[SOLVED] How to Fix Jenkins Host Key Verification Failed Error - jenkins?

[SOLVED] Fixing the Jenkins Host Key Verification Failed Error

In this chapter, we will look at a common problem called the Jenkins Host Key Verification Failed Error. This error happens when Jenkins tries to connect to a remote server using SSH. It can cause issues in our Continuous Integration (CI) processes. But don’t worry, we have several ways to fix it easily. We will explain why this error happens and provide simple steps to help Jenkins connect safely without any breaks.

Solutions We Will Discuss:

What is the Host Key Verification Error
How to Add the Host Key Manually
How to Set Up SSH to Skip Host Key Check
How to Update the Known Hosts File in Jenkins
How to Use the Jenkins Credentials Plugin for SSH
How to Automate Host Key Verification in Jenkins Pipeline

By fixing the Jenkins Host Key Verification Failed Error, we can make our CI pipeline more reliable and secure. If we also want to learn how to set up Jenkins CI, we can check our guide on how to set up Jenkins CI with Git. For those who face permissions issues, our article on how to fix permission denied errors can help too. Now let’s explore each solution and get our Jenkins working again!

Part 1 - Understanding the Host Key Verification Error

We see the “Host Key Verification Failed” error in Jenkins when the SSH client does not know the remote server’s host key. This is a safety feature. It helps to stop man-in-the-middle attacks. When Jenkins tries to connect to a remote host using SSH, it checks the host’s key with the keys in the known_hosts file. If the key is missing or has changed, we get the error.

The error message usually looks like this:

Host key verification failed.

Key Points to Understand:

Host Key: This is a special ID for a server. It is like a digital fingerprint.
Known Hosts File: This file is at ~/.ssh/known_hosts. It keeps the fingerprints of hosts we connected to before.
Security Implication: If the host key changes, it could mean a possible security risk.

To fix this, we can add the new host key by hand. We can also set up Jenkins to skip the host key check. For more details on setting up Jenkins, please check this guide on setting up Jenkins CI.

Part 2 - Adding the Host Key Manually

To fix the Jenkins Host Key Verification Failed error, we can add the host key by hand. Here are the steps we need to follow:

Get the Host Key: First, we need to get the SSH host key from the remote server. We can do this by running this command on our local machine:
```
ssh-keyscan -H <remote-server-ip> >> ~/.ssh/known_hosts
```
We should change <remote-server-ip> to the real IP address or hostname of our Jenkins server.
Check the Key: Next, we need to make sure the key has been added correctly. We can check the known_hosts file by using:
```
cat ~/.ssh/known_hosts
```
We should look for the entry that matches our remote server.
Set Permissions: Now, we need to check the permissions of the .ssh folder and the known_hosts file. We can set them like this:
```
chmod 700 ~/.ssh
chmod 644 ~/.ssh/known_hosts
```
Restart Jenkins: If Jenkins is already running, we should restart it to make the changes take effect:
```
sudo systemctl restart jenkins
```
Test the Connection: Finally, we should test the SSH connection from our Jenkins server to the remote server:
```
ssh <remote-user>@<remote-server-ip>
```
This should work without asking for host key verification.

By adding the host key manually, we can fix the Jenkins Host Key Verification Failed error. For more info on setting up Jenkins, we can check how to set up Jenkins CI.

Part 3 - Configuring SSH to Bypass Host Key Check

We can bypass the host key check in Jenkins when we use SSH. To do this, we need to change our SSH settings. This is helpful when we have changing hosts or when we do not want to check host keys every time.

Change SSH Command: We can add the -o StrictHostKeyChecking=no option to our SSH command. This lets SSH connect without checking the host key.

Example command:
```
ssh -o StrictHostKeyChecking=no user@hostname
```
Change SSH Configuration File: We can also put this option in our SSH configuration file (~/.ssh/config). We add this setting:
```
Host *
    StrictHostKeyChecking no
```
This will apply to all hosts. So we need to be careful when we use it.

Jenkins Pipeline Example: If we use a Jenkins pipeline, we can add the SSH command like this:

stage('Deploy') {
    steps {
        sh 'ssh -o StrictHostKeyChecking=no user@hostname "your-command"'
    }
}

Environment Variables: We can also set environment variables in Jenkins. This can help us avoid host key checks for some builds:
```
environment {
    GIT_SSH_COMMAND = 'ssh -o StrictHostKeyChecking=no'
}
```

By using these methods, we can bypass the host key check error in Jenkins. For more details on Jenkins settings, we can check how to set up Jenkins CI.

Part 4 - Updating Known Hosts File in Jenkins

To fix the “Host Key Verification Failed” error in Jenkins, we can update the known hosts file by hand. This helps Jenkins to recognize and trust the SSH key of the remote server.

