Jenkins in digital ocean Linux server

To follow this tutorial, you will need:

• One Ubuntu 18.04 server configured with a non-root sudo user and firewall by following the Ubuntu 18.04 initial server setup guide. We recommend starting with at least 1 GB of RAM. See Choosing the Right Hardware for Masters for guidance in planning the capacity of a production Jenkins installation.
• Java 8 installed, following our guidelines on installing specific versions of OpenJDK on Ubuntu 18.04.

Installing Jenkins
Login by ssl

wget -q -O - https://pkg.jenkins.io/debian/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 update

sudo apt install jenkins

Start Jenkins

sudo systemctl start jenkins

sudo systemctl status jenkins

Output
● jenkins.service - LSB: Start Jenkins at boot time
   Loaded: loaded (/etc/init.d/jenkins; generated)
   Active: active (exited) since Mon 2018-07-09 17:22:08 UTC; 6min ago
     Docs: man:systemd-sysv-generator(8)
    Tasks: 0 (limit: 1153)
   CGroup: /system.slice/jenkins.service

Opening the Firewall

 sudo ufw allow 8080 

sudo ufw status

Output
Status: active

To                         Action      From
--                         ------      ----
OpenSSH                    ALLOW       Anywhere
8080                       ALLOW       Anywhere
OpenSSH (v6)               ALLOW       Anywhere (v6)
8080 (v6)                  ALLOW       Anywhere (v6)

Setting Up Jenkins

Browse http://your_server_ip_or_domain:8080

Get admin password and paste to the text field

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

The next screen presents the option of installing suggested plugins or selecting specific plugins:

We’ll click the Install suggested plugins option, which will immediately begin the installation process:

When the installation is complete, you will be prompted to set up the first administrative user.

Enter the name and password for your user:

You will see 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:

After confirming the appropriate information, click Save and Finish. You will see a confirmation page confirming that “Jenkins is Ready!”:

Click Start using Jenkins to visit the main Jenkins dashboard:

At this point, you have completed a successful installation of Jenkins.

More details https://www.digitalocean.com/community/tutorials/how-to-install-jenkins-on-ubuntu-18-04