Copyright 1996-1998 by James Mohr. All rights reserved. Used by permission of the author.
Be sure to visit Jim's great Linux Tutorial web site at http://www.linux-tutorial.info/
This glossay contains a list of commonly used terms and expressions. In many cases I wrote something in bold in the definition as a flag that this is something important. The fact that a word or phrase is in bold, does not necessarily mean it has it's own glossary entry. I just felt you needed to pay attention to it.
absolute mode — Changing file permissions using the 3-digit octal numbers, instead of the letters.
absolute pathname — A pathname for a file or directory beginning at the root directory and including the leading slash (/).
accelerator keys — Keystrokes that select menu options of functions without explicitely pressing the button or selecting the menu.
access control. See security
account — The environment that a user accesses in order to log into the system.
active partition — The partition from which the hardware will try to boot.
active window — The window currently accepting input.
ACU - Automatic Call Unit. The term used in UUCP files to refer to a modem.
address — 1) A memory location. 2) The user and machine name used to send an electronic mail message.
ADF — Adapter Description File. File provided with MCA devices on the options disk which contains configuration information for that device
administrator — The person who manages your computer system or network.
AFS — Acer Fast Filesystem. Older filesystem used on SCO system that increases preformance by grouping files into 16K clusters.
AHS — Adavanced Hardware Supplement. A supplement provided by SCO that includes drivers to newer hardware
alias — A name that is more commonly used or is easier to remember that represents something else. If your shell supports aliases, an alias can be a a command that represents another command. In mail, this is an address that represents another address.
alias tracks - Tracks that are used to store data contained in bad tracks.
anchors — Hypertext links. A anchor or hypertext link is a link from one document to another
ANSI - American National Standards Institute.
anti-caching - Occurs when adding more memory makes machine go slower. Sometimes, the CPU cannot cache eveything, so it caches nothing, thereby making the whole system run slower.
APM - Advanced Power Management.
application — A computer program that performs a particular task, such as word processing or managing a database.
arbitration— Process to determine which device has access to a particular resource, such as the sytem bus.
argument — See command argument.
ARP — address resolution protocol.
ASCII — American Standard Code for Information Interchange. This is only the 128 character set and does not contain non-English characters.
AT command set. See Hayes command set
attribute — See permissions.
authorization — Ability to access a particular system function.
auto answer — setting your modem to automatically pick up when an incoming call is received.
automounter — The process that automatically mounts an NFS filesystem when a file or directory under the mount point is accessed.
awk — A programming language on many UNIX systems.
background process — A process that does not require interaction with the user to run. While a background process runs, the user can continue using other programs or commands.
back-slash — Slash that goes from the upper left to lower right (\). Also called a descening slash. Used to "escape” the special meaning of certain characters.
back-ticks - Similar to an apostrophe except that it slants from upper right to lower left. Used to "hold” the output of a command.
backup — A copy of files, directories, or filesystems, normally used as protection against accidental deletion, but also used as to maintain a copy of a object in a known state. Also the process of making a backup.
bad track — A track on the hard disk that con no longer be read from or written to properly. Bad tracks are listed in a bad track table which points to good alias tracks.
badhosts channel — A mail channel through which all mail addressed to unrecognized machines is sent. The machine to which the mail is sent is a smart host.
baduser channel — A mail channel through which all mail addressed to unrecognized machines is sent. The machine to which the mail is sent is a smart host.
bandwidth — Referes to the maximum I/O throughput of a system. Although this normally refers to communications channels such as ethernet or serial lines, it is often used to refer to any system.
base address — The setting used to access expansion cards.
basename — The file name component of a path. This can also refer to the "primary” portion of a file name. For example, the base name of the file program.c could be thought of as program. This is also the name of the command used to extract the basename. Compare this to directory name or dirname.
baud— One change in the electrical state of a signal.
baud rate - The number of electrical state changes per second.
bdflush — The buffer flushing daemon, which writes the contents of dirty buffers from the buffer cache to disk.
binary — The numerical system of counting with only two digits: 0 and 1. Also called base 2.
binding — The process of joining two components. Networking programs are often bound to a port, or key presses in the X-Windows systems are bound to a specific function.
BIOS — Basis Input/Output Services. Special chip set on the the computer that is used to access the hardware. SCO mainly uses this during boot-up and shutdown, although operating systems such as DOS use it as the primary means of accessing the hardware. The term BIOS is used for both the chip itself and the routines contained within the chip.
bit — A binary digit. Either a 0 or a 1.
bitmap — A representation such as a picture or table that is stored as a series of 0's and 1's. Each character represents a single dot in the image or a particular value in the table.
block device — A hardware device that is accessed with buffering within the operating system. Although such device can be read by an application a character at a time, input and out is buffered within the system's buffer cache. Compare this to a character device.
blocking I/O — I/O where the process is forced to wait until the operation is complete. Also known as synchronous I/O.
boot — The process by which the computer is powered on and goes through the necessary stops to load and start the operating system. This also refers to the program in the root directory that loads and starts the operating system.
boot device — The device (usually a floppy or a hard disk) from which the system is booted.
bootstring — The string passed to the boot program that it uses to detemine what operating system to load and execute as well as how to do so.
bottleneck — When demand for a particular resource is beyond the capacity of that resource or beyond the ability of the operating sustem to provide that resource.
bps - bits-per-second.
bridge - A computer or other netwokr device used to connect two networks. Bridges are often considered to connect similiar systems, such as two Ethernet networks. Compare this to a gateway.
bss — Uninitialized data. An acronym for block started by symbol. (Often called blank static storage.)
