🟡 Medium   ⏱ 5–30 min  Last verified: 20 May 2026
Affected versions: CentOS Stream 9

📖 ~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 client errors ‘no matching host key type found’ against older servers.

Environment & Reproduction

Stream 9 OpenSSH 8.x disables ssh-rsa with SHA-1 by default.

Root Cause Analysis

Legacy peers only offer ssh-rsa with SHA-1 signatures.

Quick Triage

ssh -vv shows host key algorithm negotiation.

Step-by-Step Diagnosis

sshd_config and ssh_config defaults under /etc/ssh/.

Illustrative mockup for centos-stream-9 — ssh_rsa_diag
Diagnostic view for ssh-rsa-host-key-deprecated — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Add ‘PubkeyAcceptedAlgorithms +ssh-rsa’ and ‘HostKeyAlgorithms +ssh-rsa’ in /etc/ssh/ssh_config.d/.

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Illustrative mockup for centos-stream-9 — ssh_rsa_fix
Remediation steps for ssh-rsa-host-key-deprecated — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Upgrade or regenerate ed25519/rsa-sha2-512 host keys on the peer.

Verification & Acceptance Criteria

ssh connects without algorithm errors.

Rollback Plan

Remove the drop-in to restore strict defaults.

Prevention & Hardening

Plan host-key migration to ed25519 across the fleet.

Related: crypto-policies LEGACY profile and FIPS mode.

Related tutorial: View the step-by-step tutorial for centos-stream-9.

View all centos-stream-9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

OpenSSH release notes and Red Hat crypto policies guide.

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