Unix domain socket
A Unix domain socket (UDS), a.k.a. local socket, a.k.a. inter-process communication (IPC) socket, is a communication endpoint for exchanging data between processes executing in the same Unix or Unix-like operating system.
The name, Unix domain socket, refers to the domain argument value AF_UNIX that is passed to the function that creates a socket system resource. The same communication domain is also selected by AF_LOCAL. [1]
Valid type argument values for a UDS 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 UDS facility is a standard component of a POSIX operating system.
The API for a UDS 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. A UDS may use the file system as its address name space. Some operating systems, like Linux, offer additional namespaces. Processes reference a UDS as a file system inode, so two processes can communicate by opening the same socket.
In addition to sending data, processes may send file descriptors across a UDS 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]
See also
- Network socket – Software-based endpoint of network communications
- Berkeley sockets – Inter-process communication API
- Pipeline (Unix) – Mechanism for inter-process communication using message passing
- Netlink – Linux kernel interface for inter-process communication between processes
References
- ^ a b "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
- – 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