Remove primary secret key from .gnupg

cleangpg.sh

# Your fingerprint
gpgKey=0x1234123123123

# Export the full backup to store somewhere
gpg --export-secret-keys --armor ${gpgKey} > ${gpgKey}.full_backup.asc

# Export partial backup with only your subkeys
gpg --export-secret-subkeys --armor ${gpgKey} > ${gpgKey}.only_subkeys.asc

# Erase your .gnupg
mv --no-clobber ~/.gnupg ~/.gnupg.BAK
gpg2
#ctrl+c
cp ~/.gnupg.BAK/gpg.conf ~/.gnupg
rm -rf ~/.gnupg.BAK

# Import partial backup
gpg --import ${gpgKey}.only_subkeys.asc

gpg --list-secret-keys gpg ${gpgKey}
# You see `sec# ` meaning the primary secret key is missing