gem install rails -v 4.2.4 Failed to install

Question

I receive the following error message when running this command:

gem install rails -v 4.2.4

This is the error:

/Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/yaml.rb:5:in `<top (required)>':
It seems your ruby installation is missing psych (for YAML output).
To eliminate this warning, please install libyaml and reinstall your ruby.
/Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': dlopen(/Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/x86_64-darwin15/psych.bundle, 9): Library not loaded: /usr/local/opt/libyaml/lib/libyaml-0.2.dylib (LoadError)
  Referenced from: /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/x86_64-darwin15/psych.bundle
  Reason: image not found - /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/x86_64-darwin15/psych.bundle
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/psych.rb:7:in `<top (required)>'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/yaml.rb:6:in `<top (required)>'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems.rb:628:in `load_yaml'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/config_file.rb:326:in `load_file'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/config_file.rb:198:in `initialize'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/gem_runner.rb:75:in `new'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/gem_runner.rb:75:in `do_configuration'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/gem_runner.rb:40:in `run'
    from /Users/adamgoldberg/.rvm/rubies/ruby-2.3.0/bin/gem:21:in `<main>'

Please Help - this is causing me nightmares

Answer 1

It seems your ruby installation is missing psych (for YAML output).

Install libyaml with Homebrew : http://brew.sh ; then try gem install rails -v 4.2.4

$ brew info libyaml
libyaml: stable 0.1.6 (bottled)
YAML Parser
http://pyyaml.org/wiki/LibYAML
Not installed
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/libyaml.rb
==> Options
--universal
    Build a universal binary

$ brew install libyaml
==> Downloading https://homebrew.bintray.com/bottles/libyaml-0.1.6_1.el_capitan.bottle.tar.gz
######################################################################## 100.0%
==> Pouring libyaml-0.1.6_1.el_capitan.bottle.tar.gz
🍺  /usr/local/Cellar/libyaml/0.1.6_1: 8 files, 312.8K

---

REINSTALL RUBY

If the above solution doesn't work for you, reinstall Ruby from scratch with rvm or rbenv ,

1) Try the instructions on this accepted answer: https://stackoverflow.com/a/38194139/1076207

—OR—

2) Remove all rvm files, then reinstall rvm : https://stackoverflow.com/a/38158619/1076207

—OR—

3) Remove all rvm files, then install rbenv : https://stackoverflow.com/a/38194231/1076207

After using one of the three options above, use http://bundler.io to install Rails:

$ mkdir ~/Documents/Repo
$ cd ~/Documents/Repo
$ gem install bundler
[…]
$ bundle init
Writing new Gemfile to /Users/username/Documents/Repo/Gemfile
$ echo "gem 'rails', '4.2.4'" >> Gemfile
$ bundle install
[…]
$ bundle exec rails new project_name
[…]
$ cd project_name

Personally, I recommend 3) switch to rbenv—I did.

Answer 2

The error itself clearly says that you should install libyaml first and then re-install your ruby. You can do it by running following commands.

sudo apt-get install libtool

rvm package install libyaml 

rvm reinstall ruby-2.3.0

for more reference please see this answer