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Daemon (computer software)

Daemon (computer software)

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Encyclopedia
In Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

 and other multitasking
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...

 computer operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

s, a daemon (icon or ˈ) is a computer program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

 that runs as a background
Background (computer software)
A background process is a computer process that runs "behind the scenes" and without user intervention. Typical tasks for these processes include logging, system monitoring, scheduling, and user notification....

 process
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...

, rather than being under the direct control of an interactive user. Typically daemon names end with the letter d: for example, syslogd is the daemon that implements the system logging facility, or sshd
Secure Shell
Secure Shell is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network: a server and a client...

, which services incoming SSH
Secure Shell
Secure Shell is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network: a server and a client...

 connections.

In a Unix environment, the parent process
Parent process
In computing, a parent process is a process that has created one or more child processes.- Unix :In the operating system Unix, every process except is created when another process executes the fork system call. The process that invoked fork is the parent process and the newly-created process is...

 of a daemon is often, but not always, the init
Init
init is a program for Unix-based computer operating systems that spawns all other processes. It runs as a daemon and typically has PID 1. The boot loader starts the kernel and the kernel starts init...

 process. Processes usually become daemons by forking
Fork (operating system)
In computing, when a process forks, it creates a copy of itself. More generally, a fork in a multithreading environment means that a thread of execution is duplicated, creating a child thread from the parent thread....

 a child process and then having their parent process immediately exit, thus causing init to adopt the child process. In addition, a daemon or the operating system typically must perform other operations, such as dissociating the process from any controlling terminal
Tty (Unix)
tty is a Unix command that prints to standard output the name of the terminal connected to standard input. The name of the program comes from teletypewriter, abbreviated "TTY".When the program runs, it will output something like this:$ tty/dev/pts/4...

 (tty). Such procedures are often implemented in various convenience routines such as daemon(3) in Unix.

Systems often start daemons at boot
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...

 time: they often serve the function of responding to network requests, hardware activity, or other programs by performing some task. Daemons can also configure hardware (like udev
Udev
udev is the device manager for the Linux kernel. Primarily, it manages device nodes in /dev. It is the successor of devfs and hotplug, which means that it handles the /dev directory and all user space actions when adding/removing devices, including firmware load.-History:udev was new in Linux...

d on some GNU/Linux systems), run scheduled tasks (like cron
Cron
Cron is a time-based job scheduler in Unix-like computer operating systems. Cron enables users to schedule jobs to run periodically at certain times or dates...

), and perform a variety of other tasks.

Terminology


The term was coined by the programmers of MIT's Project MAC. They took the name from Maxwell's demon
Maxwell's demon
In the philosophy of thermal and statistical physics, Maxwell's demon is a thought experiment created by the Scottish physicist James Clerk Maxwell to "show that the Second Law of Thermodynamics has only a statistical certainty." It demonstrates Maxwell's point by hypothetically describing how to...

, an imaginary being from a famous thought experiment that constantly works in the background, sorting molecules. Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

 systems inherited this terminology. Daemons
Daemon (mythology)
The words dæmon and daimôn are Latinized spellings of the Greek "δαίμων", a reference to the daemons of Ancient Greek religion and mythology, as well as later Hellenistic religion and philosophy...

 are also characters in Greek mythology, some of whom handled tasks that the gods could not be bothered with. BSD
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...

 and some of its derivatives have adopted a daemon as its mascot
BSD Daemon
The BSD daemon, nicknamed Beastie, is the generic mascot of BSD operating systems.-Overview:The BSD daemon is named after a software daemon, a computer program found on Unix-like operating systems, which through a play on words takes the cartoon shape of a mythical demon. The BSD daemon's nickname...

, although this mascot is a variation of the demon
Demon
call - 1347 531 7769 for more infoIn Ancient Near Eastern religions as well as in the Abrahamic traditions, including ancient and medieval Christian demonology, a demon is considered an "unclean spirit" which may cause demonic possession, to be addressed with an act of exorcism...

s that appear in Christian
Christian
A Christian is a person who adheres to Christianity, an Abrahamic, monotheistic religion based on the life and teachings of Jesus of Nazareth as recorded in the Canonical gospels and the letters of the New Testament...

 artwork.

The word daemon is an alternative spelling of demon, and is pronounced ˈ . In the context of computer software, the original pronunciation ˈ has drifted to ˈ for some speakers.

