gem install rails

で rails を install する際に以下のエラーが出る場合

Fetching: activesupport-4.2.2.gem (100%)
Successfully installed activesupport-4.2.2
Fetching: rails-deprecated_sanitizer-1.0.3.gem (100%)
Successfully installed rails-deprecated_sanitizer-1.0.3
Fetching: mini_portile-0.6.2.gem (100%)
Successfully installed mini_portile-0.6.2
Fetching: nokogiri-1.6.6.2.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing rails:
	ERROR: Failed to build gem native extension.

    /usr/bin/ruby2.2 -r ./siteconf20150621-3840-1ya54gj.rb extconf.rb
checking if the C compiler accepts ... yes
Building nokogiri using packaged libraries.
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
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/usr/bin/$(RUBY_BASE_NAME)2.2
	--help
	--clean
	--use-system-libraries
	--enable-static
	--disable-static
	--with-zlib-dir
	--without-zlib-dir
	--with-zlib-include
	--without-zlib-include=${zlib-dir}/include
	--with-zlib-lib
	--without-zlib-lib=${zlib-dir}/lib
	--enable-cross-build
	--disable-cross-build

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.2.0/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /var/lib/gems/2.2.0/extensions/x86_64-linux/2.2.0/nokogiri-1.6.6.2/gem_make.out

対処として

apt-get install -y libxslt-dev libxml2-dev

を実行して

gem install nokogiri

を実行。成功すれば、

gem install rails --no-document

で、rails が install できるはず。

上記の対応でも nokogiri が install できない場合

apt-get install -y zlib1g-dev

を実行してもう一度

gem install nokogiri

を実行するといけるはず。最後に

gem install rails --no-document

すれば、rails が install できる

参考 : Installing Nokogiri