# MPI fork warning

**URL:** <https://pyfr.discourse.group/t/mpi-fork-warning/194>\
**Category:** Just Starting\
**Created:** [31 January 2018 20:27 UTC](https://pyfr.discourse.group/t/mpi-fork-warning/194 "2018-01-31T20:27:48Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Yifan\_Bai](https://avatars.discourse-cdn.com/v4/letter/y/87869e/32.png) [@Yifan\_Bai](https://pyfr.discourse.group/u/Yifan_Bai)\
**Post date:** [31 January 2018 20:27 UTC](https://pyfr.discourse.group/t/mpi-fork-warning/194/1 "2018-01-31T20:27:48Z")

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Hi,

I tried to run pyfr on a cluster with the openmp backend and got the following error output:

An MPI process has executed an operation involving a call to the  
“fork()” system call to create a child process. Open MPI is currently  
operating in a condition that could result in memory corruption or  
other system errors; your MPI job may hang, crash, or produce silent  
data corruption. The use of fork() (or system() or other calls that  
create child processes) is strongly discouraged.

Any idea what might have caused this problem? Thank you!

Yifan Bai

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**Author:** ![fdw](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@fdw](https://pyfr.discourse.group/u/fdw)\
**Post date:** [1 February 2018 01:59 UTC](https://pyfr.discourse.group/t/mpi-fork-warning/194/2 "2018-02-01T01:59:12Z")

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Hi,

On 31/01/2018 12:27, Yifan Bai wrote\> I tried to ran pyfr on a cluster  
with the openmp backend and got t\>

> following error output:
> 
> An MPI process has executed an operation involving a call to the  
> "fork()" system call to create a child process. Open MPI is currently  
> operating in a condition that could result in memory corruption or  
> other system errors; your MPI job may hang, crash, or produce silent  
> data corruption. The use of fork() (or system() or other calls that  
> create child processes) is strongly discouraged.
> 
> Any idea what might have caused this problem? Thank you!

PyFR goes to great lengths to ensure that it does not fork() once MPI  
has been initialised. This is accomplished by using the pytools module  
which includes a preforker. If you are getting this warning it is  
likely that something is initialising MPI before PyFR gets a chance to  
run its prefork code.

Can you give any details regarding the versions of mpi4py, h5py  
(including MPI support information), and OpenMPI?

Regards, Freddie.