Two Keys One Hub

This is perhaps the most uninteresting post I’ve created recently, but because I’m either the main character of Memento or a starfish, I have to chronicle the process of setting up multiple SSH keys for GitHub. It’s the third time I’ve done this, it’s easy, but I still managed to forget it.

The usual situation, which we may share, is having a personal account and another account related to an organization. (Alternatively, your personal account could be invited to an organization, making you look like a contribution beast, and make this write-up useless.) But let’s stick to the first scenario.

First, generate as many keys as you need. GitHub recommends using the ed25519 algorithm, and I do too:

ssh-keygen -t ed25519 -C "main-email@example.com" -f ~/.ssh/id_main
ssh-keygen -t ed25519 -C "work-email@example.com" -f ~/.ssh/id_work

Then, add the public keys to the corresponding GitHub accounts in their settings. You can also add the private keys to the ssh-agent:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_main
ssh-add ~/.ssh/id_work

This will make you type the passphrase every time. If that is undesirable (and believe me, it is) you can add the keys to a keychain. That differs between operating systems, so good luck! (On Linux, the keychain command will help, and on macOS, ssh-add has a --apple-use-keychain flag, but psst!)

All that remains is the SSH configuration, which is presented here in its full glory:

Host *
    UseKeychain yes
    AddKeysToAgent yes

Host github.com
    HostName github.com
    IdentityFile ~/.ssh/id_main
    IdentitiesOnly yes

Host work.github.com
    HostName github.com
    IdentityFile ~/.ssh/id_work
    IdentitiesOnly yes

For all hosts entered passphrases will be remembered, and for MacOS UseKeychain has to be enabled for using the keychain (I know the cognitive load is getting heavy). Also this config will make the github.com host use the main key, and the work.github.com host use the work key. So, when you want to clone a repository from the work account, you can use:

git clone git@work.github.com:username/repository.git

Voila! That is all. I’m looking forward to forgetting this, but at least I’ll have this post. Or maybe I did this because of my very distasteful sense of humor… as always, who can tell.