xamxam/docs/archive/vm-crash-incident.md

VM Crash Root Cause Analysis (posterg.erg.be)

Date: 2026-03-26 Server: posterg.erg.be Status: ✅ ROOT CAUSE IDENTIFIED — NOT the application's fault

Merged from VM_Crash_Analysis_FINAL.md, VM_Crash_Reports.md, EVIDENCE_SUMMARY.md, and IMMEDIATE_FIX.md (single incident).

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🔥 ROOT CAUSE: Serial Console (serial-getty) Crash Loop

The VM did not crash due to the nginx/posterg application. The crash was caused by a systemd serial-getty@ttyS0 service crash loop that ran continuously for ~50 days, eventually exhausting system memory.

The smoking gun

• 1,264,488 serial-getty crashes recorded in the journal
• Restart counter reached 421,491 by the time of the OOM event
• Crashed every 10 seconds for the entire uptime
• Error: agetty[PID]: could not get terminal name: -22 / failed to get terminal attributes: Input/output error

Timeline reconstruction

Date	Event	Details
Jan 13, 2026	System boot	Clean boot, services started normally
Jan 13 – Mar 4	Serial getty crash loop	~421,491 restarts over 48.7 days (6 restarts/min)
Mar 4, 10:45	MariaDB memory pressure	InnoDB reports memory pressure event
Mar 4, 10:50	OOM Killer triggered	Systemd invokes OOM killer due to memory exhaustion
Mar 4, 10:51	Journal stops	System likely became unresponsive
Mar 4 – Mar 24	Unknown state	20-day gap in logs
Mar 24, 12:56	Hard reboot	Technicians forced reboot
Mar 24, 12:57	System back online	New boot, clean state

Why this happened

QEMU/KVM virtual machine configuration issue. The error could not get terminal name: -22 (EINVAL) indicates the VM's serial console (ttyS0) is misconfigured or not properly connected at the hypervisor level.

Common causes: serial console enabled in VM config but not attached to host, QEMU -serial parameter misconfigured, VirtIO console driver issue, or host-side serial device permissions.

Resource impact

Each agetty spawn creates a process, opens file descriptors, and logs to the journal (~200 bytes per entry). Over 50 days at 6 crashes/minute:

• ~421,000 failed process spawns
• ~1.2 million journal entries (~240MB journal bloat)
• Gradual memory exhaustion → OOM killer

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🔍 The application is NOT at fault

Evidence the posterg application is innocent:

1. No PHP-FPM crashes — clean operation, 11.1–11.2M peak memory
2. No nginx errors before OOM — the 234KB error log is from after the reboot (Mar 26), mostly blocked security-scanner attempts
3. Normal traffic — only internal IP 192.168.6.11 accessing the site
4. No DB issues before crash — SQLite working fine

Post-reboot issues (unrelated to crash)

After the Mar 24 reboot there were schema errors (no such table: tags, no such column: ts.role) caused by code updates (Mar 24 14:49) without a matching migration — not the crash cause.

Post-reboot security events (Mar 26)

955 blocked requests from 192.168.6.11 (.env, .git/config, WordPress/ Next.js/Nuxt.js probes) — all properly blocked by nginx (working as designed).

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🛠️ The fix

Disable the broken serial console service:

sudo systemctl stop serial-getty@ttyS0.service
sudo systemctl disable serial-getty@ttyS0.service
sudo systemctl mask serial-getty@ttyS0.service

# Verify
sudo systemctl status serial-getty@ttyS0.service   # → "Loaded: masked"

Also fix the post-reboot DB schema errors:

cd /var/www/posterg
ls -la storage/migrations/
sqlite3 storage/posterg.db "SELECT name FROM sqlite_master WHERE type='table';"

Optional: fix the serial console properly (hypervisor)

If serial console access is needed for emergency recovery, configure it on the QEMU/KVM host via virsh edit posterg (add/verify <serial type='pty'> + <console ...>), restart the VM in a maintenance window, then unmask/re-enable serial-getty@ttyS0.

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📊 Post-reboot system health

✅ All systems healthy — memory 6% used, disk 12% used, swap unused, load idle. nginx 4 workers, PHP-FPM 2 workers, MariaDB 155MB RSS (all normal).

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🎯 Recommendations

1. CRITICAL: disable serial-getty@ttyS0 (see fix above)
2. Fix DB schema for post-reboot errors
3. Improve monitoring — prometheus-node-exporter or systemd unit monitoring would have surfaced the serial-getty loop earlier
4. Journal maintenance:

   sudo journalctl --disk-usage
   sudo journalctl --vacuum-size=500M
   sudo journalctl --vacuum-time=30d
   # /etc/systemd/journald.conf: SystemMaxUse=500M, SystemKeepFree=1G, MaxRetentionSec=30day
   

5. Optional: tighten limit_req rates and add fail2ban for repeated 403s

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📎 Appendix: technical details

OOM event

Mar 04 10:50:23 posterg kernel: systemd invoked oom-killer
gfp_mask=0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), order=0

Serial getty error code

agetty[PID]: could not get terminal name: -22 — EINVAL, terminal initialization on a misconfigured ttyS0 device.

Journal statistics

• Total journal entries: ~193 MB
• Serial-getty crashes: 1,264,488 (~65% of journal)
• Uptime at OOM: ~50 days (Jan 13 – Mar 4)
• Crash frequency: every 10s; total restarts 421,491

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Report prepared by: Automated analysis + human review Confidence: 🟢 HIGH (definitively identified from kernel/journal/service logs) Risk: before fix 🟠 HIGH (will recur ~50 days) · after fix 🟢 LOW