Poll SCM configuration in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Understanding Poll SCM Cron Syntax

What is the effect of the following Poll SCM cron schedule in Jenkins?

H/15 * * * *

A Polls the SCM every 15 minutes at a random offset to reduce load spikes.

B Polls the SCM exactly at minute 15 of every hour.

C Polls the SCM once daily at 15 minutes past midnight.

D Polls the SCM every 15 seconds continuously.

💡 Hint

The 'H' character in Jenkins cron means a hashed value to spread load.

The 'H/15' means Jenkins will pick a random minute offset and then poll every 15 minutes from that offset, preventing all jobs from polling at the same time.

❓ Configuration

intermediate

Correct Poll SCM Configuration for Hourly Polling

Which Poll SCM cron expression correctly configures Jenkins to poll the SCM once every hour at the 0th minute?

A 0 0 * * *

B H * * * *

C */60 * * * *

D 0 * * * *

💡 Hint

Look for the expression that triggers at minute zero of every hour.

The expression '0 * * * *' means at minute 0 of every hour, poll SCM once.

❓ Troubleshoot

advanced

Poll SCM Not Triggering Builds

A Jenkins job is configured with Poll SCM using the schedule 'H/10 * * * *' but no builds are triggered even though the repository has changes. What is the most likely cause?

A The Jenkins workspace is corrupted and prevents polling from detecting changes.

B The Poll SCM schedule syntax is invalid and causes Jenkins to skip polling.

C The Jenkins user does not have permission to access the SCM repository.

D The SCM plugin is disabled in Jenkins.

💡 Hint

Check permissions and access rights first when polling does not detect changes.

If Jenkins cannot access the SCM repository due to permission issues, polling will not detect changes and no builds will trigger.

✅ Best Practice

advanced

Efficient Poll SCM Scheduling

Which Poll SCM schedule is best to reduce load on the SCM server when multiple Jenkins jobs poll frequently?

A Use 'H/5 * * * *' to poll every 5 minutes with a hashed offset.

B Use '*/5 * * * *' to poll every 5 minutes exactly on the 0,5,10... minutes.

C Use '0 * * * *' to poll once every hour at minute 0.

D Use 'H H * * *' to poll once daily at a hashed hour and minute.

💡 Hint

Hashed offsets help distribute polling times evenly.

Using 'H/5' spreads polling every 5 minutes but staggered per job, reducing simultaneous load spikes on SCM.

🧠 Conceptual

expert

Poll SCM Behavior with Multiple Branches

In a Jenkins Multibranch Pipeline, how does Poll SCM behave when configured with a schedule like 'H/15 * * * *'?

A Polling is disabled for multibranch pipelines; builds trigger only on webhooks.

B Each branch is polled independently at its own hashed offset every 15 minutes.

C Only the default branch is polled every 15 minutes; other branches are ignored.

D All branches are polled simultaneously every 15 minutes causing load spikes.

💡 Hint

Multibranch pipelines treat branches as separate jobs with their own schedules.

Each branch job gets its own hashed polling schedule, so polling is spread out evenly across branches.