Add VM serial console logging for fast-cycle diagnosis#12
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VMs cycling in <60 seconds leave no trace of what failed inside them.
Firecracker's stdout (the serial console) was previously discarded.
- Add console=ttyS0 to DEFAULT_BOOT_ARGS so the VM's kernel and
systemd output goes to Firecracker's stdout
- Redirect Firecracker stdout to {work_dir}/console.log per slot
- After any cycle shorter than 60 seconds, log the last 40 lines of
the console to the manager journal so failures are visible without
manual intervention
- Include duration_secs in the "Firecracker exited" log line
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Problem
VMs cycle in ~1–2 seconds with
exit_code=0, but we have no visibility into what fails inside them. Firecracker's stdout (the VM serial console, where systemd/journald output goes) was discarded viaStdio::null().Changes
console=ttyS0added toDEFAULT_BOOT_ARGS— routes the VM kernel and systemd output to Firecracker's stdout (the serial console){work_dir}/console.logper slot — Firecracker stdout is now written to a file instead of/dev/nullslot.rs— after any cycle shorter than 60 seconds, the last 40 lines ofconsole.logare emitted to the manager journal at WARN level, with thecyclefield for correlationduration_secsadded to the "Firecracker exited" log line for easier cycle-length filteringEffect
journalctl -u actions-runnerwill now show the VM's systemd boot output, service start/stop messages, and any error fromconfig.shorrunner.serviceimmediately after each short cycle — no manual Firecracker test needed to diagnose failures.