gpg failed to sign the data fatal: failed to write commit object [Git 2.10.0]

Resolving 'gpg failed to sign the data' in Git 2.10.0

Encountering 'gpg failed to sign the data fatal: failed to write commit object' can halt your Git workflow. This article provides comprehensive solutions for this common issue, particularly with Git 2.10.0 and GPG signing.

When working with Git, especially when enforcing signed commits for security or compliance, you might encounter the error gpg failed to sign the data fatal: failed to write commit object. This issue typically arises when Git attempts to use GPG to sign a commit but fails for various reasons. This article will guide you through understanding and resolving this problem, focusing on common causes and solutions applicable to Git 2.10.0 and later versions.

Understanding the GPG Signing Process in Git

Git uses GPG (GNU Privacy Guard) to cryptographically sign commits, tags, and other objects. This signing process verifies the identity of the committer and ensures the integrity of the committed data. When you configure Git to sign commits globally or for a specific repository, Git invokes your GPG agent to perform the signing operation. The error gpg failed to sign the data indicates that this invocation or the subsequent signing process failed.

sequenceDiagram
    actor User
    participant Git
    participant GPG_Agent
    participant GPG_Program

    User->>Git: git commit -S -m "My commit"
    Git->>GPG_Agent: Request signing (commit data)
    GPG_Agent->>GPG_Program: Invoke GPG for signing
    alt Successful Signing
        GPG_Program-->>GPG_Agent: Signed data
        GPG_Agent-->>Git: Signed data
        Git->>Git: Write signed commit object
        Git-->>User: Commit successful
    else Failed Signing
        GPG_Program--xGPG_Agent: Error: GPG failed to sign
        GPG_Agent--xGit: Error: GPG failed to sign
        Git--xUser: fatal: failed to write commit object
    end

Sequence diagram of Git GPG commit signing process and potential failure point.

Common Causes and Solutions

The gpg failed to sign the data error can stem from several issues, ranging from misconfigured GPG keys to environmental problems. Identifying the root cause is crucial for a quick resolution.

1. Incorrect GPG Key Configuration in Git

Git needs to know which GPG key to use for signing. This is typically configured using user.signingkey.

git config --global user.signingkey YOUR_GPG_KEY_ID

Setting your GPG signing key globally.

To find your GPG key ID, you can list your secret keys:

gpg --list-secret-keys --keyid-format LONG

Listing GPG secret keys to find your key ID.

Look for the sec line, and the 16-character string after the slash (e.g., 0x1234ABCD1234ABCD) is your key ID.

2. GPG Agent Issues

The GPG agent is responsible for managing your GPG keys and handling passphrase prompts. If the agent isn't running or is misconfigured, signing will fail.

Ensure your GPG agent is running. You can often start it or ensure it's properly configured in your shell's startup scripts (e.g., .bashrc, .zshrc).

# Add to your shell's startup file (e.g., ~/.bashrc or ~/.zshrc)
export GPG_TTY=$(tty)
gpgconf --launch gpg-agent

Configuring GPG_TTY and launching gpg-agent.

3. GPG Program Path or Version Incompatibility

Git needs to know where to find the gpg executable. While usually in your PATH, sometimes it might be in a non-standard location, or an older version might be causing issues.

You can explicitly tell Git where to find the GPG program:

git config --global gpg.program /path/to/your/gpg

Specifying the GPG program path.

For Git 2.10.0, ensure you are using a compatible GPG version. Generally, GnuPG 2.x is recommended.

gpg --version

Checking your GPG version.

4. Permissions Issues or Corrupted GPG Files

Incorrect permissions on your ~/.gnupg directory or corrupted GPG key files can prevent signing.

1. Check Permissions

Ensure your ~/.gnupg directory has the correct permissions (usually 700 or rwx------).

2. Fix Permissions

Use chmod 700 ~/.gnupg to correct permissions if necessary.

3. Consider Key Regeneration (Last Resort)

If all else fails and you suspect key corruption, you might need to generate a new GPG key pair and update your Git and GitHub settings accordingly. Back up your existing keys before attempting this.

5. GitHub GPG Key Configuration

While not directly causing the gpg failed to sign the data error (which occurs locally), an improperly configured GPG key on GitHub will prevent your signed commits from showing as 'Verified'. Ensure the public part of your GPG key is added to your GitHub account.

gpg --armor --export YOUR_GPG_KEY_ID

Exporting your public GPG key to add to GitHub.

Copy the output, including the -----BEGIN PGP PUBLIC KEY BLOCK----- and -----END PGP PUBLIC KEY BLOCK----- lines, and add it to your GitHub GPG keys settings.