ruby - How to avoid "cannot load such file -- utils/popen" from homebrew on OSX

Question

I'm getting an error when I run brew in the terminal:

 /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- utils/popen (LoadError)
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/Library/Homebrew/utils.rb:6:in `<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/Library/Homebrew/global.rb:9:in `<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/local/Library/brew.rb:16:in `<main>'

These are my gem settings:

- RUBYGEMS VERSION: 2.0.14
- RUBY VERSION: 2.0.0 (2014-02-24 patchlevel 451) [universal.x86_64-darwin13]
- INSTALLATION DIRECTORY: /Library/Ruby/Gems/2.0.0
- RUBY EXECUTABLE: /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
- EXECUTABLE DIRECTORY: /usr/bin
- RUBYGEMS PLATFORMS:
  - ruby
  - universal-darwin-13
- GEM PATHS:
  - /Library/Ruby/Gems/2.0.0
  - /Users/ronaldkwan/.gem/ruby/2.0.0
  - /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/gems/2.0.0
- GEM CONFIGURATION:
  - :update_sources => true
  - :verbose => true
  - :backtrace => false
  - :bulk_threshold => 1000

Answer 1

Original Answer

The problem mainly occurs after updating OS X to El Capitan (OS X 10.11) or macOS Sierra (macOS 10.12).

This is because of file permission issues with El Capitan’s or later macOS's new SIP process. Try changing the permissions for the /usr/local directory:

$ sudo chown -R $(whoami):admin /usr/local  

If it still doesn't work, use these steps inside a terminal session and everything will be fine:

cd /usr/local/Library/Homebrew
git reset --hard
git clean -df
brew update

If /usr/local/Library/Homebrew doesn't work, try /usr/local/Homebrew. The problem might be that Homebrew is outdated.

Apr 2021 Update

The command above doesn't work for macOS High Sierra or above, as explained in this GitHub issue. You have to run this instead:

sudo chown -R $(whoami) $(brew --prefix)/*