Creation


In a strictly technical sense, a Unix-like system process is a daemon when its parent process terminates and the daemon is assigned the init
Init
init is a program for Unix-based computer operating systems that spawns all other processes. It runs as a daemon and typically has PID 1. The boot loader starts the kernel and the kernel starts init...

 process (process number 1) as its parent process and has no controlling terminal. However, more commonly, a daemon may be any background process, whether a child of init or not.

The common method for a process to become a daemon involves:
  • Dissociating from the controlling tty
    Tty (Unix)
    tty is a Unix command that prints to standard output the name of the terminal connected to standard input. The name of the program comes from teletypewriter, abbreviated "TTY".When the program runs, it will output something like this:$ tty/dev/pts/4...

  • Becoming a session leader
  • Becoming a process group
    Process group
    In POSIX-conformant operating systems, a process group denotes a collection of one or more processes. Process groups are used to control the distribution of signals. A signal directed to a process group is delivered individually to all of the processes that are members of the group.Process groups...

     leader
  • Executing as a background task
    Background (computer software)
    A background process is a computer process that runs "behind the scenes" and without user intervention. Typical tasks for these processes include logging, system monitoring, scheduling, and user notification....

     by forking
    Fork (operating system)
    In computing, when a process forks, it creates a copy of itself. More generally, a fork in a multithreading environment means that a thread of execution is duplicated, creating a child thread from the parent thread....

     and exiting
    Exit (operating system)
    On many computer operating systems, a computer process terminates its execution by making an exit system call. More generally, an exit in a multithreading environment means that a thread of execution has stopped running. The operating system reclaims resources that were used by the process...

     (once or twice). This is required sometimes for the process to become a session leader. It also allows the parent process to continue its normal execution.
  • Setting the root directory
    Root directory
    In computer file systems, the root directory is the first or top-most directory in a hierarchy. It can be likened to the root of a tree — the starting point where all branches originate.-Metaphor:...

     ("/") as the current working directory
    Working directory
    In computing, the working directory of a process is a directory of a hierarchical file system, if any, dynamically associated with each process. When the process refers to a file using a simple file name or relative path , the reference is interpreted relative to the current working directory of...

     so that the process does not keep any directory in use that may be on a mounted file system (allowing it to be unmounted).
  • Changing the umask
    Umask
    umask is a command and a function in POSIX environments that sets the file mode creation mask of the current process which limits the permission modes for files and directories created by the process...

     to 0 to allow open, creat, et al. operating system calls to provide their own permission masks and not to depend on the umask of the caller
  • Closing all inherited files at the time of execution that are left open by the parent process, including file descriptor
    File descriptor
    In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...

    s 0, 1 and 2 (stdin, stdout, stderr). Required files will be opened later.
  • Using a logfile
    Log file
    The term log file can refer to:*Text saved by a computer operating system to recored its activities, such as by the Unix syslog facility*Output produced by a data loggerAlso see Wikibooks chapter...

    , the console
    System console
    The system console, root console or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the kernel, from the init system and from the system logger...

    , or /dev/null
    /dev/null
    In Unix-like operating systems, /dev/null or the null device is a special file that discards all data written to it and provides no data to any process that reads from it ....

     as stdin, stdout, and stderr
    Standard streams
    In Unix and Unix-like operating systems , as well as certain programming language interfaces, the standard streams are preconnected input and output channels between a computer program and its environment when it begins execution...


Implementation in MS-DOS and Microsoft Windows


In the Microsoft DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...

 environment, daemon-like programs were implemented as Terminate and Stay Resident
Terminate and Stay Resident
Terminate and Stay Resident is a computer system call in DOS computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory...

 (TSR) software. On Microsoft Windows NT systems, programs called Windows service
Windows Service
On Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...

s perform the functions of daemons. They run as processes, usually do not interact with the monitor, keyboard, and mouse, and may be launched by the operating system at boot time. In Windows 2000 and later versions, Windows services are configured and manually started and stopped using the Control Panel
Control Panel (Windows)
The Control Panel is a part of the Microsoft Windows graphical user interface which allows users to view and manipulate basic system settings and controls via applets, such as adding hardware, adding and removing software, controlling user accounts, and changing accessibility options...

 or the net start and net stop commands.

However, any Windows application can perform the role of a daemon, not just a service, and some daemons for Windows have the option of running as a normal process.

