Zombie Process

Zombie processes occur when child processes aren't properly reaped, exhausting process table and file descriptors.

Zombie Process is a Reliability failure seen during ML training runs. Zombie processes occur when child processes aren't properly reaped, exhausting process table and file descriptors. Common tags: Zombie, Defunct, Process, Multiprocessing.

Parent process not calling wait(). SIGCHLD handler not installed. Process leak from training workers. Distributed worker not properly cleaned up. 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.

• Process count grows over time
• ps shows defunct processes
• System becomes unresponsive

• Multi-process training
• Distributed training
• Fork-based multiprocessing

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: Z state in ps output
• ✓Verified signal present: defunct process
• ✓Verified signal present: Process not reaped after exit
• ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.

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.

• Parent process not calling wait()
• SIGCHLD handler not installed
• Process leak from training workers
• Distributed worker not properly cleaned up