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DevOps-Jenkins

Configuration as Code

The Jenkins Configuration as Code (JCasC) feature defines Jenkins configuration parameters in a human-readable YAML file that can be stored as source code. This essentially captures the configuration parameters and values that are used when configuring Jenkins from the web UI. The configuration can then be modified by editing this file and then applying it.

Traditionally, experienced Jenkins administrators created Apache Groovy init scripts to automate the configuration for their Jenkins instances. This works but requires in-depth understanding of Jenkins APIs and the ability to write Groovy scripts. Such scripts are powerful and can do almost anything, but they also provide few protections against configuration errors.

JCasC provides the convenience and flexibility of configuring controllers without using the UI. It does not require more understanding of the configuration parameters than is required to configure Jenkins through the UI and it provides some checks on the values that are provided.

The JCasC configuration file can be checked into an SCM, which enables you to determine who made what modifications to the configuration and to roll back to a previous configuration if necessary.

The Configuration as Code plugin must be installed on the Jenkins controller that you will use to build out your JCasC configuration. If you do not see the Configuration as Code tile in the System Configuration section of the Manage Jenkins page on your dashboard, you need to install the plugin.

Viewing the JCasC file

When the Configuration as Code plugin is installed, you will see Configuration as Code in the System Configuration section of the Manage Jenkins page on your dashboard. Click on this link, then click on View Configuration to view the YAML file.

This file is an export of the current configuration on this controller. In most cases, it is ready to use without modification although you usually want to customize it before deploying it. You may want to push the unmodified version to SCM so you have it as part of your history.

The Configuration as Code UI page shows the full pathname of the YAML file being used and gives a box where you can specify a different file to use. See the information below about how to modify the location used for JCasC YAML files.

The default JCasC YAML file has four sections:

jenkins section defines the root Jenkins object, with configurations that can be set with the Manage Jenkins >> Configure System and Manage Jenkins >> Configure Nodes and Clouds screens.
tool section defines build tools that can be set on the Manage Jenkins >> Global Tool Configuration screen.
unclassified section defines all other configurations, including configuration for installed plugins.
credentials section defines credentials that can be set on the Manage Jenkins >> Manage Credentials screen. You may want to delete this section from your YAML file; this is discussed in How to Install Jenkins on CentOS 7 Using Ansible and JCasC.

YAML file syntax

JCasC defines the controller configuration in a YAML file. YAML is a popular serialization language for configuration information, with a syntax that is straight-forward and easy to read but precise.

Some key points about YAML syntax:

YAML files are case sensitive.
Indentation is very significant and specific.
Each item is a key/value pair.
- The key is followed by a colon ( : ) and a space.
- YAML converts certain strings into other types unless they are in quotes.
  - Values such as true , false , Yes , and No are converted to Boolean values.
  - Values such as 2 and 3.0 are converted to floating point values.
A value can be a list:
- Each list item is on a separate line starting with a dash ( - ).
- Each list item in the file must start at the same indentation.
  - Use spaces, never tabs, for indentation.
- Never leave a blank line in a YAML file — things will break!

See the YAML Reference Card for more details about YAML file syntax.

Checking the YAML files into SCM

To get the maximum benefit of JCasC, the YAML files should be stored in SCM. This gives you a history that you can use to trace changes that are made and allow you to easily roll back to an earlier version of the file if necessary.

JCasC does not require that the file be stored in SCM and so does not enforce any rules about how you do this. The most common practice is to create one SCM repository in which you store all of your JCasC files.

If you are storing your JCasC YAML files in SCM, you should commit the first default file that is generated, before you make any modifications to the file.

Modifying the JCasC file

To modify the JCasC YAML file, use the text editor of your choice to edit the file that is listed on the Manage Jenkins >> Configuration as Code UI page. By default, this is $JENKINS_HOME/jenkins.yaml .

For a simple exercise to work through the process, you can modify the value of the "System Message" that is displayed on the Jenkins dashboard.

Open the JCasC YAML file with the text editor of your choice.

