FreeBSD Glossary

This glossary contains terms and acronyms used within the FreeBSD community and documentation.

A

ACL

See: Access Control List

ACPI

See: Advanced Configuration and Power Interface

AMD

See: Automatic Mount Daemon

AML

See: ACPI Machine Language

API

See: Application Programming Interface

APIC

See: Advanced Programmable Interrupt Controller

APM

See: Advanced Power Management

APOP

See: Authenticated Post Office Protocol

ASL

See: ACPI Source Language

ATA

See: Advanced Technology Attachment

ATM

See: Asynchronous Transfer Mode

ACPI Machine Language
(AML)

Pseudocode, interpreted by a virtual machine within an ACPI-compliant operating system, providing a layer between the underlying hardware and the documented interface presented to the OS.

ACPI Source Language
(ASL)

The programming language AML is written in.

Access Control List
(ACL)
Advanced Configuration and Power Interface
(ACPI)

A specification which provides an abstraction of the interface the hardware presents to the operating system, so that the operating system should need to know nothing about the underlying hardware to make the most of it. ACPI evolves and supercedes the functionality provided previously by APM, PNPBIOS and other technologies, and provides facilities for controlling power consumption, machine suspension, device enabling and disabling, etc.

Application Programming Interface
(API)

A set of procedures, protocols and tools that specify the canonical interaction of one or more program parts; how, when and why they do work together, and what data they share or operate on.

Advanced Power Management
(APM)
Advanced Programmable Interrupt Controller
(APIC)
Advanced Technology Attachment
(ATA)
Asynchronous Transfer Mode
(ATM)
Authenticated Post Office Protocol
(APOP)
Automatic Mount Daemon
(AMD)

A daemon that automatically mounts a filesystem when a file or directory within that filesystem is accessed.

B

BAR

See: Base Address Register

BIND

See: Berkeley Internet Name Domain

BIOS

See: Basic Input/Output System

BSD

See: Berkeley Software Distribution

Base Address Register
(BAR)

The registers that determine which address range a PCI device will respond to.

Basic Input/Output System
(BIOS)

The definition of BIOS depends a bit on the context. Some people refer to it as the ROM chip with a basic set of routines to provide an interface between software and hardware. Others refer to it as the set of routines contained in the chip that help in bootstrapping the system. Some might also refer to it as the screen used to configure the boostrapping process. The BIOS is PC-specific but other systems have something similar.

Berkeley Internet Name Domain
(BIND)

An implementation of the DNS protocols.

Berkeley Software Distribution
(BSD)

This is the name that the Computer Systems Research Group (CSRG) at The University of California at Berkeley gave to their improvements and modifications to AT&T's 32V UNIX®. FreeBSD is a descendant of the CSRG work.

Bikeshed Building

A phenomenon whereby many people will give an opinion on an uncomplicated topic, whilst a complex topic receives little or no discussion. See the FAQ for the origin of the term.

C

CD

See: Carrier Detect

CHAP

See: Challenge Handshake Authentication Protocol

CLIP

See: Classical IP over ATM

COFF

See: Common Object File Format

CPU

See: Central Processing Unit

CTS

See: Clear To Send

CVS

See: Concurrent Versions System

Carrier Detect
(CD)

An RS232C signal indicating that a carrier has been detected.

Central Processing Unit
(CPU)

Also known as the processor. This is the brain of the computer where all calculations take place. There are a number of different architectures with different instruction sets. Among the more well-known are the Intel-x86 and derivatives, Sun SPARC, PowerPC, and Alpha.

Challenge Handshake Authentication Protocol
(CHAP)
Classical IP over ATM
(CLIP)
Clear To Send
(CTS)

An RS232C signal giving the remote system permission to send data.

Common Object File Format
(COFF)
Concurrent Versions System
(CVS)

A version control system, providing a method of working with and keeping track of many different revisions of files. CVS provides the ability to extract, merge and revert individual changes or sets of changes, and offers the ability to keep track of which changes were made, by who and for what reason.