BTLD — Boot-Time Loadable Driver. A device driver that is added to the operating system as it is booted. Unless such a driver is added permanently to the system or added the next time the system boots, it will not be available again.
buffer — An area of computer memory or the hardware that is used to temporarily store information.
buffer cache — The system buffer that stores the most-recently accessed blocks. Note this is only used when accessing block devices.
bus — A set of lines (such as wires or leads) used to transfer data or control information. See also expansion bus.
bus arbitration — The process of deciding which device has control of the bus.
bus mastering devices. Also bus masters. Devices which are capable of taking control of the ystem bus.
byte — Eight bits.
cache memory — Also called just cache. High-speed memory usually placed between a CPU and main memory. Cache memory holds recently accessed memory as it is more likely that this memory will be accessed again. See also level-one (L1) cache and level-two (L2) cache.
carriage return — The keyboard key usually labeled <Return> or <Enter>. When your are typing at the command line, sending a carriage return indicates to the system that you are ready for the system to process the comman. The term comes from typewritters where pressing the carriage return actually returned the carraige of the typewriter to it's starting position.
carrier — Signal that is used as a reference point from which frequency changes are measures. These frequency changes are the actual data.
CCITT — Comite Consultatif International Telegraphique et Telephoneique.
CD-ROM — A read-only optical storage media that uses the same technology as music CDs.
Centronics connector — Official name of the printer side if a parallel cable connection.
CGA — Color graphics adapter. Old, old video card.
chain — Term used to describe the connection between different layers in a network.
channel — The program used to phsyical transfer mail.
character device — A hardware device that is accessed with no buffering within the operating system. Although such device can be read by an applicationin blocks, input and out is not buffered within the system's buffer cache. Compare this to a block device.
CHARM — Character MOSAIC.
chat script — Set of Expect-Reply pairs used by UUCP to log into a remote system.
checkpointing — The process by which specific filesystems have data and control structures written regularly to the disk.
checksum — A value that is calculated based on the bites within a file. Some checksums are dependent on the order of the bytes within a file, whereas other are not. Two files with identical content must have the same checksum.
child process — The process created when one process (the parent) calls the fork() system call.
class — 1) A group of printers, normally all of the same type that behave from the users' perspective as a single printer. 2) Description giving to computer networks depending on what portion of thier IP address is the network and which is the host.
clean — The state of a data object when it has not had its contents altered. "Dirty” buffers or pages can be marked clean when the data is written to disk. Filesystems are marked as clean when the control structures are written to the disk.
client — A process or machine that is using a particular resource that is provided by a server. In X-Windows, a client is usually an application that creates a display on the screen. In a network, a client is a machine that accesses a remote filesystem or other resource.
client-server model — A model in which some components act as servers, providing resources or services and other components are clients that use those resources or services.
clock tick — The term used for an interrupt received at regular intervals from the programmable interrupt timer or clock. Clock ticks are signals to the kernel to allow it to initiate actions that need to be taken at regular intervals.
CMOS — Complementary Metal-Oxide Semiconductor. Technically any chip that uses the CMOS technology, but more commonly used to refer to a special chip that retains the basic confioguration information about your machine.
COFF — Common Object File Format. One of the executable program formats used by SCO.
COLA — Certificate of License and Authenticity.
COM port — Common term for a serial port. Although this is actually the DOS term, it is used often. the term comes from "communications port."
command — A set of words or characters that is interpreted by the operating system as a request for action on the part of the system.
command alias — An alternative name for a command. See also alias.
command argument — Subsequent information passed to a command. This normal refers to information (such as the name of a file) that needs to be acted upon. Normally arguments that change a commands bheavior are called flags or options.
command flags — See command options.
command line — A place on your screen where you input commands. The command line is usually indicated by a prompt. Also refers to the string of characters that form your command.
command line interpreter — The program that accepts your command line and reacts to it. See also shell.
command options — Arguments passed to a command that change its behavior.
compile — The process of taking the source code for a program and converting it into machine readable instructions.
concatenated disk — A logical disk composed of parts of multiple physical disks.
contention — When two devices, processes, etc. request a system resource at the same time. For example, when two devices want to use the bus at the same time.
context — The set of data, including the CPU register values and uarea that describe the state of a process.
context switch — The process by which the system goes through to change from one process being the current/active one to another.
control character — A character that has an ASCII value less than 32. These are often created by pressing the <Ctrl> key and another key. Programs can also generate control characters. These get their name from the fact that they are often used to control certian function of an applications.
control key — The key marked CTRL on most keyboards. This is used to modify the value sent by another key that is pressed at the same time.
CPU — Central Processing Unit . The primary chip or processor in a computer. The CPU is what reads and executes the machines instructions and makes the computer go.
cpu privilege level — The level of access a process has while running. This essentially determines what memory and hardware can be accessed.
crash — An abnormal shutdown of the computer. Often this exhibits itself as the system "freezing,” but it can also be that the system reboots itself or panics.
cross-over cable — A serial cable in which the transmit pin on one end of the cable goes to the receive pin on the other end and visa-versa.
current working directory — The directory that the system accesses when no paths are given. The current directory can also be specified as . or ./ depending on the context. This directory is taken as the starting point for all relative pathnames.
cursor — The symbolic indicator of where input is being taken. This is usually in the form of a box, underline, I-shaped character or other shape that make or may not be blinking.
cylinder — The set of all tracks on a harddisk that are equadistant from the center of the disk.
DAC — 1) Digital to Analog Converter. Chip (usually) on a video card that converts the digital signals from the operating system to analog signals that the monitor uses. 2) Discrentionary Access Control.
daemon — A process that performs a service for the system. Normally, daemon process are in the background and are waiting for something to occur that they must react to.
