🚀 Fix the GPG Key Error and Install Docker on Ubuntu 22.04

Follow these steps carefully to resolve the GPG key issue and ensure a clean Docker installation. Run each command exactly as shown to avoid syntax errors.

1. Remove Any Existing Docker Repository Configuration

To avoid conflicts or malformed entries, let’s clean up any existing Docker repository files:

sudo rm -f /etc/apt/sources.list.d/docker.list
sudo rm -f /etc/apt/keyrings/docker.gpg

2. Update and Install Prerequisites

Ensure your system has the necessary tools:

sudo apt-get update
sudo apt-get install -y ca-certificates curl gnupg lsb-release
  • The -y flag automatically confirms the installation.
  • This step ensures curl and gnupg are available for fetching and processing the GPG key.

3. Add Docker’s GPG Key Securely

Set up the keyring directory and fetch Docker’s GPG key:

sudo mkdir -p /etc/apt/keyrings
sudo chmod 755 /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
sudo chmod a+r /etc/apt/keyrings/docker.gpg
  • mkdir -p ensures the directory is created if it doesn’t exist.
  • chmod 755 sets correct directory permissions.
  • chmod a+r makes the key readable by all users, which apt requires.

4. Add the Docker Repository

Add the Docker repository to your APT sources:

echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] \
  https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
  • This command dynamically sets the architecture (e.g., amd64, arm64) and Ubuntu codename (e.g., jammy for 22.04).
  • The tee command writes the repository configuration to /etc/apt/sources.list.d/docker.list.
  • Verify the file content to ensure no syntax errors: 
cat /etc/apt/sources.list.d/docker.list

Expected output (example for amd64 on Ubuntu 22.04):

deb [arch=amd64 signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu jammy stable

If the output looks malformed (e.g., extra characters, missing spaces), delete the file (sudo rm /etc/apt/sources.list.d/docker.list) and rerun the echo command.

5. Update APT and Install Docker

Now update the package index and install Docker:

sudo apt-get update
sudo apt-get install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
  • If you see the GPG error again (NO_PUBKEY 7EA0A9C3F273FCD8), double-check the GPG key step and permissions on /etc/apt/keyrings/docker.gpg.
  • The -y flag skips confirmation prompts.

6. Verify Docker Installation

Test Docker to ensure it’s working:

sudo docker run hello-world

This pulls a test image and runs a container. If successful, you’ll see a message confirming Docker is working.

🙌 Optional: Run Docker Without sudo

To avoid typing sudo for Docker commands:

sudo usermod -aG docker $USER

Log out and back in, or run:

newgrp docker

Test it:

docker run hello-world

🛠 Troubleshooting the "Token" Error

The "found character that cannot start any token" error is likely unrelated to the GPG key issue but could stem from:

  1. Malformed /etc/apt/sources.list.d/docker.list:

    • If the repository file contains invalid characters (e.g., extra quotes, spaces, or tabs), apt might fail.
    • Check the file: 
     cat /etc/apt/sources.list.d/docker.list
  • If it’s incorrect, remove it and recreate it using the echo command in step 4.

  1. Docker Compose YAML File (if applicable):

    • If you’re using Docker Compose and have a docker-compose.yml file, the error could indicate a syntax issue (e.g., invalid indentation, stray characters).
    • Check the file for errors: 
     docker-compose config
  • If you have a docker-compose.yml, share its contents, and I can help identify the issue.

  1. Corrupted APT Cache:

    • Clear the APT cache and try again: 
     sudo apt-get clean
 sudo rm -rf /var/lib/apt/lists/*
 sudo apt-get update

  2. Locale or Environment Issues:

    • Ensure your system’s locale is set correctly, as some tools misbehave with invalid locales: 
     locale

  • If the output shows errors, set a valid locale:

     sudo locale-gen en_US.UTF-8
 export LC_ALL=en_US.UTF-8

🔍 If the Issue Persists

If you still encounter the GPG key error or the "token" error, please provide:

  1. The exact error message when running sudo apt-get update.
  2. The contents of /etc/apt/sources.list.d/docker.list (run cat /etc/apt/sources.list.d/docker.list).
  3. If using Docker Compose, share your docker-compose.yml file.
  4. The output of ls -l /etc/apt/keyrings/docker.gpg to verify permissions.

✅ Final Notes

  • The steps above align with Docker’s official installation guide for Ubuntu and account for Ubuntu 22.04’s stricter APT security.
  • The "token" error is likely a secondary issue, possibly from a malformed configuration. The cleanup and precise commands above should prevent it.
  • If you’re still stuck, share the additional details, and I’ll tailor the solution further.

Happy containerizing! 🐳 Let me know if you need more help.