Jenkins is an open-source tool for continuous integration that was originally developed as the Hudson project. It allows developers to commit code frequently to a shared repository, where Jenkins will automatically build and test the code. Jenkins is now the leading replacement for Hudson since Oracle stopped maintaining Hudson. It helps teams catch issues early and deliver software more rapidly through continuous integration and deployment.

1. What is Jenkins

2. An Introduction
Jenkins is the leading open source continuous integration tool.
Jenkins was originally developed as the Hudson project. Hudson's
creation started in summer of 2004 at Sun Microsystems.
In November 2010, an issue arose in the Hudson community with respect
to the infrastructure used. Negotiations were held between the principal
project contributors and Oracle; a key sticking point was the control of the
name "Hudson" itself, which Oracle claimed, and on January 11, 2011, a
proposal was made to change the project name from "Hudson" to
"Jenkins".

3. What is Jenkins...
On February 1, 2011, Oracle said that they intended to continue development of
Hudson, and considered Jenkins a fork rather than a rename. As of December
2016, the Jenkins organization on Git Hub had 638 project members and around
1,800 public repositories, compared with Hudson's 32 project members and 17
public repositories.
Hudson is not maintained anymore, Jenkins is the replacement for it.
Jenkins builds and tests our software continuously and monitors the execution
and status of remote jobs, making it easier for team members and users to
regularly obtain the latest stable code

4. What is Continuous Integration
Continuous Integration is a development practice in which
developers are required to commit changes to source code in a
shared repository several times a day. Every commit is then
build and this allows the teams to detect problems early.
It then bring following benefits to software development:
1) Catch issues fast and nip them in the bud.
2) Everyone can see what’s happening.
3) Automate the build.
4) Continuous Integration leads to Continuous Deployment
allowing us to deliver software more rapidly

5. What is Continuous Integration

6. • Continuous Integration is a software development practice in which
developers are required to frequently commit changes to the source
code in a shared repository. Each commit is then continuously pulled
& built. Jenkins is an open-source, Continuous Integration (CI) tool,
written in Java. It continuously pulls, builds and tests any code
commits made by a developer with the help of plugins.

7. Different Types of Jenkins Jobs
• Jenkins provides the option of choosing from different types of jobs to build your
project.
• Below are the types of jobs you can choose from:
Freestyle :
Freestyle build jobs are general-purpose build jobs, which provides maximum
flexibility. It can be used for any type of project.
Pipeline :
This project runs the entire software development workflow as code. Instead of
creating several jobs for each stage of software development, you can now run the
entire workflow as one code.

8. Multiconfiguration :
The multiconfiguration project allows you to run the same build job on
different environments. It is used for testing an application in different
environments.
Folder :
This project allows users to create folders to organize and categorize
similar jobs in one folder or subfolder.
GitHub Organization :
This project scans your entire GitHub organization and creates Pipeline
jobs for each repository containing a Jenkinsfile

9. Multibranch Pipeline
This project type lets you implement different Jenkinsfiles for different
branches of the same project.

10. Pipeline Concepts :
The below fundamentals are common to both, scripted and declarative
pipeline :
Pipeline: A user-defined block which contains all the stages. It is a key part of
declarative pipeline syntax.
Node: A node is a machine that executes an entire workflow. It is a key part
of the scripted pipeline syntax.
Agent: instructs Jenkins to allocate an executor for the builds. It is defined
for an entire pipeline or a specific stage.

11. Jenkins Tips and Tricks
Start, stop and restart Jenkins
• Follow the below command to start, stop and restart Jenkins through
the CLI.
• $ sudo service jenkins restart
• $ sudo service jenkins stop
• $ sudo service jenkins start