Skip to main content

Jenkins

To get your Ubuntu remote agent ready for Jenkins, you'll need to run these commands on the remote machine (the agent) and one or two on your local machine (the controller).

Prepare the Remote Ubuntu Agent​

Install Java (OpenJDK 21)​

Jenkins requires Java to run the agent .jar file. Match this to your Jenkins controller's version.

sudo apt update
sudo apt install openjdk-21-jdk -y
# Verify installation
java -version

Managing Multiple Versions

sudo update-alternatives --config java

Create a Dedicated Jenkins User​

It is safer to run builds under a non-root user.

# Create a system user named 'jenkins' with a home directory
sudo adduser --system --group --home /home/jenkins jenkins

# Create the workspace directory for Jenkins
sudo mkdir -p /home/jenkins/agent
sudo mkdir /home/jenkins/.ssh
sudo touch /home/jenkins/.ssh/authorized_keys
sudo chown -R jenkins:jenkins /home/jenkins

# Run on the remote machine
ls -ld /home/jenkins/agent

# Change the shell to bash for the jenkins user
sudo chsh -s /bin/bash jenkins

The "No Password" Way (Most Common for Jenkins)

sudo visudo

Add this line to the very bottom of the file:

jenkins ALL=(ALL) NOPASSWD: ALL

Set Up SSH Access​

You need to allow your local Jenkins controller to log into the remote agent without a password.

# Open the SSH configuration file
sudo nano /etc/ssh/sshd_config

PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys

sudo systemctl restart ssh

On your LOCAL machine (Controller) Generate and Inject SSH Keys​

Since Jenkins is in a container, the private key needs to be accessible to the Jenkins UI so it can pass it to the remote agent.

# 1. Generate keys on your host
ssh-keygen -t ed25519 -f ~/jenkins_agent_key

# 2. Copy the public key to the remote agent
cat ~/jenkins_agent_key.pub
sudo nano /home/jenkins/.ssh/authorized_keys


# 3. View the PRIVATE key (you will copy-paste this into Jenkins UI)
cat ~/jenkins_agent_key
# Test the login manually
ssh -i ~/jenkins_agent_key jenkins@mdldocker.adrianoruseler.com

ssh -i ~/jenkins_agent_key jenkins@iot.adrianoruseler.com

ssh -i ~/jenkins_agent_key jenkins@moodleconf.ct.utfpr.edu.br

ssh -i ~/jenkins_agent_key jenkins@nupet.daelt.ct.utfpr.edu.br

ssh -i ~/jenkins_agent_key jenkins@mini.pc

ssh -i ~/jenkins_agent_key jenkins@docker.adrianoruseler.com

ssh -i ~/jenkins_agent_key jenkins@mysql.adrianoruseler.com

Remove jenkins user​

  • Stop Jenkins Processes
# Kill any processes owned by the 'jenkins' user
sudo pkill -u jenkins
  • Delete the User
# Remove the user and their home directory (/home/jenkins)
sudo deluser --remove-home jenkins
  • Re-creating the User (The "Clean" Way)
# 1. Create the user with a standard home and bash shell
sudo adduser jenkins --shell /bin/bash

# 2. Create the agent workspace
sudo mkdir -p /home/jenkins/agent
sudo chown -R jenkins:jenkins /home/jenkins/agent

# 3. Add your SSH key manually now while logged in as root
sudo mkdir -p /home/jenkins/.ssh
# Replace the string below with your actual public key
echo "ssh-ed25519 ..." | sudo tee /home/jenkins/.ssh/authorized_keys
sudo chown -R jenkins:jenkins /home/jenkins/.ssh
sudo chmod 700 /home/jenkins/.ssh
sudo chmod 600 /home/jenkins/.ssh/authorized_keys

# Add the Jenkins user to the Docker group (Recommended)
sudo usermod -aG docker jenkins

Configuration Reference​

When you go back to the Jenkins UI to add the node, use these paths based on the commands above:

  • Remote root directory: /home/jenkins/agent
  • Launch method: Launch agents via SSH
  • Host: [Your Remote IP]

Credentials: Select the SSH Private Key you generated in Step 2.

Host Key Verification Strategy​

Controls how Jenkins verifies the SSH key presented by the remote host whilst connecting.

  • Inside the Running Container (Direct)

If you don't want to hunt for volume paths, you can inject the key directly into the running container:

# 1. Enter the container as the jenkins user
docker exec -u jenkins -it <container_id_or_name> bash

# 2. Create the directory and the file
mkdir -p ~/.ssh
ssh-keyscan mysql.adrianoruseler.com >> ~/.ssh/known_hosts
ssh-keyscan moodleconf.ct.utfpr.edu.br >> ~/.ssh/known_hosts
ssh-keyscan docker.adrianoruseler.com >> ~/.ssh/known_hosts
ssh-keyscan iot.adrianoruseler.com >> ~/.ssh/known_hosts
ssh-keyscan mdldocker.adrianoruseler.com >> ~/.ssh/known_hosts

# 3. Secure the permissions
chmod 700 ~/.ssh
chmod 644 ~/.ssh/known_hosts