Jenkins is an open-source Continuous Integration and Continuous Delivery tool and is written in Java language.

Jenkins helps to build and test the software system continuously making it easier for developers to integrate changes to the system and obtain a fresh build.

Additionally, it is used to enable developers to continuously check their code and also analyze the post-build actions, if any. With the help of this, the automation testers can use to run their tests when the code is modified.

Jenkins have the following features:

• It is a free open-source tool.
• It can be easily installed on various operating systems.
• Configuration Setup is very easy.
• It provides build pipeline support.
• It is extensible with the use of third-party plugins.

The various advantages of Jenkins are:

• We do not need to check the code and start build manually.
• Build failures are cached during the integration stage.
• Email notifications are sent to the developer if there are any build failures.
• Defects are easily tracked and resolved at early stages.
• Helps in achieving Continuous Integration in Agile development and test-driven development.

Follow the following steps to start Jenkins:

• Open Command Prompt
• Browse the directory where jenkins.war resides from the command prompt

• Run the below command:

java –jar jenkins.war

Some of the important plugins in Jenkins are as follows:

• Gits
• HTML Publisher
• Maven 2 Project
• Join
• Copy Artcraft
• Green Balls
• Amazon EC2

At the time of development, when multiple developers or teams are working on various segments of the same web application, there is a need to perform integration testing by integrating all modules.

In order to do that an automated process is performed for each piece of code on a daily basis so that all the code get tested.

The basic requirements to use Jenkins are:

• A source code repository which is easily accessible, for example, a Git repository
• A working build script, for example, a Maven script that is checked into the repository.

To start Jenkins manually, the following commands can be used:

• (Jenkins_url)/restart: This command is used to force restart without waiting for build completion.
• (Jenkins_url)/safeRestart: This command waits until all build gets completed before restarting.

The pipeline is defined as the suite of plugins that support the implementation and integration of continuous delivery pipelines in Jenkins.

Continuous Integration or Continuous Delivery pipeline consists of build, deploy, test, and release. The pipeline feature helps in saving a lot of time and error in maintaining the builds.

In simple terms, a pipeline is a group of build jobs that are chained and integrated in sequence.

SCM stands for Source Control Management. It helps in providing a history of code development and also helps to resolve conflicts when merging code from multiple sources.

SCM module specifies source code location. The entry point to SCM is specified as jenkins_job.scm

SCM tools that are supported in Jenkins are:

• GIT
• CVS
• Subversion
• Clearcase
• Perforce
• RTC
• AccuRev

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Jenkins saves all the settings, builds artifacts, and logs in the JENKINS_HOME directory. To create a back-up of the Jenkins setup, we need to copy this JENKINS_HOME directory.

You can maintain a separate backfile and can copy it whenever needed. You can also copy the Jenkins job directory to clone or replicate a job or to rename the directory.

To clone a GIT repository via Jenkins, you need to enter the e-mail and username for your Jenkins system.

To do the same, you need to switch into your job directory and execute the “git config” command.

To set up a new job in Jenkins, the following steps should be followed:

• Open the Jenkins dashboard and log in with registered login credentials.
• Click on “New Item” present in the left panel of the page
• Select a “FreeStyle Project” and specify the name for the job in the textbox.
• Click on OK to create a new job in Jenkins.
• The next page will further enable to configure the job.

To move or copy Jenkins from one server to another, the following steps need to be followed:

• First of all, copy the related job directory and slide a job from one installation of Jenkins to another.
• Make a copy of an already existing job by making a clone of a job directory by a different name.
• Rename an existing job by renaming a directory.

To make sure that the project build doesn’t break in Jenkins, the following steps need to be followed:

• Perform successful clean installation on your local machine with all unit tests.
• Check all the code changes.
• Synchronize with the repository to verify that all required configuration and POM changes and any differences are checked into the repository.

Open the Console Output for the broken build check the error and verify if any file changes were missed.

If no issue is found from there in that way, then clean and update the local workspace to replicate the problem local and then try to solve it.

There is no difference between Hudson and Jenkins.

Hudson was the former name of the current Jenkins. After going through several issues, the project name was changed from Hudson to Jenkins.

Jenkinsfile is the text file in which all the definition of pipelines of Jenkins are defined.Jenkinsfile is being checked into the source control repository.

Post is a section in Jenkins configuration that contains several additional steps that might execute after the completion of the pipeline. The execution of the steps within the condition block depends upon the completion status of the pipeline.

The condition block contains the following conditions: changed success, always, failure, unstable, and aborted.

Triggers in Jenkins are used to define the way in which the Jenkins pipeline should be executed frequently.

PollSCM, Cron, etc. are some of the currently available triggers.

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