Recently GitHub changed it so I could no longer push using https protocol. At work, I always used ssh to push. So when this happened, I thought, “No problem, I’ll just add my ssh key to my GitHub profile.”

So when I went to do that, I was getting an error saying “Key is already in use.”

So it took me a long time to realize that this was happening because I had already added my ssh key to my work github profile, which I rarely have occasion to use. But it left me wondering how I could use ssh to push and pull to both my work and my personal github repository.

Create Another SSH Key

The answer for me was, make another ssh key. It’s simple enough to create another ssh key:

ssh-keygen -t ed25519 -C "me@example.com"

This will create a keypair in a pair of files, for the private and public keys respectively:

~/.ssh/id_ed25519
~/.ssh/id_ed25519.pub

Update my Personal Account’s SSH Key

Paste the contents of ~/.ssh/id_ed25519.pub into my personal github profile’s SSH keys section.

Configure git to use non-default key

My ~/.ssh/config file specifies a default IdentityFile for all hosts:

Host * 
 UseKeyChain yes
 AddKeysToAgent yes
 IdentityFile ~/.ssh/id_rsa

So, I cannot differentiate using the hostname for my personal and work github.com repositories.

For now, the best solution I found is to override the default identity file for the repositories that I wish to synchronize with my personal github.

I just have to remember to do configure each repository. From somewhere within the repository directory structure, do:

git config core.sshCommand "ssh -i ~/.ssh/id_ed25519"

This will update the .git/config file in the repo to override the key used to idenity me with github.com.