Find the systemMessage line near the top of the file:

jenkins:
  systemMessage: "Jenkins configured automatically by Jenkins Configuration as Code plugin\n\n"

Modify the text between the quotation marks to contain your new text
Write/save the file
Click the Reload existing configuration button to apply the changes
View the modified "System Message" on your dashboard

It is not necessary to restart Jenkins to apply the JCasC changes, although you should try to restart Jenkins with the modifications before you check the modified YAML file into SCM, especially when making more substantive configuration changes.

When you have made and tested your desired changes, push the modified JCasC YAML file to your SCM.

Configuring a plugin with JCasC

To configure a plugin with JCasC:

Use the UI of the current system to install and configure the plugin
Click Apply >> Save to save the configuration
Use Manage Jenkins >> Configuration as Code >> View Configuration to view the JCasC file with the plugin configured
Click on Download Configuration to save the modified configuration file locally
Edit the JCasC YAML file to modify the configuration, if necessary
Save the file
Click Reload existing configuration to load the local changes onto the Jenkins server
Verify the changes on the UI
When you have thoroughly tested the plugin configuration, push the modified YAML file to your SCM

See the Configure Plugins with JCasC blog for detailed instructions and an embedded video demonstration of this process.

YAML file location

By default, the YAML file for the CasC configuration is located in $JENKINS_HOME/jenkins.yaml . The location and name of the file being used is displayed on the Configuration as Code UI page. You can specify a different file to view by typing the full pathname into the Path or URL field.

You can specify a different location or a different file name for the creation of the JCasC YAML file by doing either of the following:

Populate the CASC_JENKINS_CONFIG environment variable to point to a comma-separated list that defines where configuration files are located.
Use the casc.jenkins.config Java property to control the file name and location. This is useful when installing Jenkins via a package management tool. Most package management systems support configuration files that are retained across upgrades. It is best to not modify a file installed by a package manager because it could be overwritten by an update.

On Linux systems, you can run systemctl edit jenkins and add the following:
```
[Service]
Environment="JAVA_OPTS=-Dcasc.jenkins.config=/jenkins/casc_configs"
```

The file location and name can be specified as any of the following:

Path to a folder containing a set of config files such as /var/jenkins_home/casc_configs .
A full path to a single file such as /var/jenkins_home/casc_configs/jenkins.yaml .
A URL pointing to a file served on the web such as https://acme.org/jenkins.yaml .

The value of the CASC_JENKINS_CONFIG variable is unpacked according to the following rules:

If an element of CASC_JENKINS_CONFIG points to a folder, the plugin recursively traverses the folder to find file(s) with the .yml, .yaml, .YAML, or .YML suffix.
It excludes hidden files or files that contain a hidden folder (such as/ jenkins/casc_configs/.dir1/config.yaml ) in any part of the full path.
It follows symbolic links for both files and directories.
The order of traversal does not matter to the final outcome because all configuration files that are discovered MUST be supplementary. If a file attempts to overwrite configuration values from another file, it creates a conflict and raises a ConfiguratorException .

CasC configuration and UI modifications

Configuration for a Jenkins controller should be implemented either with CasC or with the UI, but not by both. The system allows administrators to modify configuration options on the UI even when they were configured by CasC, but these modifications are overwritten the next time the controller restarts.

You can install the Extended Read Permission Plugin, which allows you to grant read-only access to configuration parameters to users. See JEP-224: Readonly system configuration for more details.

A small group of administrators may have write access to the UI configuration fields. They should understand that JCasC will overwrite changes they make on the UI.

For more information

General information

Look Ma! No Hands! — Manage Jenkins Configuration as Code is a video of the 2018 DevOps World presentation that introduced the JCasC feature.
Configure Plugins with JCasC is a blog post with video that demonstrates how to configure a plugin with JCasC.
How to Install Jenkins on CentOS 7 Using Ansible and JCasC is a video presentation with details about using JCasc.

Implementation details

Much of the detailed JCasC documentation is provided in the Github repository.

Implementation details
- The demos directory contains sample *.yaml files for configuring specific Jenkins components and plugins, with a README file in each directory that describes the configurations for that component.
- How to create the initial "seed" job with Job DSL
- Usage scenarios
- Triggering Configuration Reload
- Exporting configurations

Information for plugin developers and maintainers

Developer documentation for JCasC
JCasC Requirements - guide for plugin maintainers

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Change System Time Zone

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Change System Time Zone

Table of Contents

User Defined Time Zone
System Time Zone properties

The system time zone configuration is the default time zone displayed by Jenkins. The "Manage Jenkins" ⇒ "System Information" page shows the value of the system properties that define the time zone for the Jenkins controller.

