffers are arranged in a circular pattern. When commands that automatically move from one buffer to the next get to the end of the set, the next movement will be to the first buffer in the ring.

Korn Shell

A user interface for UNIX with extensive scripting (programming) support. Written by David G. Korn. The shell features command line editing and will also accept scripts written for the Bourne Shell.

LAN (Local Area Network)

A collection of networking hardware, software, desktop computers, servers, and hosts all connected together within a defined local area. A LAN could be an entire college campus.

limits

See quota.

line address

(vi and ex) The way a selected set of lines is indicated in ex mode is through a line address. A line address can be an absolute line number, relative line number, or special symbols which refer to the beginning or of the file.

link

1. hard

Directory entry that provides an alias to another file that is in the same filesystem. Multiple entries appear in the directory (or other directories) for one physical file without replication of the contents.

2. soft

See symbolic link.

3. symbolic

Directory entry that provides an alias to another file that can be in another filesystem. Multiple entries appear in the directory for one physical file without replication of the contents. Implemented through link files; see also link file.

4. file

File used to implement a symbolic link producing an alias on one filesystem for a file on another. The file only contains the fully qualified filename of the original (linked-to) file.

lisp

A programming language used in artificial intelligence. The name stands for LISt Processing. It is the programming language that Emacs is written in and also refers to three major modes within it.

literal text string

An exact character text string, with no wildcards.

login

The process that a user gains access to a UNIX system. This can also refer to the user id that is typed at the login prompt.

macro

A recorded series of keystrokes which can be played back to accomplish the same task repetitively.

major mode

(emacs) A named set of behavioral characteristics; a buffer can be in only one major mode at a time. For examples, text mode for writing a letter; c mode for writing c source code.

man page

On-line reference tool under UNIX that contains the documentation for the system--the actual pages from the printed manuals. It is stored in a searchable form for improved capability to locate information.

manual page

See man page.

mappings

(vi) User-defined character sequences (which may include control keys) that are interpreted as a command sequence (which may also include control keys).

memory

1. real

The amount of storage that is being used within the system (silicon; it used to be magnetic cores).

2. virtual

Memory that exists but you cannot see. Secondary storage (disk) is used to allow the operating system to allow programs to use more memory than is physically available. Part of a disk is used as a paging file and portions of programs and their data are moved between it and real memory. To the program, it is in real memory. The hardware and operating system performs translation between the memory address the program thinks it is using the where it is actually stored.

meta-character

A printing character that has special meaning to the shell or another command. It is converted into something else by the shell or command - the asterisk <*> is converted by the shell to a list of all files in the current directory.

MIME (Multipurpose Internet Mail Extensions)

A set of protocols or methods of attaching binary data (executable programs, images, sound files, and so on) or additional text to e-mail messages.

mini-buffer

(emacs) The last line on the screen, where commands are entered.

minor mode

(emacs) A particular characteristic which can be independently toggled on or off. For example, auto-fill mode for easing the creation of document text.

mode

Many programs offer only subsets of their functions at any given time, because only certain functions are relevant within an immediate context; further, the same keystroke may invoke different commands in these different contexts; such a context is referred to as a mode. Major modes in vi are insert mode (for adding new text into the buffer), and command mode (for most other editing actions).

MPTN (MultiProtocol Transport Network)

IBM networking protocol to connect mainframe to TCP/IP network.

named buffer

(vi)A memory location where text objects can be stored during a single vi session; named buffers persist when you switch from one file to another during a session and are the primary way of moving and copying text between files.

named pipe

An expanded function of a regular pipe (redirecting the output of one program to become the input of another). Instead of connecting stdout to stdin, the output of one program is sent to the named pipe and another program reads data from the same file. This is implemented through a special file known as a pipe file or fifo. The operating system ensures the proper sequencing of the data. Little or no data is actually stored in the pipe file; it just acts as a connection between the two.

Netnews

This is a loosely controlled collection of discussion groups. A message (similar to an e-mail) is posted in a specific area and then people can comment on it, publicly replying to the same place ("posting a response") for others to see. A collection of messages along the same theme is referred to as a thread. Some of the groups are moderated, which means that nothing is posted without the approval of the "owner." Most are not and the title of the group is no guarantee that the discussion will be related. The "official" term for this is Usenet News.

