Steps To install Jenkins on an Ubuntu system.

Update the System

update the system.

sudo apt update

Install Java

Jenkins requires Java to run, so you need to install OpenJDK.

sudo apt install openjdk-11-jdk -y

Verify the Java installation.

java -version

You should see an output like this

openjdk version "11.0.11" 2021-04-20

Add Jenkins Repository

Add the Jenkins repository key to your system.

curl -fsSL https://pkg.jenkins.io/debian/jenkins.io.key | sudo tee \
  /usr/share/keyrings/jenkins-keyring.asc > /dev/null

Add the Jenkins repository to your sources list.

echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] \
  https://pkg.jenkins.io/debian binary/ | sudo tee \
  /etc/apt/sources.list.d/jenkins.list > /dev/null

Install Jenkins

Now, update the package index again and install Jenkins.

sudo apt update
sudo apt install jenkins -y

Start and Enable Jenkins

Once Jenkins is installed, start the service and enable it to run at boot.

sudo systemctl start jenkins
sudo systemctl enable jenkins

Allow Jenkins Through Firewall (Optional)

If you're using a firewall (e.g., ufw), allow port 8080, which Jenkins uses by default.

sudo ufw allow 8080
sudo ufw reload

Access Jenkins

Jenkins runs on port 8080 by default; to access it, open a web browser and enter your server's IP address or domain name followed by :8080.

http://your_server_ip_or_domain:8080

Unlock Jenkins

When you first access Jenkins, it will prompt you for an Administrator Password, which you can retrieve using a specific command.

sudo cat /var/lib/jenkins/secrets/initialAdminPassword

Copy the password, paste it into the Jenkins setup page, and continue with the setup.

Complete Jenkins Setup

Install the suggested plugins or select specific plugins based on your needs.
Create an admin user.
Finish the setup.

Installation of Jenkins on ubuntu