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Jenkinsdevops~5 mins

Jenkins WAR file execution - Cheat Sheet & Quick Revision

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Recall & Review
beginner
What is the Jenkins WAR file?
The Jenkins WAR file is a single executable file that contains the entire Jenkins application. It can be run directly with Java to start Jenkins without needing a separate installation.
Click to reveal answer
beginner
How do you start Jenkins using the WAR file?
You start Jenkins by running the command: java -jar jenkins.war. This launches Jenkins on the default port 8080.
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intermediate
How can you change the port Jenkins runs on when using the WAR file?
Use the command java -jar jenkins.war --httpPort=9090 to run Jenkins on port 9090 instead of the default 8080.
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beginner
What happens when you run java -jar jenkins.war for the first time?
Jenkins starts and creates initial setup files. It shows a URL with an initial admin password stored in a file. You use this password to unlock Jenkins in the browser.
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beginner
How do you stop Jenkins when running from the WAR file?
You can stop Jenkins by pressing Ctrl+C in the terminal where Jenkins is running. This safely shuts down the server.
Click to reveal answer
Which command starts Jenkins using the WAR file on the default port?
Ajenkins start
Bjava -jar jenkins.war
Cjava jenkins.war
Dstart-jenkins
How do you specify a custom port when running Jenkins WAR?
Ajava -jar jenkins.war --port=9090
Bjava -jar jenkins.war -port 9090
Cjava -jar jenkins.war -p 9090
Djava -jar jenkins.war --httpPort=9090
What file contains the initial admin password after first Jenkins WAR run?
Asecrets/initialAdminPassword
Bjenkins.log
Cconfig.xml
Dadmin.password
How do you stop Jenkins running from the WAR file?
ARun 'jenkins stop' command
BClose the browser
CPress Ctrl+C in the terminal
DRestart the computer
What port does Jenkins use by default when started with the WAR file?
A8080
B443
C9090
D80
Explain how to start Jenkins using the WAR file and how to access it in a browser.
Think about the command, port, and first-time setup steps.
You got /4 concepts.
    Describe how to change the port Jenkins runs on when using the WAR file and how to stop Jenkins safely.
    Focus on command options and stopping Jenkins.
    You got /3 concepts.

      Practice

      (1/5)
      1. What does running java -jar jenkins.war do in Jenkins?
      easy
      A. Deletes Jenkins configuration files
      B. Installs Jenkins permanently on the system
      C. Updates Jenkins to the latest version
      D. Starts Jenkins server without installing it

      Solution

      1. Step 1: Understand the command purpose

        The command java -jar jenkins.war runs the Jenkins server directly from the WAR file without installation.

      2. Step 2: Differentiate from installation

        This method does not install Jenkins permanently but starts it temporarily for use or testing.

      3. Final Answer:

        Starts Jenkins server without installing it -> Option D

      4. Quick Check:

        Run WAR file = Start Jenkins temporarily [OK]
      Hint: WAR file runs Jenkins without install, just start it [OK]
      Common Mistakes:
      • Thinking it installs Jenkins permanently
      • Confusing it with Jenkins update command
      • Assuming it deletes files
      2. Which command correctly starts Jenkins on port 9090 using the WAR file?
      easy
      A. java -jar jenkins.war --httpPort=9090
      B. java -jar jenkins.war -p 9090
      C. java -jar jenkins.war --port 9090
      D. java -jar jenkins.war -httpPort 9090

      Solution

      1. Step 1: Recall Jenkins WAR port option syntax

        The correct option to specify port is --httpPort=9090 when running the WAR file.

      2. Step 2: Check other options for correctness

        Options B, C, and D use incorrect flags or syntax not recognized by Jenkins WAR execution.

      3. Final Answer:

        java -jar jenkins.war --httpPort=9090 -> Option A

      4. Quick Check:

        Use --httpPort=number to set port [OK]
      Hint: Use --httpPort=PORT to set Jenkins port [OK]
      Common Mistakes:
      • Using -p or --port which Jenkins WAR does not recognize
      • Missing equal sign in option
      • Using single dash for long option
      3. What will be the output if you run java -jar jenkins.war --httpPort=8080 when port 8080 is already in use?
      medium
      A. Error: Address already in use, Jenkins fails to start
      B. Jenkins automatically switches to port 8081
      C. Jenkins starts successfully on port 8080
      D. Jenkins ignores the port option and uses default

      Solution

      1. Step 1: Understand port conflict behavior

        If the specified port (8080) is busy, Jenkins cannot bind to it and will fail to start with an error.

      2. Step 2: Check Jenkins automatic port fallback

        Jenkins WAR does not automatically switch ports; it requires manual change if port is busy.

      3. Final Answer:

        Error: Address already in use, Jenkins fails to start -> Option A

      4. Quick Check:

        Port busy = Jenkins start error [OK]
      Hint: Busy port causes Jenkins start error, no auto-switch [OK]
      Common Mistakes:
      • Assuming Jenkins auto-switches ports
      • Thinking Jenkins ignores port option
      • Believing Jenkins starts anyway on busy port
      4. You ran java -jar jenkins.war --httpPort=abc and Jenkins did not start. What is the likely cause?
      medium
      A. Jenkins requires root privileges to start
      B. Jenkins WAR file is corrupted
      C. Invalid port number format causes startup failure
      D. Java is not installed on the system

      Solution

      1. Step 1: Analyze the port option value

        The port option --httpPort=abc uses non-numeric characters, which is invalid for a port number.

      2. Step 2: Understand Jenkins port validation

        Jenkins expects a numeric port; invalid format causes startup failure with error.

      3. Final Answer:

        Invalid port number format causes startup failure -> Option C

      4. Quick Check:

        Port must be numeric for Jenkins to start [OK]
      Hint: Port must be a number, not letters [OK]
      Common Mistakes:
      • Blaming Jenkins WAR file corruption
      • Assuming Java is missing without checking
      • Thinking root privileges are always needed
      5. You want to run Jenkins WAR file on port 7070 and also specify a custom Jenkins home directory at /data/jenkins_home. Which command is correct?
      hard
      A. java -jar jenkins.war --httpPort=7070 --jenkinsHome=/data/jenkins_home
      B. java -Djenkins.home=/data/jenkins_home -jar jenkins.war --httpPort=7070
      C. java -jar jenkins.war --httpPort=7070 --jenkins.home=/data/jenkins_home
      D. java -jar jenkins.war --httpPort=7070 -DjenkinsHome=/data/jenkins_home

      Solution

      1. Step 1: Set port option correctly

        The port is set with --httpPort=7070, which is correct syntax.

      2. Step 2: Set Jenkins home directory properly

        Jenkins home is set via Java system property -Djenkins.home=path, not as a command option.

      3. Step 3: Verify option correctness

        The correct command places the -Djenkins.home= option before -jar to set the system property properly.

      4. Final Answer:

        java -Djenkins.home=/data/jenkins_home -jar jenkins.war --httpPort=7070 -> Option B

      5. Quick Check:

        Use -Djenkins.home=PATH for custom Jenkins home [OK]
      Hint: Use -Djenkins.home=PATH to set Jenkins home [OK]
      Common Mistakes:
      • Using --jenkinsHome or --jenkins.home as options
      • Confusing Java system properties with command options
      • Missing -D prefix for system properties
      • Placing -D option after -jar which is incorrect
      Recommended

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