NFS (Network File System)

Means of connecting disks that are mounted to a remote system to the local system as if they were physically connected.

NIS (Network Information Service)

A service that provides information necessary to all machines on a network, such as NFS support for hosts and clients, password verification, and so on.

NNTP (Net News Transport Protocol)

Used to transmit Netnews or usenet messages over top of TCP/IP. See Netnews for more information on the messages transmitted.

null statement

A program step that performs no operation but to hold space and fulfill syntactical requirements of the programming language. Also known as a NO-OP for no-operation performed.

numeric setting

A setting which takes a numeric value, rather than an enabled or disabled state. Applies to many tools including vi and the different shells.

object

An object in the truest sense of the word is something that has physical properties, such as automobiles, rubber balls, and clouds. These things have attributes and behavior. They can be abstracted into data (attribute) and code (behavior). Instead of just writing functions to work on data, they are encapsulated into a package that is known as an object.

open mode

The visual mode of the ex editor.

operator

Meta-character that performs a function on values or variables. The plus sign <+> is an operator that adds two integers.

options

Program- or command-specific indicators that control behavior of that program. Sometimes called flags. The -a option to the ls command shows the files that begin with a . (such as .profile, .kshrc, and so on.) Without it, these files would not be shown, no matter what wildcards were used. These are used on the command line. See also parameters.

package

(emacs) A feature set which can be added to the editor. Major modes and many functions are implemented via packages. Numerous packages are built in to standard Emacs; many others are freely or otherwise available.

parameters

Data passed to a command or program through the command line. These can be options (see options) that control the command or arguments that the command works on. Some have special meaning based on their position on the command line.

parent process identifier

Shown in the heading of the ps command as PPID. The process identifier of the parent-process. See also parent-process.

parent-process

Process that controls another often referred to as the child- or sub-process. See process.

parent-shell

Shell (typically the login shell) that controls another, often referred to as the child- or sub-shell. See shell.

password

The secure code that is used in combination with a user id to gain access to a UNIX system.

pathname

The means used to represent the location of a file in the directory structure. If you do not specify a pathname, it defaults to the current directory. Also see absolute pathname and relative pathname.

PDP (Personal Data Processor)

Computers manufactured by Digital Equipment Corporation. UNIX was originally written for a PDP-7 and gained popularity on the PDP-11. The entire series were inexpensive mini-computers popular with educational institutions and small businesses.

Perl (Practical Extraction and Report Language)

Programming language developed by Larry Wall. (Perl stands for "Practical Extraction and Report Language" or "Pathologically Eclectic Rubbish Language", both are equally valid). The language provides all of the capabilities of awk and sed, plus many of the features of the shells and C.

permissions

When applied to files, they are the attributes that control access to a file. There are three levels of access: owner (the file creator), group (people belonging to a related group as determined by the system administrator), and other (everyone else). The permissions may be r for read, w for write, and x for execute. The execute permissions flag is also used to control who may search a directory.

pipe

A method of sending the output of one program (redirecting) to become the input of another. The pipe character <|> tells the shell to perform the redirection.

pipe file

See named pipe.

polymorphism

Allows code to be written in a general fashion to handle existing and future related classes. Properly developed, the same behavior can act differently depending on the derived object it acts on. With an automobile, the acceleration behavior might be different for a station wagon and a dragster which are subclasses of the superclass automobile. The function would still be accelerate(), but the version would vary (this may sound confusing, but the compiler keeps track and figures it all out).

POSIX

POSIX stands for "Portable Operating System Interface, UNIX". It is the name for a family of open system standards based on UNIX. The name has been credited to Richard Stallman. The POSIX Shell and Utilities standard developed by IEEE Working Group 1003.2 (POSIX.2) concentrates on the command interpreter interface and utility programs.