D

DAC

See: Discretionary Access Control

DDB

See: Debugger

DES

See: Data Encryption Standard

DHCP

See: Dynamic Host Configuration Protocol

DNS

See: Domain Name System

DSDT

See: Differentiated System Description Table

DSR

See: Data Set Ready

DTR

See: Data Terminal Ready

DVMRP

See: Distance-Vector Multicast Routing Protocol

Discretionary Access Control
(DAC)
Data Encryption Standard
(DES)

A method of encrypting information, traditionally used as the method of encryption for UNIX passwords and the crypt(3) function.

Data Set Ready
(DSR)

An RS232C signal sent from the modem to the computer or terminal indicating a readiness to send and receive data.

Data Terminal Ready
(DTR)

An RS232C signal sent from the computer or terminal to the modem indicating a readiness to send and receive data.

Debugger
(DDB)

An interactive in-kernel facility for examining the status of a system, often used after a system has crashed to establish the events surrounding the failure.

Differentiated System Description Table
(DSDT)
Distance-Vector Multicast Routing Protocol
(DVMRP)
Domain Name System
(DNS)

The system that converts humanly readable hostnames (i.e., mail.example.net) to Internet addresses and vice versa.

Dynamic Host Configuration Protocol
(DHCP)

A protocol that dynamically assigns IP addresses to a computer (host) when it requests one from the server. The address assignment is called a “lease”.

E

ECOFF

See: Extended COFF

ELF

See: Executable and Linking Format

ESP

See: Encapsulated Security Payload

Encapsulated Security Payload
(ESP)
Executable and Linking Format
(ELF)
Extended COFF
(ECOFF)

F

FADT

See: Fixed ACPI Description Table

FAT

See: File Allocation Table

FAT16

See: File Allocation Table (16-bit)

FTP

See: File Transfer Protocol

File Allocation Table
(FAT)
File Allocation Table (16-bit)
(FAT16)
File Transfer Protocol
(FTP)

A member of the family of high-level protocols implemented on top of TCP which can be used to transfer files over a TCP/IP network.

Fixed ACPI Description Table
(FADT)

G

GUI

See: Graphical User Interface

Giant

The name of a mutual exclusion mechanism (a sleep mutex) that protects a large set of kernel resources. Although a simple locking mechanism was adequate in the days where a machine might have only a few dozen processes, one networking card, and certainly only one processor, in current times it is an unacceptable performance bottleneck. FreeBSD developers are actively working to replace it with locks that protect individual resources, which will allow a much greater degree of parallelism for both single-processor and multi-processor machines.

Graphical User Interface
(GUI)

A system where the user and computer interact with graphics.

H

HTML

See: HyperText Markup Language

HUP

See: HangUp

HangUp
(HUP)
HyperText Markup Language
(HTML)

The markup language used to create web pages.

I

I/O

See: Input/Output

IASL

See: Intel's ASL compiler

IMAP

See: Internet Message Access Protocol

IP

See: Internet Protocol

IPFW

See: IP Firewall

IPP

See: Internet Printing Protocol

IPv4

See: IP Version 4

IPv6

See: IP Version 6

ISP

See: Internet Service Provider

IP Firewall
(IPFW)
IP Version 4
(IPv4)

The IP protocol version 4, which uses 32 bits for addressing. This version is still the most widely used, but it is slowly being replaced with IPv6.

See Also: IP Version 6.

IP Version 6
(IPv6)

The new IP protocol. Invented because the address space in IPv4 is running out. Uses 128 bits for addressing.

Input/Output
(I/O)
Intel's ASL compiler
(IASL)

Intel's compiler for converting ASL into AML.

Internet Message Access Protocol
(IMAP)

A protocol for accessing email messages on a mail server, characterised by the messages usually being kept on the server as opposed to being downloaded to the mail reader client.

See Also: Post Office Protocol Version 3.

