STEP1

First of all, check if you have had public key by:

cd ~/.ssh
ls

If you have foo and foo.pub, it means that you aleardy have a private key and a public key. Repeat the following methods will overwritten the keys if they have the same name.

To generate ssh key, use the command below:

ssh-keygen -t rsa -C "your_email@youremail.com"

Feel free to enter ENTER during the generation.

However, if you are generating another ssh key, you may want to set a different name for it in the first step.

STEP2

To check your public key (Note, id_rsa is the default name):

cat ~/.ssh/id_rsa.pub

Copy it and paste into GitHub's settings page in Account Settings->SSH Keys->Add SSH key.

Note: if you use this key to access to your remote server, then you can copy the content of your public key and paste it into the ~/.ssh/authorized_keys file.

STEP3

To test it:

ssh -T git@github.com

NOTE

If you want to generate another ssh key with different account at the same time, you can first generate another ssh key named other_rsa.

Then add those by using:

$ ssh-add ~/.ssh/id_rsa
$ ssh-add ~/.ssh/other_rsa

Finally, add a file named config in the ~/.ssh folder and append those content:

host github // alias
    Hostname github.com
    User git
    IdentityFile ~/.ssh/id_rsa

host gitlab // alias
    Hostname gitlab.com
    User git
    IdentityFile ~/.ssh/other_rsa