Use multiple SSH keys for different GitHub accounts

Rather than entering the username and password, you often use SSH keys to access GitHub repositories. It's a more secured and recommended way to communicate with remote GitHub servers.
Sometimes you have more than one GitHub account. For example, one for accessing personal repositories, another one for your daily works.
The question is how your local Git recogranizes a repository that comes with which GitHub account. This tip will help you.

Creating different keys

Assume that foo and bar are two GitHub usernames that you would like to use in the same computer. You can follow the official GitHub guide to generate SSH key.
// Generate SSH key for `foo`
$ ssh-keygen -t ed25519 -C ""
When you're asked to indicate the file to save the key, don't use the default key. Change the name of file to something associate with the account, for example:
Enter a file in which to save the key (/home/you/.ssh/id_ed25519):
Repeat the same steps for the bar account. Now, we have two private keys, id_foo and id_bar located at the ~/.ssh folder.

Adding keys to SSH agent

// Delete cached keys
$ ssh-add -D
// Start the ssh-agent in the background
$ eval "$(ssh-agent -s)"
// Add your SSH private keys to the ssh-agent
$ ssh-add ~/.ssh/id_foo
$ ssh-add ~/.ssh/id_bar

Mapping keys to GitHub repos

This step lets SSH know which private key should be used for particular hosts.
$ cd ~/.ssh
$ touch config
Add the following content to the config file:
  User git
  IdentityFile ~/.ssh/id_foo
  IdentitiesOnly yes
  User git
  IdentityFile ~/.ssh/id_bar
  IdentitiesOnly yes
You'll realize that and look invalid hosts, but actually they are treated as aliases. SSH maps it with the HostName option and uses the private key in the IdentityFile option.

Changing GitHub settings

Let's say that the foo account accesses a GitHub repose whose URL is Go to its cloned folder, and change the .git/config file as below.
It's worth noting that the SSH host created in the previous step is used:
[remote "origin"]
  url =
Apply the similar settings for the bar repositories.