Day 68 · Jenkins

Set Up Jenkins Server

By Published Updated Jenkins~1h to complete

Technical Overview

Deploying a continuous integration and continuous deployment (CI/CD) server like Jenkins requires setting up a Java runtime environment (JRE) and configuring official package repositories to ensure clean lifecycle management.

Jenkins operates as a standalone Java application hosting its own embedded servlet container (Jetty). In a standard Linux infrastructure, installing Jenkins involves:

  1. Java Environment Provisioning: Installing a supported Java Runtime Environment (JRE).
  2. Package Repository Configuration: Adding the official Jenkins Debian repository and registering its GPG key to verify package signatures.
  3. Daemon Integration: Managing Jenkins as a background service via system init scripts (service or systemctl).
  4. Initial Setup Wizard: Unlocking the application using a generated file-based secret, installing baseline plugins, and creating the master admin user account.
graph TD subgraph ClientSystem ["Client System"] User["CI/CD Administrator"] end subgraph TargetServer ["Jenkins Target Server"] APT["APT Package Manager"] Java["OpenJDK 21 JRE"] JenkinsService["Jenkins Daemon on Port 8080"] JenkinsKeyring["GPG Keyring File"] JenkinsSource["Jenkins Source File"] SecretPath["Unlock Keyfile Secret"] SetupWizard["Web Setup Wizard"] end APT -->|Installs| Java APT -->|Installs| JenkinsService JenkinsKeyring -.->|Verifies Signatures| APT JenkinsSource -.->|Configures Repo| APT SecretPath -->|Unlock Code| SetupWizard User -->|SSH as root| APT User -->|HTTP Access| SetupWizard

Debian Repositories & Java Service Architecture Deep Dive

1. Secure Package Management with APT GPG Keys

Debian-based distributions use GPG (GNU Privacy Guard) keys to sign package metadata. This guarantees that packages installed using apt have not been tampered with.

  • Keyring Registry: GPG keys are downloaded and saved into a secure keyring directory (such as /etc/apt/keyrings/).
  • Sources List Configuration: The repository definition /etc/apt/sources.list.d/jenkins.list is configured with a signed-by option pointing directly to this keyring. When apt update runs, the package manager checks the downloaded package metadata against this local key.

2. Servlet Containers & JRE Prerequisites

Jenkins is written in Java and runs inside a servlet container.

  • Version Compatibility: Modern versions of Jenkins require Java 17 or Java 21. Running Jenkins on unsupported versions of Java will cause compilation errors or application failure upon startup.
  • Dependency Management: The openjdk-21-jre package installs the core Java Virtual Machine (JVM). Additionally, graphic libraries (e.g., fontconfig) are installed to support PDF rendering, graph generation, and user interface elements.

Infrastructure & Configuration Requirements

  • Target Server Hostname: jenkins
  • User Credentials: root (Password: S3curePass)
  • Installation Utility: apt (Debian-based package manager)
  • Service Manager: service CLI utility

Jenkins Admin User Specification

  • Username: theadmin
  • Password: Adm!n321
  • Full Name: Rose
  • E-mail Address: rose@jenkins.stratos.xfusioncorp.com

Step-by-Step Installation

Step 1: Connect to the Jenkins Server

Establish an SSH connection to the destination server using the target host and credentials:

ssh root@jenkins
# Enter password: S3curePass

Step 2: Install Java Runtime Environment (JRE)

Update the package registry index and install the OpenJDK runtime dependency along with system font helpers:

sudo apt update
sudo apt install -y fontconfig openjdk-21-jre

Verify that the JVM has been successfully added to the executable search path:

java -version

Expected Output:

openjdk version "21.0.x" ...
OpenJDK Runtime Environment ...
OpenJDK 64-Bit Server VM ...

Step 3: Add the Official Jenkins Repository

Download and save the Jenkins repository GPG key into the system keyrings directory:

sudo wget -O /etc/apt/keyrings/jenkins-keyring.asc https://pkg.jenkins.io/debian-stable/jenkins.io-2026.key

Add the Jenkins package repository source file pointing to the keyring:

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

Step 4: Install Jenkins Package

Update the package source cache to discover the new Jenkins repository index, then install the package:

sudo apt update
sudo apt install -y jenkins

Step 5: Start the Jenkins Daemon Service

Start the Jenkins background service using the system init CLI utility:

# Check initial status
service jenkins status

# Start the background daemon
service jenkins start

Confirm that the service is running and listening on default port 8080:

service jenkins status

Expected Output:

● jenkins.service - LSB: Start Jenkins at boot time
     Loaded: loaded (/etc/init.d/jenkins; generated)
     Active: active (running) since Wed 2026-07-22 20:25:00 UTC; 10s ago
     ...

Initial Setup Wizard Walkthrough

Step 1: Retrieve the Initial Admin Password

To unlock the Jenkins administrative interface, read the generated unique password hash from the local filesystem:

cat /var/lib/jenkins/secrets/initialAdminPassword

Expected Output:

a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6

Copy the output hash, paste it into the Administrator password field on the Jenkins landing page (http://<server-ip>:8080), and click Continue.

Unlock Jenkins

Step 2: Install Suggested Plugins

On the customize page, click the Install suggested plugins option. This installs basic plugins for source control (Git), pipelines, credentials management, and node configurations.

Customize Jenkins

The setup wizard will begin installing the baseline set of plugins:

Installing Plugins

Step 3: Create the Admin Account

In the Create First Admin User screen, fill out the form using the exact configurations required:

  • Username: theadmin
  • Password: Adm!n321
  • Confirm password: Adm!n321
  • Full name: Rose
  • E-mail address: rose@jenkins.stratos.xfusioncorp.com

Click Save and Continue.

Create First Admin User

Step 4: Complete Instance Configuration

  1. Verify that the Jenkins URL is auto-detected correctly (e.g., http://jenkins:8080/ or the server's IP address).

Instance Configuration

  1. Click Save and Finish.
  2. Click Start using Jenkins to log into the main Jenkins dashboard.

Jenkins is Ready

Once finished, the web browser will load the default Jenkins welcome page:

Jenkins Dashboard

Troubleshooting & Verification

1. Verify Service Daemon

If a service timeout occurs during start, check the status or restart the service:

service jenkins restart

2. Inspect Jenkins Log Output

If Jenkins fails to boot, inspect the standard output log stream:

cat /var/log/jenkins/jenkins.log

The Jenkins CI/CD Server is now fully installed, configured, and ready to host automation jobs!

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