Unix domain socket

A Unix domain socket or IPC socket (inter-process communication socket) is a data communications endpoint for exchanging data between processes executing on the same host operating system. Valid socket types in the UNIX domain are:
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 codice_4 and codice_5 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. 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.