Re: proc fs and shared pids

Lex Spoon (
Tue, 30 Jul 1996 22:19:29 -0400 (EDT)

Michiel Boland wrote:
> >Kernelthreads? They dont shre the same pid. Userthreads are not visible to
> >the kernel at all and therefore there is no proc entry.
> As I understand it, kernel threads are implemented in linux with
> clone(), and hence they *can* share the same PID. Whether this
> is a good idea is perhaps another matter.
> Just did some experimenting with clone() and the CLONE_PID flag.
> This creates a new process with the same process ID as the original
> process. The proc fs has two directory entries for this with the same
> i-number. (!) So I guess the status of one of the two processes can never
> be retrieved.

And /proc is not the only problem! What about kill()? waitpid()?

It's NICE to be able to identify a process by just knowing its pid;
are there any real uses for two processes having the same pid?