🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026
Affected versions: RHEL 10

📖 ~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

SMB shares fail to mount with `mount error(126/13)` after auth stack updates.

Environment & Reproduction

Observed when CIFS uses sec=krb5 with stale keytabs or unsupported dialect options.

mount -t cifs //fileserver/share /mnt/share -o sec=krb5,cruid=$(id -u)
klist
rpm -q krb5-workstation cifs-utils

Root Cause Analysis

Kerberos ticket/keytab mismatch or SMB signing/dialect changes cause auth negotiation failure.

Quick Triage

Capture kernel and auth messages.

dmesg | tail -n 50
journalctl -n 80 --no-pager | grep -Ei 'cifs|krb5|gssapi'
getenforce

Step-by-Step Diagnosis

Validate keytab principal and mount options.

klist -k /etc/krb5.keytab
cat /etc/krb5.conf | head -n 80
modinfo cifs | head -n 20
Illustrative mockup for rhel-10 — terminal_or_shell
Reviewing mount.cifs and Kerberos failures — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Refresh Kerberos credentials and use compatible CIFS options.

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kdestroy || true
kinit [email protected]
sudo mount -t cifs //fileserver/share /mnt/share -o sec=krb5,vers=3.1.1,cruid=$(id -u)
Illustrative mockup for rhel-10 — log_or_config
Updating mount options and keytab configuration — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Use machine keytab principal for service mounts and automount retries.

sudo kinit -k -t /etc/krb5.keytab host/$(hostname -f)
systemctl restart autofs

Verification & Acceptance Criteria

Mount succeeds and file operations complete under expected identity.

mount | grep cifs
ls /mnt/share
touch /mnt/share/.cifs_test && rm -f /mnt/share/.cifs_test

Rollback Plan

Revert to previous tested mount options if new flags break compatibility.

sudo umount /mnt/share
sudo mount -a

Prevention & Hardening

Pin validated cifs-utils versions in change windows and monitor Kerberos ticket renewal.

dnf versionlock add cifs-utils
klist

Related to DNS SPN mismatches, clock skew, and SMB signing policy changes on AD servers.

Related tutorial: View the step-by-step tutorial for rhel-10.

View all rhel-10 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

RHEL CIFS and Kerberos integration documentation for secure enterprise file access.

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