DAT — Digital Audio Tape. A form of backup (tape) media.
data mode — The mode a modem is in when it is transfering data.
DCE — Data Communication Equipment.
decimal — The numerical system of counting with ten digits:0123456789. Also called base 10.
decode — To convert date from an encoded format into a form that readable by the approapriate process. (human, program, etc.) See also encode.
default — The standard configuration or values for a program, field or any other aspect of the system
default boot string — The bootstring that is executed when you press return at the Boot:. This is the defined in /etc/default/boot by the entry defbootstr.
defunct process — A process that has made the exit() system call. This process does not use any system resources (including memory) except that it takes up a slot in the process table.
descriptor — Pointers to specific memory locations that are used by the kernel. These are stored in descriptor tables.
device — Any peripheral hardware attached to the system. These are accessed by device drivers through device nodes.
device driver — A set of routines internal to the kernel that performs I/O with a peripheral device. Although it is normal a user's process that wishes to access that peripheral device, it is the kernel that is actually doing the work.
device nodes — Special files that are the entry points into the device drivers. Also referred to as device files.
digitalus enormus — The technical term for making mistakes while typing. This translates as "fat fingers.”
DIN connector - Deutsche Industrie Norm connector. Small 9-pin connector used to attach peripheral device such as mice and keyboards.
DIPP — Dual In-line Pin Package. Usually refers to memory chips that are connected via two rows of parallel pins.
directory — A file in a particular format that is read by the system as a an inode and filename pair. The files contained within a directory can also be other directories.
directory name — Also referred to simply as directory. This is the name of the directory path used to access a file. The directory component can be access with the dirname command.
dirty — The state of a buffer or memory page that has had its contents changed.
discretionary access control. Security of a system where access is determined by the system administrator (at his or her discrention) and not forced by the system.
disk mirroring — The process by which the entire contents of a hard disk are duplicated on another disk.
disk pieces — The components of a virtual disk.
disk striping — The process by which parts of a logical or virtual disk is spread across multiple physical disks. This differs from a concatenated disk in that disks are not seen as being read in sequence, but rather in parallel. The portion of the virtual disk that resides on a on physical disk is referred to a stripe.
diskette — Also called a floppy disk or floppy. A thin, flexible data disk within a protective jacket. Data is stored on the floppy and accessed through the media access hole.
division — A portion of a hard disk partition that may or may not contain a file system. The start location of each division is stored at the begining of the partition in the division table or divvy table.
DLPI — Data Link Provider Interface. A standard by which networking protocols access networking hardware.
DMA — Direct Memory Access. The means by which devices can access memory directly without the intervention of the CPU. DMA is controlled by the DMA controller.
DNS — Domain Name System. Also called Domain Name Service and Domain Name Server. The system by which information about a computer network is stored on specific machines rather than spread out on every machine. Information is obtained by making a query which is then resolved by the domain name server or name server.
domain — A set of machines on a network that are controled by a single administrative authority. The domain name is the name by which the domain is known.
DOS — A sort of operating system. Although the term refers to several different operating systems, it is most commonly associated with Microsoft's DOS, MS-DOS.
dot file — A UNIX file that has a period (dot) as it's first character. With the exception of the root users, dot file are normally not visible. Because they are only visible with specific options to certian commands, they are often equated to DOS "hidden files.”
dotted-decimal notation — The notation used to indicate IP addresses as decimal numbers.
double-quotes — (") Used to partially remove the special significance os certain characters. Characters such as the $, single-quotes(‘) and back-ticks (`) retain their special significance.
DPI — dots-per-inch.
DRAM — Dynamic Random Access Memory. Must be refreshed regularly with electric signals. Compare this to SRAM.
Driver.o — The machine readable version of a device driver. The Driver.o files are linked into to the kernel to provide access to the devices.
DTE — Data Terminal Equipment
DTFS — Desk Top File System. SCO's compression filesystem.
dtnode — An inode from a DTFS.
Dual In-Line Pin Package. See DIPP
dump device — The device that the system will write to (if it can) when the system panics.
Dynamic Link Libraries (DLLs) — Libraries of functions that are linked into the program as needed (at run-time) and not when the program is compiled.
EAFS — Extended Acer Fast Filesystem.
ECC — Error Checking and Correcting.
edge-triggered interrupts — Interrupts that are activated by the rising edge of the signal. That is when the signal is making the transition from low to high. Compare this to level-triggered interrupts
EFS — Extended Functionality Supplement. Supplement supplied by SCO that provide functionality not included in the standard product. Compare this to SLS.
EGA — Enhanced Graphics Adapter. Another old, old video adpater.
EIDE — Enhanced Integrated Digital Electronics. A newer device interface. Most often used in in hard disks and can overcome size limitations of IDE drives.
EIP — Extended Instruction Pointer. The register containg the memory location that the CPU is currently executing.
EISA — Extended Industry Standard Architecture. Ehanced version of the ISA. Developed by a consortium of companies abd providing advantages over ISA.
ELF — Executable and Linking Format. A new executable program format used by SCO.
encapsulation — The process by which one data format is enclosed inside of another. This technique is used in networking to pass data between the various layers.
encode — Converting data from one form to another. The newer form is generally more easily handled than the original. For example, 8-bit data converted to 7-bit data to send via mail is encoded.
encrypt — Encode something so that it is no longer readable by humans or other processes.
encrypted password — The user's password that is stored in encoded form in the /etc/shadow and the Protected Password Database.
enduser — See user.
environment — The settings and values that control the way you work on the system. These include the shell you use, your home and current directories, and your user and groups IDs. There are also a set of variables called environment variables that contain many of these settings and values.
environment variable — Variables that modify the behavior of your login shell as well as other programs.
error message — A message indicating a problem. This can be something as simple as when input incorrect syntax to a command or something more significant like a needed file is missing. Usually the messages indicates the nature of the problem.
escape character — Decimal 27, octal 033 and hexidecimal 1b. Character used in many cases as a flag to indicating the following sequence of characters has special meaning.
escape key — The key which is marked ESC on most keyboards. This key is used to generate and escape character that is often used to remove the special significance of certian other characters.
escape sequences — A sequence of characters preceeded by an escape character. This usually changes the behavior of something. For example, escape sequences to printers might turn on bold printing.
escaping characters — The process by which you remove the specially significance of characters. This is often accomplished by preceeding the special character by a back-slash.
