Lost the SSH public key? Derive it from the private key
An SSH .pub file is only the public half of a key pair. If it is missing, or if it is an old file that no longer matches the private key, regenerate it from the private key:
cp ~/.ssh/id_rsa.pub ~/.ssh/id_rsa.pub.backup 2>/dev/null || true
ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub
chmod 644 ~/.ssh/id_rsa.pub
ssh-keygen -y derives and prints the public key without exposing the private key. This also fixes errors such as:
identity_sign: private key ... contents do not match public
Verify the resulting public-key fingerprint with:
ssh-keygen -lf ~/.ssh/id_rsa.pub