help.joomla.org/content/view/51/276/
WARNING: On some hosted servers after the configuration.php Unwritable check box is checked, the check box will no longer be available to allow access to the " Override write protection while saving" option and it will be necessary to manually reset the write permissions of the configuration.php in the joomla_root/ directory. If there is no access permitted to files by an FTP program or Control Panel, it will be necessary to contact the host to get them to do it.