Unixdomain

Unixdomain, commonly referred to as Unix domain sockets or local sockets, is an interprocess communication mechanism provided by Unix and Unix-like systems. It enables processes on the same host to exchange data with lower latency and overhead than network sockets by avoiding the network protocol stack. A Unixdomain socket is addressed using a local identifier, typically a pathname such as /tmp/server.sock; some implementations also support an abstract namespace not represented in the filesystem.

Unix domain sockets support two communication styles: stream-oriented (SOCK_STREAM), which provides a reliable, message-oriented byte stream, and datagram-oriented (SOCK_DGRAM), which delivers discrete messages. The lifecycle generally involves creating a socket, binding it to an address, and then either listening and accepting connections (for stream sockets) or sending and receiving datagrams (for datagram sockets).

Security and access control are managed through filesystem permissions on the socket node and through system security modules such as SELinux or AppArmor. When using the filesystem-based namespace, the socket appears as a special file whose permissions govern which processes may connect. Linux also offers an abstract namespace, which can avoid filesystem permissions but is not portable to all Unix variants.

Compared with network sockets, Unix domain sockets are limited to communication within a single host, but they typically offer lower latency and higher throughput for IPC. They are commonly used for local daemons, services, and IPC within operating system components.

Technical notes: the socket family is usually identified in APIs as AF_UNIX or AF_LOCAL, and the exact features and path length limits vary by system.