Prometheus Full Disk Crash Fix

The Week 32 Last Week in Cloud Native roundup called out Prometheus v3.13.2, a small patch release with a very practical PromQL bug fix: preallocating the active query tracker file to avoid SIGBUS crashes when the data disk is full.

That sounds narrow, but it points at a broad SRE rule. Observability components are production databases. They need disk budgets and failure-mode tests.

What Changed In Prometheus?

Prometheus keeps local time-series data on disk and runs PromQL queries against that storage. It also maintains an active query tracker file for in-flight queries.

In v3.13.2, Prometheus changed that tracker behavior so the file is preallocated. The release notes say this avoids SIGBUS crashes when the data disk is full. In Linux terms, SIGBUS can happen when a process touches memory mapped file pages that the filesystem cannot back with real storage.

The release also bumps dependencies for security fixes in golang.org/x/text and google.golang.org/grpc, so the patch is worth scheduling even if you have not seen this crash.

Why SREs Should Care

Prometheus is often treated as a safety net, but it has its own blast radius. If the data volume fills during an incident, restarts can break dashboards, alerts, and forensic timelines.

A disk-full condition can come from traffic growth, label cardinality mistakes, runaway scrape targets, remote write backpressure, retention changes, or a node-level storage issue. Detect it before responders depend on the affected Prometheus server.

Upgrade Check

Start by checking your running version and disk headroom:

prometheus --version
df -h /prometheus
du -sh /prometheus/* 2>/dev/null | sort -h | tail

If you run Prometheus through Helm or an operator, pin the image tag instead of floating on a broad version range:

prometheus:
  prometheusSpec:
    image:
      tag: v3.13.2

Then roll one environment first. Watch process restarts, WAL replay time, query latency, rule evaluation duration, and remote write queues before continuing to production.

Disk Failure Runbook

Treat Prometheus disk alerts as paging signals, not cleanup chores.

• Alert when free bytes and free inode percentage fall below your tested floor.
• Alert on fast disk growth over 30 to 60 minutes.
• Track high-cardinality series growth after deploys.
• Keep retention and retention-size settings explicit.
• Document which data can be dropped during emergency recovery.
• Test a restore or replacement path for every critical Prometheus shard.

Also keep dashboards that do not depend only on the same Prometheus instance. Node-level disk health, Kubernetes volume status, and Prometheus process health need an independent path during incident response.

Conclusion

Prometheus v3.13.2 is a small patch with a useful reminder: monitoring databases fail like databases. Upgrade for the SIGBUS fix, then use it as a prompt to review disk alerts, retention settings, and recovery drills.

If your team wants AI-assisted incident workflows built on reliable operational context, Akmatori helps SRE teams investigate alerts, coordinate response, and automate safe infrastructure actions. Powered by Gcore for global infrastructure reliability.