How to fix error: gpg failed to sign the data fatal: failed to write commit object in Git

First, verify that GPG can sign data outside of Git:

echo "test" | gpg --clearsign

If this fails, the problem is with GPG itself, not Git. If it succeeds and shows a PGP signature block, proceed to check Git configuration.

GPG needs to know which terminal to use for passphrase prompts. Add this to your shell profile (~/.bashrc, ~/.zshrc, or ~/.bash_profile):

export GPG_TTY=
ot a tty

Then reload your shell configuration:

source ~/.bashrc  # or ~/.zshrc

Kill any existing GPG agent processes and let it restart fresh:

gpgconf --kill gpg-agent

Alternatively, you can use:

killall gpg-agent && gpg-agent --daemon

Then try your Git commit again.

List your GPG keys and check their expiration dates:

gpg --list-keys

Look for "expired" next to your key. If expired, you need to extend the expiration or generate a new key:

gpg --edit-key YOUR_KEY_ID
gpg> expire
# Follow prompts to set new expiration
gpg> save

Ensure Git is configured with the correct signing key. First, list your secret keys:

gpg --list-secret-keys --keyid-format=long

Copy the key ID (the long hex string after the slash) and configure Git:

git config --global user.signingkey YOUR_KEY_ID

Also check for conflicting local configuration:

git config --local --get user.signingkey

If this shows a different key, unset it:

git config --local --unset user.signingkey

On some systems, Git may use the wrong GPG version. Explicitly set the GPG program:

# For systems using gpg2
git config --global gpg.program gpg2

# Or for standard gpg
git config --global gpg.program gpg

Verify which gpg is being used:

which gpg
which gpg2

On macOS, install pinentry-mac for a graphical passphrase prompt:

brew install pinentry-mac

Configure GPG to use it:

echo "pinentry-program " >> ~/.gnupg/gpg-agent.conf
gpgconf --kill gpg-agent

For Apple Silicon Macs, ensure the path is correct (/opt/homebrew/bin/pinentry-mac).