This article describes how to use the Jenkins continuous integration build server.

1. Using the Jenkins build server

Continuous integration is a process in which all development work is integrated as early as possible. The resulting artifacts are automatically created and tested. This process allows to identify errors in an early stage of the project.

Jenkins is a popular open source tool to perform continuous integration and build automation. The basic functionality of Jenkins is to execute a predefined list of steps, e.g. to compile Java source code and build a JAR from the resulting classes. The trigger for this execution can be time or event based. For example, every 20 minutes or after a new commit in a Git repository.

Possible steps executed by Jenkins are for example:

  • perform a software build using a build system like Apache Maven or Gradle

  • execute a shell script

  • archive a build result

  • run software tests

Jenkins monitors the execution of the steps and allows to stop the process, if one of the steps fails. Jenkins can also send out notifications in case of a build success or failure.

Jenkins can be extended by additional plug-ins. For example, you can install plug-ins to support building and testing Android applications.

2. Installation and setup of Jenkins

For most platforms you have native packages, see the Jenkins Homepage.

2.1. Installing the Jenkins server on Ubuntu

Jenkins provides Debian/Ubuntu packages which install Jenkins and register Jenkins as start service. See the Install Jenkins on Ubuntu description. The Linux installation creates a /etc/init.d/jenkins script which starts Jenkins automatically at boot time.

Jenkins stores all the settings, logs and build artifacts in its home directory. The default installation directory under Ubuntu is /var/lib/jenkins.

2.1.1. Using the .war file to start Jenkins

Download the jenkins.war file from the Jenkins Homepage. From this file you can start Jenkins directly via the command line with java -jar jenkins*.war.

If you start it locally, you find it running under the following URL: http://localhost:8080/

To run it in your Tomcat server, put the .war file into the webapps directory. If you start Tomcat, your Jenkins installation will be available under

http://localhost:8080/jenkins

If the jenkins.war is deployed in your webapps directory, but can not be started and the tomcat manager says FAIL - Application at context path /jenkins could not be started, you may need to grant the permissions for JENKINS_HOME.

sudo mkdir .jenkins
sudo
chown tomcat7:nogroup .jenkins

This makes the .jenkins folder writable and Jenkins can use it.

3. Configure Jenkins

3.1. Connect to Jenkins for the initial configuration

After installation, open a browser and connect to it. The default port of Jenkins is :8080, therefore on your local machine you find it under the following URL:

http://localhost:8080/

You will need to copy the initial password from the file system of the server.

Afterwards you can select to install Plugins. Select the Install suggested Plugins to get a typical configuration.

Create an admin user and press Save and Finish.

3.2. User management Jenkins

Select Manage Jenkins and then Configure Global Security. Select the Enable security flag. The easiest way is to use Jenkins own user database. Create at least the user "Anonymous" with read access. Also create entries for the users you want to add in the next step.

Access restrictions

On the login page, select Create an account to create the users you just gave access.

Create Jenkins account
Sign up a new Jenkins user

3.3. Assign roles to users

If you want to create a role based authorization Strategy you first need to install the Role-based Authorization Strategy Plugin. Go to Manage Jenkins  Manage Plugins  Available enter Role-based Authorization Strategy in the filter box and select and install the Plugin. To see a list of commonly used Plugins go to Plugin management.

Now go to Manage Jenkins  Manage and Assign Roles  Assign Roles to grant users additional access rights.

Sign up a new Jenkins user

Navigate to Manage Roles to define access restrictions in detail. Pattern is a regex value of the job name. The following grants unregistered users read-only access to your build jobs that start with the L-, C-, I- or M- and only those.

Sign up a new Jenkins user

3.4. Generate ssh key for Jenkins user

If you want to access a private Git repo, for example at GitHub, you need to generate an ssh key-pair. Create a SSH key with the following command.

sudo -u jenkins ssh-keygen

The public key must be uploaded to the service you are using, e.g., GitHub.

3.5. Configure the default port of the Jenkins build server

The default port number can be changed in the config file at

sudo vim /etc/default/jenkins

Here you can set a different port number, e.g. HTTP_PORT=8082

Now you need to restart Jenkins with

service jenkins restart

or by adding /restart at the end of the Jenkins URL, e.g. https://yourjenkinsurl/ci/restart.

4. Setting up a Jenkins job

The build of a project is handled via jobs in Jenkins. Select New Item. Afterwards, enter a name for the job and select Freestyle project and press OK.

Setting up a Jenkins job

Enter a description for the job (project name) and configure how many builds should be retained and for how long.

Setting up a Jenkins job

Configure how the source code can be retrieved. If you are for example using Git, enter the URL to the Git repository. If the repository is not public, you may also need to configure the credentials.

Setting up a Jenkins job

Specify when and how your build should be triggered. The following example polls the Git repository every 15 min. It triggers a build, if something has changed in the repo.

Setting up a Jenkins job

To trigger a build after a commit on the Git repository, select GitHub hook trigger for GITScm polling instead of Poll SCM.

If you want an automatic build after a commit you must also configure the Jenkins URL on the Git Repository. For details on how to do this with GitHub see our GitHub tutorial.

If you want to delete the workspace before a build to avoid any side-effects, you can add a build step in the Build section.

Setting up a Jenkins job

Press Save to finish the job definition. Press Build Now on the job page to validate that the job works as expected.

Setting up a Jenkins job

After a while the job should go to green or blue (depending on your configuration), if successful. Click on the job and afterwards on Console Output to see the log file. Here you can analyze the build errors.