Refer to the following video for tips on changing the time zone

Changing the time zone in Jenkins

User Defined Time Zone

A user defined time zone for the account can be set from the configure option in the user settings.

System Time Zone properties

If you cannot change the time zone of your server, you can force jelly to use a given time zone for formatting time stamps.

You need to start your Jenkins with the following java system property:

java -Dorg.apache.commons.jelly.tags.fmt.timeZone=TZ ...

where TZ is a java.util.TimeZone ID ("Europe/Paris" for example).

Note that user.timezone=Europe/Paris will work as well, but it can interfere with other contexts.

If running Jenkins via a Linux package, this can be accomplished by running systemctl edit jenkins and adding the following:

[Service]
Environment="JAVA_OPTS=-Dorg.apache.commons.jelly.tags.fmt.timeZone=America/New_York"

or, if that doesn’t work:

[Service]
Environment="JAVA_OPTS=-Duser.timezone=America/New_York"

On FreeBSD, the file to edit is /etc/rc.conf, and the option to use is:

jenkins_java_opts="-Dorg.apache.commons.jelly.tags.fmt.timeZone=America/Denver"

On windows, edit %INSTALL_PATH%/jenkins/jenkins.xml . Put -Dargs before -jar :

<arguments>-Duser.timezone="Europe/Minsk" -jar "%BASE%\jenkins.war"</arguments>

You can also set it from the Jenkins Script Console on a live system without the need for a restart. This can also be included in a Post-initialization script to make it permanent.

System.setProperty('org.apache.commons.jelly.tags.fmt.timeZone', 'America/New_York')

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Jenkins CLI

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Jenkins CLI

Table of Contents

Using the CLI over SSH
- Authentication
- Common Commands
Using the CLI client
- Comparing SSH and CLI client
- Downloading the client
- Using the client
- Client connection modes
- Common Problems with the CLI client

Jenkins has a built-in command line interface that allows users and administrators to access Jenkins from a script or shell environment. This can be convenient for scripting of routine tasks, bulk updates, troubleshooting, and more.

The command line interface can be accessed over SSH or with the Jenkins CLI client, a .jar file distributed with Jenkins.

This document assumes Jenkins 2.54 or newer. Older versions of the CLI client are considered insecure and should not be used.

WebSocket support is available when using both server and client 2.217 or newer.

Using the CLI over SSH

In a new Jenkins installation, the SSH service is disabled by default. Administrators may choose to set a specific port or ask Jenkins to pick a random port in the Configure Global Security page. In order to determine the randomly assigned SSH port, inspect the headers returned on a Jenkins URL, for example:

% curl -Lv https://JENKINS_URL/login 2>&1 | grep -i 'x-ssh-endpoint'
< X-SSH-Endpoint: localhost:53801
%

With the random SSH port ( 53801 in this example), and Authentication configured, any modern SSH client may securely execute CLI commands.

Authentication

Whichever user used for authentication with the Jenkins controller must have the Overall/Read permission in order to access the CLI. The user may require additional permissions depending on the commands executed.

Authentication in SSH mode relies on SSH-based public/private key authentication. In order to add an SSH public key for the appropriate user, navigate to JENKINS_URL/me/configure and paste an SSH public key into the appropriate text area.

Common Commands

Jenkins has a number of built-in CLI commands which can be found in every Jenkins environment, such as build or list-jobs . Plugins may also provide CLI commands; in order to determine the full list of commands available in a given Jenkins environment, execute the CLI help command:

% ssh -l kohsuke -p 53801 localhost help

The following list of commands is not comprehensive, but it is a useful starting point for Jenkins CLI usage.

build

One of the most common and useful CLI commands is build , which allows the user to trigger any job or Pipeline for which they have permission.

The most basic invocation will simply trigger the job or Pipeline and exit, but with the additional options a user may also pass parameters, poll SCM, or even follow the console output of the triggered build or Pipeline run.

