Use multiple SSH keys for different GitHub accounts.

Create different public key

Follow GitHub document and create a ssh key.

Start the ssh-agent in the background.

$ eval "$(ssh-agent -s)"

Then, add the key as following.

$ ssh-add ~/.ssh/ssh-key-file

You can check your saved keys

$ ssh-add -l

Modify the ssh config

Create the ~/.ssh/config file.

Then add as following

#jstfun account
Host github.com-jstfun
HostName github.com
User git
IdentityFile ~/.ssh/jstfun

Clone your repo and modify your ssh repo URL

Tell the GitHub to not fetch the repo from github.com but from github.com-jstfun.

There is no impact on the github URL but tell our computer that the host for the repo is connected to the jstfun ssh key. A git clone command should be like this:

before: git clone git@github.com:jstfun/project.git
after:  git clone git@github.com-jstfun:jstfun/project.git 

If you already have fetched the repo on your local machine, you can change the remote URL properly.

Check later

Simply, set the config as following:

Host github.com
HostName github.com
User your_user_account_github
PreferredAuthentications publickey
IdentityFile ~/.ssh/your_user_account_github_rsa
IdentitiesOnly yes