Implementation in Mac OS


On the original Mac OS
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...

, optional features and services were provided by files loaded at startup time that patched the operating system; these were known as system extensions
Extension (Mac OS)
On the Apple Macintosh operating system prior to Mac OS X, extensions were small pieces of code that extended the system's functionality. They were run initially at start-up time, and operated by a variety of mechanisms, including trap patching and other code modifying techniques. Initially an...

 and control panels
Control panel (Mac OS)
Under Mac OS 9 and earlier, a control panel is a small application which enabled the user to modify software and hardware settings such as the sound volume and desktop pattern. Control panels differ from extensions in that they allow the user to specify options, whereas extensions provide the user...

. Later versions of classic Mac OS augmented these with fully fledged faceless background applications: regular applications that ran in the background. To the user, these were still described as regular system extensions.

Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

, being a Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

 system, has daemons. There is a category of software called services as well, but these are different in concept from Windows services.

Etymology


According to Fernando J. Corbato
Fernando J. Corbató
Fernando José "Corby" Corbató is a prominent American computer scientist, notable as a pioneer in the development of time-sharing operating systems....

 who worked on Project MAC in 1963 his team is the first to use the term daemon. The use of the term daemon was inspired by Maxwell's demon
Maxwell's demon
In the philosophy of thermal and statistical physics, Maxwell's demon is a thought experiment created by the Scottish physicist James Clerk Maxwell to "show that the Second Law of Thermodynamics has only a statistical certainty." It demonstrates Maxwell's point by hypothetically describing how to...

, an imaginary agent in physics and thermodynamics that helped to sort molecules.
We fancifully began to use the word daemon to describe background processes which worked tirelessly to perform system chores.


In the general sense, daemon is an older form of the word demon, from the Greek δαίμων. In the Unix System Administration Handbook, Evi Nemeth states the following about daemons:

Many people equate the word "daemon" with the word "demon", implying some kind of satanic
Satanism
Satanism is a group of religions that is composed of a diverse number of ideological and philosophical beliefs and social phenomena. Their shared feature include symbolic association with, admiration for the character of, and even veneration of Satan or similar rebellious, promethean, and...

 connection between UNIX and the underworld
Underworld
The Underworld is a region which is thought to be under the surface of the earth in some religions and in mythologies. It could be a place where the souls of the recently departed go, and in some traditions it is identified with Hell or the realm of death...

. This is an egregious misunderstanding. "Daemon" is actually a much older form of "demon"; daemons have no particular bias towards good or evil, but rather serve to help define a person's character or personality. The ancient Greeks' concept of a "personal daemon" was similar to the modern concept of a "guardian angel"—eudaemonia is the state of being helped or protected by a kindly spirit. As a rule, UNIX systems seem to be infested with both daemons and demons. (p.403)

A further characterization of the mythological symbolism is that a daemon is something which is not visible yet is always present and working its will. Plato
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

's Socrates
Socrates
Socrates was a classical Greek Athenian philosopher. Credited as one of the founders of Western philosophy, he is an enigmatic figure known chiefly through the accounts of later classical writers, especially the writings of his students Plato and Xenophon, and the plays of his contemporary ...

 describes his own personal daemon to be something like the modern concept of a moral conscience:

Notable service daemons in Unix-like systems


  • amd: Berkeley Automounter
    Berkeley Automounter
    The Berkeley Automounter first appeared in 4.4BSD, and is a computer automounter daemon. The original Berkeley automounter was created by Jan-Simon Pendry in 1989 and was donated to Berkeley...

  • anacron
    Anacron
    anacron is a computer program that performs periodic command scheduling which is traditionally done by cron, but without assuming that the system is running continuously. Thus, it can be used to control the execution of daily, weekly, and monthly jobs on systems that don't run 24 hours a day...

    : Executed delayed cron
    Cron
    Cron is a time-based job scheduler in Unix-like computer operating systems. Cron enables users to schedule jobs to run periodically at certain times or dates...

     tasks at boot time
  • apmd: Advanced Power Management
    Advanced Power Management
    Advanced power management is an API developed by Intel and Microsoft and released in 1992 which enables an operating system running an IBM-compatible personal computer to work with the BIOS to achieve power management.Revision 1.2 was the last version of the APM specification, released in 1996....

