A Unix ___domain socket aka UDS or IPC socket (inter-process communication socket) is a data communications endpoint for exchanging data between processes executing on the same host operating system. It is also referred to by its address family AF_UNIX. Valid socket types in the UNIX ___domain are:[1]
SOCK_STREAM(compare to TCP) – for a stream-oriented socketSOCK_DGRAM(compare to 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)SOCK_SEQPACKET(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 systems.
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. 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 inodes, so two processes can communicate by opening the same socket.
In addition to sending data, processes may send file descriptors across a Unix ___domain socket connection using the sendmsg() and recvmsg() 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.[2][3] This can be used to implement a rudimentary form of capability-based security.[4] For example, this allows the Clam AntiVirus scanner to run as an unprivileged daemon on Linux and BSD, yet still read any file sent to the daemon's Unix ___domain socket.
See also
References
- ^ "Linux Programmer's Manual (unix - sockets for local interprocess communication)". 30 April 2018. Retrieved 22 February 2019.
- ^ "Archive of the "Postfix Discussions" mailing list". 30 September 2000. Archived from the original on 18 May 2013. Retrieved 29 September 2014.
- ^ "Linux man page - cmsg(3): access ancillary data". Retrieved 9 October 2018.
- ^ ""Secure Programming for Linux and Unix HOWTO", Section 3.4 "Sockets and Network Connections"". dwheeler.com. David A. Wheeler. 22 August 2004. Retrieved 29 September 2014.
External links
- – System Interfaces Reference, The Single UNIX Specification, Version 5 from The Open Group
- – System Interfaces Reference, The Single UNIX Specification, Version 5 from The Open Group
- – System Interfaces Reference, The Single UNIX Specification, Version 5 from The Open Group
- – Linux Programmer's Manual – Library Functions
- ucspi-unix, UNIX-___domain socket client-server command-line tools
- Unix sockets vs Internet sockets
- Unix Sockets - Beej's Guide to Unix IPC
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