Re: setsid() semantics changed...

Miquel van Smoorenburg (
15 Jul 1996 10:00:44 +0200

In article <>,
<> wrote:
>Miquel van Smoorenburg:
>: Now a process that gets spawned by a shell that sets up the process group
>: for it (so it's the leader of it's own group, not session) cannot do
>: a setsid() anymore because the "if (p->pgrp == current->pid)" check will
>: match on itself.
>: I now do a "setpgrp(0, getpgid(getppid()))" before setsid() and that works,
>: but I think the check should be
>: if (p != current && p->pgrp == current->pid)
>: return -EPERM;
>: But that could easily break POSIX conformance, I don't know...
>You are quite right, and your version is POSIX conformant, not the kernel.
>POSIX reads:
> EPERM The calling process is already a process group leader,
> or the process group ID of a process other than the calling
> process matches the process ID of the calling process.

Reading this carefully, I see that the current Linux behaviour _is_
Posix compliant; read the first line after EPERM again. It says
"The calling process is already a process group leader". So what I did,
calling "setpgrp(0, getpgid(getppid()))" first is indeed the right thing
to do if you really want to setsid(). I still think it doesn't make sense,
but.. I'll attribute a section to the setsid() manpage about this if
you want ;) (what is the latest version?)


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