ESDI — Enhanced Small Device Interface. An older hard disk interface.
Ethernet — A local area network standard developed by the Xerox corporation.
event — An occurence on the system. For the kernel this might be that a device is ready to provide requested data. For X-Windows this can be keystrokes, mouse movement, or resizing windows.
exception — An unexpected event.
exception handlers — Special functions within the kernel that are used to deal with expection.
executable file — A file containing a program or a set of commands. In order to be executable, these files must also have the execute permission bit set.
exitcode — The value returned by a process as it is completing.
expanded memory — In DOS-based computers a means of getting around the 640K base memory problem. With this technique, blocks of 64k are shuffled in and out of "accessable" memory.
expansion bus — The bus in a computer into which expansion cards are inserted.
expansion card — A card inserted into the expansion bus that expands the functionality of the system such as a hard disk controller or a serial port.
export — The process by which a filesystem or directory is made available to be remotely mounted.
extended memory — Addition memory above 1Mb. This memory is not switched in as with expanded memory but is treated as a single, linear unit.
extended minor numbers — A technique used to allow the system to have more devices that are premitted by the single byte available for minor numbers. Normally extended minor numbers are only used for hard disks.
fault — An exception that occurs before the instruction is executed (e.g., page faults).
field separator — A special character used to delimit fields within a file or input.
file — A named collection of information stored on a hard disk, floppy or other media. Although a file is normally considered to contain data or executable instructions, hardware in UNIX is accessed through files. These do not have any size and therefore contain no data, their mere existance is what contains the information.
file creation mask — See umask.
file descriptor — A number associated with an open file. This is used to refer to file during I/O operations.
file permissions — The access permissions on a specific file.
file table — A table internal to the kernel that maintains the the relationship between the file descriptors and the physical file on the hard disk.
filesystem — A hierarchical organization of directories and files.
first level cache — The cache contained with the CPU.
flags — See command options.
flow control — The process by which data transfer is regulated so that it does not arrive too quickly for the receiving process.
foregound — A process is said to be in the foreground when it is interacting with the user.
fork — The process and system call by which new processes are created.
format — The process by which a disk is prepared for use.
forward slash — Slash that goes from the upper right to lower left (/). Also called an ascending slash. Used as the path seperator.
FQDN — Fully Qualified Domain Name. Machine name containing both the host name and the domain name. This name is used to uniquely indentify a computer.
fragmentation — When parts of a file are spread out across different parts of a hard disk. Although the term is also used to refer to memory, accessing memory from different locations has no effect on the process. However, when reading a file, being forced to go to different locations, the physical movement of the hard disk components slow down the access.
freelist — A linked list of unallocated (free) data structures.
ftp — A file transfer program that allows you to copy files to and from a remote computer in a network.
full path — See absolute pathname.
gateway — Gateways are often considered as connecting dissimilar systems such as one network running TPC/IP and the other running NetWare.
Gb — See gigabyte.
GDT — Global Descriptor Table.
GID — Group ID.
gigabyte — 230 bytes. Often thought of (erroneously) as one billion bytes.
group — A set of users. These users are listed under a group name within the /etc/group file. The group name is associated with a GROUP ID (GID). Each file on the system has a group associated with it. This is indicated by the GID of the file.
GUI — Graphical User Interface. A graphic oriented interface such as X-Windows.
hard link — A file with a different full path name but the same inode number. Compare this to a symbolic link.
hardware flow control — Controlling the flow of data across a serial cable by using line signals rather than control characters.
hardware-mediated bus — A bus to which the access is determined by special hardware and not software.
Hayes command set — Standard set of modem commands.
header — Information included at the beginning (head) of transmitted data. A header will indentify the information being sent and may contain other information. For example, a mail header would contain the recipient whereas an IP header contains the source and destination IP addresses.
hexadecimal — The numerical system of counting with sixteen digits: 023456789ABCDEF. Also called base 16.
hit ratio — The ratio of times that information was available to the number of times it was requested. For example, if data is requested from cache memory and is available, this is a cache hit. If the data is not available, this is a cache miss..
home directory — The directory defined by your $HOME environment variable. This is normally the same directory you end up in after you log into the system.
hops — The number of connections that need to be made to reach a destination. For example, if you want to go from machine A to machine B, but first need to go to machine C, this is two hops (A->C then C->B).
host — Any computer. Normally used when the computer is on a network.
host adapter — An expansion card that serves as the interface between the system's expansion bus and a SCSI bus. This is often (erroneously) called a SCSI controller.
hostname — The system name or machine name.
HPPS — High-Performance Pipe System. System used in SCO OpenServer where pipes are stored in memory and not on the hard disk.
htepi_daemon — The kernel daemon that manages filesystem control structures.
HTFS — High-Throughput File System. One of SCO's new filesystems.
HTML — HyperText Markup Language. Text formatting language used in WWW documents.
HTTP — HyperText Transfer Protocol. Protocol used to transfer WWW documents.
