Fatal error: session_start(): Failed to initialize storage module: user (path: /tmp) in /home/user/public_html/administrator/index.php on line 87
I ran into it when first trying to login to the back end after a new install. To skip my troubleshooting path, drop to #4.
1. My first search attempt began with reply #10 (http://forum.joomla.org/index.php/topic,23607.0.html):
session.save_path = "/tmp"
The directory (in this case "tmp") in the save path in php.ini must exist.
My phpinfo() display shows my path is, indeed, "/tmp". The "/tmp" directory does exist. A command line "ls"display shows that I am the owner of /tmp, "user:user". Permissions were 755. I changed them to 777. The error still showed. Returned permissions back to 755.
2. reply #11 (http://forum.joomla.org/index.php/topic,23607.0.html):
It's a Safe Mode problem. Safe Mode should be "Off".
My pre-installer and phpinfo() displays both showed Safe Mode to be "Off", as recommended.
3. reply #13 (http://forum.joomla.org/index.php/topic,23607.0.html) has a login-loop problem, which he resolved by changing the php.ini lines from
tosession.save_path = "C:\Temp"
session.cookie_path = \
session.save_path = "C:\Temp"
Hmm. I don't have access to php.ini.
4. reply #1 ( http://forum.joomla.org/index.php/topic,60280.0.html ):
In your administrator/index.php (and when needed also at index2.php) insert the middle line:
session_name( md5( $mosConfig_live_site ) );
-->INSERT THIS LINE --> ini_set('session.save_handler', 'files');
Inserting the line into index2.php got me into my backend.