PPP (Point-to-Point Protocol)

Internet protocol over serial link (modem).

process

A discrete running program under UNIX. The user's interactive session is a process. A process can invoke (run) and control another program that is then referred to as a sub-process. Ultimately, everything a user does is a subprocess of the operating system.

process identifier

Shown in the heading of the ps command as PID. The unique number assigned to every process running in the system.

quota

General description of a system-imposed limitation on a user or process. It can apply to disk space, memory usage, CPU usage, maximum number of open files, and many other resources.

quoting

The use of single and double quotes to negate the normal command interpretation and concatenate all words and whitespace within the quotes as a single piece of text.

range

(vi, ed, and ex) a line address which indicates one or more lines from a starting line to an ending line; indicated as start,end where both start and end are individual line addresses.

recursive edit

(emacs) A feature that allows a query-replace operation to be temporarily suspended while other editing is done.

redirection

The process of directing a data flow from the default. Input can be redirected to get data from a file or the output of another program. Normal output can be sent to another program or a file. Errors can be sent to another program or a file.

regular expression

A way of specifying and matching strings for shells (filename wildcarding), grep (file searches), sed, and awk.

relative pathname

The means used to represent the location of a file in a directory other than the current by navigating up and down through other directories using the current directory as a base.

reserved word

A set of characters recognized by UNIX and related to a specific program, function, or command.

RFC (Request For Comment)

Document used for creation of Internet and TCP/IP related standards.

rlogin (Remote Login)

Gives the same functionality of telnet, with the added functionality of not requiring a password from trusted clients, which can also create security concerns. See telnet.

root

1) The user who owns the operating system and controls the computer. 2) The processes of the operating system run as though a user, root, signed on and started them. The root user is all powerful and can do anything he or she wants. For this reason, the root user is often referred to as a super-user. It is also the very top of the directory tree structure.

routing

The process of moving network traffic between two different physical networks; also decides which path to take when there are multiple connections between the two machines. It may also send traffic around transmission interruptions.

RPC (Remote Procedural Call)

Provides the capability to call functions or subroutines that run on a remote system from the local one.

scripts

A program written for a UNIX utility including shells, AWK, perl, sed, and others. Also see shell scripts.

sed

A common tool used for stream text editing, having ed-like syntax.

server, database

A system designated to run database software (typically a relational database like Oracle, SQL Server, Sybase, or others). Other systems connect to this one to get the data (client applications).

settings

vi is governed by a number of internal variable called settings; these control how certain actions take place.

Shell

The part of UNIX that handles user input and invokes other programs to run commands. Includes a programming language. See also Bourne Shell, C Shell, Korn Shell, tcsh, and BASH.

shell environment

The shell program (Bourne, Korn, C, tcsh, or BASH), invocation options, and preset variables that define the characteristics, features and functionality of the UNIX command line and program execution interface.

shell buffer

(emacs) A buffer in which an interactive UNIX shell session has been started.

shell scripts

A program written using a shell programming language like those supported by Bourne, Korn, or C shells.

shift-key sequence

(emacs) To perform a shift-key sequence, hold down the designated shift key (for example, Shift, Ctrl, Alt, or Meta), then press the second designated key, then release both keys. When typing several consecutive shift-key sequences that use the same shift key, you can keep holding down the shift key for the duration.

signal

A special flag or interrupts that is used to communicate special events to programs by the operating system and other programs.

SLIP (Serial Line Internet Protocol)

Internet over a serial link (modem). The protocol frames and controls the transmission of TCP/IP packets of the line.

SNA(System Network Architecture)

IBM networking architecture.

special keys

See control keys.

stderr

The normal error output for a program that is sent to the screen by default. Can be redirected to a file.

stdin

The normal input for a program, taken from the keyboard by default. Can be redirected to get input from a file or the output of another program.

stdout

The normal output for a program that is sent to the screen by default. Can be redirected to a file or to the input of another program.

sticky bit

One of the status flags on a file that tells UNIX to load a copy of the file into the page file the first time it is executed. This is done for programs that are commonly used so the bytes are available quickly. When the sticky bit is used on frequently used directories, they are cached in memory.

stream

A sequential collection of data. All files are streams to the UNIX operating system. To it, there is no structure to a file--that is something imposed by application programs or special tools (ISAM packages or relational databases).

sub-directory

See directory.

sub-process

Process running under the control of another, often referred to as the parent-process. See process.

sub-shell

Shell running under the control of another, often referred to as the parent-shell (typically the login shell). See shell.

subnet

A portion of a network that shares a common IP address component. Used for security and performance reasons.

super-user

See root.

system administrator

The person who takes care of the operating system and user administrative issues on UNIX systems. Also called a system manager although that term is much more common in DEC VAX installations.

system manager

See system administrator.

system programmer

See system administrator.

