We strongly recommend using an SSH connection when interacting with GitHub. SSH keys are a way to identify trusted computers, without involving passwords. The steps below will walk you through generating an SSH key and then adding the public key to your GitHub account.
Tip:
We recommend that you regularly review your SSH keys list and revoke any that haven't been used in a while.

Step 1: Check for SSH keys

First, we need to check for existing SSH keys on your computer. Open up your Terminal and type:
cd ~/.ssh
ls -al
# Lists the files in your .ssh directory
Check the directory listing to see if you have files named either id_rsa.pub or id_dsa.pub. If you don't have either of those files go to step 2. Otherwise, you can skip to step 3.

Step 2: Generate a new SSH key

To generate a new SSH key, copy and paste the text below, making sure to substitute in your email. The default settings are preferred, so when you're asked to "enter a file in which to save the key,"" just press enter to continue.
ssh-keygen -t rsa -C "your_email@example.com"
# Creates a new ssh key, using the provided email as a label
# Generating public/private rsa key pair.
# Enter file in which to save the key (/home/you/.ssh/id_rsa):
Next, you'll be asked to enter a passphrase:
# Enter passphrase (empty for no passphrase): [Type a passphrase]
# Enter same passphrase again: [Type passphrase again]
Which should give you something like this:
# Your identification has been saved in /home/you/.ssh/id_rsa.
# Your public key has been saved in /home/you/.ssh/id_rsa.pub.
# The key fingerprint is:
# 01:0f:f4:3b:ca:85:d6:17:a1:7d:f0:68:9d:f0:a2:db your_email@example.com
Then add your new key to the ssh-agent:
ssh-add ~/.ssh/id_rsa

Step 3: Add your SSH key to GitHub

Run the following code to copy the key to your clipboard.
sudo apt-get install xclip
# Downloads and installs xclip. If you don't have `apt-get`, you might need to use another installer (like `yum`)

xclip -sel clip < ~/.ssh/id_rsa.pub
# Copies the contents of the id_rsa.pub file to your clipboard
Alternatively, using your favorite text editor, you can open the ~/.ssh/id_rsa.pub file and copy the contents of the file manually
Now that you have the key copied, it's time to add it into GitHub:
  1. Account settings buttonIn the user bar in the top-right corner of any page, click Account Settings.
  2. SSH Keys menuClick SSH Keys in the left sidebar
  3. SSH Key buttonClick Add SSH key
  4. The key fieldPaste your key into the "Key" field
  5. The Add key buttonClick Add key
  6. Confirm the action by entering your GitHub password

Step 4: Test everything out

To make sure everything is working, you'll now try SSHing to GitHub. When you do this, you will be asked to authenticate this action using your password, which for the passphrase you created earlier.
Open up your Terminal and type:
ssh -T git@github.com
# Attempts to ssh to github
It's possible that you'll see this error message:
...
Agent admitted failure to sign using the key.
debug1: No more authentication methods to try.
Permission denied (publickey).
This is a known problem with certain Linux distributions. For a possible resolution, see our help article.
You may see this warning:
# The authenticity of host 'github.com (207.97.227.239)' can't be established.
# RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
# Are you sure you want to continue connecting (yes/no)?
Don't worry! This is supposed to happen. Verify that the fingerprint in your terminal matches the one we've provided up above, and then type "yes."
# Hi username! You've successfully authenticated, but GitHub does not
# provide shell access.
If that username is yours, you've successfully set up your SSH key! Don't worry about the "shell access" thing, you don't want that anyway.
If you receive a message about "access denied," you can read these instructions for diagnosing the issue.