FreeBSD Glossary

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



See: Access Control List


See: Advanced Configuration and Power Interface


See: Automatic Mount Daemon


See: ACPI Machine Language


See: Application Programming Interface


See: Advanced Programmable Interrupt Controller


See: Advanced Power Management


See: Authenticated Post Office Protocol


See: ACPI Source Language


See: Advanced Technology Attachment


See: Asynchronous Transfer Mode

ACPI Machine Language

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

The programming language AML is written in.

Access Control List

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

Advanced Configuration and Power Interface

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

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

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 APM has been superseded by the much more generic and powerful ACPI specification for most applications.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
Advanced Technology Attachment
Asynchronous Transfer Mode
Authenticated Post Office Protocol
Automatic Mount Daemon

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



See: Base Address Register


See: Berkeley Internet Name Domain


See: Basic Input/Output System


See: Berkeley Software Distribution

Base Address Register

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

Basic Input/Output System

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

An implementation of the DNS protocols.

Berkeley Software Distribution

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.



See: Carrier Detect


See: Challenge Handshake Authentication Protocol


See: Classical IP over ATM


See: Common Object File Format


See: Central Processing Unit


See: Clear To Send


See: Concurrent Versions System

Carrier Detect

An RS232C signal indicating that a carrier has been detected.

Central Processing Unit

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

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

Classical IP over ATM
Clear To Send

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

See Also: Request To Send.

Common Object File Format
Concurrent Versions System

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.



See: Discretionary Access Control


See: Debugger


See: Data Encryption Standard


See: Dynamic Host Configuration Protocol


See: Domain Name System


See: Differentiated System Description Table


See: Data Set Ready


See: Data Terminal Ready


See: Distance-Vector Multicast Routing Protocol

Discretionary Access Control
Data Encryption Standard

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

Data Set Ready

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

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


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

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

Distance-Vector Multicast Routing Protocol
Domain Name System

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

Dynamic Host Configuration Protocol

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”.



See: Extended COFF


See: Executable and Linking Format


See: Encapsulated Security Payload

Encapsulated Security Payload
Executable and Linking Format
Extended COFF



See: Fixed ACPI Description Table


See: File Allocation Table


See: File Allocation Table (16-bit)


See: File Transfer Protocol

File Allocation Table
File Allocation Table (16-bit)
File Transfer Protocol

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



See: Graphical User Interface


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

A system where the user and computer interact with graphics.



See: HyperText Markup Language


See: HangUp

HyperText Markup Language

The markup language used to create web pages.



See: Input/Output


See: Intel's ASL compiler


See: Internet Message Access Protocol


See: Internet Protocol


See: IP Firewall


See: Internet Printing Protocol


See: IP Version 4


See: IP Version 6


See: Internet Service Provider

IP Firewall
IP Version 4

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

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

Intel's ASL compiler

Intel's compiler for converting ASL into AML.

Internet Message Access Protocol

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
Internet Protocol

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

A company that provides access to the Internet.



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


See: Key Distribution Center


See: Kernel ld(1)


See: Kernel Scheduler Entities


See: Kernel Virtual Address


See: Kilo Bits Per Second

Kernel ld(1)

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

Kernel Scheduler Entities

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

Kernel Virtual Address
Key Distribution Center
Kilo Bits Per Second

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.



See: Local Area Network


See: Lock Order Reversal


See: Line Printer Daemon

Line Printer Daemon
Local Area Network

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

Lock Order Reversal

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 and the LORs Seen page before posting to the mailing lists.



See: Mandatory Access Control


See: Multiple APIC Description Table


See: Merge From Current


See: Merge From Perforce


See: Merge From Stable


See: Massachusetts Institute of Technology


See: Multi-Level Security


See: Message Of The Day


See: Mail Transfer Agent


See: Mail User Agent

Mail Transfer Agent

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

An application used by users to display and write email.

Mandatory Access Control
Massachusetts Institute of Technology
Merge From Current

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

Merge From Perforce

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

See Also: Perforce.

Merge From Stable

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

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

Multi-Level Security
Multiple APIC Description Table



See: Network Address Translation


See: Project Evil


See: Network File System


See: New Technology File System


See: Network Time Protocol

Network Address Translation

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
New Technology File System

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

A means of synchronizing clocks over a network.



See: Overtaken By Events


See: On-Demand Mail Relay


See: Operating System

On-Demand Mail Relay
Operating System

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

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.



See: Perforce


See: Physical Address Extensions


See: Pluggable Authentication Modules


See: Password Authentication Protocol


See: Personal Computer


See: Personal Computer Network File System Daemon


See: Portable Document Format


See: Process ID


See: Principle Of Least Astonishment


See: Post Office Protocol


See: Post Office Protocol Version 3


See: PostScript Printer Description


See: Point-to-Point Protocol


See: PPP over ATM


See: PPP over Ethernet

PPP over ATM
PPP over Ethernet

See: Problem Report


See: Preboot eXecution Environment

Password Authentication Protocol

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
Personal Computer Network File System Daemon
Physical Address Extensions

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
Point-to-Point Protocol
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
Post Office Protocol

See Also: Post Office Protocol Version 3.

Post Office Protocol Version 3

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
Preboot eXecution Environment
Principle Of Least Astonishment

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

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

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.



See: Router Advertisement


See: Redundant Array of Inexpensive Disks


See: Random Access Memory


See: Received Data


See: Request For Comments


See: Reduced Instruction Set Computer


See: Remote Procedure Call


See: Recommended Standard 232C


See: Request To Send

Random Access Memory
Received Data

An RS232C pin or wire that data is recieved on.

See Also: Transmitted Data.

Recommended Standard 232C

A standard for communications between serial devices.

Reduced Instruction Set Computer

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
Remote Procedure Call

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

A set of documents defining Internet standards, protocols, and so forth. See

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

Request To Send

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

See Also: Clear To Send.

Router Advertisement



See: System Control Interrupt


See: Small Computer System Interface


See: Signal Ground


See: Server Message Block


See: Symmetric MultiProcessor


See: Simple Mail Transfer Protocol


See: SMTP Authentication


See: Secure Shell


See: Suspend To RAM


See: Subversion

SMTP Authentication
Server Message Block
Signal Ground

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

Simple Mail Transfer Protocol
Secure Shell
Small Computer System Interface

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

See Also: Concurrent Versions System.

Suspend To RAM
Symmetric MultiProcessor
System Control Interrupt



See: Transmission Control Protocol


See: Transmission Control Protocol/Internet Protocol


See: Transmitted Data


See: Trivial FTP


See: Ticket-Granting Ticket


See: Time Stamp Counter

Ticket-Granting Ticket
Time Stamp Counter

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

Transmission Control Protocol

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

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

Transmitted Data

An RS232C pin or wire that data is transmitted on.

See Also: Received Data.

Trivial FTP



See: User Datagram Protocol


See: Unix File System Version 1


See: Unix File System Version 2


See: User ID


See: Uniform Resource Locator


See: Universal Serial Bus

Uniform Resource Locator

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

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

Unix File System Version 2

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

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

User ID

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

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.



See: Virtual Private Network

Virtual Private Network

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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