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# 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)

  A list of permissions attached to an object, usually either a file or a network device.

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 supersedes 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)

  An API enabling the operating system to work in conjunction with the BIOS in order to achieve power management. APM has been superseded by the much more generic and powerful ACPI specification for most applications.

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)

  A method of authenticating a user, based on a secret shared between client and server.

Classical IP over ATM
(CLIP)
Clear To Send
(CTS)

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

  See Also: Request To Send.

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.

  See Also: Data Terminal Ready.

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)

  An ACPI table, supplying basic configuration information about the base system.

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 extremely 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 bandwidth (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)

  A technique where IP packets are rewritten on the way through a gateway, enabling many machines behind the gateway to effectively share a single IP address.

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)

  A means of synchronizing clocks over a network.

# 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)

  See Also: Post Office Protocol Version 3.

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)
Revision Control System
(RCS)

  The Revision Control System (RCS) is one of the oldest software suites that implement “revision control” for plain files. It allows the storage, retrieval, archival, logging, identification and merging of multiple revisions for each file. RCS consists of many small tools that work together. It lacks some of the features found in more modern revision control systems, like CVS or Subversion, but it is very simple to install, configure, and start using for a small set of files. Implementations of RCS can be found on every major UNIX-like OS.

  See Also: Concurrent Versions System, Subversion.

Received Data
(RD)

  An RS232C pin or wire that data is received 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

SVN

  See: Subversion

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)
Subversion
(SVN)

  Subversion is a version control system, similar to CVS, but with an expanded feature list.

  See Also: Concurrent Versions System.

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)

  A method of locating a resource, such as a document on the Internet and a means to identify that resource.

Unix File System Version 1
(UFS1)

  The original UNIX file system, sometimes called the Berkeley Fast File System.

Unix File System Version 2
(UFS2)

  An extension to UFS1, introduced in FreeBSD 5-CURRENT. UFS2 adds 64 bit block pointers (breaking the 1T barrier), support for extended file storage and other features.

Universal Serial Bus
(USB)

  A hardware standard used to connect a wide variety of computer peripherals to a universal interface.

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)

  A simple, unreliable datagram protocol which is used for exchanging data on a TCP/IP network. UDP does not provide error checking and correction like TCP.

# V

VPN

  See: Virtual Private Network

Virtual Private Network
(VPN)

  A method of using a public telecommunication such as the Internet, to provide remote access to a localized network, such as a corporate LAN.

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