TCP/IP (Transport Control Protocol/Internet Protocol)

The pair of protocols and also generic name for suite of tools and protocols. that forms the basis for the Internet. Originally developed to connect systems to the ARPANET.

tcsh

A C shell-like user interface featuring command-line editing.

Telnet

Protocol for interactive (character user interface) terminal access to remote systems. The terminal emulator that uses the telnet protocol is often known as telnet or tnvt100.

Terminal

A hardware device, normally containing a cathode ray tube (screen) and keyboard for human interaction with a computer system.

text object

(vi) A text object is the portion of text in the buffer that would be traversed by a specific movement command; for example w refers to the next small word.

text processing languages

A way of developing documents in text editors with embedded commands that handle formatting. The file is fed through a processor that executes the embedded commands producing a formatted document. These include roff, nroff, troff, RUNOFF, TeX, LaTeX, and even the mainframe SCRIPT.

TFTP (Trivial File Transfer Protocol or Trivial File Transfer Program)

A system-independent means of transferring files between systems connected via TCP/IP. It is different from FTP in that it does not ensure that the file is transferred correctly, does not authenticate users, and is missing a lot of functionality (like the ls command).

toggle

A mode that is alternately turned on and off by successive entry of its command.

toggle setting

(vi) A setting which is either enabled or disabled; for example, for the fictitious setting named option, you would enable the setting by entering the command :set option; you would disable the setting by entering the command :set nooption.

top

A common tool used to display information about the top processes on the system.

typewriter key

The subset of a terminal keyboard that is on a standard typewriter; generally the alphanumeric keys, but not the function, cursor control, or numeric pad keys.

UDP (User Datagram Protocol)

Part of TCP/IP used for control messages and data transmission where the delivery acknowledgment is not needed. The application program must ensure data transmission in this case.

undo buffer

(vi) A location in memory where the most recent deleted text object is saved, either for later undoing of the deletion, or for copying of the object to another location.

URL (Uniform Resource Locator)

The method of specifying the protocol, format, login (usually omitted), and location of materials on the Internet.

Usenet

See Netnews.

UUCP (UNIX-to-UNIX-Copy-Program)

Used to build an early, informal network for the transmission of files, e-mail, and Netnews.

variables, attributes

The modifiers that set the variable type. A variable can be string or integer, left or right justified, read-only or changeable, and other attributes.

variables, environmental

A place to store data and values (strings and integers) in the area controlled by the shell so they are available to the current and sub-processes. They can just be local to the current shell or available to a sub-shell (exported).

variables, substitution

The process of interpreting an environmental variable to get its value.

viewport

The portion of the buffer that appears in a window on your screen; one way to think of moving through the buffer is to think of the viewport as sliding back and forth through the buffer.

Web

See World Wide Web.

whitespace

Blanks, space and tabs that are normally interpreted to delineate commands and filenames unless quoted.

wildcard

Means of specifying filename(s) where the operating system determines some of the characters. Multiple files may match and will be available to the tool.

window

The portion of your screen which is displaying a viewport into a buffer.

World Wide Web

A collection of servers and services on the Internet that run software that communicate using a common protocol (HTTP). Instead of having to remember the location of these resources, links are provided from one Web page to another through the use of URLs (Uniform Resource Locators).

WWW

See World Wide Web.

X Window System

A windowing and graphics system developed by MIT, to be used in client/server environments.

X

See X Window System.

X11

See X Window System.

X-windows

The wrong term for the X Window System. See X Window System.

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