A TCP/IP socket is used for communication across TCP/IP networks. A connected TCP socket is identified by the combination of local IP, local port, remote IP and remote port. A listening TCP socket is identified by local port and possibly local IP. As I understand it, at least on linux TCP/IP sockets always result in the generation and decoding of TCP/IP packets, even if the client and server are on the same machine.

A unix domain socket (sometimes shortened to unix socket) on the other hand operates on a single machine. Listening sockets live in the filesystem hierarchy and access to them can be controlled by filesystem permissions.

Furthermore a process accepting a connection on a Unix socket can determine the user ID of the process that connects. This can avoid the need for an authentication step. Rather than generating a password for your database server and including a copy of it in your webapp’s code you can just tell the database server that the user running the webapp has access to the corresponding user account in the database.

References

• https://serverfault.com/questions/124517/what-is-the-difference-between-unix-sockets-and-tcp-ip-sockets