title: Linux, Why can't I write even though I have group permissions?
body: <p>I want to create a file in a directory owned by the staff group which I am a member of.  Why can I not do this?</p>
  
  <pre><code>bmccann@bmccann-htpc:~$ ls -l /usr/local/lib/R/
  total 4
  drwxrwsr-x 2 root staff 4096 2010-07-31 16:21 site-library
  bmccann@bmccann-htpc:~$ id -nG bmccann
  bmccann adm dialout cdrom plugdev staff lpadmin admin sambashare
  bmccann@bmccann-htpc:~$ touch /usr/local/lib/R/site-library/tmp
  touch: cannot touch `/usr/local/lib/R/site-library/tmp': Permission denied
  </code></pre>