What is an Unix Domain Socket (IPC socket)?

About

An Unix domain socket is a socket implementation used for internal inter-process communication where 2 processes executing on the same host operating system can exchange data.

Because it's used for IPC, it's also known as IPC socket

Management

Set

For a UNIX domain socket, you must:

• pick a location within your filesystem that the process will be able to access in which the socket will be created where another internal process would be able to connect,
• set file permissions accordingly.

List

With netstat and the -x option of the socket argument

netstat -all -p -x

Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   PID/Program name     Path
unix  2      [ ]         DGRAM                    11270    1/systemd            /run/systemd/shutdownd
unix  2      [ ]         DGRAM                    13344    505/chronyd          /var/run/chrony/chronyd.sock
unix  2      [ ACC ]     STREAM     LISTENING     10585962 30548/master         private/rewrite
unix  2      [ ACC ]     STREAM     LISTENING     12884387 22550/netdata        /tmp/netdata-ipc
unix  2      [ ACC ]     STREAM     LISTENING     10585948 21578/pickup         public/pickup
unix  2      [ ACC ]     STREAM     LISTENING     9057     1/systemd            /run/systemd/private
unix  2      [ ACC ]     STREAM     LISTENING     14946    534/NetworkManager   /var/run/NetworkManager/private-dhcp
unix  2      [ ACC ]     STREAM     LISTENING     10585952 30548/master         public/cleanup
unix  2      [ ACC ]     STREAM     LISTENING     10585965 30548/master         private/bounce
........................

Share / Proxy

A UNIX domain socket can be secured using the filesystem (i.e., with user or group permissions), but cannot be reached from other machines that might want to share the service.

You need to use a proxy:

• TCP to Unix Socket: https://github.com/rnorth/tcp-unix-socket-proxy
• HTTP to Socket: https://kohlschutter.github.io/junixsocket/http.html

Language

Java

The most known library is junixsocket

File socketFile = new File("/path/to/your/socket");
// For docker: File socketFile = new File("/var/run/docker.sock");
AFUNIXSocket sock = AFUNIXSocket.newInstance();
sock.connect(AFUNIXSocketAddress.of(socketFile));

Documentation / Reference

• wiki/Unix_domain_socket