I'm trying to install phusion passenger.

passenger-install-nginx-module

Eventually I got an error

Permission problems



This installer must be able to write to the following directory:



  /opt/nginx



But it can't do that, because you're running the installer as alex.

Please re-run this installer as root.

I tried to do to

sudo passenger-install-nginx-module

but it says

sudo: passenger-install-nginx-module: command not found

How do I solve it?