Using socketpair and passfd

David FORT — Fri, 17 Apr 2026 06:11:00 GMT

I've always been aware of the passfd feature available on Linux, but I never had the chance to use it for real in my projects. While testing some system design, I was able to experiment with it, and I find that it opens up a lot of possibilities. Let's see that.

Socket pair

There’s nothing too complicated about socketpair, it allows you to have two interconnected sockets with a single system call, so that when you send bytes on one socket, you can read them on the other:

#include <sys/socket.h>

int socketpair(int domain, int type, int protocol, int sv[2]);

It’s more convenient than the pipe() or pipe2() system calls, which provide 2 file descriptors, one for reading and another for writing.

Hardening consulting (Posts about socketpair)

Using socketpair and passfd

Socket pair