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How to Fix “x509 Certificate Signed by Unknown Authority” Error

When you use docker on your system, you might face some issues in the beginning or within the usage process. “Docker x509 Certificate Signed by Unknown Authority” error is one of the issues that you may face. There are a few reasons for that issue to arise. So, this is our comprehensive guide which is a part of our Docker consulting service. With this blog, we’re going to help you troubleshoot x509 Certificate Signed by Unknown Authority” error easily. 

If you’ve ever encountered the “x509 Certificate Signed by Unknown Authority” error, fear not; you’re not alone. This error often appears in the world of secure connections and digital certificates. In this detailed guide, we’ll demystify this error, explaining what it means, why it occurs, and most importantly, how to fix it. By the end, you will have the knowledge to resolve this issue. Let’s start with the basics.

Understanding the “x509 Certificate Signed by Unknown Authority” Error

The “x509 Certificate Signed by Unknown Authority” error occurs when your system or application encounters a digital certificate (usually an x509 certificate) and cannot verify its authenticity. In other words, the certificate presented is not recognized or trusted by the software or system in use.

The Docker “certificate signed by unknown authority” error typically occurs when Docker tries to establish a secure connection with a registry or server. Docker relies on secure connections (often over HTTPS) to ensure the authenticity and integrity of container images. When you see this error, it means Docker has encountered a digital certificate, like an SSL/TLS certificate, that it cannot trust or verify.

To understand the “certificate signed by unknown authority” error better, we need to explore some key concepts:

Digital Certificates:

A digital certificate is like a virtual ID card for a website, server, or service.

It is issued by a Certificate Authority (CA), which is a trusted entity responsible for verifying the identity of the certificate holder.

Certificates ensure secure, encrypted connections over the internet.


x509 is a standard for digital certificates, widely used in secure connections (like HTTPS) and within various technologies, including web browsers, web servers, and applications.

The Error:

When your system encounters a certificate, it checks if it’s signed by a recognized and trusted authority (the CA).

If the certificate is self-signed or signed by an unknown or untrusted authority, your system flags it as unverified, leading to the “x509 Certificate Signed by Unknown Authority” error.

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Key Terminology:

Certificate Authority (CA): An entity that issues digital certificates and vouches for the legitimacy of the certificate holder.

Self-Signed Certificate: A certificate created and signed by the entity it represents, rather than by a recognized CA.

Common Scenarios for the Error

Now that you know what the error means, let’s explore some common situations where it tends to pop up:

1. Secure Web Browsing (HTTPS):

You might have seen this error in your web browser when trying to access a secure website. It’s a warning that the website’s certificate is unverified or self-signed.

2. API Requests:

If you’re making API requests over HTTPS and the server’s certificate isn’t trusted, your application might encounter this error.

3. Docker and Containers:

Docker uses certificates for secure communication. If a container, registry, or service within a container isn’t configured with trusted certificates, you can run into this error.

4. Self-Signed Certificates:

Self-signed certificates are often the culprits. These certificates are created and signed by the entity they represent, rather than by a recognized CA. Hence, they trigger this error.

Why Trust Matters

Certificates are the digital equivalent of ID cards in the online world. They’re issued by Certificate Authorities (CAs) that vouch for the authenticity of the certificate holder. When you connect to a secure website (usually identified by “https://” in the URL), your browser checks the website’s SSL/TLS certificate to ensure it’s valid and signed by a recognized CA. If the certificate is self-signed or signed by an unknown authority, your browser displays a warning.

Similarly, Docker ensures secure connections between your system and registries or services by verifying the certificates. If Docker doesn’t recognize the authority that signed the certificate, it rejects the connection to protect you from potential security risks.

Trust is an important thing for secure communication in the digital world. Just like you trust your ID card when passing through security, systems, and applications rely on certificates signed by trusted CAs to ensure the authenticity and integrity of the data they transmit.

Diagnose the Issue:

To recreate the issue, you can try logging into the docker with the command provided below:

docker login <docker_registry_host>:<docker_registry_port> -u user -p password
docker login -u admin -p pass@123

If there is a problem with the certificate, you will receive the following error:

Error response from daemon : Get x509 certificate
signed by unknown authority

To Resolve the Issue:

On the system where you are attempting to run the docker login command, copy the self-signed certificate to the “/etc/docker/certs.d/docker_registry_hostname>:docker_registry_host_port>/ca.crt” file. This will cause the docker to trust the certificate since it was signed by the user.

You may solve this problem by following the steps that are shown below:

1. On the server that you are using to attempt to perform the docker login command, create the following directory.


2. To copy your Docker registry certificate file, you’ll need to transfer it from your Docker registry host to the cluster where you’re running docker login.

It is strongly recommended that you rename the file containing your registry certificate to “/etc/docker/certs.d/docker_registry_host>:docker_registry_host_port>/ca.crt.”

scp <your_registry_hostname>:/opt/registry/certs/domain.crt

For example ;

mkdir-p/etc/docker/certs.d/ 5666

3. After that, you can attempt to log in to your Docker registry once more.

Fix the “x509 Certificate Signed by Unknown Authority” Error with other methods

Now, let’s look at the points to resolving this error. The process can be complex, but with a methodical approach, you can tackle it effectively:

1. Certificate Inspection:

Start by inspecting the certificate that’s triggering the error. Look for information like the issuer, expiration date, and common name (CN).

Determine if it’s self-signed or signed by an unknown authority.

2. Trustworthy Certificates:

Ensure you’re working with trustworthy certificates. If you’re responsible for a website, API, or service, obtain a certificate from a recognized CA.

3. Adding the CA to Your System:

If you’re dealing with self-signed certificates or certificates signed by an unknown authority, you can add the signing CA’s certificate to your system’s trusted root authorities.

4. Updating Configuration Files:

In the context of containers and Docker, you may need to update your Docker configuration or the configuration files of your containers to use trusted certificates.

5. API Requests and Applications:

If you’re making API requests and your application is encountering an error, ensure that your application or library is configured to trust the certificate in use.

6. Testing and Validation:

Once you’ve made changes, test the affected system, service, or application to ensure that the error no longer occurs. Make sure your software now trusts the certificate.

7. Security Considerations:

Keep in mind that security should always be a top priority. If you’re responsible for certificates, prioritize obtaining them from recognized CAs to ensure the highest level of security.

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The “x509 Certificate Signed by Unknown Authority” error is a common roadblock in communication, but it  can be overcome easily. By understanding the error, its causes, and the solutions outlined in this guide, you’re well-equipped to tackle it head-on. Whether you’re securing web connections, API requests, or Docker containers, trust and authentication are keys to a safer, more reliable digital world.

With this detailed guide, we tried to provide you with the best solution for troubleshooting the “x509 Certificate Signed by Unknown Authority” problem with easy steps. We hope you liked this blog and if you want to read more about docker and how to troubleshoot issues, you can visit our blog page. And if you want to know more about our docker consulting services and have queries about it you can contact our team any time of the day.