On 09-Feb-16, Olaf Dabrunz wrote:
> On 09-Feb-16, Olaf Dabrunz wrote:
> > Ah right, you already use this in 7.4.1274.
> >
> > To correct myself: kill the negative of the PID of the session leader,
> > this sends the signal to all processes in its process group (!), see
> > kill(2):
> >
> > mch_stop_job():
> >
> > sig = atoi((char *)how);
> > else
> > return FAIL;
> > - kill(job->jv_pid, sig);
> > + kill(-job->jv_pid, sig);
> > return OK;
> > }
> > #endif
> >
> >
> > This also triggers a sort of chain reaction that should bring down the
> > other process groups in the session (if any), unless they ignore SIGHUP:
> >
> > When the session leader exits, all processes in the foreground
> > process receive a SIGHUP.
> >
> > When the parent (typically the session leader) of a background
> > process group with at least one stopped process exits, all processes
> > in that background process group receive a SIGHUP. (And a SIGCONT,
> > which makes them continue running in the background in case they
> > ignore SIGHUP.)
>
> Processes that are not terminated by this chain reaction are
> - in a background process group where all processes are running
> (long running compute jobs)
> $ break_encryption &
The python process started from the shell in your example must have been
in its own process group and only blocked on reading from a socket, but
not stopped by a signal.
So you essentially started it as a long running compute job, which is
unaffected by session termination.
Gary's suggestion to use
/bin/sh -c "exec python demoserver.py <here >there"
should fix this, by replacing the session leader shell with the python
process executing demoserver.py, so it is not in a separate process
group and affected directly by either kill(job->jv_pid, sig) or
kill(-job->jv_pid, sig).
> - background processes that choose to survive session termination,
> even when temporarily stopped
> $ nohup break_encryption &
> $ kill -STOP %1 # give me some processing power now
>
> Daemons detach even further, by leaving the session.
>
> > See more details in
> > - http://www.win.tue.nl/~aeb/linux/lk/lk-10.html#ss10.3
> > - man 2 setpgid
>
>
> --
> Olaf Dabrunz (oda <at> fctrace.org)
>
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Olaf Dabrunz (oda <at> fctrace.org)
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