How to Change Docker's Default Directory on Linux

How to Change Docker’s Default Directory on Linux

By default, Docker stores its data, including images, containers, volumes, and networks, in the /var/lib/docker directory. However, you may want to change this directory to a different location, such as a larger disk or a specific storage partition. This tutorial will guide you through the process of changing Docker’s default directory on a Linux system.

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Step 1: Confirm the Current Docker Directory

Before making any changes, it’s important to verify the current location where Docker stores its data. You can do this by running the following command:

docker info | grep 'Docker Root Dir'

Explanation:

• docker info: Displays detailed information about the Docker installation.
• grep 'Docker Root Dir': Filters the output to show only the line containing the Docker root directory.
  This command will output something like Docker Root Dir: /var/lib/docker, confirming the current storage location.

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Step 2: Create or Edit the Docker Configuration File

Docker’s configuration file, daemon.json, is used to customize Docker’s behavior. You need to add a data-root entry to this file to specify the new directory.

Option 1: Manually Edit the File

1. Open the file /etc/docker/daemon.json in a text editor (e.g., nano or vim):

   sudo nano /etc/docker/daemon.json
   

2. Add the following JSON configuration to specify the new directory:

   {
     "data-root": "/path/to/new/docker-data"
   }
   

   Replace /path/to/new/docker-data with your desired directory path.

Option 2: Use a Command to Append the Configuration

Alternatively, you can use the echo command to append the configuration to the file:

echo '{ "data-root": "/path/to/new/docker-data" }' | sudo tee /etc/docker/daemon.json

Explanation:

• echo: Outputs the JSON configuration.
• | sudo tee: Redirects the output to the daemon.json file with root privileges.
• /etc/docker/daemon.json: The configuration file where Docker reads its settings.

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Step 3: Stop the Docker Daemon

Before moving Docker’s data, you need to stop the Docker service to ensure no files are in use.

sudo systemctl stop docker

Explanation:

• systemctl stop docker: Stops the Docker service. This ensures that no containers, images, or other Docker resources are actively using the /var/lib/docker directory.

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Step 4: Verify That Docker Is Stopped

To confirm that Docker has been stopped, check for running Docker processes:

ps aux | grep -i docker | grep -v grep

Explanation:

• ps aux: Lists all running processes.
• grep -i docker: Filters the list to show only Docker-related processes.
• grep -v grep: Excludes the grep command itself from the results.
  If Docker is stopped, this command should return no output.

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Step 5: Copy Docker Data to the New Directory

Use the rsync command to copy all Docker data from the old directory to the new one:

sudo rsync -axPS /var/lib/docker/ /path/to/new/docker-data

Explanation:

• rsync: A tool for efficiently copying and synchronizing files.
• -a: Archive mode, which preserves permissions, timestamps, and symbolic links.
• -x: Ensures that rsync stays within the same filesystem.
• -P: Shows progress during the transfer.
• -S: Handles sparse files efficiently.
• /var/lib/docker/: The source directory (current Docker data).
• /path/to/new/docker-data: The destination directory (new Docker data location).

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Step 6: Restart the Docker Daemon

After copying the data, restart Docker to apply the changes:

sudo systemctl start docker

Explanation:

• systemctl start docker: Starts the Docker service using the new configuration.

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Step 7: Confirm the New Docker Directory

Verify that Docker is now using the new directory:

docker info | grep 'Docker Root Dir'

Explanation:
This command should now output the new directory path, confirming that the change was successful.

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Step 8: Check Running Containers

Ensure that your containers are running correctly after the change:

docker ps

Explanation:

• docker ps: Lists all running containers. If everything is working, you should see your containers as expected.

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Step 9: Remove the Old Docker Data (Optional)

Once you’ve confirmed that everything is working correctly, you can safely delete the old Docker data to free up space:

sudo rm -r /var/lib/docker

Explanation:

• rm -r: Recursively removes the specified directory and its contents.
• /var/lib/docker: The old Docker data directory.
  Warning: Only perform this step after confirming that the new directory is fully functional.

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Summary

By following these steps, you’ve successfully changed Docker’s default directory to a new location. This process involves updating the Docker configuration, stopping the Docker service, copying data to the new location, and restarting Docker. Always verify the changes and ensure your containers are functioning correctly before removing the old data.

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