Fix Jenkins Build Stuck

What's Actually Happening

Jenkins builds hang in queue or during execution. Jobs show "Pending" or "Running" indefinitely without progress, blocking the pipeline.

The Error You'll See

Build stuck in queue:

```bash curl -s http://localhost:8080/queue/api/json | jq .items[].task.name

my-job (waiting for executor) ```

Build hanging during execution:

```bash curl -s http://localhost:8080/computer/api/json | jq .computer[].idle

false ```

Console output shows nothing:

Started by user admin
[Pipeline] stage
[Pipeline] { (Build)
Hangs here with no output

Why This Happens

1. 1.No available executors - All executors busy or offline
2. 2.Agent disconnected - Jenkins agent lost connection
3. 3.Resource exhaustion - Disk full, memory low
4. 4.Deadlock in pipeline - Parallel stages blocking
5. 5.External dependency stuck - Database or API call hanging
6. 6.Long-running build - Previous build not finishing
7. 7.Executor hung - Executor process stuck

Step 1: Check Jenkins Queue Status

```bash curl -s http://localhost:8080/queue/api/json | jq

curl -s http://localhost:8080/queue/api/json | jq .items[] | {id: .id, name: .task.name, why: .why}

curl -s http://localhost:8080/queue/api/json | jq .items[].why

curl -s http://localhost:8080/queue/api/json | jq .items | length

curl -X POST http://localhost:8080/queue/cancel?id=123 ```

Step 2: Check Executor Availability

```bash curl -s http://localhost:8080/computer/api/json | jq .computer[] | {name: .name, idle: .idle, offline: .offline}

curl -s http://localhost:8080/computer/api/json | jq .computer[] | select(.offline == true)

curl -s http://localhost:8080/computer/api/json | jq [.computer[] | select(.idle == true)] | length

curl -s http://localhost:8080/computer/api/json | jq .computer[] | select(.idle == false) ```

Step 3: Check Agent Connectivity

```bash curl -s http://localhost:8080/computer/agent-name/api/json | jq {offline: .offline, offlineCause: .offlineCause}

cat /var/log/jenkins-agent.log

ps aux | grep jenkins-agent

ssh -p 22 jenkins@agent-host

systemctl restart jenkins-agent ```

Step 4: Check Running Builds

```bash curl -s http://localhost:8080/job/my-job/123/api/json | jq {building: .building, duration: .duration}

curl -X POST http://localhost:8080/job/my-job/123/stop

curl -X POST http://localhost:8080/job/my-job/123/kill ```

Step 5: Check Disk and Memory

```bash df -h /var/lib/jenkins

find /var/lib/jenkins/jobs -name builds -exec sh -c ls -t "$1" | tail -n +20 | xargs rm -rf _ {} \;

find /var/lib/jenkins/workspace -type d -mtime +30 -exec rm -rf {} \;

free -h

ps aux | grep jenkins | awk {print $6}

cat /etc/default/jenkins | grep JAVA_ARGS

systemctl restart jenkins ```

Step 6: Check Pipeline Deadlock

```bash curl -s http://localhost:8080/job/my-pipeline/123/wfapi/describe | jq .stages[] | {name: .name, status: .status}

curl -s http://localhost:8080/job/my-pipeline/123/wfapi/describe | jq .stages[] | select(.status == "IN_PROGRESS")

curl -X POST http://localhost:8080/job/my-pipeline/123/resume

curl -X POST http://localhost:8080/job/my-pipeline/123/stop ```

Step 7: Check External Dependencies

ping -c 3 external-api
nc -zv external-api 443
nslookup external-api
curl -m 10 https://external-api/health
mysql -h db-host -u user -p -e "SELECT 1"
git ls-remote https://github.com/org/repo

Step 8: Restart Hung Executors

```bash curl -X POST http://localhost:8080/computer/agent-name/toggleOffline?reason=restart

ssh agent-host systemctl restart jenkins-agent

curl -X POST http://localhost:8080/computer/agent-name/toggleOffline?reason=back%20online

systemctl restart jenkins

curl -X POST http://localhost:8080/safeRestart ```

Step 9: Check Jenkins Logs

```bash journalctl -u jenkins -f

tail -f /var/log/jenkins/jenkins.log

grep -i "error" /var/log/jenkins/jenkins.log | tail -50

curl -s http://localhost:8080/threadDump > jenkins-threads.txt ```

Step 10: Monitor and Prevent Stuck Builds

```bash curl -s http://localhost:8080/queue/api/json | jq .items | length

curl -s http://localhost:8080/computer/api/json | jq .computer[] | {name: .name, idle: .idle}

watch -n 30 curl -s http://localhost:8080/queue/api/json | jq ".items | length" ```

Jenkins Build Stuck Checklist

Verify the Fix

```bash curl -s http://localhost:8080/queue/api/json | jq .items | length

curl -s http://localhost:8080/computer/api/json | jq [.computer[] | select(.idle)] | length

curl -X POST http://localhost:8080/job/my-job/build

curl -s http://localhost:8080/job/my-job/lastBuild/api/json | jq .building

curl -s http://localhost:8080/job/my-job/lastBuild/api/json | jq .duration ```

Related Issues

• [Fix Jenkins Agent Offline](/articles/fix-jenkins-agent-offline)
• [Fix Jenkins Pipeline Failed](/articles/fix-jenkins-pipeline-failed)