Internet Printing Protocol
(IPP)
Internet Protocol
(IP)

The packet transmitting protocol that is the basic protocol on the Internet. Originally developed at the U.S. Department of Defense and an extremly important part of the TCP/IP stack. Without the Internet Protocol, the Internet would not have become what it is today. For more information, see RFC 791.

Internet Service Provider
(ISP)

A company that provides access to the Internet.

K

KAME

Japanese for “turtle”, the term KAME is used in computing circles to refer to the KAME Project, who work on an implementation of IPv6.

KDC

See: Key Distribution Center

KLD

See: Kernel ld(1)

KSE

See: Kernel Scheduler Entities

KVA

See: Kernel Virtual Address

Kbps

See: Kilo Bits Per Second

Kernel ld(1)
(KLD)

A method of dynamically loading functionality into a FreeBSD kernel without rebooting the system.

Kernel Scheduler Entities
(KSE)

A kernel-supported threading system. See the project home page for further details.

Kernel Virtual Address
(KVA)
Key Distribution Center
(KDC)
Kilo Bits Per Second
(Kbps)

Used to measure bandwith (how much data can pass a given point at a specified amount of time). Alternates to the Kilo prefix include Mega, Giga, Tera, and so forth.

L

LAN

See: Local Area Network

LOR

See: Lock Order Reversal

LPD

See: Line Printer Daemon

Line Printer Daemon
(LPD)
Local Area Network
(LAN)

A network used on a local area, e.g. office, home, or so forth.

Lock Order Reversal
(LOR)

The FreeBSD kernel uses a number of resource locks to arbitrate contention for those resources. A run-time lock diagnostic system found in FreeBSD-CURRENT kernels (but removed for releases), called witness(4), detects the potential for deadlocks due to locking errors. (witness(4) is actually slightly conservative, so it is possible to get false positives.) A true positive report indicates that “if you were unlucky, a deadlock would have happened here”.

True positive LORs tend to get fixed quickly, so check http://lists.FreeBSD.org/mailman/listinfo/freebsd-current and the LORs Seen page before posting to the mailing lists.

M

MAC

See: Mandatory Access Control

MADT

See: Multiple APIC Description Table

MFC

See: Merge From Current

MFP4

See: Merge From Perforce

MFS

See: Merge From Stable

MIT

See: Massachusetts Institute of Technology

MLS

See: Multi-Level Security

MOTD

See: Message Of The Day

MTA

See: Mail Transfer Agent

MUA

See: Mail User Agent

Mail Transfer Agent
(MTA)

An application used to transfer email. An MTA has traditionally been part of the BSD base system. Today Sendmail is included in the base system, but there are many other MTAs, such as postfix, qmail and Exim.

Mail User Agent
(MUA)

An application used by users to display and write email.

Mandatory Access Control
(MAC)
Massachusetts Institute of Technology
(MIT)
Merge From Current
(MFC)

To merge functionality or a patch from the -CURRENT branch to another, most often -STABLE.

Merge From Perforce
(MFP4)

To merge functionality or a patch from the Perforce repository to the -CURRENT branch.

See Also: Perforce.

Merge From Stable
(MFS)

In the normal course of FreeBSD development, a change will be committed to the -CURRENT branch for testing before being merged to -STABLE. On rare occasions, a change will go into -STABLE first and then be merged to -CURRENT.

This term is also used when a patch is merged from -STABLE to a security branch.

See Also: Merge From Current.

Message Of The Day
(MOTD)

A message, usually shown on login, often used to distribute information to users of the system.

Multi-Level Security
(MLS)
Multiple APIC Description Table
(MADT)

N

NAT

See: Network Address Translation

NDISulator

See: Project Evil

NFS

See: Network File System

NTFS

See: New Technology File System

NTP

See: Network Time Protocol

Network Address Translation
(NAT)
Network File System
(NFS)
New Technology File System
(NTFS)

A filesystem developed by Microsoft and available in its “New Technology” operating systems, such as Windows® 2000, Windows NT® and Windows XP.

