IBM AIX 7.1 – Common Problem 115 – 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

ssh login to the AIX 7.2 LPAR pauses for 10-30 seconds before prompt.

Environment & Reproduction

AIX OpenSSH performing reverse DNS lookup on the client IP.

Root Cause Analysis

DNS server unreachable or PTR record missing for the client.

Quick Triage

Test name resolution with nslookup CLIENT_IP and host CLIENT_IP.

Step-by-Step Diagnosis

Confirm sshd config with cat /etc/ssh/sshd_config | grep -i useDNS.

Solution – Primary Fix

Set ‘UseDNS no’ in /etc/ssh/sshd_config and run stopsrc -s sshd; startsrc -s sshd.

Solution – Alternative Approaches

Fix or add the PTR record on the DNS server to keep UseDNS yes.

Verification & Acceptance Criteria

ssh login completes in under one second and auth.log shows no DNS delay.

Rollback Plan

Revert UseDNS yes after DNS health is restored if policy requires.

Prevention & Hardening

Monitor DNS health and document UseDNS posture across LPARs.

Related Errors & Cross-Refs

Pairs with GSSAPI auth delays if Kerberos lookups also stall.

Related tutorial: View the step-by-step tutorial for aix-7.1.

View all aix-7.1 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

IBM Docs: OpenSSH on AIX, sshd_config UseDNS option.