What does this failure look like in production?

In production this failure typically appears during the first tens-to-hundreds of training steps: loss curves become non-monotonic, validation metrics plateau above the baseline, and downstream checkpoints either diverge or fail to improve. Engineers frequently misread it as data drift when the underlying mechanism is the training process was interrupted (e.g. by oom, preemption, or crash) while pytorch was executing `torch.save()`. because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state.. Validating against the symptom list in this entry is the fastest way to confirm the diagnosis.

Is this a hardware or a software issue?

Storage failures can look like either layer depending on the symptom. The discriminator is the resolution of the symptom to the recommended fix: if applying the steps under "How to fix it" eliminates the symptom, this is a software/configuration class issue regardless of the hardware it surfaced on. Repeat the fix on a fresh node to confirm.

How long does the fix typically take?

Most resolutions from this entry take 10 to 30 minutes of engineer time once the diagnosis is confirmed. Long fixes come from skipping the diagnosis step and chasing apparent symptoms (validation drift, memory growth, slow throughput) instead of the actual root cause listed above. Apply the fix in a small experiment first, then roll it forward.

Does this affect inference or only training?

Primarily this is a storage failure observed during training, but the same misconfiguration can leak into downstream evaluation and serving. Treat the prevention checklist as a guardrail: any pipeline that touches a trained checkpoint should re-validate the failure mode before promoting the model.

What's the cheapest way to confirm this is the problem?

Cheapest signal: reproduce the symptom on a 1-GPU toy run with the same configuration. If the toy run exhibits the same behavior, the cause is the configuration rather than the cluster. If only the multi-GPU run is affected, the failure is a distributed interaction, so PyTorch is the most likely layer to inspect.

Can the Denpex platform detect this automatically?

Yes. Denpex correlates the symptoms in this entry against your training logs in real time and surfaces the failure taxonomy, root cause, and exact remediation command on the console. Three full diagnoses are included free during signup, and the encyclopedia entry you are reading is generated from the same signal library that powers the platform.

What related failures should I check next?

Closely related failures cluster around #Checkpoint Corruption. After applying this fix, validate against the related entries below to confirm no overlapping cause is masking as this one. Engineers routinely discover that the dominant failure mode is actually a second, sibling failure compounded on top.

Will this recur after the fix?

Applied once with the prevention checklist, this failure does not recur under normal operation. The recurring variant most engineers encounter is the re-emergence of the same symptom on a different model or stack after Checkpoint Corruption is upgraded. Pin compatible versions and rerun the prevention smoke test on every dependency change.

Is there a fingerprint I can monitor?

Yes. Training crashes when loading a checkpoint is the highest-signal fingerprint. Wire a metric or alert on that signal (or its absence after the fix) so you can detect the recurrence automatically. The Denpex platform encodes this exact fingerprint and surfaces it directly in the dashboard.

What is the official documentation that covers this?

Reference documentation is listed in the References section at the bottom of this entry. The most authoritative URLs are the upstream framework docs and the issue trackers cited; the Denpex entry synthesizes both into the executive, engineer, and on-call perspectives so each audience can act without reading every linked source.

Does this entry include working code?

Yes. The "Code Examples" section contains copy-paste-ready snippets that target the most common stacks (PyTorch, Hugging Face Trainer, DeepSpeed, Megatron-LM, vLLM/Transformers). Each snippet is annotated with why it works so you can adapt the pattern to your own framework without losing fidelity.

Non-Atomic Checkpoint Save Interruption

Q: How does this scale from 1 GPU to 1000 GPUs?

At single-GPU scale the symptom usually looks like slow convergence or a single anomalous loss value. At 64+ GPU scale, distributed interactions amplify the training process was interrupted (e.g. by oom, preemption, or crash) while pytorch was executing `torch.save()`. because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state. through collectives, and the failure can manifest as a full job abort. Always reproduce the fix at the smallest cluster configuration that still exhibits the symptom before promoting to production scale.

The training process was interrupted (e.g. by OOM, preemption, or crash) while PyTorch was executing `torch.save()`. Because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state.

Quick answer

The training process was interrupted (e.

Symptom: RuntimeError: unpickling failed
Root cause: The training process was interrupted (e.g. by OOM, preemption, or crash) while PyTorch was executing `torch.
Recommended fix: Implement atomic saving temp_path = checkpoint_path + '.tmp' torch.save(state_dict, temp_path) os.replace(temp_path, checkpoint_path) Writing to a temporary file and then renaming it ensures the final checkpoint file is only created once the write completes successfully.
How Denpex helps: Denpex investigates Non-Atomic Checkpoint Save Interruption using the evidence you provide or your connected workload collects. Earlier rank, host or application evidence is needed to distinguish an initiating failure from a downstream report.

Storage#Checkpoint Corruption

What this failure is

Non-Atomic Checkpoint Save Interruption is a Storage failure seen during ML training runs. The training process was interrupted (e.g. by OOM, preemption, or crash) while PyTorch was executing `torch.save()`. Because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state. Common tags: Checkpoint Corruption.

Live diagnosis, no signup

Is this what broke your run? Paste your log.

You're reading about Non-Atomic Checkpoint Save Interruption. Paste your own traceback and relevant evidence for an investigation of your workload, with a next action or a specific missing fact. A reference entry does not establish your cause. No account or card for the free diagnosis. Review data handling before submitting sensitive logs.

Before uploading, review cloud data handling and local options.

training_logs.txt

No log to hand? Try one:

Upload or drop a plain-text log

Upload your log file. Large files are processed in your browser. Only selected evidence is submitted when you run diagnosis.

3 free diagnoses/day

Why it happens (the mechanism)

The error appears during load time (`torch.load()`), making it look like a reading or parsing issue, but the actual failure occurred silently at the end of the previous training run during the write phase.

What you'll observe

EOFError: Ran out of input
RuntimeError: unpickling failed

Common symptoms and what they mean

Symptom	Why it happens
Training crashes when loading a checkpoint	The training process was interrupted (e.g. by OOM, preemption, or crash) while PyTorch was executing `torch.save()`. Because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state.
Checkpoint file size is smaller than expected or malformed	The training process was interrupted (e.g. by OOM, preemption, or crash) while PyTorch was executing `torch.save()`. Because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state.

Which systems are affected

PyTorch
Local FS

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.

✓Check file sizes of the corrupted checkpoint vs older checkpoints
✓Look for preemption or OOM signals in the logs immediately preceding the crash

Root cause

The training process was interrupted (e.g. by OOM, preemption, or crash) while PyTorch was executing `torch.save()`. Because the save operation writes directly to the destination file, the interruption leaves the file in a partially written, corrupted state.

The fix and how to prevent it

Searchable error signature

search key

RuntimeError: unpickling failed

Use this text as a lookup key in logs and upstream issue trackers. It is not presented as a captured customer log. Confirm the cause from your own preceding events, versions, configuration and the cited references.

The fix and the prevention pattern

The root cause is on this page and stays free. A free account adds the exact remediation steps, saved history, and the fix on every entry in the encyclopedia.

No credit card. Daily allowance follows verified trust tier. Instant access.

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 extension

References

↗PyTorch Checkpoint Corruption Issue

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.

Diagnose your logs free Compare a solved incident Browse all failures

Related Storage errors

Ephemeral Storage Exhaustion by Model Weights

Storage · high

Atomic Save I/O Error on Parallel FS

Storage · high

Multi-Worker Write Race Condition

Storage · critical

FSDP Checkpoint S3 Path Malformation

Storage · medium