Build triggers (poll SCM, webhook, timer) in Jenkins - Commands & Configuration

Introduction

Build triggers in Jenkins automatically start jobs based on events like code changes, scheduled times, or external signals. This helps keep your software up-to-date without manual intervention.

When you want Jenkins to check your code repository regularly for changes and start a build if there are any.

When you want Jenkins to start a build immediately after someone pushes code to your repository using a webhook.

When you want Jenkins to run builds at specific times, like every night or every hour.

When you want to automate testing and deployment without manually clicking buttons.

When you want to save time by automating repetitive build tasks triggered by events.

Config File - Jenkinsfile

Jenkinsfile

pipeline {
  agent any
  triggers {
    pollSCM('H/15 * * * *')
    // This triggers polling every 15 minutes
    // For webhook, Jenkins listens automatically if configured in repo
    cron('H 2 * * *')
    // This triggers build daily at 2 AM
  }
  stages {
    stage('Build') {
      steps {
        echo 'Building the project...'
      }
    }
  }
}

The triggers block defines when Jenkins should start the build automatically.

• pollSCM('H/15 * * * *') tells Jenkins to check the source code repository every 15 minutes for changes.
• cron('H 2 * * *') schedules a build every day at 2 AM.
• Webhook triggers are configured outside Jenkins but Jenkins listens for them to start builds immediately when code is pushed.

Commands

Manually triggers the Jenkins pipeline named 'my-pipeline' to test if the job runs correctly before setting triggers.

Terminal

jenkins-cli build my-pipeline

Expected Output

[Pipeline] Start of Pipeline

[Pipeline] echo

Building the project...

[Pipeline] End of Pipeline

Finished: SUCCESS

Retrieves the current configuration of the 'my-pipeline' job to verify trigger settings.

Terminal

jenkins-cli get-job my-pipeline

Expected Output

<?xml version="1.1" encoding="UTF-8"?>

<flow-definition plugin="workflow-job@2.40">

  <triggers>

    <hudson.triggers.SCMTrigger>

      <spec>H/15 * * * *</spec>

    </hudson.triggers.SCMTrigger>

    <hudson.triggers.TimerTrigger>

      <spec>H 2 * * *</spec>

    </hudson.triggers.TimerTrigger>

  </triggers>

</flow-definition>

Simulates a webhook POST request to Jenkins to trigger the 'my-pipeline' job immediately when code is pushed.

Terminal

curl -X POST http://jenkins.example.com/job/my-pipeline/build?token=webhooktoken

Expected Output

No output (command runs silently)

→

-X POST - Specifies the HTTP POST method to trigger the build

Lists all Jenkins jobs to confirm 'my-pipeline' exists and is ready for triggers.

Terminal

jenkins-cli list-jobs

Expected Output

my-pipeline

example-job

build-test

Key Concept

If you remember nothing else from this pattern, remember: build triggers automate job starts based on code changes, scheduled times, or external signals to save manual effort.

Common Mistakes

Setting poll SCM trigger without proper repository access permissions

Jenkins cannot check the repository for changes, so builds never start automatically.

Ensure Jenkins has correct credentials and access rights to the source code repository before enabling poll SCM.

Not configuring the webhook URL correctly in the source code repository

Jenkins never receives the push notification, so builds are not triggered immediately.

Set the webhook URL in the repository to point exactly to Jenkins job webhook endpoint with correct token.

Using incorrect cron syntax for timer triggers

The build does not run at the expected time or never runs.

Use Jenkins cron syntax carefully, for example 'H 2 * * *' for daily at 2 AM, and test with Jenkins cron syntax validator.

Summary

Use poll SCM trigger to check for code changes regularly and start builds automatically.

Use webhook trigger to start builds immediately when code is pushed to the repository.

Use timer trigger to schedule builds at specific times like nightly or hourly.

Verify triggers by checking job configuration and manually triggering builds.

Configure repository and Jenkins permissions correctly for triggers to work.