     Daemon
  • arpwatch
    Arpwatch
    arpwatch is a computer software tool for monitoring Address Resolution Protocol traffic on a computer network. It generates a log of observed pairing of IP addresses with MAC addresses along with a timestamp when the pairing appeared on the network...

    : watches for Ethernet IP address pairings that are resolved using the ARP protocol
  • atd: Runs jobs queued using the at
    At (Unix)
    In Unix-like computer operating systems,the at commandis used to schedule commands to be executed once, at a particular time in the future....

     tool
  • biod: Cooperates with a remote nfsd to handle client Network File System requests
  • bootparmd: Internet Bootstrap Protocol server daemon
  • configd: A daemon that maintains dynamic configuration information about the computer and its environment (mainly the network)
  • crond: Task scheduler
    Task Scheduler
    Task Scheduler is a component of Microsoft Windows that provides the ability to schedule the launch of programs or scripts at pre-defined times or after specified time intervals. It was first introduced in the Windows 95 Plus! pack as System Agent but was renamed to Task Scheduler in Windows 98...

     daemon
  • cupsd: CUPS printer daemon
  • devfsd: Device file system
    Device file system
    In Unix-like operating systems, a device file or special file is an interface for a device driver that appears in a file system as if it were an ordinary file. There are also special device files in MS-DOS and Microsoft Windows...

     (devfs)
  • dhcpd
    Dhcpd
    dhcpd is a common name for the daemon that allows a server to provide a Dynamic Host Configuration Protocol service to a network....

    : Dynamic Host Configuration Protocol
    Dynamic Host Configuration Protocol
    The Dynamic Host Configuration Protocol is a network configuration protocol for hosts on Internet Protocol networks. Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default...

     and Internet Bootstrap Protocol server
  • fetchmail
    Fetchmail
    Fetchmail is an open source software utility for POSIX-compliant operating systems which is used to retrieve e-mail from a remote POP3, IMAP, ETRN or ODMR mail server to the user's local system. It was developed from the popclient program, written by Carl Harris.Its chief significance is perhaps...

    : daemon to retrieve mail from servers at regular intervals
  • fingerd: Finger protocol
    Finger protocol
    In computer networking, the Name/Finger protocol and the Finger user information protocol are simple network protocols for the exchange of human-oriented status and user information.-Name/Finger protocol:...

     server
  • ftpd: File Transfer Protocol
    File Transfer Protocol
    File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...

     (FTP) server
  • gated: routing daemon that handles multiple routing protocols and replaces routed and egpup
  • gpm
    GPM (software)
    GPM which means "general purpose mouse" provides mouse support in Linux virtual consoles. It is included in most Linux distributions.ncurses supports GPM; many applications use ncurses mouse-support....

    : General Purpose Mouse Daemon
  • httpd: Hypertext Transfer Protocol
    Hypertext Transfer Protocol
    The Hypertext Transfer Protocol is a networking protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web....

     (HTTP) daemon (web server
    Web server
    Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....

    )
  • identd: Provides the identity of a user of a particular TCP connection
  • inetd
    Inetd
    inetd is a super-server daemon on many Unix systems that manages Internet services. First appearing in 4.3BSD , it is generally located at /usr/sbin/inetd.-Function:...

    : Internet Superserver Daemon
  • init
    Init
    init is a program for Unix-based computer operating systems that spawns all other processes. It runs as a daemon and typically has PID 1. The boot loader starts the kernel and the kernel starts init...

    : Initial process that spawns other processes
  • imapd: Internet Message Access Protocol
    Internet Message Access Protocol
    Internet message access protocol is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol...

     (IMAP) server daemon
  • innd: InterNetNews server daemon
  • ipchains
    Ipchains
    Linux IP Firewalling Chains, normally called ipchains, is free software to control the packet filter/firewall capabilities in the 2.2 series of Linux kernels. It superseded ipfwadm, but was replaced by iptables in the 2.4 series. Unlike iptables, ipchains is stateless.It is a rewrite of Linux's...

    : A deprecated packet forwarding and firewall daemon
  • isdn: Integrated Services Digital Network
    Integrated Services Digital Network
    Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...

     (ISDN) interfacing server daemon
  • kerneld: Automatically loads and unloads kernel modules
  • klogd: Kernel log daemon (intercepts and logs Linux kernel messages)
  • kswapd: Kernel page swapping daemon
  • kudzu
    Kudzu (computer daemon)
    Kudzu is a hardware probing program which relies on a library of hardware device information.When the computer boots, kudzu detects changes in the running system's hardware configuration, if any, and activates the newly-detected hardware . kudzu only runs at boot time, and then exits...

