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Last active May 15, 2019 19:47
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MPI always gives rank=0, size = 1
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I accidentally installed multiple versions of MPI's (openmpi, mpich2, ...) in my Ubuntu 12.04 machine. I removed them all, and installed openmpi again; however, after fixing that (I never try before that), my MPI always gives rank=0, size = 1. The reason is that the removal process is incomplete, hence causes file sharing conflict. It can be seen from the following test

beta@landmark:~$ whereis mpicc
mpicc: /usr/bin/mpicc.mpich2 /usr/bin/mpicc.openmpi /usr/bin/mpicc 
/usr/bin/X11/mpicc.mpich2 /usr/bin/X11/mpicc.openmpi /usr/bin/X11/mpicc 
/usr/share/man/man1/mpicc.1.gz

It turns out that the packages libmpich2-3 and libmpich2-dev failed to be removed. So after apt-get remove libmpich2-3 libmpich2-dev, everything goes fine.

beta@landmark:~$ mpicc -o hello_mpi hello_mpi.c
beta@landmark:~$ mpirun -np 4 ./hello_mpi
Hello World from processor 0 out of 4, executing on landmark
Hello World from processor 1 out of 4, executing on landmark
Hello World from processor 2 out of 4, executing on landmark
Hello World from processor 3 out of 4, executing on landmark
@VSMent
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VSMent commented May 15, 2019

Thanks. It worked for me too. However, my packages were little different.

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