I/O — Abbreviation for input/output. This refers to the transfer of data to and from peripheral devices.
ICMP — Internet Control Message Protocol.
icon — A graphical representation of something.
IDE — Integrated Drive Electronics. Common hard disk interface.
IDT — Interrupt Descriptor Table. Table containing pointers to the interrupt handling routines.
init — The process "spawner" that is created at system start up.
inode — Index or Information Node. This is a structure containg the basic information about a file such as owner, type, access permissions and pointers to the actual data on the disk. Inodes are stored in the per filesystem inode table and are referenced through inode numbers. See also file.
intent logging — Process by which pending filesystem transactions are logged. If the system goes down unexpectedly, such transactions can be completed or ignored depending on the state they were in.
interrupt — A signal from a hardware device indicating the devices wants "attention.” This can include things like an indicator that requested data is available or an error has occured.
interrupt handler — Special routines within the kernel that handle interrupts.
Interrupt Service Routine. See interrupt handler.
IP — Internet Protocol. Standard by which packets of information are sent to the appropriate location within a network.
IP address — Unique address within a network that uses the Internet Protocol.
IQM — Installation Query Manager. SCO's installation program.
IRQ — interrupt vector. The hardware setting indicating what line a device will generate an interrupt.
ISA — Industry Standard Architecture.
ISDN — Intergrated Services Digital Network.
ISO — Internation Standards Organization.
ISR — Interrupt Service Routine. See interrupt handler.
ITU — International Telecommunications Union.
K or Kb - See Kilobyte.
kernel — The primary part of the operating system. This manages all system functions such as memory, task scheduling, how devices are accessed, etc.
kernel mode. See system mode
kernel parameter — A value defined that controls the configuration of the kernel.
Kilobyte — 210 bytes.
Lan — Local Area Network.
LDT — Local descriptor table.
level-one (L1) cache — Cache memory within the CPU.
level-triggered interrupts — Interrupts that are indicated by them eltrical signal being level, but at the state opposite from what it normally is.
level-two (L2) cache — Cache memory external to, but directly accessed by the CPU.
library call — A call to a library function. Library functions are collections of system calls.
link — 1) hard link.2) soft link. 3) The processes of combining all the drivers and other kernel components to create an new copy of the kernel.
link count — The number of file names that point to a particular set of data.
linkkit — The name used to refer the collection of tools and files used to create a copy of the kernel.
LLI – Link Layer Interface. Older method used on SCO systems to interface network protocols with network device drivers.
locale — The set of values that indicate your location such as language, keyboard type, etc.
localhost — The special name name given to the machine you are currently working on.
locality principle — Principle that the computer instruction which are executed are generally within the same area of memory (spatial locality) and that the same instructions are likely to be executed again (temporal locality).
logging — See transaction intent logging.
logical block addressing — The means by which blocks on the hard disk are accessed based on a logical address and not the absolute address on the hard disk. The logical address is what is presented to the operating system by the hard disk controller.
login — The process of gaining access to the system. Here you enter you login name (logname) and password.
login group — The GID that you are assinged by default.
logname — The name you use to gain access to the system.
logout — The process of disconnecting yourself from the system.
LUN — Logical Unit Number. Number used to identify a device controller by a single SCSI host adapter. Compare this to SCSI ID.
MAC address — Media Access Control address. The unique identifier given to a network interface card. (NIC).
magic number — A number at the beginning of a file used to indicate what type of file it is.
maintenance mode. See system maintenance mode.
major number — A number indicating which device driver should be used to access a particular device. See also minor number.
man-page — A reference page containing useful information about a specific topic.
mask — A series of bits that "cover up'' existing settings. For example, the umask masks out file permissions and the netmask masks out network addresss.
maskable interrupts — Interrupts that can be "ignored."
masterboot block — The first block of your hard disk (or floppy) containing infrormation necessary to find the active partition and boot your operating system.
Mb — See megabyte.
MBR — Master Boot Record. See masterboot block.
MCA — Micro-Channel Architecture. A computer bus architecture developed by IBM. It provides many advantages over the ISA architecture.
megabyte — 220 bytes
metacharacter — A special character that is replaced by character strings by the shell..
MIME — Multipurpose Internet Mail Extensions. A standard for mail exchange, which supports graphical, audio, video, and other binary data.
minor number — A number serving as a flag to a device driver. See also major number.
mirroring — See disk mirroring.
MMDF — Multichannel Memorandum Distribution Facility. One of the two SCO MTAs.
MO drives — Magneto-Optical drives. A storage media that uses both magetical properties and lasers to store data.
modem control port — A serial port that reacts to the carrier signal.
modem – Modulator/Demodulator. An electronic device attached to your computer that converts digital signal from the computer to analog signals (modulation) to be transmitted across telephone cable. When receving the analog signals, a modem converts them back into digital signals (demodulation).
mount — The process by which filesystem are made available.
mount point — The directory through which the mounted filesystem is accessed.
mount table — The table containing all of the mounted filesystems.
mouse — A pointing device used to move a pointer on the screen.
MTA — Mail Transfer Agent. The collection of programs used to transfer mail from one system to another. SCO systems provide two MTAs: MMDF and sendmail.
MTU — Maximum Transmission Unit. Maximum size of a transmitted piece of data.
