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How to fix Docker exec format error? 

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Docker is an open-source platform allowing developers to build, deploy, run, update and manage containers that are standardised executable components that combine to form an application. 

While there are advantages to using Docker, it’s far from perfect and can still run into seemingly random errors from time to time. In this article, we’re talking about how to fix the Docker exec format error and what causes it in the first place. 

Also read: 4 ways to fix Docker: Error response from daemon: missing or empty content-length header

What causes the Docker exec format error?

Several factors can cause the error but the most common is an incorrect build architecture. For example, if you’re building the app for Arm but end up compiling for x86  or x64, you’ll see this error.

Other causes include:

  • Incorrect Docker version installed
  • Docker installation is incomplete
  • Missing shebang in the script

How to fix the Docker exec format error?

Here are three fixes you can try out.

Build for the right version

First up, make sure you’re building for the target architecture instead of your development machine. You can check the architecture, version and target OS of the current build using this command.

docker image inspect rethkevin/rf:v1
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Photo by Shahadat Shemul

If the specs aren’t in line with your target architecture and OS. You can build your app using the GitLab CI runner or using docker-build in case you want to build for multiple architectures at once. 

Add a script shebang

Script shebang might seem like a small thing but it can cause quite a fuss at times, including this error. To avoid that, add the following line on top of everything in your build script. 

# ! / bin / bash

Alternatively, you can also run the following command to fix the error.

 docker run - entrypoint = " / bin / bash " -i [script name]

Be sure to remove any additional spaces from the two commands before executing them or adding them to your script.

Check your docker registry

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There’s a chance that your implementation of docker has some flaws that are causing the API endpoint to return a blank or no value to the content-length header. If you’ve made changes to the standard docker implementation, try reverting those changes to their default settings to resolve the issue. 

Also read: What is Docker? How is it different from VM?

Yadullah Abidi

Yadullah Abidi

Yadullah is a Computer Science graduate who writes/edits/shoots/codes all things cybersecurity, gaming, and tech hardware. When he's not, he streams himself racing virtual cars. He's been writing and reporting on tech and cybersecurity with websites like Candid.Technology and MakeUseOf since 2018. You can contact him here:

  • Saved my day! I was struggling with the Docker exec format error and this guide gave me the solution in a clear and concise way. Thank you so much for sharing this helpful information!

  • when trying to run a Docker container. The error is caused by attempting to run a container on a host with a different architecture. The solution is to rebuild the container on the correct architecture or use a multi-architecture base image.

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