Working with multiple SSH keys: setting up git over SSH with GitHub and Bitbucket

My SSH key was setup for GitHub and working fine, but I wanted to add a separate one for Bitbucket¹. It was daunting playing around with this when everything was already working largely as I expected, but it was simple to get this as I wanted.

First, backup your existing keys first in case something goes wrong and you accidentally overwrite them. (You're backing up your data anyway, right?)

Create a new key. If you've got an id_rsa key already, you can name the new key e.g. ~/.ssh/id_rsa.1 (or 2, 3…). (Initially, I put the new key in a separate Bitbucket directory and I don't think that the ssh-agent would automatically pick it up there, so I moved it back to the .ssh directory.)

Add the following to ~/.ssh/config:

Host github.com
User git
IdentityFile ~/.ssh/id_rsa
IdentitiesOnly yes

Host bitbucket.org
User git
IdentityFile ~/.ssh/id_rsa.1
IdentitiesOnly yes

IdentitiesOnly ensures that only the specified key is used for that host; if you don't have this, you may end up failing to authenticate as too many incorrect keys have been passed to the server.

If you're using the key in this session, you might need to ssh-add it. In my case, on Ubuntu 12.04, on subsequent logins, the new key was made available automatically.