[r0@r0mini rubyPrac]$ gem install nokogiri -v 1.6.1
Building native extensions.  This could take a while...
ERROR:  Error installing nokogiri:
	ERROR: Failed to build gem native extension.

    /usr/bin/ruby -r ./siteconf20160110-5046-1fn0bgg.rb extconf.rb
Extracting libxml2-2.8.0.tar.gz into tmp/x86_64-redhat-linux/ports/libxml2/2.8.0... OK
Running 'configure' for libxml2 2.8.0... OK
Running 'compile' for libxml2 2.8.0... OK
Running 'install' for libxml2 2.8.0... OK
Activating libxml2 2.8.0 (from /home/r0/.gem/ruby/gems/nokogiri-1.6.1/ports/x86_64-redhat-linux/libxml2/2.8.0)...
Extracting libxslt-1.1.26.tar.gz into tmp/x86_64-redhat-linux/ports/libxslt/1.1.26... OK
Running 'configure' for libxslt 1.1.26... OK
Running 'compile' for libxslt 1.1.26... OK
Running 'install' for libxslt 1.1.26... OK
Activating libxslt 1.1.26 (from /home/r0/.gem/ruby/gems/nokogiri-1.6.1/ports/x86_64-redhat-linux/libxslt/1.1.26)...
checking for libxml/parser.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.

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}/lib64
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/usr/bin/$(RUBY_BASE_NAME)
	--with-zlib-dir
	--without-zlib-dir
	--with-zlib-include
	--without-zlib-include=${zlib-dir}/include
	--with-zlib-lib
	--without-zlib-lib=${zlib-dir}/lib
	--with-iconv-dir
	--without-iconv-dir
	--with-iconv-include
	--without-iconv-include=${iconv-dir}/include
	--with-iconv-lib
	--without-iconv-lib=${iconv-dir}/lib
	--with-xml2-dir
	--without-xml2-dir
	--with-xml2-include
	--without-xml2-include=${xml2-dir}/include
	--with-xml2-lib
	--without-xml2-lib=${xml2-dir}/lib
	--with-xslt-dir
	--without-xslt-dir
	--with-xslt-include
	--without-xslt-include=${xslt-dir}/include
	--with-xslt-lib
	--without-xslt-lib=${xslt-dir}/lib
	--with-libxslt-config
	--without-libxslt-config
	--with-pkg-config
	--without-pkg-config
	--with-libxml-2.0-config
	--without-libxml-2.0-config
	--with-libiconv-config
	--without-libiconv-config
/usr/share/ruby/mkmf.rb:456:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
	from /usr/share/ruby/mkmf.rb:587:in `try_cpp'
	from /usr/share/ruby/mkmf.rb:1113:in `block in find_header'
	from /usr/share/ruby/mkmf.rb:911:in `block in checking_for'
	from /usr/share/ruby/mkmf.rb:351:in `block (2 levels) in postpone'
	from /usr/share/ruby/mkmf.rb:321:in `open'
	from /usr/share/ruby/mkmf.rb:351:in `block in postpone'
	from /usr/share/ruby/mkmf.rb:321:in `open'
	from /usr/share/ruby/mkmf.rb:347:in `postpone'
	from /usr/share/ruby/mkmf.rb:910:in `checking_for'
	from /usr/share/ruby/mkmf.rb:1112:in `find_header'
	from extconf.rb:166:in `<main>'

extconf failed, exit code 1