% ssh -l kohsuke -p 53801 localhost help build

java -jar jenkins-cli.jar build JOB [-c] [-f] [-p] [-r N] [-s] [-v] [-w]
Starts a build, and optionally waits for a completion.  Aside from general
scripting use, this command can be used to invoke another job from within a
build of one job.  With the -s option, this command changes the exit code based
on the outcome of the build (exit code 0 indicates a success) and interrupting
the command will interrupt the job.  With the -f option, this command changes
the exit code based on the outcome of the build (exit code 0 indicates a
success) however, unlike -s, interrupting the command will not interrupt the
job (exit code 125 indicates the command was interrupted).  With the -c option,
a build will only run if there has been an SCM change.
 JOB : Name of the job to build
 -c  : Check for SCM changes before starting the build, and if there's no
       change, exit without doing a build
 -f  : Follow the build progress. Like -s only interrupts are not passed
       through to the build.
 -p  : Specify the build parameters in the key=value format.
 -s  : Wait until the completion/abortion of the command. Interrupts are passed
       through to the build.
 -v  : Prints out the console output of the build. Use with -s
 -w  : Wait until the start of the command
% ssh -l kohsuke -p 53801 localhost build build-all-software -f -v
Started build-all-software #1
Started from command line by admin
Building in workspace /tmp/jenkins/workspace/build-all-software
[build-all-software] $ /bin/sh -xe /tmp/hudson1100603797526301795.sh
+ echo hello world
hello world
Finished: SUCCESS
Completed build-all-software #1 : SUCCESS
%

console

Similarly useful is the console command, which retrieves the console output for the specified build or Pipeline run. When no build number is provided, the console command will output the last completed build’s console output.

% ssh -l kohsuke -p 53801 localhost help console

java -jar jenkins-cli.jar console JOB [BUILD] [-f] [-n N]
Produces the console output of a specific build to stdout, as if you are doing 'cat build.log'
 JOB   : Name of the job
 BUILD : Build number or permalink to point to the build. Defaults to the last
         build
 -f    : If the build is in progress, stay around and append console output as
         it comes, like 'tail -f'
 -n N  : Display the last N lines
% ssh -l kohsuke -p 53801 localhost console build-all-software
Started from command line by kohsuke
Building in workspace /tmp/jenkins/workspace/build-all-software
[build-all-software] $ /bin/sh -xe /tmp/hudson1100603797526301795.sh
+ echo hello world
yes
Finished: SUCCESS
%

who-am-i

The who-am-i command is helpful for listing the current user’s credentials and permissions available to the user. This can be useful when debugging the absence of CLI commands due to the lack of certain permissions.

% ssh -l kohsuke -p 53801 localhost help who-am-i

java -jar jenkins-cli.jar who-am-i
Reports your credential and permissions.
% ssh -l kohsuke -p 53801 localhost who-am-i
Authenticated as: kohsuke
Authorities:
  authenticated
%

Using the CLI client

While the SSH-based CLI is fast and covers most needs, there may be situations where the CLI client distributed with Jenkins is a better fit. For example, the default transport for the CLI client is HTTP which means no additional ports need to be opened in a firewall for its use.

Comparing SSH and CLI client

Both SSH and jenkins-cli.jar provide access to a set of commands that lets you interact with Jenkins from a command line, but they have a few differences:

Jenkins SSH does not require any custom jar file on the client side, making it easier to access Jenkins from a variety of sources
SSH client was build to be a generic tool to serve several purposes. It doesn’t offer an easy way to do basic things that are common and specific to Jenkins environments. Using the jenkins-cli.jar instead of the ssh client may increase productivity and improve the development experience

Downloading the client

The CLI client can be downloaded directly from a Jenkins controller at the URL /jnlpJars/jenkins-cli.jar , in effect JENKINS_URL/jnlpJars/jenkins-cli.jar

While a CLI .jar can be used against different versions of Jenkins, should any compatibility issues arise during use, please re-download the latest .jar file from the Jenkins controller.

Using the client

The general syntax for invoking the client is as follows:

java -jar jenkins-cli.jar [-s JENKINS_URL] [global options...] command [command options...] [arguments...]

