Ubuntu 22.04 Samba Share Permission Denied with POSIX ACL Mismatch

📖 ~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

Users authenticate to Samba but receive permission denied on file read/write operations.

Environment & Reproduction

Ubuntu 22.04 file server using smbd with POSIX ACLs and mixed local/group ownership patterns.

Root Cause Analysis

Samba share permissions and underlying filesystem ACLs diverge, so SMB auth succeeds but file access checks fail.

Quick Triage

Check smb.conf share directives, run testparm, and inspect path ownership/ACLs with ls -l and getfacl.

Step-by-Step Diagnosis

Correlate Samba log entries with effective UNIX permissions and ACL inheritance behavior on target directories.

Solution – Primary Fix

Normalize directory ownership, apply consistent setfacl defaults, and align Samba create mask/force group settings.

Solution – Alternative Approaches

Use dedicated service groups per share, enable vfs_acl_xattr for AD environments, or simplify permission model.

Verification & Acceptance Criteria

Authorized users can read/write as intended while unauthorized users remain blocked according to policy.

Rollback Plan

Restore prior ACL snapshots and smb.conf backup if new permission model causes access regression.

Prevention & Hardening

Template share provisioning, enforce ACL standards, and audit Samba permissions after identity/group changes.

Related Errors & Cross-Refs

Related Ubuntu 22.04 file service issues include UID/GID mapping drift and stale credential cache behavior.

Related tutorial: View the step-by-step tutorial for Ubuntu 22.04 LTS.

View all Ubuntu 22.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Samba HOWTO, man smb.conf, man setfacl/getfacl, and Ubuntu server file-sharing documentation.