# Using multiple processes

**URL:** <https://discourse.channelflow.ch/t/using-multiple-processes/111>\
**Category:** Usage\
**Created:** [February 25, 2021, 3:26am UTC](https://discourse.channelflow.ch/t/using-multiple-processes/111 "2021-02-25T03:26:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mjchan](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@mjchan](https://discourse.channelflow.ch/u/mjchan)\
**Post date:** [February 25, 2021, 3:26am UTC](https://discourse.channelflow.ch/t/using-multiple-processes/111/1 "2021-02-25T03:26:59Z")

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So I installed Channelflow 2.0 on my Manjaro Linux machine, with -DUSEMPI=on. I have openMPI on this machine.

Channelflow installed successfully and passed all make tests, but when I attempt to set -np0 and -np1 to anything other than 1 and 1, I get

CfMPI: number of MPI-processes \< nproc0\*nproc1

Which seems to indicate to me that I need to do something else in order to enable the usage of multiple processes. Can someone help with this?

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**Author:** ![jlangham](https://avatars.discourse-cdn.com/v4/letter/j/a88e4f/32.png) [@jlangham](https://discourse.channelflow.ch/u/jlangham)\
**Post date:** [March 4, 2021, 6:21pm UTC](https://discourse.channelflow.ch/t/using-multiple-processes/111/2 "2021-03-04T18:21:07Z")

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It might depend on your local mpi setup. Are you running with mpirun / mpiexec?

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**Author:** ![mjchan](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@mjchan](https://discourse.channelflow.ch/u/mjchan)\
**Post date:** [March 4, 2021, 8:28pm UTC](https://discourse.channelflow.ch/t/using-multiple-processes/111/3 "2021-03-04T20:28:52Z")

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Hi Jake, thanks. I didn’t know I had to use mpiexec; not familiar with OpenMPI

For anyone curious, mpiexec -np _number of processes_ simulateflow -args values worked out.

Also, I found my openmpi-default-hostfile to change the number of threads to 2x my number of cores on my machine. This made things better! Source: [mpi - Change the number of cores OpenMPI can "see" - Stack Overflow](https://stackoverflow.com/questions/56432943/change-the-number-of-cores-openmpi-can-see)