    : Detects and configures new or changed hardware during boot
  • launchd
    Launchd
    launchd is a unified, open-source service management framework for starting, stopping and managing daemons, applications, processes, and scripts...

    : Init
    Init
    init is a program for Unix-based computer operating systems that spawns all other processes. It runs as a daemon and typically has PID 1. The boot loader starts the kernel and the kernel starts init...

     and operating system service management
    Operating system service management
    In computing, mechanisms and techniques for managing services often differ by operating system. Operating system service management can refer to the following:...

     implementation on Mac OS X
    Mac OS X
    Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

  • lpd: Line Printer Daemon protocol
    Line Printer Daemon protocol
    The Line Printer Daemon protocol/Line Printer Remote protocol is a network protocol for submitting print jobs to a remote printer. The original implementation of LPD was in the Berkeley printing system in the BSD UNIX operating system; the LPRng project also supports that protocol...

  • memcached
    Memcached
    In computing, memcached is a general-purpose distributed memory caching system that was originally developed by Danga Interactive for LiveJournal, but is now used by many other sites. It is often used to speed up dynamic database-driven websites by caching data and objects in RAM to reduce the...

    : In-memory distributed memory caching daemon
  • mpd: Music Player Daemon
    Music Player Daemon
    Music Player Daemon is a music player server.- Design :MPD simply runs in the background playing music from its playlist. Client programs communicate with MPD to manipulate playback, the playlist, and the database...

  • mountd: Part of typical Network File System implementation
  • mysql
    MySQL
    MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...

    : Database server
    Database server
    A database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model. The term may also refer to a computer dedicated to running such a program...

     daemon
  • named: A Domain Name System
    Domain name system
    The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...

     (DNS) server daemon
  • nfsd: Network File System (NFS) daemon
  • nmbd: Network Message Block Daemon; part of Samba
    Samba (software)
    Samba is a free software re-implementation, originally developed by Andrew Tridgell, of the SMB/CIFS networking protocol. As of version 3, Samba provides file and print services for various Microsoft Windows clients and can integrate with a Windows Server domain, either as a Primary Domain...

  • ntpd
    Ntpd
    The Network Time Protocol daemon is an operating system daemon program that maintains the system time in synchronization with time servers using the Network Time Protocol .-Description:...

    : Network Time Protocol
    Network Time Protocol
    The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L...

     (NTP) service daemon
  • pcmcia: Provides generic PCMCIA services
  • portmap
    Portmap
    The port mapper is an ONC RPC service that runs on network nodes that provide other ONC RPC services.....

  • postfix
    Postfix (software)
    In computing, Postfix is a free and open-source mail transfer agent that routes and delivers electronic mail. It is intended as a fast, easier-to-administer, and secure alternative to the widely-used Sendmail MTA....

    : A mail transfer agent
    Mail transfer agent
    Within Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...

     used as a replacement for sendmail
    Sendmail
    Sendmail is a general purpose internetwork email routing facility that supports many kinds of mail-transfer and -delivery methods, including the Simple Mail Transfer Protocol used for email transport over the Internet....

  • postgresql
    PostgreSQL
    PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...

    : Database server
    Database server
    A database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model. The term may also refer to a computer dedicated to running such a program...

     daemon
  • retchmail: A mail retrieval agent
    Mail retrieval agent
    A mail retrieval agent is a computer application that retrieves or fetches e-mail from a remote mail server and works with an mail delivery agent to deliver mail to a local or remote email mailbox. MRAs may be external applications by themselves or be built into a bigger application like an MUA...

  • rlprd: Remote line printer proxy daemon
  • routed: Manages routing table
    Routing table
    In computer networking a routing table, or Routing Information Base , is a data table stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics associated with those routes. The routing table contains information about the...

    s
  • rpcbind: Remote Procedure Call Bind Daemon
  • rquotad: Remote quota reporting, associated with Network File System
  • rwalld: Allows users to write messages on remote terminals using rwall
  • rwhod: Maintains the database used by the rwho and ruptime tools
  • sched, swapper: Copies process regions to swap space to reclaim physical pages of memory
  • sendmail
    Sendmail
    Sendmail is a general purpose internetwork email routing facility that supports many kinds of mail-transfer and -delivery methods, including the Simple Mail Transfer Protocol used for email transport over the Internet....

