我在 ubuntu 16.04上安装了 Ruby。
$which ruby
/usr/bin/ruby
$ruby -v
ruby 2.3.0p0 (2015-12-25) [x86_64-linux-gnu]
$gem install bundler
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions for the /var/lib/gems/2.3.0 directory.