系统中的 nginx 是这样安装的

 sudo apt-get install nginx

安装了passenger后

 gem install passenger

还需安装nginx module才能在nginx中配置使用它。在安装时

 passenger-install-nginx-module

提示

 Automatically download and install Nginx?

Nginx doesn't support loadable modules such as some other web servers do,
so in order to install Nginx with Passenger support, it must be recompiled.

Do you want this installer to download, compile and install Nginx for you?

 1. Yes: download, compile and install Nginx for me. (recommended)
    The easiest way to get started. A stock Nginx 1.4.4 with Passenger
    support, but with no other additional third party modules, will be
    installed for you to a directory of your choice.

 2. No: I want to customize my Nginx installation. (for advanced users)
    Choose this if you want to compile Nginx with more third party modules
    besides Passenger, or if you need to pass additional options to Nginx's
    'configure' script. This installer will  1) ask you for the location of
    the Nginx source code,  2) run the 'configure' script according to your
    instructions, and  3) run 'make install'.

Whichever you choose, if you already have an existing Nginx configuration file,
then it will be preserved.

【问题1】这样再次安装nginx的话，和原来的版本没有冲突吗？

直接安装的nginx的启动方法是

 sudo service nginx start
sudo service nginx restart
sudo service nginx stop

通过 passenger-install-nginx-module 安装的nginx的启动方法是

 sudo nginx
sudo nginx -s reload
sudo nginx -s stop

【问题2】为什么会有这样的区别呢？

【问题3】在已经存在nginx的系统中，有其它方式安装passenger的nginx module吗？