How to connect to the same host with different SSH keys

I keep a personal and a work GitHub account on the same laptop, and this SSH config is how they stay apart. It builds on my note on generating an SSH key pair.

Set up your SSH configuration file

To connect to a remote server over SSH, you would normally type the user name, host name and port every time:

$ ssh [email protected] -p 4321

Add these lines to your ~/.ssh/config, and ssh avengers does the same thing:

Host avengers
    HostName avengers.com
    User tony
    Port 4321

You can also choose which key to use for each server with IdentityFile:

Host avengers
    HostName avengers.com
    User tony
    Port 4321
    IdentityFile ~/.ssh/id_rsa_avengers
    
Host marvel
    HostName marvel.com
    User tony
    Port 8080
    IdentityFile ~/.ssh/id_rsa_marvel

IdentityFile is most useful when you connect to the same host with different keys. A common case is having two GitHub accounts, one personal and one for work:

Host github_personal
    HostName github.com
    IdentityFile ~/.ssh/github_personal
    
Host github_work
    HostName github.com
    IdentityFile ~/.ssh/github_work
    
# Default key for every other host
Host *
    IdentityFile ~/.ssh/id_rsa

Using the configuration file above, you can clone repositories from your personal GitHub account with:

$ git clone git@github_personal:tonystark/ultron.git

Notice that instead of @github.com, the host is @github_personal, the name defined in the configuration file.

Updating the configuration file

Open your favorite terminal
Create or open the SSH configuration file

$ nano ~/.ssh/config

Resources

SSH config file syntax