libxml2 is missing. try 'port install libxml2' or 'yum install libxml2-d

ubuntu下安装webrat, 出现以下错误

Building native extensions.  This could take a while...
ERROR:  Error installing webrat-0.5.3.gem:
	ERROR: Failed to build gem native extension.

/usr/bin/ruby1.8 extconf.rb
checking for iconv.h in /opt/local/include/,/opt/local/include/libxml2,/opt/local/include,/opt/local/include,/opt/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/include,/usr/include/libxml2,/usr/include,/usr/include/libxml2... yes
checking for libxml/parser.h in /opt/local/include/,/opt/local/include/libxml2,/opt/local/include,/opt/local/include,/opt/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/include,/usr/include/libxml2,/usr/include,/usr/include/libxml2... no
libxml2 is missing.  try 'port install libxml2' or 'yum install libxml2-devel'
*** 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/ruby1.8
	--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


Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0 for inspection.
Results logged to /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/ext/nokogiri/gem_make.out

执行如下命令即可
sudo aptitude install libxslt1-dev libxml2-dev