📖 ~1 min read
Table of contents
Symptom & Impact
Applications fail file or socket access despite correct UNIX permissions, causing runtime errors.
Environment & Reproduction
Ubuntu 18.04 with AppArmor enabled and services like snap, nginx, or custom daemons constrained by profiles.
Root Cause Analysis
AppArmor policy denies a required path, capability, or network operation not permitted in active profile.
Quick Triage
Run sudo dmesg | grep DENIED and sudo journalctl -k to locate exact AppArmor rule violations.
Step-by-Step Diagnosis
Identify profile in complain/enforce mode with aa-status and map denied paths to service behavior.
Solution – Primary Fix
Adjust profile rules under /etc/apparmor.d, reload with apparmor_parser -r, and keep enforce mode after validating required access.
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Solution – Alternative Approaches
Temporarily switch affected profile to complain mode using aa-complain during controlled troubleshooting.
Verification & Acceptance Criteria
Service functions as expected with no new AppArmor DENIED events in kernel logs.
Rollback Plan
Restore previous profile version and reload AppArmor if behavior regresses.
Prevention & Hardening
Track profile changes in version control and review denials regularly instead of permanently relaxing enforcement.
Related Errors & Cross-Refs
Permission denied with clean filesystem ACLs, snap confinement errors, and denied capability logs.
Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.
View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
man apparmor, aa-status, and Ubuntu AppArmor profile management docs.
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