使用git clone命令从github上同步github上的代码库时，如果使用SSH链接（如我自己的beagleOS项 目：git@github.com:DamonDeng/beagleOS.git），而你的SSH key没有添加到github帐号设置中，系统会报下面的错误：
Permission denied (publickey).
fatal: The remote end hung up unexpectedly
这时需要在本地创建SSH key，然后将生成的SSH key文件内容添加到github帐号上去。
创建SSH key的方法很简单，执行如下命令就可以：
ssh-keygen
然后系统提示输入文件保存位置等信息，连续敲三次回车即可，生成的SSH key文件保存在中～/.ssh/id_rsa.pub
然后用文本编辑工具打开该文件，我用的是vim,所以命令是：
vim ~/.ssh/id_rsa.pub
接着拷贝.ssh/id_rsa.pub文件内的所以内容，将它粘帖到github帐号管理中的添加SSH key界面中。
打开github帐号管理中的添加SSH key界面的步骤如下：
1. 登录github
2. 点击右上方的Accounting settings图标
3. 选择 SSH key
4. 点击 Add SSH key
在出现的界面中填写SSH key的名称，填一个你自己喜欢的名称即可，然后将上面拷贝的~/.ssh/id_rsa.pub文件内容粘帖到key一栏，在点击“add key”按钮就可以了。
添加过程github会提示你输入一次你的github密码
添加完成后再次执行git clone就可以成功克隆github上的代码库了。
cd ~/.ssh
# Checks to see if there is a directory named ".ssh" in your user directory
ls
# Lists all the subdirectories in the current directory
# config id_rsa id_rsa.pub known_hosts
mkdir key_backup
# Makes a subdirectory called "key_backup" in the current directory
cp id_rsa* key_backup
# Copies the id_rsa keypair into key_backup
rm id_rsa*
# Deletes the id_rsa keypair
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 (/home/you/.ssh/id_rsa):
Enter passphrase (empty for no passphrase): [Type a passphrase]
Enter same passphrase again: [Type passphrase again]
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
sudo apt-get install xclip
# Downloads and installs xclip
xclip -sel clip < ~/.ssh/id_rsa.pub
# Copies the contents of the id_rsa.pub file to your clipboard