5. Build Pipelines

Jenkins pipelines help you align the build process of a project. This is done by specifying tasks and the order in which they are executed. There are all kinds of possible tasks that a Jenkins pipeline can do for you. For example, build assets, send an email on error, send the build artifacts via SSH to your application server, etc.

5.1. Setup of Pipelines

Jenkins allows to specify pipelines using a Jenkinsfile. This is just a textfile that contains the necessary data for Jenkins to execute the pipeline. It is called Jenkinsfile (notice: no file extension) and should be placed in the root of your project.

This file should be checked into version control as it is needed on your Jenkins instance.

Jenkins supports two different syntaxes.

  1. Declarative (since Pipeline version 2.5)

  2. Scripted

For this tutorial we will focus on the declarative approach.

The following example shows a pipeline with 2 stages:

pipeline {
    agent any (1)

    stages {
        stage('Build Assets') {
            agent any (1)
            steps {
                echo 'Building Assets...'
            }
        }
        stage('Test') {
            agent any
            steps {
                echo 'Testing stuff...'
            }
        }
    }
}
1 The agent directive tells Jenkins to allocate a workspace and an executor for the pipeline. Without it, the pipeline is not valid and therefore required.

5.2. Setup using the Blue Ocean Plugin

The above process can also be done using the Blue Ocean Jenkins Plugin.

5.2.1. Installation

To install the Plugin go to Manage Jenkins  Manage Plugins  Available and select the Blue Ocean Plugin.

After the installation is finished you have an additional menu entry called Open Blue Ocean in your main Jenkins navigation.

jenkins pipeline10

5.2.2. Creating a new Pipeline

Click on New Pipeline to create a new Pipeline.

jenkins pipeline20

Select your version control provider.

jenkins pipeline21
For this example we will use a GitHub repository.

Depending on your provider you will need to pass some kind of credentials.

GitHub provides the ability to generate access-tokens that applications can use to access the platform with your user. You can also restrict what the access-token can do.

The Blue Ocean application will provide a link to the GitHub page you need to visit. The necessary permissions that Blue Ocean needs to operate are already selected. Add a description and click on Generate Token at the bottom of the page.

Copy the generated token and paste it in the Blue Ocean mask.

Select the account the repository belongs to and select the repository.

jenkins pipeline30

If you already have a Jenkinsfile with pipelines in the repository it will show up in the last step. If not, Blue Ocean will offer to create one for you.

5.2.3. Adding steps to your Pipeline

In the next screen you will see a visual representation of your Pipeline. Here you can add or remove steps.

jenkins pipeline40

To create a new step click on + in the canvas. A menu will open on the right that lets you specify a name and what steps you want to perform.

jenkins pipeline50

After you have finished editing the Pipeline Blue Ocean will offer you to commit the newly created pipeline to your repository.

Under the hood Blue Ocean only created a valid Jenkinsfile to be used by Jenkins.

After committing Jenkins will build the project using the newly modified Pipelines.

6. Jenkins management

6.1. Plugin management

Jenkins can be extended via additional Plugins with more functionality. You can configure your Plugins via the Manage Jenkins  Manager Plugins link.

To install Plugins in Jenkins select the Manage Jenkins  Manager Plugins link and search for the Plugin you want to install. Select it from the list and select to install it and restart Jenkins.

The following table is a summary of commonly used Plugins.

Table 1. Jenkins Plugins
Plug-in name Description URL

Git Plugin

This Plugin allows to use Git as a build SCM.

https://wiki.jenkins-ci.org/display/JENKINS/Git+Plugin

Xvnc Plugin

This Plugin allows projects to run xvnc during a build. This allows for example to run tests which require a display to run on a virtual display. To use this Plugin you need to connect once to your vncserver on the command line to provide a password. Use for example the following commands.

# install vncserver
apt-get install vnc4server

# switch to jenkins user
sudo su jenkins

# connect to vncserver which creates the password
vncserver :10

https://wiki.jenkins-ci.org/display/JENKINS/Xvnc+Plugin

Gradle Plugin

This Plugin allows to run Gradle builds, e.g., as required for Android, via Jenkins.

https://wiki.jenkins-ci.org/display/JENKINS/Gradle+Plugin

Maven Plugin

This Plugin allows to run Maven builds.

https://wiki.jenkins-ci.org/display/JENKINS/Maven+Project+Plugin

GitHub Plugin

This Plugin integrates Jenkins with Github projects.

https://wiki.jenkins-ci.org/display/JENKINS/Github+Plugin

Publish Over SSH Plugin

This Plugin allows to publish build artifacts via ssh

https://wiki.jenkins-ci.org/display/JENKINS/Publish+Over+SSH+Plugin

Workspace Cleanup Plugin

This Plugin allows to delete the workspace before the build or when a build is finished and artifacts are saved.

https://wiki.jenkins-ci.org/display/JENKINS/Workspace+Cleanup+Plugin

Github Pull Request Builder

This Plugin allows to build GitHub Pull Requests

https://wiki.jenkins-ci.org/display/JENKINS/GitHub+pull+request+builder+plugin

6.2. Restart your Jenkins

After installing Plugins you will need to restart Jenkins. You can do so by adding restart as URL parameter,

How to manually restart Jenkins

or with the following command:

service jenkins restart

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Copyright © 2012-2019 vogella GmbH. Free use of the software examples is granted under the terms of the Eclipse Public License 2.0. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.