OpenMPI / MPI Issue
OpenMPI and general MPI issues cause distributed training to fail at initialization or hang during collectives.
OpenMPI and general MPI issues cause distributed training to fail at initialization or hang during collectives.
What this failure is
OpenMPI / MPI Issue is a Environment failure seen during ML training runs. OpenMPI and general MPI issues cause distributed training to fail at initialization or hang during collectives. Common tags: Mpi, Openmpi, Horovod, Deepspeed.
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Why it happens (the mechanism)
Mpirun hostfile not configured. SSH keys not set up for passwordless MPI. MPI version mismatch between nodes. Firewall blocking MPI ports. Different MPI installations on different nodes. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.
What you'll observe
- Distributed training fails to start with MPI
- mpirun hangs or errors
- MPI processes don't connect
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| ORTE_ERROR | mpirun hostfile not configured |
| MPI_Init failed | SSH keys not set up for passwordless MPI |
| Primary process exited before connection | MPI version mismatch between nodes |
Which systems are affected
- Training with Horovod on MPI
- DeepSpeed with MPI backend
- Custom distributed training with MPI
How to confirm this is the problem
Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.
- ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
- ✓Verified signal present: ORTE_ERROR
- ✓Verified signal present: MPI_Init failed
- ✓Verified signal present: Primary process exited before connection
- ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.
The fix and the prevention pattern
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Diagnose this failure in VS Code
Select the traceback or open the failed terminal, then run Denpex locally to see the initiating rank, collateral failures, exact fix, and verification command without uploading the log.
Install the free VS Code extensionDeepSpeed errors in context
DeepSpeed changes when parameters, gradients and optimizer state are created, partitioned, gathered and offloaded. The hub separates ZeRO, memory, checkpoint and pipeline failures by lifecycle phase.
Compare every deepspeed error side by sideRelated failures to investigate next
Root cause
- mpirun hostfile not configured
- SSH keys not set up for passwordless MPI
- MPI version mismatch between nodes
- Firewall blocking MPI ports
- Different MPI installations on different nodes
The fix and how to prevent it
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Don't just read the fix, diagnose your run
The encyclopedia tells you what went wrong. Denpex tells you what went wrong in YOUR training run. With your logs, your config, and your stack.