MUA — Mail User Agent. The program that you use to interface into the mail system, including reading and composing mail.
multi-tasking — The process by which a computer system is able to maintain multiple programs (tasks) in memory and to switch fast enough to appear as if all programs are being run simultaneously.
multi-user — The process by which a computer system is able to maintain multiple programs (tasks) in memory and to ensure that they do not interfer with each other. Normally each task is associated with a specific user.
multi-user mode — The run state of the system in which access is allowed on terminals other than the system console.
multiprocessor system — A computer system with more than one CPU.
multiscreen — One of the 12 console "terminals."
mwm — Motif window manager. A program that controls window configuration and behavior. and creates window frames.
name server — A program running on a network that provides a centralized database of information on the names and IP Addresses of machines on that network.
namei cache — A data structure within the kernel that stores the most-recently accessed translations of pathnames to inode numbers.
netmask — A binary mask used to mask out the network portion on an IP address.
network — A group of computers that are linked together.
NFS — Network Filesystem. The set of programs and the protocol used to make filesystems and directories avaialble across a network.
nice value — A weighting factor that is used to calculate a processes priority.
NIS — Network Information System. System by which files and user information can be automatically spread across a network.
NMI — non-maskable interrupt. An interrupt that cannot be ignored.
octal — The numerical system of counting with eight digits:01234567. Also called base 8.
ODT — A common abbreviation for SCO's Open Desktop.
OMF — Intel Object Module Format. One of the executable program formats used by SCO.
operating system — A group of programs and functions that provide basic functionality on a computer. This software that manages access to a system's hardware and other resources.
options disk — A disk provided with MCA devices that contains an ADF for that device.
OSD — Operating System Direct. A support service provide by SCO.
owner — 1. The user who created a file or directory. 2. The user that started a process.
package — A collection of related programs that perform a common function. Packages are parts of products.
packet — A unit of data being sent across a serial line or network.
page — A 4KB block of memory. The primary unit of memory.
page directory — A structure in memory that the kernel uses to access page tables.
page fault — A hardware event that occurs when a process tries to access a virtual address that is not in physical memory.
page table — A structure in memory that the kernel uses to access pages.
panic — The process the kernel goes through when an unexpected event occurs that it cannot deal with.
parallel — The process by which data is sent bytes at a time. Compare this to serial.
parent directory — The directory which contains the directory you are refering to. For example. if you refer to the /etc/default directory, then the parent directory is /etc. If your current directory is /usr/jimmo, then the parent directory is /usr.
parent process — The process that executed a fork() system call to create a new, child process.
parity — An error detection mechanisms in which the number of bits is counted and an extra bit is added to make the total number of bits set even for even parity or odd for odd paritiy.
parity bit — The extra bit used for parity.
partition — A section of a hard disk, which can be the entire hard disk. The starting location and size of each partition is stored in a partition table.
password — A string of characters that you use to confirm your identity when you log in. An encrypted version of this is stored in the TCB and /etc/shadow, which then compared to your input when attempting to login.
path — 1. The set of directories that are needed to reach a specific file. Also referred to as the pathname.
2. The list of directories through which the shell searches to find the commands you type.
PCI — 1) Peripheral Component Interconnect. One of the newer bus types. 2) PC-Interface. Product provided by SCO that allows PCs access to an SCO system.
PCL — Printer Control Langauge.
peer — Another computer at the same "level" as yours. You can provide services to them and they to you. Computers in this situation use a peer-to-peer model. Compare this to a client-server model.
permissions — The settings associated with each file or directory that determine who can access the file and directory and what types of access are permitted. Also called properties or attributes.
physical memory — RAM.
PIC — Programmable Interrupt Controller. Chip on the motherboard that manages hardware interrupts.
PID — Process ID. Unique identifier for a process. This is simply the process' slot number in the process table.
pipe — A way of joining commands on the command line where the the output of the first command provides the input for the next. The term also refers to the symbol used to create the pipe: |.
PMWM — Panning Motif Window Manager.
polling — The process by which a device driver queries a devices for a response rather than waiting for the device to generate an interrupt.
POST — Power-On Self-Test. Self-test that the computer goes through when you first turn it on.
PPID — Parent Process ID.
PPP — Point-to-Point Protocol. Networking protocol used across serial lines.
pre-initialized data — Variables and other structures within a program that already have their value set before the program is run.
pre-emption — What occurs when a process that was running on a CPU is replaced by a process with a higher priority.
print queue — A queue (waiting line) in which print requests are stored awaiting to be sent to the printer.
print spooler — The term used to described the files and programs used to manage files to be printed.
printer class — Multiple printers that are treated as one destination in order to spread the load more equally.
printer interface scripts — Shell scripts that actually sent the file to the printer.
priority — The value that the scheduler calculates to determine which process should next run on the CPU. This is calculated from its nice value and its recent CPU usage.
privileges . See sub-system authorizations.
process — An instance of a program that is being execution. Each process has a unique PID, which is that process's entry in the kernel's process table.
process table — A data structure within the kernel that stores information about all the current processes.
prompt — One or more characters or symbols that identify that the system is ready to accept a command.
protected mode — A CPU mode in which mechanisms are implemented to allow or deny access to particular areas of memory. In other words, memory is protected.
protected subsystems — Certain actions within the system that are controlled by system privilidges.
protocol — A set of rules and procedures used to establish and maintain communication. That can be between hardware or software.
protocol stack — A set or protocols which appears to be stacked as one protocol hands off information to another.
protocol suite — A collection of related protocols.
pseudo-terminal — Also called a pseudo-tty. A device driver that allows one process to communicate with another as if it were a physical terminal.
queue — A list. A waiting line.
quoting — The mechanism that is used to control the substitution of special characters. See single-quotes, double-quotes and back-ticks.
RAID— Redundant Array of Inexpensive Disks. Combining multiple disks to improve reliablility or performance.
