This happened to me after re-installing my OS and using a fresh install of rbenv. I cloned my application repository and went to execute a bundle install and received the following error:

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Fetching source index from http://rubygems.org/


Your user account isn't allowed to install to the system Rubygems.
You can cancel this installation and run:

    bundle install --path vendor/bundle

to install the gems into ./vendor/bundle/, or you can enter your password
and install the bundled gems to Rubygems using sudo.

Password:

What? rbenv should not be prompting me to use sudo, it was trying to install gems on the system version of ruby. Running rbenv local returned 2.1.4 as expected, what the heck was going on?

gem list | grep bundler returned nothing – doh! I didn’t have bundler installed via rbenv so it was falling back to the system ruby. I was not expecting it to use a different version of bundler.

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rbenv local
gem install bundler
rbenv rehash
bundle

And all was right with the world again!