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From Jos Backus <j...@cncdsl.com>
Subject Re: Running Apache in the foreground
Date Sat, 29 Dec 2001 07:38:01 GMT
On Fri, Dec 28, 2001 at 05:35:13PM -0800, Aaron Bannert wrote:
> On Fri, Dec 28, 2001 at 05:03:06PM -0800, Jos Backus wrote:
> > Interestingly in the Samba code the setsid() call comes _after_ the fork()
> > (see my previous e-mail) and that seems to work just fine. So it looks like
> > the order suggested is not an absolute requirement; any thoughts on this?
> 
> Let me clarify a little:
> 
> setsid() MUST be called by a proces that is NOT a process group leader,
> else it will fail with -1.
 
Yes.

> Apache is normally started in two ways: 
> 1) bin/apachectl
> 2) bin/httpd
> 
> Normally when starting a program from the shell, that program becomes the
> process group leader of a new process group. In case #1 the apachectl
> script becomes the process leader and httpd becomes it's child (which
> will inherit the PGID). This means httpd is NOT a process group leader. In
> case #2, httpd IS the process group leader, and hence setsid() will fail.

Yes. In the daemontools case, the supervise program forks and its child runs
the ``run'' script, which in turn execs the daemon. So I'm assuming that the
daemon is _not_ the pgrp leader. Consider this evidence: on my FreeBSD
-current system I see the following:

    % ps -ax -o pid,ppid,pgid,command
      246     1    46 svscan /service
      273   246    46 supervise nmbd
      282   246    46 supervise smbd
    22124   273 22124 /usr/local/sbin/nmbd -F
    22127 22124 22124 /usr/local/sbin/nmbd -F
    22125   282 22125 /usr/local/sbin/smbd -F

The ``run'' script (for nmbd) is simply

    #!/bin/sh
    exec /usr/local/sbin/nmbd -F

The above output clearly shows {n,s}mbd running in their own pgrps, which is
what we want; when I down those services using ``svc -d /service/?mbd'' they
go away, without killing the members of pgrp 46. Without the -F flag/patch all
the members of pgrp 46 do get killed, which is obviously undesirable. So I am
really hoping that the Samba people will adopt my patch :-)

> Therefore the only way to ensure that the calling process is NOT the
> process group leader is to call fork() before calling setsid().

I understand. Surely there is a way to make this work with httpd also?

And thank you for the clarification.

-- 
Jos Backus                 _/  _/_/_/        Santa Clara, CA
                          _/  _/   _/
                         _/  _/_/_/             
                    _/  _/  _/    _/
josb@cncdsl.com     _/_/   _/_/_/            use Std::Disclaimer;

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