Ubuntu 24.04 LTS – unattended-upgrades causes sustained high CPU and I/O

📖 ~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

CPU and disk usage spike for long periods during automatic updates.

Environment & Reproduction

Seen on busy servers where maintenance tasks overlap.

ps -eo pid,cmd,%cpu,%mem --sort=-%cpu | head
iostat -xz 1 3

Root Cause Analysis

Unattended package downloads, unpacking, and triggers contend with workload I/O.

Quick Triage

Confirm unattended-upgrades is the dominant load source.

systemctl status unattended-upgrades --no-pager
sudo journalctl -u unattended-upgrades -n 80 --no-pager

Step-by-Step Diagnosis

Review timer schedules and overlap with peak workload windows.

systemctl list-timers --all | grep -E 'apt|unattended'
vmstat 1 5

Solution – Primary Fix

Reschedule apt timers and reduce update-step contention.

sudo systemctl edit apt-daily.timer
sudo systemctl edit apt-daily-upgrade.timer
sudo systemctl restart apt-daily.timer apt-daily-upgrade.timer

Solution – Alternative Approaches

Use manual maintenance windows for highly latency-sensitive hosts.

sudo systemctl disable --now unattended-upgrades
sudo apt-get update && sudo apt-get upgrade -y

Verification & Acceptance Criteria

Resource usage stays within acceptable limits during update cycles.

systemctl list-timers --all | grep apt
ps -eo cmd,%cpu --sort=-%cpu | head

Rollback Plan

Restore default timer settings if updates no longer execute reliably.

sudo systemctl revert apt-daily.timer apt-daily-upgrade.timer

Prevention & Hardening

Align update windows with low-traffic periods and monitor execution duration.

sudo unattended-upgrade --dry-run --debug

Related Errors & Cross-Refs

Related patterns include apt lock contention and delayed package processing.

Related tutorial: View the step-by-step tutorial for Ubuntu 24.04 LTS.

View all Ubuntu 24.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu unattended-upgrades and systemd timer documentation.