A Unix domain socket aka UDS or IPC socket (
inter-process communication
In computer science, inter-process communication or interprocess communication (IPC) refers specifically to the mechanisms an operating system provides to allow the processes to manage shared data. Typically, applications can use IPC, categori ...
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:
*
SOCK_STREAM (compare to
TCP) – for a stream-oriented socket
*
SOCK_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
The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the p ...
) – 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
The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s.
The
API
An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standa ...
for Unix domain sockets is similar to that of an
Internet socket
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
, but rather than using an underlying network protocol, all communication occurs entirely within the operating system
kernel
Kernel may refer to:
Computing
* Kernel (operating system), the central component of most operating systems
* Kernel (image processing), a matrix used for image convolution
* Compute kernel, in GPGPU programming
* Kernel method, in machine learnin ...
. Unix domain sockets may use the file system as their address
name space
In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified.
Namespaces ...
. (Some operating systems, like
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
, offer additional namespaces.) Processes reference Unix domain sockets as file system
inode
The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attribute ...
s, so two processes can communicate by opening the same socket.
In addition to sending data, processes may send
file descriptor
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket.
File descriptors typically have ...
s 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.
This can be used to implement a rudimentary form of
capability-based security
Capability-based security is a concept in the design of secure computing systems, one of the existing security models. A capability (known in some systems as a key) is a communicable, unforgeable token of authority. It refers to a value that refe ...
.
See also
*
Network socket
A network socket is a software structure within a network node of a computer network that serves as an endpoint for sending and receiving data across the network. The structure and properties of a socket are defined by an application programming ...
*
Berkeley sockets
Berkeley sockets is an application programming interface (API) for Internet sockets and Unix domain sockets, used for inter-process communication (IPC). It is commonly implemented as a library of linkable modules. It originated with the 4.2BSD Un ...
*
Pipeline
Pipeline may refer to:
Electronics, computers and computing
* Pipeline (computing), a chain of data-processing stages or a CPU optimization found on
** Instruction pipelining, a technique for implementing instruction-level parallelism within a s ...
*
Netlink
Netlink is a socket family used for inter-process communication (IPC) between both the kernel and userspace processes, and between different userspace processes, in a way similar to the Unix domain sockets available on certain Unix-like operati ...
References
External links
*
*
*
*
ucspi-unix UNIX-domain socket client-server command-line tools
Network socket
Unix
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