setsid2(sid) proposal - assign current process to existing session

From: Devin Bayer
Date: Tue Aug 04 2020 - 09:11:19 EST


I'm wondering about the possibility of introducing a new system call for moving a process to an existing session. If `sid` is an existing session with the same owner as the current process, one could call:


This would have similar behavior to setpgid(), and would probably effectively call setpgid() internally too.

The use case is for something like `flatpak-spawn --host`, which allows you to launch a program in an outer namespace from an inner namespace. It behaves as a child of the caller but is actually a child of an external daemon.

It works by connecting stdin/out/err to those of the caller, for example a PTY for xterm running in the inner namespace. This works fine for non-interactive programs, but it's impossible for the spawned task to share the controlling TTY with the shell running in xterm.

I can't see where the problems are, though I'm surprised such functionally doesn't yet exist. Because it deals with such basic concepts, I'm wondering if such a change will even be considered.

There is a workaround; one can create a new PTY on the host and copy the I/O streams manually. Not ideal, but okay.

Any comments welcome.

~ dev