Telling git To Use Specific Private Key

Sometimes, you need to use specific keys. To do it, use ssh config, something like below in ~/.ssh/config

1host github.com
2 HostName github.com
3 IdentityFile ~/.ssh/id_rsa_github
4 User git

See details in https://superuser.com/questions/232373/how-to-tell-git-which-private-key-to-use