如何生成SSH key
本文载于Gevin的博客
原文地址：http://blog.igevin.info/posts/generate-ssh-key-for-git/
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
步骤
检查SSH keys是否存在
生成新的ssh key
将ssh key添加到GitHub中
如何生成SSH KEY
1. 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
2. 生成新的ssh key
第一步：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):
第二步：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]
sample result:
Your identification has been saved in /your_home_path/.ssh/id_rsa.
Your public key has been saved in /your_home_path/.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
第三步：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
3. 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
