（诊断）为GitHub添加SSH key时出现“Could not open a connection to your authentication agent”错误的应对方案。

　　在为windows 环境下的github账户添加SSH key时，需要在Git Bash执行如下命令：

第一步：检查已有的SSH keys

$ ls -al ~/.ssh

第二步：生成新的SSH key

$ 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 (/c/Users/you/.ssh/id_rsa): [Press enter]
Enter passphrase (empty for no passphrase): [Type a passphrase]
# Enter same passphrase again: [Type passphrase again]

接着会得到如下的提示：

Your identification has been saved in /c/Users/you/.ssh/id_rsa.
# Your public key has been saved in /c/Users/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

然后将这个新的key添加到ssh-agent中：

$ ssh-agent -s
# Agent pid 59566
$ ssh-add ~/.ssh/id_rsa

*注： 如果执行 ssh-add 时显示错误 Could not open a connection to your authentication agent. 那么执行

eval `ssh-agent -s`

后重新执行 ssh-add 那条命令即可。

第三步：将SSH key添加到你的GitHub账户

首先将公钥复制到粘贴板：

$ clip < ~/.ssh/id_rsa.pub
# Copies the contents of the id_rsa.pub file to your clipboard

或者使用文本编辑工具也能解决。

然后在github的账户页的右上角，点击配置（settings, 齿轮图形），在sidebar中点击“SSH keys”，接着点击“Add SSH key”，在"title"栏输入一个自己喜欢的标题，“key”栏中粘贴刚刚复制的公钥内容，最后点击“Add key”按钮。

第四步：检查SSH key是否成功设置

$ ssh -T git@github.com
# Attempts to ssh to GitHub

可能会看到如下的警告：

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)?

输入“yes”，如果得到下面的结果，说明你的设置是成功的！

Hi username! You've successfully authenticated, but GitHub does not
# provide shell access.