GitHub's implementation of git over ssh identifies accounts (for purposes of access control) solely by ssh public key. As a consequence, a particular public key can be associated with, at most, one account. Deploy keys are even more restricted - they can only be associated with a single repository. While ssh can try several keys, GitHub doesn't know what you're trying to access until after you authenticate, so a workaround is required to select the right key.

There a few systems that I frequently work on from multiple locations. I like to be able to log back in and pick up where I left off after disconnecting and screen is great for that, but I have to remember to start it before I do anything else. After forgetting one too many times, I figured out how to start it automatically when I open an interactive SSH session. Here's what I came up with: