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Here we will list fixes to problems that were encountered when building or running Linktest. These fixes may not necessarily be up to date or even work on your system. We hope they will solve your problem or point you in the right direction.
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[[_TOC_]]
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# ParastationMPI and `shmget(0, sizeof(shm_com_t), IPC_CREAT | 0777) : No space left on device`
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When using ParastationMPI and testing MPI you may encounter an error-message of the following form:
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```
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<PSP:r§TASKID§:shmget(0, sizeof(shm_com_t), IPC_CREAT | 0777) : No space left on device>
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```
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where `§TASKID§` is a 8-digit zero-filled task id, also known as a rank. If other terminating error messages occur afterwards Linktest will terminate, otherwise it will hang.
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This silent error message occurs when so many connections are to be tested that no more shared memory can be allocated on the communication device. This is a hardware limitation, not a software limitation. This commonly occurs when oversubscribing or overcommitting nodes with tasks, for example when using twice as many tasks on a node as it has logical cores.
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This error was produced using ParaStation MPI version 5.4.9-1.
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At the time of writing three potential solutions exist:
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1. Use a different MPI implementation like OpenMPI version 4.1.1.
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2. Set the `PSP_UCP` environment variable to `2`. This is an undocumented option and it is unknown what it does. This may change in future ParaStation MPI versions.
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3. Upgrade your communication hardware such that it has more memory and can support more connections. Depending on how many connections you want to test this may be enough. |
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