RAM — Random access or main memory.
raw device — See character device.
redirection — The process by which one of the three base file descriptors (stdin, stout and stderr) reference something other than the default.
region — An area of memory grouped by function. For example, text, data and stack.
region descriptor — A descriptor pointing to a region.
region table — A structure within the kernel pointing to the currently active regions.
regular expression — A notation for matching sequences of characters without having to specific all possible combinations. Regular expressions are composed of literal characters as well as metacharacters.
relative path — A pathname that shows a path in relation to the current working directory.
relink — The process by which a new kernel is generated.
remote host — A computer in a network other than the one that you originally logged in to.
RFC — request for comments. A specific document that relates to networking standards and activity.
ROM — Read Only Memory.
root — 1. The top directory of a UNIX filesystem, represented as a slash (/). Also called the root directory. 2. the login name of the super user.
root filesystem — The file system onto which all the other filesystem are mounted and which usually contains most of the system files.
route — A path to a particular computer. The set of other computers need to reach that destiantion.
router — A device used to redirect network connections to the proper machine.
RPC — Remote Procedure Call. A system call that is executed on a remote machine.
RTS/CTS flow control — A form of flow control using the two signals Request-To-Send and Clear-To-Send.
run-level — Also called run-state. An abstract term that is used to determine which process should be run or started.
scatter-gather — The process by which request for data from a hard disk that are spread out across the disk (scattered) are ordered into a more efficient list (gather) to minimize the total access time.
sched — The system swapper daemon. This deamon determines which process get to run.
SCO — The Santa Cruz Operation.
SCSI — Small Computer System Interface. An expansion bus that is controlled by a host adapter and supports several different device types.
second level cache — See L1 Cache.
security — The mechanisms and policies used to pevent unauthorized access to system resources.
sector — The smallest administrative unit on a hard disk. It contains 512 bytes of data.
sed — Stream Editor. A stream/file manipulation program. The term is also used to refer to the language used to program the sed program.
segment — See Region.
serial — The process by which data is sent one bit at a time. Compare this to parallel.
serial ports — A device port that supports serial communication.
SES — Software Enhancement Service. A service provided by SCO giving you upgrades and updates at a reduced costs as well as the Software Support Library.
shared data region — A data region that can be accessed by multiple processes.
shared libraries — Sets of common library routines that are not part of a program, but exist as separate files on the disk and can be accessed by different processes.
shell — The program that controls the user interaction to the operating system.
shell escape — A command or character you type from inside an interactive program to escape to the shell.
shell script — A text file containing written UNIX commands, shell built-in commands and shell programming syntax. Shell scripts must be made executable by setting the execute permission bit.
shell variable — A variable associated with a shell script.
signal — A flag sent to a process indicating a certain event has occured.
SIMM — Single In-Line Memory Module.
single-quotes — (') Quotes that remove the special significance of all other characters. See double-quotes and back-ticks.
single-user mode. See system maintenance mode
SLIP — Serial Line Internet Protocol. A networking procotol used on serial lines.
SLS — Support Level Supplement. Supplement provided by SCO free of charge that usually include patch or updates.
smart host — A computer that has more complete information about the mail network. This includes both information on users and other machines.
SMTP — Simple Mail Transfer Protocol. A mail transfer protocol used over TCP/IP and the Internet.
SNEAKER-Net — A old method of transfering data between two machines using sneakers.
SNMP — Simple Network Management Protocol. A protocol used to manager information within a network.
SOA — Start of Authority. A record with DNS used to determine which machine is the authoritative soruce of information.
soft link. See symbolic link.
Software Enhancement Service. See SES.
software flow control — Flow control using the XON and XOFF characters. Compare this to hardware flow control.
software interrupts — Interrupts generated by software and not hardware.
sosco — The name of the machine with SCO's bulletin board.
space.c — A file within the linkkit containing device driver configuration information.
SPL — Software Priority Level.
spooler — Although refering to any process that routes requests to a file or memory for later processing, this term in normally used for the print spooler.
SRAM — Static RAM.
SSL — Software Support Library. A CD containing SCO's Information Tools, SLSs and EFSs.
SSO — Software Storage Object. The primary way of storing files and packages in OpenServer.
stack — A list of temporary data used by a process when making function calls.
stack region — The area of a process' virtual memory that contains it's stack.
standard error — The place where a process usually writes error messages, by default the screen. Also called stderr.
standard input — The place where a process usually takes its input, by default, the keyboard. Also called stdin.
standard output — The place where a process usually writes its output, by default, the screen. Also called stdout.
start bit — The bit indicating the begining of a byte being transmitted.
stop bit(s) — The bit(s) indicating the end of a byte being transmitted.
streams — A mechanism for implementing a layered interface between applications and a device driver. Most often used to implement network protocol stacks and X-Windows.
stripe width — The number of physical drives in a striped disk. See disk striping.
striped array — See disk striping.
sub-shell — A shell that was started by another process.
sub-system authorizations — Access to specific, but varied, parts of the system, such as printing, backups, and memory.
subdirectory — A directory residing within another directory.
subdomain — A name that describes a smaller orgnaization unit within a domain. An example would be the SCO subdomain within the COM domain.
subnet — A logical portion of a network.
SUID — SET USER ID. The premissions bit that enables the process to run under a different user ID.
superblock — An area at the beginning of a filessytem containing information about that filesystem.
superuser — The user who has the special privileges needed to administer and maintain the system. The super user logs in as root.
SVGA — Super VGA. A newer video standard.
swap device — An area on the disk reserved for swapping out portions of processes, if the physical memory available becomes too small.
swapping — The action taken by the operating system (the swapper daemon) when the system is short of physical memory. The changable portion (data) of a process os moved from physical memory to the swap device.
symbolic link — A file that contains the path to another file or directory. Since this is just a path, symbolic links can cross mount points. Depending on the length of the path specified and the filesystem, symbolic links can also be stored within a file's inode.
symbolic mode — Changing file permissions using keyletters to specify the set of permissions to change and how to change them. Compare this to absolute mode.
system call — A low-level system function. Compare this to a library call.
system maintenance mode — The run-level in which access is only allowed through the system console. Used for maintenance, hence the name.
system mode — The state of a CPU where the kernel needs to ensure that it has privileged access to data and physical devices. Also called kernel mode.
