SSH key提供了一种与GitHub通信的方式，通过这种方式，能够在不输入密码的情况下，将GitHub作为自己的remote端服务器，进行版本控制

  1. 检查SSH keys是否存在
  2. 生成新的ssh key
  3. 将ssh key添加到GitHub中

检查SSH keys是否存在

输入下面的命令，如果有文件id_rsa.pub 或 id_dsa.pub，则直接进入步骤3将SSH key添加到GitHub中，否则进入第二步生成SSH key

ls -al ~/.ssh
# Lists the files in your .ssh directory, if they exist

生成新的ssh key

生成public/private rsa key pair 在命令行中输入ssh-keygen -t rsa -C "your_email@example.com"
默认会在相应路径下（/your_home_path）生成id_rsa和id_rsa.pub两个文件，如下面代码所示

ssh-keygen -t rsa -C "your_email@example.com"
# Creates a new ssh key using the provided email
Generating public/private rsa key pair.
Enter file in which to save the key (/your_home_path/.ssh/id_rsa):

输入passphrase（本步骤可以跳过）

设置passphrase后，进行版本控制时，每次与GitHub通信都会要求输入passphrase，以避免某些“失误”
Enter passphrase (empty for no passphrase): [Type a passphrase]
Enter same passphrase again: [Type passphrase again]

将新生成的key添加到ssh-agent中:

# start the ssh-agent in the background
eval "$(ssh-agent -s)"
Agent pid 59566
ssh-add ~/.ssh/id_rsa

将ssh key添加到GitHub中

用自己喜欢的文本编辑器打开id_rsa.pub文件，里面的信息即为SSH key，将这些信息复制到GitHub的Add SSH key页面即可

不同的操作系统，均有一些命令，直接将SSH key从文件拷贝到粘贴板中，如下：

mac

pbcopy < ~/.ssh/id_rsa.pub

# Copies the contents of the id_rsa.pub file to your clipboard

windows

clip < ~/.ssh/id_rsa.pub

# Copies the contents of the id_rsa.pub file to your clipboard

linux

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