The JENKINS_URL can be specified via the environment variable $JENKINS_URL . Summaries of other general options can be displayed by running the client with no arguments at all.

Client connection modes

There are three basic modes in which the client may be used, selectable by global option: -http , -webSocket , and -ssh .

HTTP connection mode

This is the default mode, though you may pass the -http option explicitly for clarity.

Authentication is preferably with an -auth option, which takes a username:apitoken argument. Get your API token from /me/configure :

java -jar jenkins-cli.jar [-s JENKINS_URL] -auth kohsuke:abc1234ffe4a command ...

(Actual passwords are also accepted, but this is discouraged.)

You can also precede the argument with @ to load the same content from a file:

java -jar jenkins-cli.jar [-s JENKINS_URL] -auth @/home/kohsuke/.jenkins-cli command ...

For security reasons the use of a file to load the authentication credentials is the recommended authentication way.

An alternative authentication method is to configure environment variables in a similar way as the $JENKINS_URL is used. The username can be specified via the environment variable $JENKINS_USER_ID while the apitoken can be specified via the variable $JENKINS_API_TOKEN . Both variables have to be set all at once.

export JENKINS_USER_ID=kohsuke
export JENKINS_API_TOKEN=abc1234ffe4a
java -jar jenkins-cli.jar [-s JENKINS_URL] command ...

In case these environment variables are configured you could still override the authentication method using different credentials with the -auth option, which takes preference over them.

Generally no special system configuration need be done to enable HTTP-based CLI connections. If you are running Jenkins behind an HTTP(S) reverse proxy, ensure it does not buffer request or response bodies.

This mode is known to not work reliably or at all when using certain reverse proxies. Prefer WebSocket mode.

WebSocket connection mode

In Jenkins 2.217 and above, the -webSocket mode may be used as an alternative to -http . The advantage is that a more standard transport is used, avoiding problems with many reverse proxies or the need for special proxy configuration.

SSH connection mode

Authentication is via SSH keypair. You must select the Jenkins user ID as well:

java -jar jenkins-cli.jar [-s JENKINS_URL] -ssh -user kohsuke command ...

In this mode, the client acts essentially like a native ssh command.

By default the client will try to connect to an SSH port on the same host as is used in the JENKINS_URL . If Jenkins is behind an HTTP reverse proxy, this will not generally work, so run Jenkins with the system property -Dorg.jenkinsci.main.modules.sshd.SSHD.hostName=ACTUALHOST to define a hostname or IP address for the SSH endpoint.

Common Problems with the CLI client

There are a number of common problems that may be experienced when running the CLI client.

Server key did not validate

You may get the error below and find a log entry just below that concerning mismatched keys :

org.apache.sshd.common.SshException: Server key did not validate
    at org.apache.sshd.client.session.AbstractClientSession.checkKeys(AbstractClientSession.java:523)
    at org.apache.sshd.common.session.helpers.AbstractSession.handleKexMessage(AbstractSession.java:616)
    ...

This means your SSH configuration does not recognize the public key presented by the server. It’s often the case when you run Jenkins in dev mode and multiple instances of the application are run under the same SSH port over time.

In a development context, access your ~/.ssh/known_hosts (or in C:/Users/<your_name>/.ssh/known_hosts for Windows) and remove the line corresponding to your current SSH port (e.g. [localhost]:3485 ). In a production context, check with the Jenkins administrator if the public key of the server changed recently. If so, ask the administrator to do the the steps described above.

UsernameNotFoundException

If your client displays a stacktrace that looks like:

org.acegisecurity.userdetails.UsernameNotFoundException: <name_you_used>
    ...

This means your SSH keys were recognized and validated against the stored users but the username is not valid for the security realm your application is using at the moment. This could occur when you were using the Jenkins database initially, configured your users, and then switched to another security realm (like LDAP, etc.) where the defined users do not exist yet.

To solve the problem, ensure your users exist in your configured security realm.

Troubleshooting logs

To get more information about the authentication process:

Go into Manage Jenkins > System Log > Add new log recorder .
Enter any name you want and click on Ok .
Click on Add
Type org.jenkinsci.main.modules.sshd.PublicKeyAuthenticatorImpl (or type PublicKeyAuth and then select the full name)
Set the level to ALL .
Repeat the previous three steps for hudson.model.User
Click on Save

When you try to authenticate, you can then refresh the page and see what happen internally.

