The Silent Stall: Diagnosing a Stuck Entrypoint in a Distributed Proving Pipeline

Introduction

In the complex world of distributed Filecoin proving infrastructure, where Docker containers, GPU instances, and custom management services must dance in perfect synchronization, the most frustrating failures are often the quiet ones. Message 978 of this opencode session captures a moment of diagnostic tension: the assistant has deployed a new vast.ai instance, watched it successfully download terabytes of proving parameters, observed the entrypoint signal readiness—and then encountered silence. No benchmark process. No GPU activity. Just a lone shell script PID, running but accomplishing nothing. This message is a snapshot of the investigative process, where the assistant transitions from deployment logistics to runtime debugging, trying to understand why a pipeline that appeared to be working suddenly stalled.

Context: The State of Play

To understand what this message means, we must first understand the infrastructure it operates within. The assistant has been building a sophisticated system for deploying Filecoin/CuZK proving workers on vast.ai, a GPU rental marketplace. The architecture involves:

• A Docker image (theuser/curio-cuzk:latest) containing the CuZK proving engine, Curio daemon, and a lifecycle management script (entrypoint.sh)
• A vast-manager service running on a central controller host that tracks instances, monitors their state, and handles lifecycle events
• An entrypoint.sh script that runs inside each container, orchestrating the sequence: parameter download → benchmark → proving The system had just weathered a series of platform-specific challenges. The VAST_CONTAINERLABEL environment variable was found to be injected by vast.ai but only as a non-exported shell variable, invisible to SSH sessions but available to the Docker entrypoint. The vast-manager's monitor logic had been fixed to use ID-based fallback matching instead of relying solely on the API's label field (which vast.ai leaves null). A new instance (C.32710471, a 2× RTX 3090 machine in British Columbia) had been created using the --ssh --onstart-cmd workaround to run the entrypoint alongside SSH access. By the time we reach message 978, the instance has been running for some time. The user's preceding message (msg 976) showed the setup logs: parameter fetch completed successfully at 00:50:57, the entrypoint signaled param-done to the manager, and then announced "Starting benchmark: 12 proofs, concurrency 5, partition-workers 10." But the user also noted a troubling observation: "there are no benchmark logs, seemingly, also no bench in nvidia smi." The assistant's initial response (msg 977) confirmed this—a ps aux check showed only the entrypoint shell script running, with no benchmark.sh, cuzk-daemon, or cuzk-bench process in sight.

The Subject Message: A Diagnostic Probe

Message 978 is the assistant's second look at the problem. It opens with a clear statement of the observed state:

The entrypoint is still running (PID 369) but there's no benchmark.sh, cuzk-daemon, or cuzk-bench process. The entrypoint is stuck somewhere after signaling param-done.

This is a critical diagnostic framing. The assistant has already established that the entrypoint did progress past the parameter download phase—it signaled param-done to the manager, which means the paramfetch command completed and the script advanced to the next step. But then it stalled. The entrypoint process is alive (PID 369), but it hasn't launched the benchmark subprocess. This narrows the failure window to the code path between the param-done API call and the invocation of benchmark.sh.

The assistant then executes a targeted data-gathering command:

ssh -p 48191 root@[REDACTED] "tail -30 /var/log/entrypoint.log"

This is a sensible next step. The entrypoint script logs its activities to /var/log/entrypoint.log, so examining the tail of this file should reveal what the script was doing most recently. The assistant is looking for error messages, unexpected output, or evidence of where the script got stuck.

The Log Output: A Puzzle in Progress Bars

The response from the instance is revealing but ambiguous:

[#00da3c 55GiB/56GiB(97%) CN:16 DL:111MiB ETA:13s]
[#00da3c 55GiB/56GiB(97%) CN:16 DL:111MiB ETA:12s]
[#00da3c 55GiB/56GiB(97%) CN:16 DL:111MiB ETA:11s]
...
[#00da3c 56GiB/56GiB(99%) CN:16 DL:111MiB ETA:...

These lines show the output of aria2c (or a similar download tool) that paramfetch uses to download Filecoin proving parameters. The format shows: a download ID (#00da3c), progress (55-56 GiB out of 56 GiB, 97-99%), connection count (CN:16), download rate (DL:111MiB/s), and estimated time remaining.

This output is puzzling because the user's earlier message (msg 976) showed that paramfetch completed successfully at 00:50:57, with both parameter files verified as OK. Yet here, the log tail shows download progress at 97-99%. There are several possible explanations for this discrepancy:

1. The log file is large and the tail only shows the last 30 lines. The download progress lines are emitted frequently (one per second), so they could easily dominate the tail of the log file even though the completion messages occurred earlier and are now scrolled out of the 30-line window.
2. There are multiple parameter files. The log shows a 56 GiB file, which matches the v28-proof-of-spacetime-fallback parameter file. The completion message in msg 976 showed two files verified: a smaller one and this large one. The download progress lines could be from the final moments of downloading this large file, with the completion message following shortly after.
3. The entrypoint script is buffering or has a race condition. It's possible that the paramfetch process completed and wrote completion messages to stdout, but the script's logic for detecting completion and proceeding to the benchmark phase has a bug or a race condition. The most likely interpretation is that the log tail simply shows the last lines written to the log file before the script got stuck. The download completed (as evidenced by the user's setup logs), but something in the transition from parameter fetch to benchmark execution failed silently.