Tb — See terabyte.
TCB — Trusted Computing Base. The file used to control and manage C2 security on an SCO system.
TCP — Transmission Control Protocol. A reliable protocol that is used transmit data from one process to another across a network.
terabyte — 240 bytes.
terminal — Video display unit with a keyboard and a monitor.
terminating resistors — Resistors at the end of a thin-wire network connect or SCSI bus that absorbs the signals and prevents them from bouncing back, potentially interfering with other signals.
text — The executable machine portion of a porgram. That is, the part of a program containing the instructions that a CPU can interpret and act on.
text file — A file containing text.
text region — Also called text segment.
thrashing — When the system spends all of its time swapping and not performing any real work.
throughput — The amount of work that a part of the system can process in a specified time. This can be anything from the number of bytes send to the number of jobs completed.
time slice — The maximum amount of time a process can run without being preempted.
TLB — Translation Lookaside Buffer. Buffer within the CPU that contains pointers to pages.
toggle — To switch between any two conditions. For example, to toggle from OFF to ON.
track — The set of sectors on a hard disk at the same distance from the center and on the same surface.
transaction intent logging — A new feature in OpenServer and one of the functions of the htepi_daemon. This is the process by which the the intention to change filesystem control data is written to a log file on disk.
transport layer — The layer of a network protocol stack responsible for getting the data from one machine to another.
trap — An exception that is processes immedaitely after executing the instruction that generates the exception.
TSS — Task State Segment. Contains the contents of all registers when a process is context switched out.
type — The category that describes whether the file is a regular file, a directory, or other type of file.
uarea — The area of a process (user area) that contrains the private data about the process that only the kernel may access. Also called ublock.
UART — Universal Asynchronous Receiver-Transmitter.
ublock — See uarea.
UDP — User Datagram Protocol. An unreliable protocol that is used transmit data from one process to another across a network
UID — User ID.
umask — A mask that controls the permissions assigned to new files as they are create.
UNIX — An operating system originally developed at Bell Laboratories. The version developed by SCO is the topic of this book.
UPS — Uninterrupted Power Supply.
URL — Uniform Resource Locator. A "network extension" to the standard filename concept. This allows access to files and directories on remote machines, to which you may not have a constant connection, such as NFS. URLs can also point to resources on the local machine and provide a means of transporting the base files without having to change paths.
user account — 1) The enviroment under which a user gains access to the system. This includes the logname, shell, home directory, etc. 2) The records and other information a UNIX system keeps for each user on the system.
user equivalence — The process by which accounts on two system are considered equal and authentication is not longer required for certain network operations.
user mode — The state of a CPU when it is executing the code for a user program that is accessing its own data space.
user name — See logname.
utilities — Any command that performs more than just a simply function. An example would be fdisk as you can use it to create, delete and make partitions active.
UUCP — Unix-to-Unix Copy. A set of programs and protocols used to transfile files across serial lines, as well as perform remote execute of commands.
variable — An object known to a proces that stores a particular value. Shell variables are known to a particular shell process and enviroment variables (generally) known to all of a particular user's processes.
VDM - Virtual Disk Manager.
version number — The number associated with a particular version of a file.
versioning — The ability to store multiple copies of the "same" file on the system.
VESA — Video Electronics Standards Association.
VGA — Video Graphics Array.
vhand — The system name for the page stealing daemon.
virtual address — An address that exists within a process' virtual memory space.
virtual disk — A disk composed of pieces of several physical disks.
virtual memory — A method of being able to access more memory than is physically available on your system. This combines physical RAM with the swap space as well taking advantage of the fact that the entire program is not accessed at once and does not need to all be in memory.
VLB — Video Electronics Standards Association Local Bus.
Wabi — Windows Application Binary Interface.
wait channel — The addresss of an event on which a particular process is waiting.
WCHAN — see wait channel.
well connected host — A host that is connected to many machines or networks.
whitespace — A space, tab or carriage return.
wildcard — Any character (such as ? or *) that is substituted with another character or a group of characters. See also metacharacter.
write policy — How cache memory writes its contents to main memory.
Write-Back — The write policy when cache memory is written to main memory at regular intervals.
Write-Dirty — The write policy when cache memory is written to main memory only when it has been changed
Write-Through — The write policy when cache memory is written to at the same time as main memory.
WWW — World Wide Web. A collection of machines on the Internet that contain documents. These documents contain hypertext links to other documents which may of may not be on the same machine.
X — See X-Windows Systemn
X client — A process that communicates with an X server to request that it display information on a screen or to receive input events from the keyboard or a pointing device such as a mouse.
X server — The software that controls the screen, keyboard and pointing device under X.
X Window System — A windowing system based on the client-server model.
XON/XOFF flow control — Flow controlling using the XON (Ctrl-Q) and XOFF(Ctrl-S) character. Also called software flow control.
ZIF — Zero-Insertion-Force. A special socket with a lever that locks the chip (normally the CPU) with no force required. Hence the name.
zombie process — An entry in the process table that corresponds to a process that no longer exists. This is used to hold the exitcode of that process.
Copyright 1996-1998 by James Mohr. All rights reserved. Used by permission of the author.
Be sure to visit Jim's great Linux Tutorial web site at http://www.linux-tutorial.info/