Fixing Gpg No Valid OpenPGP Data Found Error During Erlang Installation

by StackCamp Team 72 views

When building images using Packer, encountering errors during the installation of Erlang can be a significant roadblock. One common issue is the "gpg: no valid OpenPGP data found" error, which typically arises during the execution of the install-erlang.sh script. This error indicates a problem with the GPG key used to verify the Erlang Solutions package repository. This article will delve into the causes of this error, provide a detailed explanation, and offer solutions to resolve it, ensuring a smooth Erlang installation process in your Packer builds. By following the steps outlined in this guide, you can overcome this hurdle and successfully create images with Erlang installed.

Understanding the Issue

The error message "gpg: no valid OpenPGP data found" suggests that the GPG key being imported is either corrupted, incomplete, or not in the expected format. In the context of the install-erlang.sh script, this usually means that the script is unable to properly download and import the Erlang Solutions GPG key. This key is crucial for verifying the authenticity of the Erlang packages, and without it, the package manager will refuse to install Erlang. To effectively address this, it's essential to understand the underlying mechanisms of package verification and how GPG keys play a role in this process. The integrity of your build process hinges on successfully resolving this issue, allowing you to proceed with confidence.

Analyzing the install-erlang.sh Script

To better understand the problem, let's examine the relevant parts of the install-erlang.sh script:

#!/bin/bash -e
# Source the helpers for use with the script
source $HELPER_SCRIPTS/install.sh

source_list=/etc/apt/sources.list.d/eslerlang.list
source_key=/usr/share/keyrings/eslerlang.gpg

# Install Erlang
wget -q -O - https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc | gpg --dearmor >$source_key
echo "deb [signed-by=$source_key]  https://packages.erlang-solutions.com/ubuntu $(lsb_release -cs) contrib" >$source_list
apt-get update

apt-get install --no-install-recommends esl-erlang

Key Steps in the Script

  1. Downloading the GPG Key: The script uses wget to download the Erlang Solutions GPG key from https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc. The -q option makes wget run in quiet mode, and -O - directs the output to standard output.
  2. Importing the Key: The downloaded key is then piped to gpg --dearmor, which converts the ASCII armored key into a binary format suitable for GPG. The output is saved to $source_key (/usr/share/keyrings/eslerlang.gpg).
  3. Adding the Repository: The script creates a new APT source list file (/etc/apt/sources.list.d/eslerlang.list) and adds the Erlang Solutions repository URL to it. The signed-by option specifies the GPG key to use for verifying packages from this repository.
  4. Updating APT: apt-get update is run to refresh the package lists, including the newly added Erlang Solutions repository.
  5. Installing Erlang: Finally, apt-get install --no-install-recommends esl-erlang installs the Erlang package.

Potential Failure Points

The "gpg: no valid OpenPGP data found" error can occur at several points in this process:

  • Download Failure: wget might fail to download the key due to network issues or an incorrect URL. Ensuring a stable internet connection and verifying the URL are crucial first steps. Network interruptions, even brief ones, can lead to incomplete downloads and subsequent errors.
  • Key Corruption: The downloaded key might be corrupted during the download process. This can happen due to network instability or issues on the server hosting the key. Implementing retry mechanisms and verifying the key's integrity can mitigate this risk.
  • GPG Issues: There might be issues with the gpg command itself, such as incorrect usage or missing dependencies. Verifying that the GPG suite is correctly installed and configured is essential. Furthermore, checking for any system-level issues that might interfere with GPG's operation is advisable.
  • File Permissions: Incorrect file permissions on the $source_key file can prevent GPG from accessing the key. Ensuring that the script has the necessary permissions to create and write to this file is vital. Proper file permission management is a key aspect of system security and stability.

Diagnosing the Issue

To diagnose the issue, consider the following steps:

  1. Verify Network Connectivity: Ensure that the Packer build environment has a stable internet connection. Intermittent connectivity issues can lead to incomplete downloads and subsequent failures. Testing the connection independently can help isolate this as a potential cause.
  2. Check the GPG Key URL: Double-check that the GPG key URL (https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc) is correct and accessible. Typos or outdated URLs can easily lead to errors. Regularly verifying the accuracy of URLs used in scripts is a best practice.
  3. Inspect the Downloaded Key: Try downloading the key manually using wget and inspect the downloaded file. Check if the file is empty or contains any error messages. This can help determine if the issue lies in the download process itself. Analyzing the file's contents can provide valuable clues about the nature of the problem.
  4. Run GPG Manually: Attempt to import the key manually using gpg --dearmor < downloaded_key_file. This can help isolate issues with the gpg command or the key file itself. Manual execution allows for closer observation of the process and can reveal specific error messages.
  5. Check File Permissions: Ensure that the script has the necessary permissions to write to /usr/share/keyrings/. Insufficient permissions can prevent the script from creating or modifying files, leading to errors. Verifying file permissions is a fundamental aspect of system administration.

