Jenkins

Installation Steps for Ubuntu:

Installing the Default JRE/JDK
sudo apt install default-jdk

Example:
ptn@ptn-virtual-machine:~$ sudo apt install default-jdk
ptn@ptn-virtual-machine:~$ javac -version
javac 11.0.14.1

Installing Jenkins
wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key | sudo apt-key add -

sudo sh -c 'echo deb http://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'

sudo apt install jenkins

htttp://localhost:8080
sudo cat /var/lib/jenkins/secrets/initialAdminPassword

References:
https://www.digitalocean.com/community/tutorials/how-to-install-jenkins-on-ubuntu-20-04

Install Docker
https://docs.docker.com/engine/install/ubuntu/

https://www.digitalocean.com/community/tutorials/how-to-set-up-continuous-integration-pipelines-in-jenkins-on-ubuntu-16-04