bundle install しようとするとエラーがでる

Question

bundle installしようとすると、
赤文字で

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

```というエラーがでて、下記のようにでます。

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory:
/Users/◯◯/projects/◯◯/vendor/bundle/ruby/2.4.0/gems/nio4r-2.2.0/ext/nio4r
/Users/◯◯/.rbenv/versions/2.4.0/bin/ruby -r ./siteconf20180115-38397-1ao9lmx.rb extconf.rb
checking for unistd.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.

An error occurred while installing nio4r (2.2.0), and Bundler cannot continue.
Make sure that gem install nio4r -v '2.2.0' succeeds before bundling.

In Gemfile:
rails_admin was resolved to 1.2.0, which depends on
rails was resolved to 5.0.6, which depends on
actioncable was resolved to 5.0.6, which depends on
nio4r

ググってもなかなか解決しませんでした・・。
よろしければ対応方法を教えていただけますと幸いです。

Answer 1

エラー内容はgem install nio4r -v '2.2.0'を実行しろと言っているので、実行してみてはいかがでしょうか？