CentOS Stream 9 – Common Problem 108 – Diagnosis and Fix

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Legacy monitoring or container tools fail because /sys/fs/cgroup/memory is missing.

Environment & Reproduction

CentOS Stream 9 enables unified cgroups v2 by default.

Root Cause Analysis

Old agents read v1 hierarchies that no longer exist.

Quick Triage

stat -f /sys/fs/cgroup shows cgroup2fs magic.

Step-by-Step Diagnosis

systemd-cgls and grep cgroup /proc/mounts confirm v2 mode.

Solution – Primary Fix

Upgrade the agent to a v2-aware release.

Solution – Alternative Approaches

Boot kernel with systemd.unified_cgroup_hierarchy=0 via grubby to restore v1 temporarily.

Verification & Acceptance Criteria

Agent reports memory/cpu metrics matching systemd-cgtop.

Rollback Plan

grubby –update-kernel ALL –remove-args=systemd.unified_cgroup_hierarchy=0 to revert.

Prevention & Hardening

Plan agent upgrades before adopting Stream 9 at scale.

Related Errors & Cross-Refs

Related: Docker storage driver and runc cgroup driver mismatch.

Related tutorial: View the step-by-step tutorial for centos-stream-9.

View all centos-stream-9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

kernel.org cgroup-v2 docs and Red Hat release notes.