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Groovy Hook Scripts

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â Managing Jenkins Index

Managing Nodes â

Groovy Hook Scripts

This section is a work in progress. Want to help? Check out the jenkinsci-docs mailing list. For other ways to contribute to the Jenkins project, see this page about participating and contributing.

Table of Contents

Post initialization script (init hook)
Boot failure hook

In several places inside Jenkins, a series of "hook scripts" get executed to allow some actions to take place in reaction to some key events.

These scripts are written in Groovy, and get executed inside the same JVM as Jenkins, allowing full access to the domain model of Jenkins. For given hook HOOK , the following locations are searched:

WEB-INF/HOOK.groovy in jenkins.war
WEB-INF/HOOK.groovy.d/*.groovy in the lexical order in jenkins.war
$JENKINS_HOME/HOOK.groovy
$JENKINS_HOME/HOOK.groovy.d/*.groovy in the lexical order

HOOK.groovy.d is suitable to avoid conflicts â multiple entities can insert stuff into the hook without worrying about overwriting each other’s code.

The following events use this mechanism by replacing HOOK in HOOK.groovy.d or HOOK.groovy by one of the below mentioned types:

init : Post-initialization script
boot-failure : Boot failure hook

Post initialization script (init hook)

You can create a Groovy script file $JENKINS_HOME/init.groovy , or any .groovy file in the directory $JENKINS_HOME/init.groovy.d/ , to run some additional things right after Jenkins starts up. The groovy scripts are executed at the end of Jenkins initialization. This script can access classes in Jenkins and all the plugins. So for example, you can write something like:

import jenkins.model.Jenkins;

// start in the state that doesn't do any build.
Jenkins.instance.doQuietDown();

Output is logged to the Jenkins log file. For Debian based users, this isÂ /var/log/jenkins/jenkins.log

Boot failure hook

When Jenkins encounters a fatal problem during boot, it’ll invoke "boot-failure" hook script to allow automatic corrective actions to be taken (such as notifying somebody, raising alerts, restarting, and so on.)

These scripts get the cause of the problem as the "exception" variable when run.

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Managing Jenkins

â Blue Ocean

Index

Configuring the System â

Managing Jenkins

Chapter Sub-Sections

Table of Contents

System Configuration group
Security group
Status Information group
Troubleshooting group
Tools and Actions group
Uncategorized group

Most standard administrative tasks can be performed from the screens in the Manage Jenkins section of the dashboard. In this chapter, we look at these screens and explain how to use them.

The tiles displayed on the Manage Jenkins page are grouped logically. Here we discuss the pages that are part of the standard installation. Plugins may add pages to this screen.

The top of the Manage Jenkins screen may contain "Monitors" that alert you when a new version of the Jenkins software or a security update is available. Each monitor includes a description of the issue it is reporting and links to additional information about the issue

Inline help is available on most Manage Jenkins pages:

To access the help, select the ? icon to the right of each field.
Click the ? icon again to hide the help text.

The Manage Jenkins screens were modernized in 2020 to provide a more attractive user interface for all users and a much better experience for users on narrow devices such as tablets and phones. The main changes made were:

Configuration screens now use HTML div tags rather than the HTML table tags that were used in older releases.
The screens linked from this page are grouped somewhat logically, whereas older versions presented a long list of tasks in somewhat random order.
Some configuration fields were moved or added.

For more information about these and other changes that have been implemented, see:

2.277.1 LTS Changelog
Jenkins 2.264+: Major changes in the weekly release line
Jenkins LTS Upgrade Guide

Other system administration topics are discussed in Jenkins System Administration.

System Configuration group

Screens for configuring resources for your Jenkins instance.

Configure System: Configure global settings and paths for the Jenkins instance
Global Tool Configuration: Configure tools, their locations, and automatic installers
Manage Plugins: Add, update, remove, disable/enable plugins that extend the functionality of Jenkins.
Manage Nodes and Clouds: Add, remove, control, and monitor the nodes used for the agents on which build jobs run.
Configuration as Code: Configure your Jenkins instance using a human-readable YAML file rather than the UI. This is an optional feature that appears in this group only when the plugin is installed on your controller.

