generator-angular模块不会创建新项目

我是yeoman工具的新手.我在Ubuntu 12中运行以下命令

$ npm install -g yo
$ npm install -g generator-webapp
$ yo webapp           

我能够创建一个Web应用程序项目.之后我尝试创建一个角度项目.首先我运行一个命令

$ npm install -g generator-angular

安装此发电机时不会显示错误.

当我运行命令

$ yo angular 

我收到错误:

Error angular
You don't seem to have a generator with the name angular installed.
You can see available generators with npm search yeoman-generator and then install them with npm install [name].
To see the 2 registered generators run yo with the `--help` option.

怎么解决这个？当我运行命令

 $ ls $(npm config get prefix)/lib/node_modules

输出是:

bower  generator-angular  generator-karma  generator-mocha  generator-webapp  grunt-cli  yo

当我使用安装生成器骨干时发生同样的问题

$ npm install -g generator-backbone

它成功安装包,当我在空文件夹中运行命令时

$ yo backbone 

它给出了输出

Error backbone 

You don't seem to have a generator with the name backbone installed.
You can see available generators with npm search yeoman-generator and then install them with npm install [name].
To see the 2 registered generators run yo with the `--help` option.

当我运行命令

$ npm config get prefix

它给了我输出

/home/ritesh/npm

也许我在这条路上犯了一些错误.任何人都可以告诉你如何解决它？