The Thinking Process: What the Assistant Knows and Doesn't Know

The assistant's reasoning in this message reveals a methodical diagnostic approach. The key observations are:

1. The entrypoint process is alive — The script hasn't crashed or been killed. This rules out OOM kills, segfaults, or other fatal errors.
2. No benchmark subprocess exists — The script hasn't successfully launched benchmark.sh. This means the failure is in the script logic between the param-done signal and the benchmark invocation.
3. The log shows download activity — This suggests the script might still be in the parameter fetch phase, or the log is showing stale output from that phase. The assistant is operating under several implicit assumptions: - The entrypoint script is single-threaded and sequential. The script likely runs paramfetch, then signals completion, then runs benchmark.sh. If it's stuck, it's stuck in one of these phases. - The param-done signal was actually sent. The user's log showed "Signaled param-done," which suggests the API call was made. But the assistant might be questioning whether the signal was received and processed correctly by the vast-manager. - The benchmark script exists and is executable. If benchmark.sh is missing or has incorrect permissions, the entrypoint might fail silently. - The log file is the authoritative source of truth. The assistant is using the log tail to understand what the script is doing, assuming the script writes all significant events to this log. One potential blind spot in the assistant's approach is that it's looking at the log file from an SSH session, not from within the container's execution context. The vast.ai platform's --ssh mode replaces the Docker ENTRYPOINT with its own init script, and the entrypoint is run via --onstart-cmd as a background nohup process. This means the entrypoint's stdout/stderr might be captured differently than in a normal Docker execution. The log file /var/log/entrypoint.log is created by the entrypoint script itself (via shell redirection), so it should be reliable, but the SSH session's environment might differ from the container's runtime environment.

Input Knowledge Required

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

1. The Filecoin proving stack — The concept of proof parameters (large binary files downloaded once and cached), the paramfetch tool, and the benchmark process that validates GPU proving performance.
2. The vast.ai platform — How instances are created, the --ssh vs --onstart-cmd distinction, how VAST_CONTAINERLABEL is injected, and the quirks of SSH-based container management.
3. The entrypoint script architecture — The three-phase lifecycle (paramfetch → benchmark → proving), the signaling mechanism to the vast-manager, and the logging setup.
4. The previous debugging context — The long history of platform-specific fixes (label matching, OOM issues, Docker build problems) that led to this deployment.
5. Unix process management — Understanding that a shell script (PID 369) can be alive but stuck, and that ps aux can reveal whether child processes have been spawned.

Output Knowledge Created

This message produces several important pieces of knowledge:

1. A confirmed symptom — The entrypoint is alive but stalled after param-done. This narrows the search space for the root cause.
2. A log data point — The log tail shows download progress, which either means the download is still ongoing (contradicting the user's earlier report) or the log is showing stale output. This ambiguity needs to be resolved.
3. A diagnostic direction — The assistant now needs to investigate what happens inside the entrypoint script after the param-done signal. Possible next steps include: examining the full log file (not just the tail), checking for error messages in the script's stderr, verifying that benchmark.sh exists and is executable, or attaching to the running entrypoint process to see what it's doing.
4. A platform-specific observation — The fact that the entrypoint is running but stuck highlights the fragility of the --onstart-cmd approach, where the script runs as a background process with no supervisor to restart it if it hangs.

The Broader Significance

This message is a classic example of the "last mile" problem in distributed systems deployment. The assistant had successfully navigated a maze of challenges: Docker build failures, platform-specific environment variable quirks, matching logic bugs in the management service, and database state corruption. The instance was created, the parameters were downloading, the management service was tracking it correctly—everything looked good. But the final transition from "setup complete" to "benchmark running" failed silently, with no error message, no crash, no obvious indicator of what went wrong.

This kind of failure is particularly insidious because it looks like success until you check for actual output. The system reports "benchmark started" but nothing happens. The process is alive but not progressing. The logs show the previous phase's output, not the current phase's activity. Debugging requires the operator to notice the absence of expected activity—the GPU not being utilized, the benchmark process not appearing in ps aux—and then trace backward to find where the pipeline broke.

The message also illustrates the importance of log design in distributed systems. The entrypoint script writes its progress to a log file, but the log's tail is dominated by high-frequency output from the download tool, potentially obscuring the critical transition point where the failure occurred. A well-designed logging system would separate high-volume operational output from state transition events, or would ensure that state changes are always the most recent entries.

Conclusion

Message 978 captures a moment of diagnostic pivot in a complex deployment. The assistant has moved from building and deploying infrastructure to investigating a runtime anomaly. The symptom is clear—a stalled entrypoint—but the cause remains hidden. The log tail provides a clue (download progress) but also raises questions (why is the log showing download output if the download completed?). The message ends with the assistant holding this data, ready to formulate the next diagnostic step.

What makes this message interesting is what it doesn't contain: a resolution. It's pure investigation, a snapshot of the reasoning process in real-time. The assistant has gathered a data point and is presenting it for consideration. The next message will likely build on this, perhaps by examining the entrypoint script itself, checking for file existence, or looking at the script's internal state. But in this moment, the assistant is simply observing, documenting, and preparing to dig deeper.