Network Time Protocol
(NTP)

O

OBE

See: Overtaken By Events

ODMR

See: On-Demand Mail Relay

OS

See: Operating System

On-Demand Mail Relay
(ODMR)
Operating System
(OS)

A set of programs, libraries and tools that provide access to the hardware resources of a computer. Operating systems range today from simplistic designs that support only one program running at a time, accessing only one device to fully multi-user, multi-tasking and multi-process systems that can serve thousands of users simultaneously, each of them running dozens of different applications.

Overtaken By Events
(OBE)

Indicates a suggested change (such as a Problem Report or a feature request) which is no longer relevant or applicable due to such things as later changes to FreeBSD, changes in networking standards, the affected hardware having since become obsolete, and so forth.

P

p4

See: Perforce

PAE

See: Physical Address Extensions

PAM

See: Pluggable Authentication Modules

PAP

See: Password Authentication Protocol

PC

See: Personal Computer

PCNSFD

See: Personal Computer Network File System Daemon

PDF

See: Portable Document Format

PID

See: Process ID

POLA

See: Principle Of Least Astonishment

POP

See: Post Office Protocol

POP3

See: Post Office Protocol Version 3

PPD

See: PostScript Printer Description

PPP

See: Point-to-Point Protocol

PPPoA

See: PPP over ATM

PPPoE

See: PPP over Ethernet

PPP over ATM
(PPPoA)
PPP over Ethernet
(PPPoE)
PR

See: Problem Report

PXE

See: Preboot eXecution Environment

Password Authentication Protocol
(PAP)
Perforce

A source code control product made by Perforce Software which is more advanced than CVS. Although not open source, its use is free of charge to open-source projects such as FreeBSD.

Some FreeBSD developers use a Perforce repository as a staging area for code that is considered too experimental for the -CURRENT branch.

Personal Computer
(PC)
Personal Computer Network File System Daemon
(PCNFSD)
Physical Address Extensions
(PAE)

A method of enabling access to up to 64 GB of RAM on systems which only physically have a 32-bit wide address space (and would therefore be limited to 4 GB without PAE).

Pluggable Authentication Modules
(PAM)
Point-to-Point Protocol
(PPP)
Pointy Hat

A mythical piece of headgear, much like a dunce cap, awarded to any FreeBSD committer who breaks the build, makes revision numbers go backwards, or creates any other kind of havoc in the source base. Any committer worth his or her salt will soon accumulate a large collection. The usage is (almost always?) humorous.

Portable Document Format
(PDF)
Post Office Protocol
(POP)
Post Office Protocol Version 3
(POP3)

A protocol for accessing email messages on a mail server, characterised by the messages usually being downloaded from the server to the client, as opposed to remaining on the server.

See Also: Internet Message Access Protocol.

PostScript Printer Description
(PPD)
Preboot eXecution Environment
(PXE)
Principle Of Least Astonishment
(POLA)

As FreeBSD evolves, changes visible to the user should be kept as unsurprising as possible. For example, arbitrarily rearranging system startup variables in /etc/defaults/rc.conf violates POLA. Developers consider POLA when contemplating user-visible system changes.

Problem Report
(PR)

A description of some kind of problem that has been found in either the FreeBSD source or documentation. See Writing FreeBSD Problem Reports.

Process ID
(PID)

A number, unique to a particular process on a system, which identifies it and allows actions to be taken against it.

Project Evil

The working title for the NDISulator, written by Bill Paul, who named it referring to how awful it is (from a philosophical standpoint) to need to have something like this in the first place. The NDISulator is a special compatibility module to allow Microsoft Windows™ NDIS miniport network drivers to be used with FreeBSD/i386. This is usually the only way to use cards where the driver is closed-source. See src/sys/compat/ndis/subr_ndis.c.

R

RA

See: Router Advertisement

RAID

See: Redundant Array of Inexpensive Disks

RAM

See: Random Access Memory

RD

See: Received Data

RFC

See: Request For Comments

RISC

See: Reduced Instruction Set Computer

RPC

See: Remote Procedure Call

RS232C

See: Recommended Standard 232C

RTS

See: Request To Send

Random Access Memory
(RAM)
Received Data
(RD)

An RS232C pin or wire that data is recieved on.

