Unix ___domain socket: Difference between revisions

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{{shortShort description|SocketCommunications endpoint for exchanging data between processes executing on the same OS; similar to an Internet socket, but all communication occurs within the same OS}}

A '''Unix ___domain socket''' aka ('''UDS''' or), '''IPClocal socket''', ([[or '''inter-process communication]]''' socket('''IPC''') '''socket''' is a data [[Communication endpoint|communicationscommunication endpoint]] for [[inter-process communication|exchanging data between processes]] executing onin the same host[[Unix]] or [[Unix-like]] operating system. It is also referred to by its address family <code>AF_UNIX</code>. Valid socket types in the UNIX ___domain are:<ref name="man-unix-sockets">{{cite web

The name ''Unix ___domain socket'' refers to the <code>___domain</code> argument value <code>AF_UNIX</code> that is passed to the function that creates a socket [[system resource]]. The same communication ___domain is also selected by <code>AF_LOCAL</code>. <ref name="man-unix-sockets"></ref>

Valid <code>type</code> argument values for a UDS are:<ref name="man-unix-sockets">{{cite web

| url = http://man7.org/linux/man-pages/man7/unix.7.html

| date = 30 April 2018

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* <code>SOCK_DGRAM</code> (compare to [[User Datagram Protocol|UDP]]) – for a datagram-oriented socket that preserves message boundaries (as on most UNIX implementations, UNIX ___domain datagram sockets are always reliable and don't reorder datagrams)

* <code>SOCK_SEQPACKET</code> (compare to [[SCTP]]) – for a sequenced-packet socket that is connection-oriented, preserves message boundaries, and delivers messages in the order that they were sent

The Unix ___domain socket facility is a standard component of [[POSIX]] [[operating system]]s.

The Unix ___domain socketUDS facility is a standard component of a [[POSIX]] [[operating system]]s.

The [[API]] for Unix ___domain sockets is similar to that of an [[Internet socket]], but rather than using an underlying network protocol, all communication occurs entirely within the operating system [[Kernel (operating system)|kernel]]. Unix ___domain sockets may use the file system as their address [[name space]]. (Some operating systems, like Linux, offer additional namespaces.) Processes reference Unix ___domain sockets as file system [[inode]]s, so two processes can communicate by opening the same socket.

The [[API]] for Unixa ___domain socketsUDS is similar to that of an [[Internet socket]], but rather than using an underlying network protocol, all communication occurs entirely within the operating system [[Kernelkernel (operating system)|kernel]]. UnixA ___domain socketsUDS may use the file system as theirits address [[name space]]. (Some operating systems, like [[Linux]], offer additional namespaces.) Processes reference Unixa ___domainUDS socketsas asa file system [[inode]]s, so two processes can communicate by opening the same socket.

In addition to sending data, processes may send [[file descriptor]]s across a Unix ___domain socket connection using the <code>sendmsg()</code> and <code>recvmsg()</code> system calls. This allows the sending processes to grant the receiving process access to a file descriptor for which the receiving process otherwise does not have access.<ref name="neohapsis">{{cite web |url=http://archives.neohapsis.com/archives/postfix/2000-09/1476.html |date=30 September 2000 |title=Archive of the "Postfix Discussions" mailing list |access-date=29 September 2014 |archive-url=https://web.archive.org/web/20130518084034/http://archives.neohapsis.com/archives/postfix/2000-09/1476.html |archive-date=18 May 2013 |url-status=dead |df=dmy-all}}</ref><ref name="linux-cmsg-man-page">{{cite web |url=https://linux.die.net/man/3/cmsg |title=Linux man page - cmsg(3): access ancillary data |access-date=9 October 2018 |df=dmy-all}}</ref> This can be used to implement a rudimentary form of [[capability-based security]].<ref name="wheeler-secure-linux-howto">{{cite web |url=https://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/sockets.html |title="Secure Programming for Linux and Unix HOWTO", Section 3.4 "Sockets and Network Connections" |date=22 August 2004 |website=dwheeler.com |publisher=David A. Wheeler |access-date=29 September 2014}}</ref> For example, this allows the [[Clam AntiVirus]] scanner to run as an [[Privilege (computing)#Unix|unprivileged]] [[Daemon (computing)|daemon]] on Linux and BSD, yet still read any file sent to the daemon's Unix ___domain socket.

In addition to sending data, processes may send [[file descriptor]]s across a Unix ___domain socketUDS connection using the <code>sendmsg()</code> and <code>recvmsg()</code> system calls. This allows the sending processes to grant the receiving process access to a file descriptor for which the receiving process otherwise does not have access.<ref name="neohapsis">{{cite web |url=http://archives.neohapsis.com/archives/postfix/2000-09/1476.html |date=30 September 2000 |title=Archive of the "Postfix Discussions" mailing list |access-date=29 September 2014 |archive-url=https://web.archive.org/web/20130518084034/http://archives.neohapsis.com/archives/postfix/2000-09/1476.html |archive-date=18 May 2013 |url-status=dead |df=dmy-all}}</ref><ref name="linux-cmsg-man-page">{{cite web |url=https://linux.die.net/man/3/cmsg |title=Linux man page - cmsg(3): access ancillary data |access-date=9 October 2018 |df=dmy-all}}</ref> This can be used to implement a rudimentary form of [[capability-based security]].<ref name="wheeler-secure-linux-howto">{{cite web |url=https://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/sockets.html |title="Secure Programming for Linux and Unix HOWTO", Section 3.4 "Sockets and Network Connections" |date=22 August 2004 |website=dwheeler.com |publisher=David A. Wheeler |access-date=29 September 2014}}</ref> For example, this allows the [[Clam AntiVirus]] scanner to run as an [[Privilege (computing)#Unix|unprivileged]] [[Daemon (computing)|daemon]] on Linux and BSD, yet still read any file sent to the daemon's Unix ___domain socket.

==See also==

* [[{{Annotated link|Network socket]]}}

* [[{{Annotated link|Berkeley sockets]]}}

* [[{{Annotated link|Pipeline (Unix)|Pipeline]]}}

* [[{{Annotated link|Netlink]]}}

==References==

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==External links==

* {{man|sh|socket|SUS||create a socket}}

* {{man|sh|socketpair|SUS||create a pair of connected sockets}}

* {{man|sh|sendmsg|SUS||send a message on a socket}}

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[[Category:Network socket]]

[[Category:Unix]]

{{compsci-stub}}

[[fr:Berkeley sockets#Socket unix]]