您可能在防火墙后面。尝试通过https进行克隆 - 有更高的机会不被阻止：

  git clone https://github.com/angular /angular-phonecat.git 
 

I am trying to clone the angular-phonecat git repository, but I am getting the following message when I enter the command in my Git Bash:

$ git clone git://github.com/angular/angular-phonecat.git  
Cloning into 'angular-phonecat'...  
fatal: unable to connect to github.com:  
github.com[0: 204.232.175.90]: errno=No error

You are probably behind a firewall. Try cloning via https – that has a higher chance of not being blocked:

git clone https://github.com/angular/angular-phonecat.git