Security group

Screens for configuring security features for your Jenkins instance. See Securing Jenkins for general information about managing Jenkins security.

Configure Global Security: Set configuration parameters that secure your Jenkins instance.
Manage Credentials: Configure the credentials that provide secure access to third-party sites and applications that interact with Jenkins.
Configure Credential Providers: Configure credential providers and types
Manage Users: Manage users defined in the Jenkins user database. This is not used if you use a different security realm such as LDAP or AD.

Status Information group

System Information: Displays information about the Jenkins environment.
System Log: Jenkins log that contains all java.uil.logging output related to Jenkins.
Load Statistics: Displays information about resource utilization on you Jenkins instance.
About Jenkins: Provides version and license information for your Jenkins instance.

Troubleshooting group

Manage Old Data: Remove configuration information related to plugins that have been removed from the instance.

Tools and Actions group

Screens for common management tasks and management tools that enable you to do administrative tasks without using the UI.

Reload Configuration from Disk: Discard all data that is loaded in memory and reload everything from the file system. This is useful when you modify configuration files directly on disk.
Jenkins CLI: How to use the Jenkins CLI from a shell or script.
Script Console: Execute an Apache Groovy script for administration, troubleshooting, and diagnostics.
Prepare for Shutdown: Prevents new builds from starting so that the system can be shut down safely. Displays a red banner with a custom message so that users know what is about to happen.

Red headband with a custom message

This does not ask Jenkins to stop; this action will just prevent new builds from starting. If you need to stop or restart Jenkins, you should use the command line or the /restart and /safeRestart end points. There is also a plugin called Safe Restart that will add a Restart Safely link in the UI.

Uncategorized group

Screens for plugins that have not yet declared the category of their page.

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Managing Nodes

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Managing Nodes

Table of Contents

Components of Distributed Builds
Creating Agents
Launch inbound agent via Windows Scheduler
Installing a Jenkins agent on Windows
Creating a macOS agent for Jenkins

Components of Distributed Builds

Builds in a Distributed Builds Architecture use nodes, agents, and executors which are distinct from the Jenkins controller itself. Understanding what each of these components are is useful when managing nodes:

Jenkins controller: The Jenkins controller is the Jenkins service itself and is where Jenkins is installed. It is a webserver that also acts as a "brain" for deciding how, when and where to run tasks. Management tasks (configuration, authorization, and authentication) are executed on the controller, which serves HTTP requests. Files written when a Pipeline executes are written to the filesystem on the controller unless they are off-loaded to an artifact repository such as Nexus or Artifactory.
Nodes: Nodes are the "machines" on which build agents run. Jenkins monitors each attached node for disk space, free temp space, free swap, clock time/sync and response time. A node is taken offline if any of these values go outside the configured threshold.

The Jenkins controller itself runs on a special built-in node . It is possible to run agents and executors on this built-in node although this can degrade performance, reduce scalability of the Jenkins instance, and create serious security problems and is strongly discouraged, especially for production environments.

Agents: Agents manage the task execution on behalf of the Jenkins controller by using executors. An agent is actually a small (170KB single jar) Java client process that connects to a Jenkins controller and is assumed to be unreliable. An agent can use any operating system that supports Java. Tools required for builds and tests are installed on the node where the agent runs; they can be installed directly or in a container (Docker or Kubernetes). Each agent is effectively a process with its own PID (Process Identifier) on the host machine.

In practice, nodes and agents are essentially the same but it is good to remember that they are conceptually distinct.

Executors: An executor is a slot for execution of tasks; effectively, it is a thread in the agent. The number of executors on a node defines the number of concurrent tasks that can be executed on that node at one time. In other words, this determines the number of concurrent Pipeline stages that can execute on that node at one time.

The proper number of executors per build node must be determined based on the resources available on the node and the resources required for the workload. When determining how many executors to run on a node, consider CPU and memory requirements as well as the amount of I/O and network activity:

One executor per node is the safest configuration.
One executor per CPU core may work well if the tasks being run are small.
Monitor I/O performance, CPU load, memory usage, and I/O throughput carefully when running multiple executors on a node.

