IBM AIX 7.3 – Common Problem 225 – 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

Applications fail with shmat or ‘not enough space’ errors for shared memory segments.

Environment & Reproduction

Large in-memory databases (Oracle, DB2) on 32-bit applications or tight vmo limits.

ipcs -m
vmo -L | head
svmon -G

Root Cause Analysis

Per-process segment limits, 32-bit address space, or vmo memory tunables cap shared memory.

Quick Triage

Inspect IPC and vmo limits.

ipcs -m
vmo -L | head
svmon -G

Step-by-Step Diagnosis

Check process model (32 vs 64-bit) and EXTSHM/LDR_CNTRL usage.

file /opt/app/bin/app
env | grep -E 'EXTSHM|LDR_CNTRL'
vmo -L | grep -E 'minfree|maxfree'

Solution – Primary Fix

Enable EXTSHM or LDR_CNTRL=MAXDATA for the application and tune vmo as needed.

EXTSHM=ON LDR_CNTRL=MAXDATA=0x80000000 /opt/app/bin/app
vmo -p -o minfree=960
ipcs -m

Solution – Alternative Approaches

Rebuild the application 64-bit or migrate to an LPAR with larger memory.

Verification & Acceptance Criteria

Application allocates shared memory and ipcs reports expected segments.

ipcs -m
ps gv | head
svmon -P -O sortseg=shared

Rollback Plan

Remove EXTSHM/LDR_CNTRL settings if they affect stability of other apps.

unset EXTSHM LDR_CNTRL
/opt/app/bin/app
ipcs -m

Prevention & Hardening

Standardize on 64-bit binaries and document vmo tunables per workload.

Related Errors & Cross-Refs

Related to DB2 SQL30081N, Oracle ORA-27102, and paging activity spikes.

Related tutorial: View the step-by-step tutorial for aix-7.3.

View all aix-7.3 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

IBM AIX 7.3 shared memory and tunables reference.