Jenkins Interview Questions and Answers

By Umesh Singh
Last update: 11 Jan 2020, 17 Questions
Jenkins Interview Questions

Jenkins is a free and open-source CI-based automation server. It helps to automate the non-human part of development using continuous integration and technical factors of continuous delivery.

Being a server-based system that runs on servlet containers, for example, Apache Tomcat, supporting various version control tools such as AccuRev, Subversion, CVS, Git, Mercurial and is able to execute ApacheAnt, Apache Maven and sbt oriented projects.

Jenkins Interview Questions is a guide to budding developers to help focus on important questions being asked in organizations nowadays.

Most Frequently Asked Jenkins Interview Questions

1. What are the features of Jenkins?
  • Easy to install on multiple OS
  • Easy-to-use with good User Interface
  • Easily scalable with over 400 third party plugin support
  • User Interface is very friendly with respect to customization. The setup environment can be configured inside.
  • JUnit; a test harness is integrated with Jenkins so as to provide results in graphical and tabular forms
  • Inside the environment, build scheduling is based on Cron Expression
2. What is the difference between Jenkins and Bamboo?
Open Source Not Open-Source
UI has a simple functionality More efficient and organized UI
Basic config(Jira & Bitbucket) is limited In-built basic Configurations
A wider range of Plugins with 1000+ plugins available Less Plugin support with only 100+ plugins available
Provides scope for Basic Automation More focused on Build, Test and Deployment sectors

Note: These are basic questions that are asked during a Jenkins interview question for DevOps candidates.

3. What is pipeline in Jenkins? Alos explain its types?

A pipeline in Jenkins refers to a suite of plugins that help implement & integrate Continuous Delivery Pipelines throughout Jenkins. A continuous delivery pipeline is an automated expression for getting software from version control right through to your users and consumers.

There are two types of pipeline syntax to define a JenkinsFile
  • Declarative Pipeline: This type of syntax offers an easy way for the creation of pipelines. It contains a predefined hierarchy and offers users the ability to control all aspects of a pipeline execution in a simple, straightforward manner.
  • Scripted Pipeline: This type of Jenkins pipeline runs on the Jenkins master using a lightweight executor. It uses few resources to translate the pipeline into atomic commands.
4. What is the difference between hudson and jenkins?
Fewer releases with more focus on backward compatibility More releases with riskier compatibility issues
Focused more on Maven and/or Nexus Integration Focused on more active community support
Professional support from Sonatype or Oracle, sometimes Support only from Original Creator
A small community of plugin developers Classic OSS Style Development Ecosystem
5. How do you secure Jenkins?

By default, Jenkins 1.x does not perform any security checks. But, you can manually change that by customizing access controls and configuring it as per one’s need.

Access control locks down access to the Jenkins UI Console and users may log in to get access via Passwords.

One more feature in Jenkins for security is the additional subsystems to prevent direct and indirect attacks on the system.

6. How do I start Jenkins service in Windows?

After downloading the Jenkins installation file for Windows, go to your CMD Terminal and run the following command:

jenkins.exe start

Note: These are basic Jenkins interview questions a candidate must know the answers to.

9. How do you create a pipeline in Jenkins?

To create pipelines in Jenkins, you must have a Jenkins instance setup with the appropriate plugins:

  • Jenkins 1.580.1 or later (Jenkins 2.0 is best)
  • Core Pipeline Plugin
To create a simple pipeline, follow these steps:
  • Click on New Item on Jenkins home, enter a name for Pipeline and click OK.
  • Go to the Script text area of the config screen and enter your pipeline syntax.
  • Check the Groovy Sandbox option below the Script text Area to increase efficiency
  • Click Save
  • To create the pipeline, click on Build Now
  • Click on this and select Console Output to view the output
10. What is the use of poll SCM in Jenkins?

Poll SCM periodically polls the SCM to check whether the changes were made (i.e. new commits) and also builds the project if there are new commits pushed since the last updated build.

11. What is Jenkins file parameter?

A file parameter is Jenkins allows a build to accept new files which are to be submitted by the user when scheduling a new build. The uploaded file shall be placed inside the workspace at the set location after the process of check-out/update is done.

12. What is difference between Jenkins and Docker?
CI Engine which is used to build/test apps Container engine used to manage and create containers
Automated Server Tool used for testing apps Used to build and run multiple portable environments of a software stack
Provides an easy interface to create and manage multiple CI/CD Pipelines It's only a container engine to hold a software application
Can be used to build Docker Images based on a DockerFile Its plugin can be used to build containers for any application in Jenkins
13. Where is Jenkins home directory?

Jenkins home directory contains all the details of the Jenkins server configuration, the details that are configured in the Manage Jenkins screen. These configuration details are stored in the form of a set of XML files, for example, a config.xml file It’s default directory is .jenkins or .hudson (for older version)

Note: These are basic Jenkins interview questions and have a higher probability of being asked.

14. What is CI and CD in Jenkins?

CI stands for Continuous Integration and it is the practice of automating the integration of code changes from multiple contributors in a software application.

CD stands for Continuous Delivery and it refers to the ability to get change such as configuration, bug fixes and experiments from build to production or directly to the end-user in a quick and sustainable way.

15. What are upstream and downstream projects in Jenkins?

An upstream project is one in which a job is triggered before the actual project is triggered. Whereas, Downstream project is one in which a job is triggered after the project has been triggered.

16. What is groovy script in jenkins?

Groovy Script is a Java-syntax compatible Object-Oriented Programming language for a Java Platform. It is used in Jenkins to orchestrate/create pipelines. Being flexible in terms of languages, it's used as a glue for combining code in different languages into a single project.

17. How do I reset my Jenkins admin password?

To reset the Jenkins admin password, simply disable the security in the config.xml file.

  • If running on Linux, edit the following file:
    vi /var/lib/jenkins/config.xml file
  • Search for the term <useSecurity>true</useSecurity> and change the word True to False
  • Restart the Jenkins Server
    Service Jenkins Restart
Pros of using Jenkins
  • It's open-source & hosted internally
  • Very easy to deploy with support to build pipelines
  • A vast range of plugins available
  • Integrates with major tools (CVS, Kubernetes, Apache Ant and more)
  • Jenkins is flexible and scalable for all sorts of business
  • Jenkins has a complimentary API Suite
  • Easy to use and a strong community of developers for support
Cons of using Jenkins
  • Jenkins can be expensive due to variable load on the server end
  • Accountability and management can be challenging due to a single master user
  • Lack of efficient and overall analytics besides plugins
  • Requires more human resources for the overall management