The cause for the Unwritable message for PHP session save path is pretty straight forward, that’s Joomla! installer unable detects any value set for session save path. To fix and solve the problem simply configure the session save path variable in the web server environment, so that session save path will be shown as Writable when Joomla! installer re-check the environment. Depending on the web hosting service you used, there are several possible solutions as listed below.
Define session.save_path directive in PHP.INI
If you have root access or control to the web host (for example, in VPS or dedicated server), edit the PHP.INI PHP configuration file in the web server to add in the environment variable. Normally the session.save_path directive is already included in the default PHP.INI, but been commented out. Add or edit the line so that it looks like below:
session.save_path = /tmp
Modify /tmp to the path to a folder that is writable by Apache web server process. If you don’t have shell access to the web host, such as in shared hosting, try asking hosting service provider to include the session save path parameter, or make the path writable.
Include session.save_path in .htaccess file
If you can’t modify PHP.INI global configuration file, or just want to make the change affect Joomla! or Mambo application only, create or edit the .htaccess file in the installation directory for Joomla! or Mambo, and add the following line (only works in Apache web server which configured to support .htaccess – most cPanel hosts do):
php_value session.save_path ‘/tmp’
Change the ‘/tmp’ to a folder that is writable and prefer to be a session saved folder by you which has been created first. The trick above should work if PHP is runing as a server module (ISAPI), which most did, and not as CGI mode.