Creating Agents

Jenkins agents are the "workers" that perform operations requested by the Jenkins controller. The Jenkins controller administers the agents and can manage the tooling on the agents. Jenkins agents may be statically allocated or they can be dynamically allocated through systems like Kubernetes, OpenShift, Amazon EC2, Azure, Google Cloud, IBM Cloud, Oracle Cloud, and other cloud providers.

This 30 minute tutorial from Darin Pope creates a Jenkins agent and connects it to a controller.

How to create an agent node in Jenkins

Launch inbound agent via Windows Scheduler

If you are having trouble getting the inbound agent installed as a Windows service (i.e., you followed the instructions on installing the agent as a service here but it didn’t work), an alternative method of starting the service automatically when Windows starts is to use the Windows Scheduler.Â

We take advantage of the Windows Scheduler’s ability to run command at system startup

Configure your node to use the "Launch agents by connecting it to the master" launch method
- Click Save
Note the command required to launch the agent
- On the new agent node’s Jenkins page, note the agent command line shown.Â
  - It will be like:

java -jar agent.jar \
-jnlpUrl http://<JenkinsHostName>:8080/computer/<nodeName>/slave-agent.jnlp \
-secret <some_long_hex_string>

Obtain the agent.jar file and copy it to your new Windows agent node
- In the command line noted in the last step, the "agent.jar" is a hyperlink. Click it to download the agent.jar file.
- Copy the agent.jar file to a permanent location on your agent machine
Ensure that you have a java version available on your agent machine
- If not, obtain and install a supported version of Java
Run the command manually from a CMD window on your agent to confirm that it works
- Open the CMD window
- Run the command the one like

java -jar agent.jar -jnlpUrl \
http://<JenkinsHostName>:8080/computer/<nodeName>/slave-agent.jnlp -secret <some_long_hex_string>

Go back to the node’s web page in Jenkins.Â If everything works then page should say "Agent is connected"
Stop the command (control-c)
1. Register a new scheduled job to run the same command
Open "Task Scheduler" on your windows machine
- Start → Run: task Scheduler
Create a basic task (Menu: Action → Create Basic Task)
- First page of the wizard:
  - Name: Jenkins Agent
  - Description (optional)
  - Click Next
- Next page of the wizard
  - When do you want the task to start: select "When the computer starts"
  - Click Next
- Next page of the wizard
  - What action do you want the task to perform: select "Start a program"
  - Click Next
- Next page of the wizard
  - Program/Script: enter "java.exe" (or the full path to your java.exe)
  - Add arguments: enter the rest of the command, like

-jar agent.jar -jnlpUrl http://<JenkinsHostName>:8080/computer/<nodeName>/slave-agent.jnlp \
-secret <some_long_hex_string>

-jar D:\Scripts\jenkins\agent.jar \
-jnlpUrl http://jenkinshost.example.com:8080/computer/buildNode1/slave-agent.jnlp -secret \
d6a84df1fc4f45ddc9c6ab34b08f13391983ffffffffffb3488b7d5ac77fbc7

Click Next
- Next page of the wizard
Click the check box "Open the Properties dialog for this task when I click Finish
Click Finish
- Update the task’s properties
  - On the General tab
Select the user to run the task as
Select "Run whether user is logged on or not"
- On the settings tab
Uncheck "Stop the task if it runs longer than"
Check "Run the task as soon as possible after a scheduled start is missed"
Check "If the task failed, restart every: 10 minutes", and "Attempt to restart up to: 3 times"
- Click OK
  1. Start the scheduled task and again check that the agent is connected
    
    Go back to the node’s web page in Jenkins.Â If everything works then page should say "Agent is connected"

Installing a Jenkins agent on Windows

You can install a Jenkins agent on Windows using the command line. In this video, Darin reviews setting up and installing the Jenkins agent, including how to create any necessary files.

How to install a Jenkins agent on Windows

Creating a macOS agent for Jenkins

This video reviews the process of creating a macOS agent for Jenkins using Java 11.

â Groovy Hook Scripts

â Managing Jenkins Index

In-process Script Approval â

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