title: Unable to install R package in Ubuntu 11.04
body: <p>I'm new to Linux and R.</p>
  
  <p>I installed R 2.12 in Ubuntu 11.04. Today I tried to install a new package, so I ran the following command:</p>
  
  <pre><code>install.packages('XML')
  </code></pre>
  
  <p>But the installation failed and gave the following information:</p>
  
  <pre><code>* installing *source* package ‘XML’ ...
  checking for gcc... gcc
  checking for C compiler default output file name... a.out
  checking whether the C compiler works... yes
  checking whether we are cross compiling... no
  checking for suffix of executables... 
  checking for suffix of object files... o
  checking whether we are using the GNU C compiler... yes
  checking whether gcc accepts -g... yes
  checking for gcc option to accept ISO C89... none needed
  checking how to run the C preprocessor... gcc -E
  No ability to remove finalizers on externalptr objects in this verison of R
  checking for sed... /bin/sed
  checking for pkg-config... /usr/bin/pkg-config
  checking for xml2-config... no
  Cannot find xml2-config
  ERROR: configuration failed for package ‘XML’
  * removing ‘/home/spirit/R/i686-pc-linux-gnu-library/2.12/XML’
  
  The downloaded packages are in
      ‘/tmp/RtmpoZYxnv/downloaded_packages’
  Warning message:
  In install.packages("XML") :
    installation of package 'XML' had non-zero exit status
  </code></pre>
  
  <p>I also tried:</p>
  
  <pre><code>sudo install.packages('XML')
  </code></pre>
  
  <p>But it gives the same error information.</p>
  
  <p>Anyone can give me any advice?</p>