RHEL 10 – swap not activating after reboot causing memory pressure – Fix & Prevention

📖 ~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

OOM events increase and workload stability declines under memory spikes.

Environment & Reproduction

Common after disk migration or UUID changes to swap partitions/files.

swapon --show
free -h
cat /etc/fstab

Root Cause Analysis

Invalid fstab swap entry, missing swap signature, or SELinux label mismatch on swapfile.

Quick Triage

Confirm swap device visibility and activation errors.

lsblk -f
blkid | grep swap
journalctl -xb | grep -i swap

Step-by-Step Diagnosis

Validate swap signature and fstab mapping.

file -s /dev/vdb2
awk '!/^#/ && /swap/' /etc/fstab
findmnt --verify

Solution – Primary Fix

Recreate swap signature and enable entry persistently.

mkswap /dev/vdb2
swapon /dev/vdb2
vi /etc/fstab

Solution – Alternative Approaches

Create a dedicated swapfile when partition changes are impractical.

fallocate -l 4G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile

Verification & Acceptance Criteria

Swap appears active before and after reboot.

swapon --show
free -h
reboot

Rollback Plan

Disable new swap target and restore previous configuration if performance degrades.

swapoff -a
cp -a /etc/fstab.bak /etc/fstab
swapon -a

Prevention & Hardening

Track fstab and storage UUID changes during infrastructure updates.

blkid
cp -a /etc/fstab /etc/fstab.bak

Related Errors & Cross-Refs

Can coincide with kernel OOM kills and cgroup memory limit pressure.

Related tutorial: View the step-by-step tutorial for rhel-10.

View all rhel-10 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

RHEL memory management and swap provisioning best practices.