The Vanishing Benchmark: Diagnosing a Silent Process Crash in a Distributed Proving System

Introduction

In the complex ecosystem of distributed Filecoin proving infrastructure, few moments are as tense as the first end-to-end test of a freshly deployed worker instance. After hours of debugging platform quirks, fixing service logic, and hardening scripts against edge cases, the moment arrives when the system should finally work. The parameters download completes, the benchmark is signaled to start, and then... nothing. No logs, no GPU activity, no indication of work being done. This is exactly the scenario captured in message 977 of the opencode session, where an AI assistant performs a critical diagnostic probe on a remote Vast.ai instance that has gone silent at the worst possible moment.

The Message

The subject message is brief but consequential. It reads:

The entrypoint moved to benchmark, but something is wrong — no cuzk log output and no GPU activity. Let me check what's happening:

>

``bash ssh -o StrictHostKeyChecking=no -p 48191 root@70.69.192.6 "ps aux | grep -E 'cuzk|bench|curio|entrypoint'" 2>&1 ``

>

Welcome to vast.ai. If authentication fails, try again after a few seconds, and double check your ssh key. Have fun! root 369 0.0 0.0 4456 1024 ? S 00:33 0:00 bash /usr/local/bin/entrypoint.sh root 5182 0.0 0.0 4752 3092 ? Ss 00:59 0:00 bash -c ps aux | grep -E 'cuzk|bench|curio|entrypoint' root 5184 0.0 0.0 4096 1040 ? S 00:59 0:00 grep -E cuzk|bench|curio|entrypoint

The assistant's reasoning is stated plainly: the entrypoint script has progressed to the benchmark phase, but the expected processes are absent and the GPUs sit idle. The response is a targeted SSH command that checks for any of the four process categories that should be present: cuzk (the CuZK proving engine), bench (the benchmark script), curio (the Curio worker), and entrypoint (the lifecycle manager). The output is stark: only the entrypoint shell script (PID 369) and the diagnostic commands themselves appear. The benchmark process, whatever it was, has vanished.

Context and Background

To understand the significance of this message, one must appreciate the journey that led to this moment. The session's broader context (Segment 7) involved deploying a sophisticated proving pipeline onto rented GPU instances from Vast.ai, a marketplace for distributed compute. The system comprised multiple layers: a Docker container running CuZK (a GPU-accelerated proof generation engine), Curio (a Filecoin storage mining worker), and a custom entrypoint script that managed the lifecycle of parameter fetching, benchmarking, and production proving.

The preceding messages in the conversation (msg 975–976) had just resolved a critical bug in the vast-manager service, where the monitoring system was incorrectly matching database instances to Vast API instances because the API's label field remained null unless explicitly set. The fix introduced an ID-based fallback map (idMap) that extracted the Vast instance ID from the C.<id> label pattern used internally by the container. This was a significant milestone — the instance 32710471 (a 2x RTX 3090 machine in BC Canada, costing $0.38/hour) had successfully downloaded its proving parameters and signaled readiness. The user's status update (msg 976) showed the parameter fetch completing successfully at 00:50:58 UTC, followed by the entrypoint announcing "Starting benchmark: 12 proofs, concurrency 5, partition-workers 10." But then the user noted the absence of benchmark logs and GPU activity — a red flag that prompted the assistant's diagnostic response.

Why This Message Was Written

The message exists at the intersection of two forces: the user's report of anomalous behavior and the assistant's need to gather empirical data before formulating a hypothesis. The user's update was itself a diagnostic observation — they could see the entrypoint log claiming benchmark had started, but the expected downstream effects (CuZK processes consuming GPU cycles, log output from proof generation) were absent. This is a classic "heisenbug" scenario in distributed systems: the system says it's working, but the observable evidence contradicts the claim.

The assistant's motivation is straightforward: before attempting any fix, it must understand the actual state of the remote system. The ps aux command is the most direct way to answer the question "is the benchmark process actually running?" The assistant's reasoning text — "The entrypoint moved to benchmark, but something is wrong — no cuzk log output and no GPU activity" — reveals the cognitive frame: the assistant has a mental model of what should be happening (CuZK processes consuming GPU time, log lines appearing), and the absence of those signals triggers a diagnostic intervention.

The Diagnostic Decision

The choice of ps aux | grep -E 'cuzk|bench|curio|entrypoint' is not arbitrary. It reflects a deep understanding of the system architecture. The assistant knows that:

  1. cuzk is the GPU proving engine — if proof generation were happening, a cuzk-daemon or cuzk-bench process would be visible.
  2. bench refers to benchmark.sh, the shell script that orchestrates proof warmup and benchmarking.
  3. curio is the Filecoin storage mining worker that consumes proofs.
  4. entrypoint is the lifecycle manager script that coordinates the entire pipeline. By checking for all four in a single grep, the assistant can determine not just whether work is happening, but where in the pipeline the breakdown occurred. The inclusion of entrypoint in the grep is particularly telling — it confirms that the lifecycle manager itself is still alive, ruling out a complete container crash or SSH session failure. The SSH command itself also reveals assumptions about the environment. The -o StrictHostKeyChecking=no flag indicates the assistant expects to connect to a host whose SSH key may not be in the known_hosts file — a common scenario with ephemeral cloud instances. The -p 48191 port specification shows this is a non-standard SSH port, typical of Vast.ai's container networking model where each instance gets a unique port on the host machine.

