Jenkins Installation on Ubuntu 20.04: Step by Step Procedure:

Step 1 – Installing the Default JRE/JDK:

• The easiest option for installing Java is to use the version packaged with Ubuntu. By default, Ubuntu 20.04 includes Open JDK 11, which is an open-source variant of the JRE and JDK.
• To install this version, first update the package index:
  • sudo apt update
• Next, check if Java is already installed:
  • java -version
• If Java is not currently installed, you’ll see the following output:
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• Execute the following command to install the default Java Runtime Environment (JRE), which will install the JRE from OpenJDK 11:
  • sudo apt install default-jre
• The JRE will allow you to run almost all Java software.
• Verify the installation with:
  • java -version
• You’ll see output similar to the following:
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• You may need the Java Development Kit (JDK) in addition to the JRE in order to compile and run some specific Java-based software. To install the JDK, execute the following command, which will also install the JRE:
  • sudo apt install default-jdk
• Verify that the JDK is installed by checking the version of javac, the Java compiler:
  • javac -version

Step 2 – Installing Jenkins:

• The version of Jenkins included with the default Ubuntu packages is often behind the latest available version from the project itself. To ensure you have the latest fixes and features, use the project-maintained packages to install Jenkins.
• First, add the repository key to the system:
  • wget -q -O – https://pkg.jenkins.io/debian-stable/jenkins.io.key | sudo apt-key add –
• After the key is added the system will return with OK.
• Next, let’s append the Debian package repository address to the server’s sources.list:
  • sudo sh -c ‘echo deb http://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list’
• After both commands have been entered, we’ll run update so that apt will use the new repository.
  • sudo apt update
• Finally, we’ll install Jenkins and its dependencies.
  • sudo apt install jenkins
• Now that Jenkins and its dependencies are in place, we’ll start the Jenkins server.

Step 3 – Starting Jenkins:

• Let’s start Jenkins by using systemctl:
  • sudo systemctl start jenkins
• Since systemctl doesn’t display status output, we’ll use the status command to verify that Jenkins started successfully:
  • sudo systemctl status jenkins
• If everything went well, the beginning of the status output shows that the service is active and configured to start at boot:
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• Now that Jenkins is up and running, let’s adjust our firewall rules so that we can reach it from a web browser to complete the initial setup.

Step 4 – Opening the Firewall:

• To set up a UFW firewall, visit Initial Server Setup with Ubuntu 20.04, Step 4- Setting up a Basic Firewall. By default, Jenkins runs on port 8080. We’ll open that port using ufw:
  • sudo ufw allow 8080
• Note: If the firewall is inactive, the following commands will allow OpenSSH and enable the firewall:
  • sudo ufw allow OpenSSH
  • sudo ufw enable
• Check ufw’s status to confirm the new rules:
  • sudo ufw status
• You’ll notice that traffic is allowed to port 8080 from anywhere:
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• With Jenkins installed and our firewall configured, we can complete the installation stage and dive into Jenkins setup.

Step 2 – Setting Up Jenkins:

• To set up your installation, visit Jenkins on its default port, 8080, using your server domain name or IP address: http://your_server_ip_or_domain:8080
• You should receive the Unlock Jenkins screen, which displays the location of the initial password:
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• In the terminal window, use the cat command to display the password:
  • sudo cat /var/lib/jenkins/secrets/initialAdminPassword
• Copy the 32-character alphanumeric password from the terminal and paste it into the Administrator password field, then click Continue.
• The next screen presents the option of installing suggested plugins or selecting specific plugins:
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• We’ll click the Install suggested plugins option, which will immediately begin the installation process.
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• When the installation is complete, you’ll be prompted to set up the first administrative user. It’s possible to skip this step and continue as admin using the initial password we used above, but we’ll take a moment to create the user.
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• Enter the name and password for your user:
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• You’ll receive an Instance Configuration page that will ask you to confirm the preferred URL for your Jenkins instance. Confirm either the domain name for your server or your server’s IP address:
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• After confirming the appropriate information, click Save and Finish. You’ll receive a confirmation page confirming that “Jenkins is Ready!”:
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• Click Start using Jenkins to visit the main Jenkins dashboard:
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