[duskwuff]

You don't even need that. If the old server process exec()s the new one, it can pass on its file descriptors -- including the listening socket -- when that happens.

[mholt]

Yep, we don't use SO_REUSEPORT. We just pass it from the old process to the new one.

[tyingq]

You could also be fancy and pass open sockets over a unix domain socket with sendmsg().

[xyzzy_plugh]

This is the best way as it avoids any sort of session/parenting issues which are not always easy to solve portably as a parent.