Solutions and Workarounds

Based on the diagnosis, here are several solutions and workarounds to address the "gpg: no valid OpenPGP data found" error:

1. Retry Mechanism

Implement a retry mechanism around the wget command to handle transient network issues. This can be done using a simple loop:

retry_download() {
  local url="$1"
  local max_attempts="$2"
  local current_attempt=1
  
  while true; do
    echo "Attempting to download $url (Attempt $current_attempt/$max_attempts)"
    if wget -q -O - "$url" | gpg --dearmor > "$source_key" 2>/dev/null; then
      echo "Successfully downloaded $url"
      return 0
    else
      if [ $current_attempt -eq $max_attempts ]; then
        echo "Failed to download $url after $max_attempts attempts"
        return 1
      fi
      current_attempt=$((current_attempt + 1))
      sleep 5 # Wait for 5 seconds before retrying
    fi
  done
}

if retry_download "https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc" 3; then
  echo "GPG key downloaded successfully"
else
  echo "Failed to download GPG key"
  exit 1
fi

Explanation of the Retry Mechanism

  • Function Definition: The retry_download function takes the URL and the maximum number of attempts as input.
  • Looping: It uses a while true loop to continuously attempt the download.
  • Download Attempt: Inside the loop, it tries to download the file using wget and import it using gpg. The 2>/dev/null redirects error messages to null, preventing them from cluttering the output unless the download fails completely.
  • Success Condition: If the download and import are successful, the function prints a success message and returns 0.
  • Failure Condition: If the download fails, the function checks if the maximum number of attempts has been reached. If so, it prints a failure message and returns 1.
  • Retrying: If the maximum attempts have not been reached, the function increments the attempt counter, waits for 5 seconds, and retries.
  • Function Call: The script calls retry_download with the Erlang Solutions GPG key URL and a maximum of 3 attempts.
  • Result Handling: It checks the return code of retry_download and prints a message indicating whether the key was successfully downloaded.

This retry mechanism adds robustness to the script by handling transient network issues that might cause the initial download to fail. By implementing such a mechanism, you can significantly reduce the likelihood of the "gpg: no valid OpenPGP data found" error.

2. Verify GPG Installation

Ensure that the gpg package is correctly installed and configured in the build environment. You can add a check in your script to verify this:

if ! command -v gpg &> /dev/null;
then
  echo "gpg is not installed. Installing..."
  apt-get update
  apt-get install -y gnupg
else
  echo "gpg is already installed."
fi

Explanation of GPG Installation Verification

  • Command Existence Check: The command -v gpg checks if the gpg command is available in the system's PATH. The &> /dev/null redirects both standard output and standard error to null, suppressing any output from the command.
  • Conditional Installation: If gpg is not found, the script enters the then block.
  • Installation Process: Inside the then block, the script updates the package lists using apt-get update and then installs the gnupg package using apt-get install -y gnupg. The -y option automatically answers "yes" to any prompts, ensuring a non-interactive installation.
  • Alternative Message: If gpg is already installed, the script executes the else block and prints a message indicating that gpg is already present.

This check ensures that the necessary GPG tools are available before attempting to import the key. By including this verification step, you can prevent errors caused by missing dependencies and ensure a smoother installation process.

3. Use apt-key (Alternative Method)

As an alternative to using gpg --dearmor, you can use the apt-key command to add the key. However, apt-key is deprecated, so this should be considered a temporary solution. If you choose to use this method, remember to transition to a more secure approach as soon as possible.

wget -q -O - https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc | apt-key add -

Explanation of apt-key Usage

  • Downloading the Key: The wget -q -O - https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc part of the command downloads the Erlang Solutions GPG key, similar to the original script.
  • Adding the Key with apt-key: The downloaded key is then piped to apt-key add -. The apt-key command is used to manage APT's list of trusted keys. The add - option tells apt-key to add the key read from standard input.

While this method is simpler, it's important to recognize that apt-key is deprecated due to security concerns. The recommended approach is to use gpg --dearmor along with the signed-by option in the APT source list, as demonstrated in the original script and the retry mechanism solution. Use this method only as a temporary workaround and plan to migrate to a more secure approach.

4. Correct File Permissions

Ensure that the script has the necessary permissions to create and write to the $source_key file. You can add a chmod command to set the permissions:

wget -q -O - https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc | gpg --dearmor >$source_key
chmod 644 $source_key

Explanation of Correcting File Permissions

  • Downloading and Importing the Key: The wget and gpg commands download and import the GPG key, as described previously.
  • Setting File Permissions: The chmod 644 $source_key command sets the file permissions for the $source_key file. The 644 permission mode means:
    • The owner has read and write permissions (6).
    • The group has read permission (4).
    • Others have read permission (4).

