I got this:
$ gem install passenger
Fetching: passenger-4.0.5.gem (100%)
ERROR: While executing gem … (Gem::FilePermissionError)
You don’t have write permissions for the /Users/snowcrash/.rvm/gems/ruby-2.0.0-p195 directory.
Fixed like this:
rvm get head
rvm fix-permissions
See also:
http://stackoverflow.com/questions/17248872/error-while-executing-gem-gemfilepermissionerror