Created a development/test server from an existing site, struggling with permissions errors on Cent OS 6 server
The best to fix the permission issue is run the fix-permission script available at https://drupal.org/node/244924 

First download the script from here and than run the script as:

sudo bash fix-permissions.sh your/drupal/path your_user_name


Note: The server group name is assumed "www-data", if it differs modify it in the script code

Drupal official doc for file permission is available at https://drupal.org/node/244924



Generally Recommended Permissions for Drupal Files and Folders is following:

drupal/sites/default                                        750
drupal/sites/default/files (including sub folders &amp; files)  755 or 770 *
drupal/sites/default/settings.php                           400 or 440 *
drupal/sites/default/default.settings.php                   400 or 440 *
drupal/sites/all/themes (including sub folders &amp; files)     755
drupal/sites/all/modules (including sub folders &amp; files)    755


* depends on system setup. Some extra modules and/or server rules may require different permissions.