What the Output Reveals

The ps aux output delivers a clear verdict. Three processes are visible:

Assumptions and Their Validity

The assistant operates under several assumptions in this message, most of which are validated by the output:

Assumption 1: SSH access is available. The connection succeeds, and the command executes. This confirms the instance is reachable and the container's SSH service is running — itself a recent achievement, since earlier in the session the --ssh launch mode was found to replace the Docker ENTRYPOINT with Vast's own init script, requiring the --onstart-cmd workaround.

Assumption 2: Process inspection via ps aux is the right diagnostic tool. The output provides exactly the information needed: a snapshot of running processes filtered to the relevant categories. This confirms the benchmark is not running.

Assumption 3: The absence of CuZK processes implies no GPU activity. This is a reasonable inference — CuZK is a GPU-bound proof generator, and if it were running, it would appear in the process list and consume GPU cycles visible in nvidia-smi.

Assumption 4: The entrypoint script is the parent orchestrator. The output confirms the entrypoint is PID 369, suggesting it was one of the first processes started in the container. Its continued presence rules out a container restart or crash.

One assumption that may be incorrect is that the benchmark failure is a transient or environmental issue. The output doesn't reveal why the benchmark process exited — it could be a crash (segfault, OOM kill), a script error (the set -e issue mentioned in the chunk summary where a warmup proof failure aborts the pipeline), or a deliberate exit by the benchmark script after detecting an unrecoverable condition. The assistant will need further investigation (checking logs, exit codes, or journal entries) to determine the root cause.

Input Knowledge Required

To fully understand this message, a reader needs knowledge of:

Output Knowledge Created

This message produces several pieces of actionable knowledge:

  1. The benchmark process has exited. The entrypoint's claim of "Starting benchmark" at 00:50:58 did not result in a persistent benchmark process. The subprocess terminated, likely within seconds or minutes of starting.
  2. The entrypoint shell script is still alive. PID 369 continues to run, meaning the lifecycle manager has not crashed. It may be in a waiting state, perhaps blocked on a command that never returns, or stuck in a loop that doesn't detect the benchmark failure.
  3. No CuZK process exists. This confirms the GPU is idle not because CuZK is hung, but because it was never launched or exited immediately.
  4. The failure is silent. The entrypoint log claimed benchmark start but produced no error output about the benchmark's exit. This suggests either the benchmark script exited with a non-zero code that the entrypoint didn't check, or the entrypoint's logging is insufficient to capture subprocess failures.

The Thinking Process

The assistant's reasoning in this message follows a classic diagnostic pattern: observe anomaly → formulate hypothesis → gather data → interpret results. The anomaly is the absence of expected GPU activity and log output. The hypothesis is that the benchmark process never actually started or crashed immediately. The data-gathering step is the ps aux SSH command. The interpretation is implicit in the message's framing — the assistant presents the raw output without commentary, letting the evidence speak for itself.

What's notable is what the assistant does not do. It doesn't immediately restart the benchmark, kill the entrypoint, or apply a fix. It first gathers information, recognizing that a premature intervention could destroy evidence needed to understand the root cause. This restraint is a hallmark of disciplined debugging — the first priority is always to understand the current state before changing it.

The assistant's thinking also reveals an understanding of the system's failure modes. The chunk summary for this segment mentions that earlier in the session, a warmup proof failed with a gRPC transport error during PCE extraction, causing set -e in benchmark.sh to abort the entire pipeline. The assistant likely suspects a similar failure here — the benchmark script started, encountered an error (perhaps the same PCE extraction issue, or an OOM condition on the 125GB RAM instance), and exited before producing any output. The ps aux output confirms the benchmark is gone, but the root cause remains to be determined.

Conclusion

Message 977 captures a pivotal moment in the deployment of a distributed proving system. It is the point where theory meets reality — where the carefully designed pipeline encounters the messy, unpredictable behavior of real hardware and real software. The assistant's response is a model of diagnostic discipline: observe, hypothesize, probe, interpret. The ps aux output provides a clear answer (the benchmark process has vanished) but raises a deeper question (why did it fail?). The subsequent messages in the conversation will trace the answer through log files, error messages, and system metrics, ultimately leading to the OOM diagnosis that reshapes the deployment strategy. But this message stands as the critical inflection point — the moment the silence was noticed and the investigation began.