"Use of Uninitialized Value" Failure in Spectrum NCM After Upgrade

Products

• Network Observability
• Spectrum

Issue/Introduction

This article addresses the "Use of Uninitialized Value" error encountered in NCM following an upgrade.

Symptoms

• NCM config capture fails.
• Error message: "Use of Uninitialized Value" reported in NCM logs or UI.
• The known_hosts file is missing or empty in the expected SSH directory ($SPECROOT/NT-Tools/SRE/home/spectrum/.ssh).

Environment

Windows based Spectrum Installations

Cause

This error typically indicates a failure in SSH host key verification, specifically when the known_hosts directory or file is missing or inaccessible, preventing Spectrum from automatically updating host keys.

The known_hosts file is missing and the ssh configuration was reverted

Resolution

To work around or recover from this issue, you can modify the SSH configuration file to disable strict host key checking.

1. Navigate to the SSH configuration directory: $SPECROOT/NT-Tools/SRE/home/spectrum/.ssh
2. Ensure you are logged in as the Spectrum install user to avoid permission issues.
3. Open the config file for editing.
4. Add the following lines to the file:
Host *
     KexAlgorithms +diffie-hellman-group1-sha1
     StrictHostKeyChecking no
5. Save the file and verify there are no syntax errors.
6. Restart the necessary Spectrum services if the change does not take effect immediately.
7. Attempt an NCM config capture to verify the issue is resolved.

 

Resolution Additional Notes

• Ensure that the StrictHostKeyChecking parameter is typed correctly, as typos in the configuration file will prevent the workaround from functioning.
• This issue is primarily observed on Windows-based deployments where SSH management differs from Linux.