Getting the following error when trying to use phantomjs from ruby on Ubuntu:
 Failure/Error: visit root_path
 Cliver::Dependency::NotFound:
   Could not fin         
        Instead of building locally, use homebrew on your mac with brew install phantomjs and all the paths will link after. I had this error myself, and you'll get the links for free and have the ability to update easily. 
For Mac Os El Capitan use following command:  
npm install -g phantomjs
Above command only works if you have installed npm, for installing npm:  
 brew install npm
Apparently, the solution was to add phantomjs not only to the PATH, but also create links:
sudo ln -s /home/myuser/phantomjs/bin/phantomjs /usr/bin/phantomjs
sudo ln -s /home/myuser/phantomjs/bin/phantomjs /usr/local/bin/phantomjs
sudo ln -s /home/myuser/phantomjs/bin/phantomjs /usr/local/share/phantomjs
Adjust the /home/myuser/phantomjs/bin/phantomjs paths to match the path to phantomjs binary on your machine.
You can also do
$ sudo apt-get install phantomjs                               
That should automatically add phantomjs to your path, and do everything else necessary for it to run correctly. This worked for me.
Other possible solution is to add executable rights to file:
# download phantomjs
$ curl --output /home/user/.rvm/bin/phantomjs https://s3.amazonaws.com/circle-downloads/phantomjs-2.1.1
# set rights 
$ chmod +x /home/user/.rvm/bin/phantomjs
# check
$ which phantomjs
/home/user/.rvm/bin/phantomjs
And also it is not recommended by poltergeist to use phantomjs from official Ubuntu repos:
DO NOT use phantomjs from the official Ubuntu repositories, since it doesn't work well with poltergeist.
add to Gemfile
gem 'phantomjs', :require => 'phantomjs/poltergeist'
or put code below to spec_helper.rb
require 'phantomjs' 
Capybara.register_driver :poltergeist do |app|
    Capybara::Poltergeist::Driver.new(app, :phantomjs => Phantomjs.path)
end
https://github.com/colszowka/phantomjs-gem