Using SSH keys in GitHub (single or multiple)

Generating new SSH key

$ ssh-keygen -t ed25519 -C "your_email@example.com"

Note: make sure the generated SSH key has correct access rights:

chmod 600 ~/.ssh/<key>

Adding PUBLIC key to Github

See official GitHub tutorial

Make sure you upload PUBLIC key!

Single SSH key setup

Edit ~/.ssh/config and put there the following content:

Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/<key>

And that's it, you can clone your private repo

Multiple SSH keys setup

Modify `~/.ssh/config`

Edit ~/.ssh/config and put there the following content:

Host github.com-<name>
    HostName github.com
    User git
    IdentityFile ~/.ssh/<key>

Replace <name> with some unique name which will identify your accounts. It might be account1, but also f.ex. your username

Set the appropriate origin url

In the git repository:

# Check current origin URL
git config --get remote.origin.url
> https://github.com/<repo-path>.git

# Remove origin URL
git remote remove origin

# Add new, modified origin URL
git remote add origin github.com-<name>:/<repo-path>.git

Replace <name> with the name you put in your ~/.ssh/config file

Set the appropriate user.name and user.email in the current repo

If you want to override your username and email in the repository, you can do it:

git config user.email "your_email@example.com"
git config user.name "Your Name"

Note: if you struggle with remembering if you have entered correct user.name and user.email in each of your repos, I recommend adding this information into command prompt - see Agnoster Theme with Git user display