    : A mail transfer agent
    Mail transfer agent
    Within Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...

     daemon
  • smbd: Samba
    Samba (software)
    Samba is a free software re-implementation, originally developed by Andrew Tridgell, of the SMB/CIFS networking protocol. As of version 3, Samba provides file and print services for various Microsoft Windows clients and can integrate with a Windows Server domain, either as a Primary Domain...

    , an Server Message Block
    Server Message Block
    In computer networking, Server Message Block , also known as Common Internet File System operates as an application-layer network protocol mainly used to provide shared access to files, printers, serial ports, and miscellaneous communications between nodes on a network. It also provides an...

     (SMB) daemon
  • smtpd: Simple Mail Transfer Protocol
    Simple Mail Transfer Protocol
    Simple Mail Transfer Protocol is an Internet standard for electronic mail transmission across Internet Protocol networks. SMTP was first defined by RFC 821 , and last updated by RFC 5321 which includes the extended SMTP additions, and is the protocol in widespread use today...

     Daemon
  • snmpd: Simple Network Management Protocol
    Simple Network Management Protocol
    Simple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...

     Daemon
  • sound: A sound server
    Sound server
    A sound server is software that manages the use of and access to audio devices, most notably, the soundcard. It usually runs as a background process...

     daemon
  • squid: A web page caching proxy server
    Proxy server
    In computer networks, a proxy server is a server that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server...

     daemon
  • sshd: Secure Shell
    Secure Shell
    Secure Shell is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network: a server and a client...

     Server Daemon
  • syncd: Keeps the file systems synchronized with system memory
  • syslogd: Syslog
    Syslog
    Syslog is a standard for computer data logging. It allows separation of the software that generates messages from the system that stores them and the software that reports and analyzes them...

     daemon
  • tcpd: Service wrapper restricts access to inetd
    Inetd
    inetd is a super-server daemon on many Unix systems that manages Internet services. First appearing in 4.3BSD , it is generally located at /usr/sbin/inetd.-Function:...

     based services through hosts.allow and hosts.deny
  • telnetd: Telnet
    TELNET
    Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...

     server daemon
  • vhand: The "page stealing daemon" releases pages of memory for use by other processes
  • vsftpd
    Vsftpd
    vsftpd, which stands for "Very Secure FTP Daemon", is an FTP server for Unix-like systems, including Linux. It is licensed under the GNU General Public License...

    : "Very Secure FTP Daemon"
  • webmin
    Webmin
    Webmin is a web-based system configuration tool for Unix-like systems, although recent versions can also be installed and run on Windows. With it, it is possible to configure operating system internals, such as users, disk quotas, services or configuration files, as well as modify and control open...

    : Web based administration server daemon
  • xfsd: X font
    Font
    In typography, a font is traditionally defined as a quantity of sorts composing a complete character set of a single size and style of a particular typeface...

     server daemon
  • xinetd
    Xinetd
    In computer networking, xinetd, the eXtended InterNET Daemon, is an open-source super-server daemon which runs on many Unix-like systems and manages Internet-based connectivity...

    : Enhanced Internet Superserver Daemon
  • ypbind: A bind server for Network Information Service
    Network Information Service
    The Network Information Service, or NIS is a client–server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network...

     ("Yellow Pages")

See also


  • List of computer term etymologies
  • Mailer Daemon (bounce message)
  • Server
    Server (computing)
    In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

  • Service Wrapper
    Service Wrapper
    A service wrapper is a computer program that wraps arbitrary programs thus enabling them to be installed and run as Windows Services or Unix Daemons, programs that run in the background, rather than under the direct control of a user. They are often automatically started at boot time...

  • Terminate and Stay Resident
    Terminate and Stay Resident
    Terminate and Stay Resident is a computer system call in DOS computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory...

  • User space
    User space
    A conventional computer operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, kernel extensions, and most device drivers...

  • Windows service
    Windows Service
    On Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...

  • Web service
    Web service
    A Web service is a method of communication between two electronic devices over the web.The W3C defines a "Web service" as "a software system designed to support interoperable machine-to-machine interaction over a network". It has an interface described in a machine-processable format...


External links