jenkins host key verification failed

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Troubleshooting "Jenkins Host Key Verification Failed" - A Deep Dive

The "Jenkins Host Key Verification Failed" error is a common stumbling block when setting up Jenkins to interact with remote servers, particularly over SSH. This error indicates that Jenkins cannot verify the authenticity of the remote server, which is crucial for maintaining security and preventing man-in-the-middle attacks. Let's break down why this happens, how to diagnose it, and most importantly, how to fix it with various strategies and code examples.

*Understanding the Problem: Host Key Verification and SSH*

*SSH (Secure Shell):* A network protocol used for secure communication between computers. It's widely used for remote access, command execution, and file transfer.
*Host Key:* When an SSH server starts, it generates a unique cryptographic key called the "host key." This key identifies the server to clients. The client (in this case, Jenkins) stores this key (or a fingerprint of it) in a known hosts file.
*Host Key Verification:* When an SSH client connects to a server for the first time (or after a change), it receives the server's host key. The client then compares this key with the key it has stored in its known hosts file. If the keys don't match, the client flags a warning (or, by default, an error) because something is amiss.
*Why the Error Occurs:* The "Host Key Verification Failed" error arises for several reasons:

1. *First Time Connection:* Jenkins has never connected to this remote server before, so it doesn't have the host key in its known hosts file.
2. *Server Host Key Changed:* The host key on the remote server has been changed. This can happen due to:
Reinstallation of the SSH server on the remote machine.
Replacing the remote server with a new one with a different host key.
In rare cases, a security compromise.
3. *Man-in-the-Middle Attack (Rare):* Someone is intercepting the communication an ...

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