# MPI Problem **URL:** \ **Category:** User Support\ **Created:** [July 15, 2013, 11:28am UTC](https://openmc.discourse.group/t/mpi-problem/37 "2013-07-15T11:28:15Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Kyungkwan\_Noh](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@Kyungkwan\_Noh](https://openmc.discourse.group/u/Kyungkwan_Noh)\ **Post date:** [July 15, 2013, 11:28am UTC](https://openmc.discourse.group/t/mpi-problem/37/1 "2013-07-15T11:28:15Z")
Hi, I have weird problem running mpi. When I use main computer only, mpi works perfectly. However, when using two or more nodes, it works independently. I’m not sure what the problem is. Thank you. ---
**Author:** ![Kyungkwan\_Noh](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@Kyungkwan\_Noh](https://openmc.discourse.group/u/Kyungkwan_Noh)\ **Post date:** [July 15, 2013, 11:43am UTC](https://openmc.discourse.group/t/mpi-problem/37/2 "2013-07-15T11:43:10Z")
I’m using OpenMPI 1.6.4 (2013 version), by the way. 2013년 7월 15일 월요일 오후 8시 28분 15초 UTC+9, Kyungkwan Noh 님의 말: ---
**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\ **Post date:** [July 15, 2013, 11:37pm UTC](https://openmc.discourse.group/t/mpi-problem/37/3 "2013-07-15T23:37:35Z")
Let’s say your MPI is installed in /opt/openmpi/1.6. You would need to do the following to get it to compile and run correctly: 1. Change the MPI variable in the Makefile to yes 2. Change the MPI\_DIR variable in the Makefile to /opt/openmpi/1.6 3. Execute ‘make’ to compile 4. To run, execute ‘/opt/openmpi/1.6/bin/mpiexec -n _NPROCS_ openmc’ where NPROCS is the number of processors you want If you have problems compiling, try running ‘make distclean’ and then re-compiling. If you get the following error when compiling: …/xml-fortran/xmlreader: error while loading shared libraries: libmpi\_f90.so.1: cannot open shared object file: No such file or directory Then add /opt/openmpi/1.6/lib to the LD\_LIBRARY\_PATH environment variable. Best regards, Paul ---
**Author:** ![smharper](https://avatars.discourse-cdn.com/v4/letter/s/f475e1/32.png) [@smharper](https://openmc.discourse.group/u/smharper)\ **Post date:** [July 16, 2013, 2:13am UTC](https://openmc.discourse.group/t/mpi-problem/37/4 "2013-07-16T02:13:34Z")
FYI, I have had the same problem with OpenMPI. I had to switch to MPICH. If you like, I can try to recreate the problem, and give you more details. ---
**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\ **Post date:** [July 16, 2013, 2:23am UTC](https://openmc.discourse.group/t/mpi-problem/37/5 "2013-07-16T02:23:55Z")
It should work fine if everything is set up properly. I just confirmed that I am able to compile/run successfully using OpenMPI on my own machine. Typically you will see the multiple processes running independently if you are using the wrong mpiexec/mpirun executable. A few more questions to narrow this down (for either of you): - What OS are you on? - Did you install OpenMPI from source, or through a package manager? (or a binary if on Windows?) - If you installed from source, what compiler did you use to compile OpenMPI? - If you installed from source, what did you put for --with-mpi-f90-size? - What version (or commit) of OpenMC are you trying to compile/run? ---
**Author:** ![Kyungkwan\_Noh](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@Kyungkwan\_Noh](https://openmc.discourse.group/u/Kyungkwan_Noh)\ **Post date:** [July 17, 2013, 8:26am UTC](https://openmc.discourse.group/t/mpi-problem/37/6 "2013-07-17T08:26:47Z")
1. I’m using Linux Red hat 2. I guess from source. 3. I used intel 13.1.1 4. I put small for --with-mpi-f90-size 5. I think the newest version since I installed through git. Well, if I use the command ‘/opt/openmpi/1.6/bin/mpiexec -n _NPROCS_ openmc’, it operates only on main computer, not on different nodes. So, I try to use mpiexec -hostfile [hostfile name] openmc. The host file may look like this: node01 slots=8 node02 slots=8 I guess my settings are right, but it still doesn’t work. Thank you. 2013년 7월 15일 월요일 오후 8시 28분 15초 UTC+9, Kyungkwan Noh 님의 말: