The Moment the Instance Vanished: A Diagnostic SSH Command That Revealed an OOM Kill

In the high-stakes world of distributed GPU proving for Filecoin, few events are as disorienting as reaching for a remote instance and finding nothing there. Message [msg 1117] captures precisely that moment: a simple SSH command, issued with the calm professionalism of a seasoned engineer, that silently fails because the target machine no longer exists. This message, outwardly mundane—a single bash invocation—sits at the inflection point between a partial success and a full system collapse, revealing the limits of a carefully engineered OOM mitigation strategy and triggering a cascade of discovery about what really happened to a 2× RTX 3090 instance running cuzk PoRep benchmarks.

The Context: An OOM Fix That Almost Worked

To understand why this message was written, one must trace the narrative arc of the preceding hours. The assistant had been locked in a battle with Out-of-Memory (OOM) failures that plagued GPU instances during the cuzk PoRep proving benchmark. The root cause was twofold: the daemon's initial Pre-Compiled Constraint Evaluator (PCE) extraction required enormous memory, and the benchmark concurrency was too aggressive for available system RAM. A fix had been deployed in benchmark.sh: detect the absence of a PCE cache, start the daemon with partition_workers=2 for the warmup proof, generate the PCE file, then restart with the full partition count for the actual timed benchmark.

The US instance (Vast.ai ID 32713080, 2× RTX 3090, 376 GB RAM) had been the testbed for this fix. Earlier messages documented its progress with cautious optimism. The warmup completed in 429 seconds—slow but stable. The PCE file was generated at 26 GB. The daemon restarted with partition_workers=10. The benchmark batch began: 12 PoRep proofs at concurrency 5. And then, silence.

The Message: A Diagnostic Probe Into the Void

The subject message itself is a single tool call:

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -p 33080 root@ssh1.vast.ai 'echo CONNECTED; tail -20 /var/log/entrypoint.log; echo "==="; ps aux | head -20' 2>/dev/null

This is a textbook diagnostic command. The -o StrictHostKeyChecking=no and -o UserKnownHostsFile=/dev/null flags are pragmatic choices for ephemeral cloud instances where host keys change on every deployment. The command constructs a three-part probe: first, a simple echo CONNECTED to confirm the SSH session is alive; second, a tail of the entrypoint log to see the most recent activity; third, a process listing to check what is still running. The 2>/dev/null suppresses SSH's own error messages, a common practice when the failure mode itself is the signal.

The message is the issuance of this command, not its result. In the opencode session protocol, all tool calls within a single message are dispatched together, and the assistant must wait for the next round to receive results. This means the assistant, at the moment of writing this message, does not yet know what the command will return. It is acting on a hypothesis: that the instance is still running, that the container survived the apparent OOM event, and that the logs will reveal what went wrong.

Why This Message Was Written: The Reasoning and Motivation

The immediate trigger was the discovery in [msg 1115] that the benchmark process had been killed. The assistant had checked memory (free -h showed 16 GB used out of 376 GB—a suspiciously low number that already hinted at a full container restart) but dmesg was unavailable inside the container. In [msg 1116], the assistant tried to check the entrypoint log and process list, but the output was not shown—perhaps the command hung or returned empty. The natural next step was to SSH directly into the instance and inspect its state firsthand.

The reasoning follows a classic debugging pattern: when a process disappears, check the logs for error messages, then check the process table for survivors. The entrypoint log (/var/log/entrypoint.log) is the central logging mechanism for the Docker container's lifecycle—it records param fetching, daemon starts and stops, benchmark phases, and any error conditions. The ps aux listing would reveal whether the daemon, the benchmark process, or the entrypoint script itself were still alive. Together, these two data sources would tell the assistant whether the OOM killed just the benchmark process (recoverable), the daemon (restartable), or the entire container (fatal).

Assumptions Embedded in the Command

The SSH command encodes several assumptions, most of which turned out to be incorrect:

The instance is still running. This is the foundational assumption. The assistant believes the container survived the OOM event, even if the benchmark process was killed. The echo CONNECTED probe is designed to quickly verify this, but the very act of issuing the SSH command assumes the host is reachable and the port is open.

The container's filesystem is intact. The assistant expects /var/log/entrypoint.log to exist and contain recent entries. If the container had been restarted by the host's OOM killer, the log might have been truncated or reset.

The SSH tunnel is still operational. The connection goes through ssh1.vast.ai on port 33080, which is Vast.ai's SSH gateway. The assistant assumes the tunnel established by portavailc (a port forwarding utility) is still active and that the vast platform hasn't reclaimed the instance.

The OOM killed only the benchmark process. The assistant's mental model, shaped by the successful warmup phase, is that the OOM fix works for the daemon but the benchmark concurrency might be too high. The diagnostic is aimed at tuning parameters, not at discovering a total system loss.

The Incorrect Assumption: When the Instance Vanishes

The result of this command, delivered in [msg 1118], is devastatingly brief:

ssh: connect to host ssh1.vast.ai port 33080: Connection refused

The instance is gone. Not just the benchmark process, not just the daemon—the entire container. The host's OOM killer, faced with a memory allocation that exceeded even 376 GB of RAM, terminated the container entirely. The Connection refused error means the SSH gateway no longer has a tunnel to forward traffic to. The instance has been destroyed at the infrastructure level.

This discovery cascades through the next several messages. In [msg 1119], the assistant checks the vast-manager dashboard and finds no instances running. In [msg 1120], vastai show instances --raw returns an empty array. In [msg 1121], the manager dashboard reveals the full picture: all three instances are in killed state, their kill_reason fields reading "bench_rate 0.0 below min_rate 50.0" or similar. The US instance's benchmark produced zero completed proofs before being destroyed, and the lifecycle management code—recently fixed to destroy underperforming instances—had done its job.

Input Knowledge Required

To fully understand this message, one needs knowledge of several systems:

The cuzk proving stack: cuzk is a GPU-accelerated proving engine for Filecoin's Proof-of-Replication (PoRep) consensus mechanism. It uses partition workers to parallelize proof synthesis across GPU cores, and the PCE (Pre-Compiled Constraint Evaluator) is a cache that accelerates repeated constraint evaluations.

Vast.ai infrastructure: Vast.ai is a marketplace for renting GPU instances. Instances are accessed via SSH through a gateway (ssh1.vast.ai) on a mapped port. The portavailc tool establishes reverse tunnels for internal services.

The benchmark pipeline: benchmark.sh orchestrates the proving benchmark, managing daemon lifecycle, warmup proofs, and timed batch runs. entrypoint.sh is the Docker container's init script, handling param fetching, daemon startup, and lifecycle coordination.

The OOM mitigation strategy: The fix deployed earlier used reduced partition workers during PCE extraction to avoid memory spikes, then restarted with full workers for the actual benchmark.

Output Knowledge Created

The message itself produces no output—it is a probe whose result arrives in the next round. But the failure of this probe creates critical knowledge:

  1. The OOM fix was insufficient. The warmup phase succeeded with reduced workers, but the benchmark phase with full workers and concurrency=5 consumed more memory than 376 GB could provide. The memory model underestimated the peak demand of 5 concurrent proofs × 10 partition workers.
  2. The container-level OOM kill is a new failure mode. Earlier OOM events killed individual processes; this one destroyed the entire container. This changes the debugging approach: there are no logs to inspect, no core dumps to analyze, no process trees to examine.
  3. The lifecycle management code is working. The vast-manager's handleBenchDone endpoint correctly detected the zero bench rate and destroyed the instance, preventing wasted expenditure on a dead container.
  4. The hardware-aware configuration needs refinement. The dynamic formula that set partition_workers=10 and concurrency=5 for a 376 GB machine was too aggressive. A new model is needed, one that accounts for the multiplicative memory demand of concurrent proofs.

The Thinking Process Visible in the Reasoning

The assistant's diagnostic chain reveals a methodical, hypothesis-driven approach. After discovering the benchmark was killed ([msg 1115]), the assistant first tries the most direct diagnostic tool (dmesg), which fails because it's unavailable in the container. The assistant then tries a two-step investigation: check the entrypoint log and check running processes ([msg 1116]). When that command's output is not visible (perhaps it returned empty or timed out), the assistant escalates to a direct SSH probe.

The choice of commands within the SSH session is telling. The echo CONNECTED is a heartbeat check—a quick verification that the session is alive before investing time in heavier commands. The tail -20 of the entrypoint log is the primary diagnostic target, expected to contain the daemon's final messages before the crash. The ps aux | head -20 is a secondary probe to assess the system's state: if the daemon is still running, the OOM killed only the benchmark client; if the daemon is gone too, the OOM was more severe; if the entrypoint script is gone, the container may have restarted.

The assistant does not yet know that the instance has been destroyed. The SSH command is written with the expectation of success, with the 2>/dev/null suppression of errors indicating that failure is considered a low-probability edge case. The subsequent discovery that the instance is completely gone will force a fundamental reassessment of the memory model and the OOM mitigation strategy.

Conclusion

Message [msg 1117] is a moment of diagnostic innocence—a carefully constructed probe sent into a system that no longer exists. It represents the boundary between controlled experimentation and catastrophic failure, between the assumption that a fix is working and the discovery that it has only shifted the failure mode to a more destructive form. The SSH command itself is technically unremarkable, but its failure reverberates through the remainder of the session, forcing a pivot from tuning parameters to redesigning the entire approach to hardware-aware configuration. In the end, this single failed connection would help drive the development of a data-driven experimental system for automatic hardware discovery, transforming a moment of loss into the seed of a more robust architecture.