🔧 Fixing “Permission Denied While Trying to Connect to the Docker Daemon Socket” in Jenkins

Running Jenkins builds that involve Docker can sometimes lead to frustrating errors. One such common error is:

permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock

If you’ve stumbled upon this error during a Jenkins pipeline or freestyle job, don’t worry — you’re not alone. In this article, we’ll break down what this error means, why it happens, and how to fix it the right way.

🧠 What Does the Error Mean?

When Jenkins tries to run a Docker command (like docker build, docker run, or docker rm), it needs to communicate with the Docker daemon. On Linux systems, Docker exposes a special Unix socket file:

/var/run/docker.sock

This socket file controls access to Docker. Only users with permission to this file (typically, members of the docker group) can interact with Docker.

So, if Jenkins shows this error:

permission denied while trying to connect to the Docker daemon socket

…it means that the user Jenkins is running as doesn't have access to Docker.

🔍 Real-Life Example

Here’s a real error output from Jenkins:

+ docker rm --force c1
permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock:
Delete "http://%2Fvar%2Frun%2Fdocker.sock/v1.47/containers/c1?force=1": 
dial unix /var/run/docker.sock: connect: permission denied
Build step 'Execute shell' marked build as failure
Finished: FAILURE

In this case, Jenkins tried to remove a Docker container but couldn’t connect to Docker due to a lack of permissions.

🛠️ How to Fix It

✅ Option 1: Add Jenkins to the Docker Group (Recommended)

Check what user Jenkins is running as:
Run:
```
ps aux | grep jenkins
```
Typically, it’s just the jenkins user.
Add the Jenkins user to the docker group:
```
sudo usermod -aG docker jenkins
```

Restart Jenkins and Docker:

sudo systemctl restart jenkins
sudo systemctl restart docker

Log out and log back in (or reboot) to apply group changes.

📝 Note: You might also need to restart your machine or at least re-login for the group membership to fully apply.

✅ Option 2: Use `sudo` with Docker (Less Secure)

If you're in a controlled environment (like a personal test server), and you’re okay with some security tradeoffs, you can run Docker commands with sudo in your Jenkins shell build steps:

Edit your Jenkins job’s shell script:
```
sudo docker rm --force c1
```
Allow the Jenkins user to run Docker without a password:
Open the sudoers file:
```
sudo visudo
```
Add this line:
```
jenkins ALL=(ALL) NOPASSWD: /usr/bin/docker
```

⚠️ Be careful: This can be dangerous in production environments. It gives Jenkins the power to run Docker commands without authentication.

🚫 Option 3: Don’t Run Jenkins as Root

Sometimes people try to fix this by running Jenkins as root. This is not recommended and should be avoided unless absolutely necessary (e.g., in temporary test setups).

✅ Test It Out

Once you've applied one of the fixes:

Restart Jenkins
Re-run the failing job
You should now see Docker commands run without permission issues

🧩 Bonus Tip: Verify Docker Access from Terminal

Before rerunning Jenkins, test Docker manually from the Jenkins user’s context:

sudo su - jenkins
docker ps

If this works without an error, Jenkins should be able to access Docker too.

🎯 Conclusion

This “permission denied” error when connecting to Docker from Jenkins is usually a simple permissions issue. The most reliable and secure solution is to add Jenkins to the docker group and restart your services. Once that's done, your Jenkins pipelines should be able to run Docker commands seamlessly.

💬 Have you faced this error in other CI tools? Let me know in the comments — and share how you fixed it!

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