Jenkins requires Java 8 or 11 (either a JRE or Java Development Kit (JDK)).

In Windows / Mac machine, download and install Oracle JDK 8.

In Linux based OS, use apt-get. It is a command-line tool which helps in handling packages in Linux. Here APT stands for the Advanced Packaging Tool.

The openjdk-8-jre package contains just the Java Runtime Environment. If you want to develop Java programs then please install the openjdk-8-jdk package.

$ sudo apt-get install openjdk-8-jre
$ sudo apt-get install openjdk-8-jdk

# Determining the default version of the JDK
$ java -version

• Download Jenkins

• Open up a terminal, and use following steps:

  $ cd ~/path-to-jenkins-war
  $ java -jar jenkins.war --httpPort=8080

• Browse to http://localhost:8080

• Follow the instructions to complete the installation

• First, we’ll add the repository key to the system:

  $ wget -q -O - https://pkg.jenkins.io/debian/jenkins-ci.org.key | sudo apt-key add -

• When the key is added, the system will return OK. Next, we’ll append the Debian package repository address to the server’s sources.list:

  $ echo deb https://pkg.jenkins.io/debian-stable binary/ | sudo tee /etc/apt/sources.list.d/jenkins.list

• When both of these are in place, we’ll run update so that apt-get will use the new repository:

  $ sudo apt-get update

• Finally, we’ll install Jenkins and its dependencies, including Java:

  $ sudo apt-get install jenkins

• Now that Jenkins and its dependencies are in place, we’ll start the Jenkins server.

• Using systemctl we’ll start Jenkins:

  $ sudo systemctl start jenkins

• Since systemctl doesn’t display output, we’ll use its status command to verify that it started successfully:

  $ sudo systemctl status jenkins

• Now that Jenkins is running, we’ll adjust our firewall rules so that we can reach Jenkins from a web browser to complete the initial set up.

• By default, Jenkins runs on port 8080, so we’ll open that port using ufw:

  $ sudo ufw allow 8080

• We can see the new rules by checking UFW’s status.

  $ sudo ufw status

• Note: If the firewall is inactive, the following commands will make sure that OpenSSH is allowed and then enable it.

  $ sudo ufw allow OpenSSH
  $ sudo ufw enable

• Now that Jenkins is installed and the firewall allows us to access it, we can complete the initial setup. Browse to http://ip_address_or_domain_name:8080 and follow the instructions to complete the installation