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Subject: Re: [OMPI users] OpenMPI exits when subsequent tail -f in script is interrupted
From: Ralph Castain (rhc_at_[hidden])
Date: 2011-04-23 11:27:31


On Apr 23, 2011, at 9:11 AM, Pablo Lopez Rios wrote:

>> > Pressing Ctrl+C should stop tail -f, and the MPI job
>> > should continue.
>
>> I don't think that is true at all. When you hit ctrl-C,
>> every process executing in the script receives it. Mpirun
>> traps the ctrl-c and immediately terminates all running
>> MPI procs.
>
> By "Ctrl+C should stop tail -f" I mean that this is the
> desired behaviour of the script, not that this is what ought
> to happen in general. My question is how to achieve this
> behaviour, since I'm having trouble working around mpirun
> catching sigint.

Like I said in my other response, you can't - mpirun automatically traps sigint and terminates the job in order to ensure proper cleanup during abnormal terminations.

I'm not sure what you are actually trying to accomplish, but there are other signals that don't cause termination. For example, we trap and forward SIGUSR1 and SIGUSR2 to your application procs, if that is of use.

But ctrl-c has a special meaning ("die"), and you can't tell mpirun to ignore it.

>
> Thanks,
> Pablo
>
>
>
> On 23/04/11 15:12, Ralph Castain wrote:
>> On Apr 23, 2011, at 6:20 AM, Reuti wrote:
>>
>>> Hi,
>>>
>>> Am 23.04.2011 um 04:31 schrieb Pablo Lopez Rios:
>>>
>>>> I'm having a bit of a problem with wrapping mpirun in a script. The script needs to run an MPI job in the background and tail -f the output. Pressing Ctrl+C should stop tail -f, and the MPI job should continue.
>> I don't think that is true at all. When you hit ctrl-C, every process executing in the script receives it. Mpirun traps the ctrl-c and immediately terminates all running MPI procs.
>>
>>
>>>> However mpirun seems to detect the SIGINT that was meant for tail, and kills the job immediately. I've tried workarounds involving nohup, disown, trap, subshells (including calling the script from within itself), etc, to no avail.
>>>>
>>>> The problem is that this doesn't happen if I run the command directly instead, without mpirun. Attached is a script that reproduces the problem. It runs a simple counting script in the background which takes 10 seconds to run, and tails the output. If called with "nompi" as first argument, it will simply run bash -c "$SCRIPT">& "$out"&, and with "mpi" it will do the same with 'mpirun -np 1' prepended. The output I get is:
>>> what about:
>>>
>>> ( trap "" sigint; exec mpiexec ...)&
>>>
>>> i.e. replace the subshell with changed interrupt handling with the mpiexec. Well, maybe mpiexec is adjusting it on its own again. This can be checked in /proc/<pid>/status
>>>
>>> -- Reuti
>>>
>>>> $ ./ompi_bug.sh mpi
>>>> mpi:
>>>> 1
>>>> 2
>>>> 3
>>>> 4
>>>> ^C
>>>> $ ./ompi_bug.sh nompi
>>>> nompi:
>>>> 1
>>>> 2
>>>> 3
>>>> 4
>>>> ^C
>>>> $ cat output.*
>>>> mpi:
>>>> 1
>>>> 2
>>>> 3
>>>> 4
>>>> mpirun: killing job...
>>>>
>>>> --------------------------------------------------------------------------
>>>> mpirun noticed that process rank 0 with PID 1222 on node pablomme exited on signal 0 (Unknown signal 0).
>>>> --------------------------------------------------------------------------
>>>> mpirun: clean termination accomplished
>>>>
>>>> nompi:
>>>> 1
>>>> 2
>>>> 3
>>>> 4
>>>> 5
>>>> 6
>>>> 7
>>>> 8
>>>> 9
>>>> 10
>>>> Done
>>>>
>>>>
>>>> This convinces me that there is something strange with OpenMPI, since I expect no difference in signal handling when running a simple command with or without mpirun in the middle.
>>>>
>>>> I've tried looking for options to change this behaviour, but I don't seem to find any. Is there one, preferably in the form of an environment variable? Or is this a bug?
>>>>
>>>> I'm using OpenMPI v1.4.3 as distributed with Ubuntu 11.04, and also v1.2.8 as distributed with OpenSUSE 11.3.
>>>>
>>>> Thanks,
>>>> Pablo
>>>> <ompi_bug.sh.gz>_______________________________________________
>>>> users mailing list
>>>> users_at_[hidden]
>>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>
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