2 dockers installed on ubuntu server help

Daniel Parker

3 min read

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01-03-2025

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Having two Docker installations on a single Ubuntu server is unusual and can lead to conflicts. This article will guide you through troubleshooting this situation, focusing on identifying the problem and providing solutions. We'll cover common causes, diagnostics, and how to resolve these issues to get your Docker environment running smoothly.

Identifying the Problem: Which Docker is Running?

The first step is to determine if you actually have two functioning Docker installations, or if there's a configuration issue leading you to believe this.

1. Check for Multiple Installations:

• List Docker Installations: Open your terminal and use dpkg -l | grep docker to see all packages related to Docker installed on your system. Look for multiple versions or entries suggesting different Docker installations.
• Check Docker Paths: Find where Docker is installed using which docker. If you get multiple paths, this confirms multiple installations.

2. Determine Active Docker Instance:

• Check Docker Version: Run docker version. This will tell you which Docker version is currently running. If you get an error, it suggests that Docker isn't running correctly.
• Check Docker Processes: Use ps aux | grep docker to see if any Docker-related processes are running. This helps identify which Docker installation (if any) is active.

Common Causes of Multiple Docker Installations

Several scenarios can lead to multiple Docker installations:

• Manual Installation: You might have installed Docker manually using different methods (e.g., using the official Docker installation script and then a package manager like apt).
• Incomplete Removal: If you attempted to remove a previous Docker installation, the process might not have been completely successful, leaving residual files or configurations.
• Multiple Package Managers: Using different package managers (like apt and snap) can sometimes lead to multiple Docker installations if not managed carefully.

Resolving Multiple Docker Installations

The best solution is usually to remove the unnecessary Docker installation and ensure only one remains correctly configured.

1. Remove Unwanted Docker Installations:

• Identify the Unwanted Installation: Based on your checks above, identify which Docker installation is redundant or causing conflicts. Check the output of dpkg -l | grep docker to identify the package names.
• Remove Docker Packages: Use sudo apt-get purge <package_name> (replace <package_name> with the name of the package you want to remove) to remove the unwanted installation. Repeat for any related packages (e.g., docker-compose, containerd).
• Remove Leftover Files: Manually remove any leftover Docker directories or configuration files. However, exercise caution as removing incorrect files can cause system instability. It's best to focus on removing the packages first.

2. Verify Single Installation:

After removing the unwanted Docker instance, repeat the checks in the first section to ensure you only have one Docker installation. Check which docker, docker version, and ps aux | grep docker.

3. Restart Docker: Once you're sure only one Docker installation is present, restart the Docker service using: sudo systemctl restart docker.

4. Test Docker Functionality: After the restart, test your Docker functionality by running a simple command like docker run hello-world.

Preventing Future Conflicts

To avoid this issue in the future:

• Use a Consistent Installation Method: Stick to one method for installing Docker (e.g., using apt from the official Docker repository).
• Carefully Remove Installations: Always use the appropriate commands to remove Docker completely. Don't just delete files manually.
• Regularly Update Docker: Keeping your Docker installation updated helps prevent compatibility issues.

Further Troubleshooting

If you're still experiencing problems, consider these points:

• Check System Logs: Examine system logs (journalctl -xe) for any Docker-related errors.
• Review Docker Configuration Files: Examine Docker's configuration files (usually located in /etc/docker/) for any inconsistencies.
• Consult Docker Documentation: The official Docker documentation offers detailed troubleshooting guidance.

By following these steps, you should be able to resolve issues caused by having two Docker installations on your Ubuntu server. Remember to always back up your data before making significant system changes.