Setting the correct file permissions ensures that the GPG key file is accessible to the system for verification purposes. This step is crucial for preventing permission-related errors during the package installation process. By explicitly setting the permissions, you can avoid issues caused by default permission settings that might not be suitable for the script's operation.

5. Specify Keyserver (If Necessary)

In some cases, the gpg command might fail to fetch the key due to issues with the default keyserver. You can try specifying a keyserver explicitly:

wget -q -O - https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc | gpg --keyserver keyserver.ubuntu.com --dearmor >$source_key

Explanation of Specifying the Keyserver

  • Downloading the Key: The wget -q -O - https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc part of the command downloads the Erlang Solutions GPG key.
  • Specifying the Keyserver: The gpg --keyserver keyserver.ubuntu.com --dearmor >$source_key command imports the key, but this time, it explicitly specifies the keyserver to use. The --keyserver keyserver.ubuntu.com option tells GPG to use keyserver.ubuntu.com as the keyserver.

Specifying a keyserver can be helpful if the default keyserver is unavailable or experiencing issues. By explicitly setting the keyserver, you ensure that GPG has a reliable source for fetching the key, which can resolve errors related to key retrieval. This approach is particularly useful in environments where network configurations or firewall settings might interfere with access to the default keyserver.

Example of a Complete Solution

Here's an example of how you can combine some of these solutions into a complete install-erlang.sh script:

#!/bin/bash -e

# Source the helpers for use with the script
source $HELPER_SCRIPTS/install.sh

source_list=/etc/apt/sources.list.d/eslerlang.list
source_key=/usr/share/keyrings/eslerlang.gpg

# Check if gpg is installed, if not install it
if ! command -v gpg &> /dev/null; then
  echo "gpg is not installed. Installing..."
  apt-get update
  apt-get install -y gnupg
else
  echo "gpg is already installed."
fi

# Retry mechanism for downloading the GPG key
retry_download() {
  local url="$1"
  local max_attempts="$2"
  local current_attempt=1
  
  while true; do
    echo "Attempting to download $url (Attempt $current_attempt/$max_attempts)"
    if wget -q -O - "$url" | gpg --dearmor > "$source_key" 2>/dev/null; then
      echo "Successfully downloaded $url"
      return 0
    else
      if [ $current_attempt -eq $max_attempts ]; then
        echo "Failed to download $url after $max_attempts attempts"
        return 1
      fi
      current_attempt=$((current_attempt + 1))
      sleep 5 # Wait for 5 seconds before retrying
    fi
  done
}

if retry_download "https://packages.erlang-solutions.com/ubuntu/erlang_solutions.asc" 3; then
  echo "GPG key downloaded successfully"
else
  echo "Failed to download GPG key"
  exit 1
fi

# Correct file permissions
chmod 644 $source_key

echo "deb [signed-by=$source_key]  https://packages.erlang-solutions.com/ubuntu $(lsb_release -cs) contrib" >$source_list

apt-get update

apt-get install --no-install-recommends esl-erlang

# Install rebar3
rebar3_url=$(resolve_github_release_asset_url "erlang/rebar3" "endswith(\"rebar3\")" "latest")
binary_path=$(download_with_retry "$rebar3_url")
install "$binary_path" /usr/local/bin/rebar3

# Clean up source list
rm $source_list
rm $source_key

invoke_tests "Tools" "erlang"

Explanation of the Complete Solution

  • Shebang and Source Helpers: The script starts with the shebang #!/bin/bash -e and sources helper scripts using source $HELPER_SCRIPTS/install.sh.
  • Variable Definitions: It defines variables for the source list file (source_list) and the GPG key file (source_key).
  • GPG Installation Check: The script checks if GPG is installed and installs it if necessary, as described in the GPG Installation Verification solution.
  • Retry Mechanism: The retry_download function is implemented to handle transient network issues during the GPG key download, as described in the Retry Mechanism solution.
  • GPG Key Download with Retry: The script calls the retry_download function to download the GPG key.
  • File Permissions: The script sets the file permissions for the GPG key file using chmod 644 $source_key, as described in the Correct File Permissions solution.
  • Adding the Repository: The script adds the Erlang Solutions repository to the APT source list.
  • APT Update: It updates the APT package lists using apt-get update.
  • Erlang Installation: The script installs Erlang using apt-get install --no-install-recommends esl-erlang.
  • Rebar3 Installation: The script installs Rebar3 by resolving the latest release asset URL, downloading the binary, and installing it to /usr/local/bin/rebar3.
  • Cleanup: The script removes the source list and GPG key files.
  • Tests: Finally, it invokes tests using `invoke_tests