Unix domain socket
A Unix domain socket (UDS), also called a local socket or inter-process communication (IPC) socket, is a communication endpoint used for data exchange between processes running on the same Unix or Unix-like operating system.
The term Unix domain socket refers to the domain argument value AF_UNIX passed to the system call that creates the socket. The same communication domain can also be selected with AF_LOCAL.[1]
Valid type argument values for a UDS are:[1]
SOCK_STREAM(compare to TCP) – a stream-oriented socketSOCK_DGRAM(compare to UDP) – a datagram-oriented socket that preserves message boundaries; on most Unix implementations, Unix domain datagram sockets are reliable and do not reorder datagramsSOCK_SEQPACKET(compare to SCTP) – a connection-oriented sequenced-packet socket that preserves message boundaries and delivers messages in the order 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 instead of using an underlying network protocol, communication takes place entirely within the operating system kernel. A UDS may use the file system as its address namespace. Some operating systems, such as Linux, provide additional namespaces. Processes refer to a UDS through a file system inode, allowing two processes to communicate by opening the same socket.
In addition to sending data, processes can pass file descriptors over a UDS connection by using the sendmsg() and recvmsg() system calls. This allows one process to grant another process access to a file descriptor that it would not otherwise be able to use.[2][3] This can be used to implement a rudimentary form of capability-based security.[4]
See also
[edit]- 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
[edit]- ^ 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
[edit]- – 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 from Manned.org
- ucspi-unix, UNIX-domain socket client-server command-line tools
- Unix sockets vs Internet sockets
- Unix Sockets - Beej's Guide to Unix IPC