ERRORの問題を解決します。rails のインストール時に gem ネイティブ拡張のビルドに失敗しました。

gem install railsの実行中にエラーが発生し、以下のエラーメッセージが表示されました。

Fetching: pkg-config-1.1.7.gem (100%)
Successfully installed pkg-config-1.1.7
Fetching: nokogiri-1.6.8.gem (100%)
This could take a while...
ERROR: Error installing rails:
    ERROR: Failed to build gem native extension.

    current directory: /var/lib/gems/2.3.0/gems/nokogiri-1.6.8/ext/nokogiri
/usr/bin/ruby2.3 -r . /siteconf20161003-4423-1bf9irh.rb extconf.rb
Using pkg-config version 1.1.7
checking if the C compiler accepts ... Yes
Building nokogiri using packaged libraries.
Using mini_portile version 2.1.0
checking for gzdopen() in -lz... no
zlib is missing; necessary for building libxml2
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
Check the mkmf.log file for more details.
You may need configuration options.

Provided configuration options:
    --without-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-out-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/usr/bin/$(RUBY_BASE_NAME)2.3
    --help
    --clean
    --use-system-libraries
    --enable-static
    --disable-static
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --enable-cross-build
    --disable-cross-build

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/nokogiri-1.6.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.3.0/gems/nokogiri-1.6.8 for inspection.
Results logged to /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/nokogiri-1.6.8/gem_make.out

ご覧の通り、nokogiriのインストールに問題がありましたので、以下を実行します。

sudo apt-get install libxml2-dev libxslt-dev

これで問題は解決です。