If you want a fast way to test pipelines without installing an entire CI farm, running Jenkins from the WAR file is the nerd friendly equivalent of a microwave dinner. It is fast, low fuss, and disposable when your experiment blows up. This guide walks through the essentials for running jenkins.war on a local machine for development and testing.

Grab the jenkins.war and pick a workspace

Download the latest jenkins.war from the official Jenkins download page or a trusted mirror. Do not download random files from sketchy sites unless you enjoy debugging cryptic errors at 2 a m.

• Create a folder to act as your server workspace. This will be your JENKINS_HOME where job data and configs live.
• Place jenkins.war in that workspace or point the Java command to the file location.
• Make sure Java 8 or newer is installed and on your path.

Run Jenkins with Java

Open a terminal in your workspace and run the WAR with a simple Java command. The default port is fine for local testing but you can change it if you need to avoid conflicts.

java -jar jenkins.war --httpPort=8080

The webapp will extract resources and start a lightweight web server on the chosen port. Watch the terminal output for progress and the initial admin password.

Unlock and finish the first setup

On first launch Jenkins prints an initialAdminPassword in the console and also writes the same value under the workspace folder at secrets/initialAdminPassword. Copy that string into the browser unlock screen to proceed. Yes it is a weird handshake but it keeps bots out and humans mildly annoyed.

Choose plugins and create the admin account

You can pick recommended plugins for a minimal, working CI setup or select specific plugins for your toolchain. After plugin installation create the first admin account and configure global tools like a JDK and Git so builds can actually run.

• Recommended plugins get you up fast.
• Custom selections let you avoid plugin bloat if you know what you need.
• Set global tool paths for JDK and Git in Manage Jenkins to avoid weird build failures.

Run Jenkins as a service for longer tests

If you plan to run this instance for more than a quick demo wrap the Java command in a service manager. On Linux systemd works well. On Windows consider NSSM or the built in service wrapper. Point the service at the java -jar command and set environment variables for JENKINS_HOME and JAVA_OPTIONS for stability.

Example systemd unit file for the impatient. Drop this in a file under systemd and tweak paths to match your setup.

[Unit]
Description=Jenkins from WAR
After=network.target

[Service]
Type=simple
User=jenkins
WorkingDirectory=/srv/jenkins
Environment=JENKINS_HOME=/srv/jenkins
Environment=JAVA_OPTIONS=-Xmx1g
ExecStart=/usr/bin/java -jar /srv/jenkins/jenkins.war --httpPort=8080
Restart=on-failure

[Install]
WantedBy=multi-user.target

On Windows wrap the command with NSSM or a similar service helper. Make sure the service user has permission to the workspace and any tool paths.

Troubleshooting and best practices

• Java version matters. Use Java 8 or newer for most Jenkins releases.
• If the port is in use pick a different port with the httpPort flag.
• Permissions. Jenkins needs read write access to JENKINS_HOME for jobs to work.
• Keep the WAR updated. This is a simple deployment but you still need security updates.
• For persistent or production use consider a proper package or container deployment instead of a raw WAR run.

Running Jenkins from jenkins.war is a great way to prototype pipelines and iterate on job configs without a heavyweight setup. It is not bulletproof but if you treat it like a lab pet and not a router for your production traffic you will be fine. Now go break something carefully and learn how to fix it.