nokogiriをビルドできずにrailsのインストールが失敗する。

railsのインストールでの失敗。

インストール時に「nokogiri-1.6.6.2 for inspection.」というエラーが出て失敗。

具体的には以下のエラー

```
# gem install --no-ri --no-rdoc rails
Fetching: thread_safe-0.3.4.gem (100%)
Successfully installed thread_safe-0.3.4
Fetching: minitest-5.5.1.gem (100%)
Successfully installed minitest-5.5.1
Fetching: tzinfo-1.2.2.gem (100%)
Successfully installed tzinfo-1.2.2
Fetching: i18n-0.7.0.gem (100%)
Successfully installed i18n-0.7.0
Fetching: activesupport-4.2.0.gem (100%)
Successfully installed activesupport-4.2.0
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/local/rbenv/versions/2.1.5/bin/ruby -r ./siteconf20150202-16570-18cdxm.rb extconf.rb
checking if the C compiler accepts ... yes
Building nokogiri using packaged libraries.
checking for gzdopen() in -lz... yes
checking for iconv... yes
************************************************************************
IMPORTANT NOTICE:

Building Nokogiri with a packaged version of libxml2-2.9.2
with the following patches applied:
        - 0001-Revert-Missing-initialization-for-the-catalog-module.patch
        - 0002-Fix-missing-entities-after-CVE-2014-3660-fix.patch

Team Nokogiri will keep on doing their best to provide security
updates in a timely manner, but if this is a concern for you and want
to use the system library instead; abort this installation process and
reinstall nokogiri as follows:

    gem install nokogiri -- --use-system-libraries
        [--with-xml2-config=/path/to/xml2-config]
        [--with-xslt-config=/path/to/xslt-config]

If you are using Bundler, tell it to use the option:

    bundle config build.nokogiri --use-system-libraries
    bundle install

Note, however, that nokogiri is not fully compatible with arbitrary
versions of libxml2 provided by OS/package vendors.
************************************************************************
Extracting libxml2-2.9.2.tar.gz into tmp/x86_64-unknown-linux-gnu/ports/libxml2/2.9.2... OK
Running patch with /usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.6.2/ports/patches/libxml2/0001-Revert-Missing-initialization-for-the-catalog-module.patch...
Running 'patch' for libxml2 2.9.2... ERROR, review '/usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.6.2/ext/nokogiri/tmp/x86_64-unknown-linux-gnu/ports/libxml2/2.9.2/patch.log' to see what happened.
*** 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/local/rbenv/versions/2.1.5/bin/ruby
        --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
/usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/mini_portile-0.6.2/lib/mini_portile.rb:279:in `block in execute': Failed to complete patch task (RuntimeError)
        from /usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/mini_portile-0.6.2/lib/mini_portile.rb:271:in `chdir'
        from /usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/mini_portile-0.6.2/lib/mini_portile.rb:271:in `execute'
        from extconf.rb:311:in `block in patch'
        from extconf.rb:308:in `each'
        from extconf.rb:308:in `patch'
        from /usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/mini_portile-0.6.2/lib/mini_portile.rb:108:in `cook'
        from extconf.rb:278:in `block in process_recipe'
        from extconf.rb:177:in `tap'
        from extconf.rb:177:in `process_recipe'
        from extconf.rb:475:in `<main>'

extconf failed, exit code 1

Gem files will remain installed in /usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /usr/local/rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/extensions/x86_64-linux/2.1.0-static/nokogiri-1.6.6.2/gem_make.out
```

他でもnokogiriがバージョンアップしたために出るエラーが出るようです。

http://qiita.com/maangie/items/5f6a7885ec977e35552d


対応は以下で。

```
# yum -y install libxml2 libxslt libxml2-devel libxslt-devel
# gem install nokogiri -- --use-system-libraries
# gem install rails
```

こちらでrailsのインストールが無事できます。

★追記
こちらのサイトが参考になりました。
http://ayumu-homes.hateblo.jp/entry/2015/02/08/174838