See Also: Transmitted Data.

Recommended Standard 232C
(RS232C)

A standard for communications between serial devices.

Reduced Instruction Set Computer
(RISC)

An approach to processor design where the operations the hardware can perform are simplified but made as general purpose as possible. This can lead to lower power consumption, fewer transistors and in some cases, better performance and increased code density. Examples of RISC processors include the Alpha, Sparc®, ARM® and PowerPC®.

Redundant Array of Inexpensive Disks
(RAID)
Remote Procedure Call
(RPC)
repocopy

See: Repository Copy

Repository Copy

A direct copying of files within the CVS repository.

Without a repocopy, if a file needed to be copied or moved to another place in the repository, the committer would run cvs add to put the file in its new location, and then cvs rm on the old file if the old copy was being removed.

The disadvantage of this method is that the history (i.e. the entries in the CVS logs) of the file would not be copied to the new location. As the FreeBSD Project considers this history very useful, a repository copy is often used instead. This is a process where one of the repository meisters will copy the files directly within the repository, rather than using the cvs(1) program.

Request For Comments
(RFC)

A set of documents defining Internet standards, protocols, and so forth. See www.rfc-editor.org.

Also used as a general term when someone has a suggested change and wants feedback.

Request To Send
(RTS)

An RS232C signal requesting that the remote system commences transmission of data.

See Also: Clear To Send.

Router Advertisement
(RA)

S

SCI

See: System Control Interrupt

SCSI

See: Small Computer System Interface

SG

See: Signal Ground

SMB

See: Server Message Block

SMP

See: Symmetric MultiProcessor

SMTP

See: Simple Mail Transfer Protocol

SMTP AUTH

See: SMTP Authentication

SSH

See: Secure Shell

STR

See: Suspend To RAM

SMTP Authentication
(SMTP AUTH)
Server Message Block
(SMB)
Signal Ground
(SG)

An RS232 pin or wire that is the ground reference for the signal.

Simple Mail Transfer Protocol
(SMTP)
Secure Shell
(SSH)
Small Computer System Interface
(SCSI)
Suspend To RAM
(STR)
Symmetric MultiProcessor
(SMP)
System Control Interrupt
(SCI)

T

TCP

See: Transmission Control Protocol

TCP/IP

See: Transmission Control Protocol/Internet Protocol

TD

See: Transmitted Data

TFTP

See: Trivial FTP

TGT

See: Ticket-Granting Ticket

TSC

See: Time Stamp Counter

Ticket-Granting Ticket
(TGT)
Time Stamp Counter
(TSC)

A profiling counter internal to modern Pentium® processors that counts core frequency clock ticks.

Transmission Control Protocol
(TCP)

A protocol that sits on top of (e.g.) the IP protocol and guarantees that packets are delivered in a reliable, ordered, fashion.

Transmission Control Protocol/Internet Protocol
(TCP/IP)

The term for the combination of the TCP protocol running over the IP protocol. Much of the Internet runs over TCP/IP.

Transmitted Data
(TD)

An RS232C pin or wire that data is transmitted on.

See Also: Received Data.

Trivial FTP
(TFTP)

U

UDP

See: User Datagram Protocol

UFS1

See: Unix File System Version 1

UFS2

See: Unix File System Version 2

UID

See: User ID

URL

See: Uniform Resource Locator

USB

See: Universal Serial Bus

Uniform Resource Locator
(URL)
Unix File System Version 1
(UFS1)
Unix File System Version 2
(UFS2)
Universal Serial Bus
(USB)
User ID
(UID)

A unique number assigned to each user of a computer, by which the resources and permissions assigned to that user can be identified.

User Datagram Protocol
(UDP)

V

VPN

See: Virtual Private Network

Virtual Private Network
(VPN)

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.