Step1: 检查SSH密钥
首先，打开终端，输入以下指令，查看是否已经生成SSH密钥。
cd ~/.ssh
ls
# Lists the files in your .ssh directory
在输入ls后，看看是否有文件 id_rsa.pub 或者 id_dsa.pub，或者两者皆有。如果已经存在这两个文件，则不需进行Step 2，之前如果输入了密码，可以直接跳过Step3。
输入下面的第一条指令，指令中输入一个邮箱，会出现要你自己定义一个文件来保存Key，直接Enter通过。
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):
输入密码（不能少于4个，否则重输入）。
# Enter passphrase (empty for no passphrase): [Type a passphrase]
# Enter same passphrase again: [Type passphrase again]
终端给出的信息如下，告诉Key的保存位置，后面需要用到。
# 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
运行下面这些指令：（打了#号的不用，）。
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
进入网站GitHub，对以下进行设置：
1. 点击账户设置（很明显的，就在右上角）；
2. 点击 "SSHKeys" 在左边；
3. 工作区出现
点击Add SSH key，出现下面。
4. 点击 "Add key"
5. 输入密码进行确认，这个密码就是在Step 3中输入的密码，这个弹出窗口会在输入
xclip -sel clip < ~/.ssh/id_rsa.pub
指令是出现。
ssh -T git@github.com
# Attempts to ssh to github
输入上面的指令，而且指令中的git@github.com是不可以随意输的，一般就是这个，其实也就是这个。
可能出现的错误信息:
...
Agent admitted failure to sign using the key.
debug1: No more authentication methods to try.
Permission denied (publickey).
警告:
# 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)?
莫担心，没事的，输入yes，直接秒杀。
# Hi username! You've successfully authenticated, but GitHub does not
# provide shell access.
成功的是：
If that username is correct, you've successfully set up your SSH key. Don't worry about the shell access thing, you don't want that anyway.