< Marvin> i am getting `OSError Errno 28 No space left on de Prefect Community #ask-marvin

<@ULVA73B9P> i am getting `OSError: [Errno 28] No ...

Peter Korolev

09/23/2025, 10:28 AM

@Marvin i am getting

OSError: [Errno 28] No space left on device

from following code. len(args) is 10000, and there are 16 processes. I have enough disk space, what can cause this error?

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with ProcessPoolTaskRunner(max_workers=args.processes) as runner:
    futures = [runner.submit(process_arg, args) for args in arguments]
    for future in futures:
        future.wait()

Marvin

09/23/2025, 10:29 AM

✅ thought for 274.4 seconds

Marvin

09/23/2025, 10:33 AM

Short answer: this is usually not your main disk. With many processes/futures, ENOSPC often comes from one of: - /dev/shm (shared memory) filling up — very common inside Docker/Kubernetes - Inode exhaustion (too many small files) even if df -h shows plenty of space - A small/isolated /tmp or container writable layer that’s full - Local result persistence creating lots of files A few checks to pinpoint it: - Check shared memory

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df -h /dev/shm
  ls -l /dev/shm | wc -l

If you’re in Docker/K8s, /dev/shm is typically tiny (64MB in Docker by default) and Python multiprocessing uses POSIX semaphores in /dev/shm; creating many can trigger “No space left on device”. - Check inodes

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df -i

If IUse% is 100% for the filesystem hosting your temp/results, you’re out of inodes. - Check temp and container layer

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df -h /
  df -h /tmp

In containers, the writable layer may be full even if the host isn’t. Mitigations: 1) If running in Docker/Kubernetes - Increase shared memory: - Docker: add

--shm-size=1g

- Kubernetes: mount an EmptyDir at

/dev/shm

with

medium: Memory

and a

sizeLimit

- Ensure your container’s writable layer or ephemeral volumes have enough space. 2) Don’t queue 10k futures at once - Submit in batches so only a small number are “in flight”; this reduces OS resources (/dev/shm objects, temp files).

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batch_size = 1000  # or 4 * args.processes
   with ProcessPoolTaskRunner(max_workers=args.processes) as runner:
       for i in range(0, len(arguments), batch_size):
           futures = [runner.submit(process_arg, a) for a in arguments[i:i+batch_size]]
           for f in futures:
               f.wait()

3) Results/temp storage - If you’ve enabled local result persistence, 10k tasks can create lots of small files; point results at a larger filesystem or disable persistence for this run. - Prefect 3.x results docs: Results in Prefect 3 4) If you see many leftover

sem.*

files in

/dev/shm

, you’re likely hitting the shared memory limit or leaking semaphores after crashes. Cleaning them up and increasing

/dev/shm

usually resolves it. If you can share: - Whether this is running in Docker/Kubernetes (and any resource limits) - The full traceback (to see if it fails creating a semaphore or writing a file) - Whether you’ve enabled result persistence …I can give more targeted guidance.

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