Correct hunch, wrong directory. The error message was referring to the /tmp (notice the leading slash), the system-wide temporary directory. Here's what is going on: PHP needs a directory to store session data. Your host has assigned /tmp to be that directory. They have also made this directory unwritable, so there is no way PHP can start a session. You have the following workarounds:
1. Give the installation directory (not its contents, just the directory) 0777 permissions. Do not run Kickstart again after changing the permissions!!!!! Launch the installation again by visiting http://www.yoursite.com/installation/index.php.
2. Create the following .htaccess file on your site's root:
php_value session.save_path "tmp"
Do not run Kickstart again after creating this file!! Launch the installation again by visiting http://www.yoursite.com/installation/index.php. If it throws a white page or an Internal Server Error 500 your host is not compatible with this workaround and you have to remove the .htaccess file.
3. The final solution is to contact your host and ask them to assign a writable PHP session save path to your account, then run the restoration again.
Nicholas K. Dionysopoulos
Lead Developer and Director
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