Find the Known Hosts File:
We usually find the known hosts file at ~/.ssh/known_hosts. Depending on your Jenkins setup, we may need to update the file for the user that Jenkins is running as.
Add the Host Key:
We use the command below to get the SSH key from the remote server and add it to the known hosts file:
```
ssh-keyscan -H <remote-server> >> ~/.ssh/known_hosts
```
Just replace <remote-server> with the real hostname or IP address of your server.
Check the Host Key:
We can look at the known hosts file to make sure the key has been added:
```
cat ~/.ssh/known_hosts
```
Set Permissions:
We need to check that the permissions for the known hosts file are right. The file should be readable and writable only by the user:
```
chmod 600 ~/.ssh/known_hosts
```
Restart Jenkins:
After we update the known hosts file, we should restart Jenkins to make the changes take effect:
```
sudo systemctl restart jenkins
```

This way should solve the host key verification error in Jenkins. For more info on setting up Jenkins, you can check this guide on setting up Jenkins CI.

Part 5 - Using Jenkins Credentials Plugin for SSH

To fix the Jenkins Host Key Verification Failed error with the Jenkins Credentials Plugin for SSH, we can follow these steps:

Install the Credentials Plugin:
- Go to Jenkins Dashboard then click on Manage Jenkins then Manage Plugins.
- Under Available tab, search for “Credentials” and install it.
Add SSH Credentials:
- Go to Jenkins Dashboard then Credentials then System then Global credentials (unrestricted) then Add Credentials.
- Choose “SSH Username with private key” from the Kind dropdown.
- Fill in the needed fields:
  - Username: Your SSH username.
  - Private Key: You can type your private key or select “Enter directly” to paste it.
  - ID: (Optional) A unique name for this credential.
- Click “OK” to save.
Use in Jobs:
- In your Jenkins job configuration, scroll to “Build Environment” section.
- Check “Use secret text(s) or file(s)” and select the credentials we just made from the dropdown.
Verify SSH Connection:
- Test your SSH connection to make sure it works without host key verification problems. You can run a shell command in the job:
```
ssh -o StrictHostKeyChecking=no user@host "echo SSH connection established"
```

By using the Jenkins Credentials Plugin, we can manage SSH credentials safely and avoid host key verification errors. For more related solutions, check out how to set up Jenkins CI and how to fix Jenkins CI pipeline errors.

Part 6 - Automating Host Key Verification in Jenkins Pipeline

We can automate host key verification in Jenkins Pipeline by using a script. This script adds the SSH host keys before running our SSH commands. This helps us avoid the “Host Key Verification Failed” error when our pipeline runs.

Here’s how we do it:

Use SSH Keyscan: We can use ssh-keyscan in our pipeline script. This will fetch and add host keys automatically.

pipeline {
    agent any
    stages {
        stage('Setup SSH Keys') {
            steps {
                script {
                    // Define the host
                    def host = 'your.remote.server'

                    // Use ssh-keyscan to add the host key to known_hosts
                    sh "ssh-keyscan -H ${host} >> ~/.ssh/known_hosts"
                }
            }
        }
        stage('Deploy') {
            steps {
                // Your deployment command using SSH
                sh "ssh user@${host} 'your deployment command'"
            }
        }
    }
}

Environment Variables: We need to check that the HOME environment variable is set. This will help the known_hosts file to be found.
```
environment {
    HOME = "/home/jenkins"
}
```

Error Handling: We should add error handling to deal with any problems when connecting via SSH.

try {
    sh "ssh user@${host} 'your command'"
} catch (Exception e) {
    error "SSH connection failed: ${e.message}"
}

By doing these steps, we can automate the host key verification in our Jenkins Pipeline. This way, our SSH commands run smoothly without needing us to do it manually.

For more details on Jenkins pipeline configurations, check our guide on how to fix Jenkins CI pipeline issues.

Frequently Asked Questions

1. What causes the Jenkins Host Key Verification Failed error?

We see the Jenkins Host Key Verification Failed error when Jenkins tries to connect to a remote server using SSH. This error happens when the server’s host key is not recognized. It can occur if the server’s key has changed or if we have not added the key to the known hosts file. For more help on fixing this error, check our article on how to fix Jenkins host key verification errors.

2. How can I add a host key manually in Jenkins?

To fix the Jenkins Host Key Verification Failed error, we can add the server’s host key to the known hosts file on the Jenkins server. We need to use SSH to connect to the server and accept the host key when it asks. For a simple guide, see our section on adding the host key manually.

3. Is it safe to bypass SSH host key verification in Jenkins?

Bypassing SSH host key verification can be risky. It may let attackers access your Jenkins instance. But if we trust the remote server, we can change SSH settings to skip this check. For more details on this, look at our section about configuring SSH to bypass host key check.

4. How do I update the known hosts file in Jenkins?

We need to update the known hosts file in Jenkins to avoid the Host Key Verification Failed error. We can do this by adding the remote server’s SSH key to the ~/.ssh/known_hosts file. For a full guide on updating the known hosts file, check our article on fixing Jenkins host key verification issues.

5. Can I automate host key verification in a Jenkins pipeline?

Yes, we can automate host key verification in a Jenkins pipeline. We can use scripts that manage SSH connections and handle the known hosts file. This way, our pipelines can run well without needing us to do it manually. For detailed steps on automating host key verification, please check our section on automating host key verification in Jenkins Pipeline.

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