How do I make passphrase prompts for ssh keys appear in the terminal, not as a graphical prompt?
the password for your key is managed by ssh-agent and it defaults to ask for your password using the GUI you mentioned. You could:


Unlock your key using the shell frontend to ssh-agent by calling ssh-add. In this case you might want to lock your key with ssh-add -D before you log out of the box.
Circumvent ssh-agent by temporarily unsetting the SSH_AUTH_SOCK variable ssh uses to connect to the agent. You can do this for a single command like this

SSH_AUTH_SOCK="" git push


or for the whole shell session by calling unset SSH_AUTH_SOCK.


Marcel