How to have a session that never expires ?

Thanks for the info !  
But i don't get it, actually when $config['sess_save_path'] is empty, the default path is "/srv/data/var/php/www" as you can see in my phpinfo()
Do i need to copy/past that in the $config['sess_save_path'] or do i need to create another custom folder ? 

Thanks a lot for your help !!

Read the documentation one more time. Oh, never mind.  It says

[The files driver] doesn’t support PHP’s directory level and mode formats used in session.save_path,

Yes, you could explicitly set it like this.

PHP Code:

$config['sess_save_path'] = "/srv/data/var/php/www"; 


But that's not a good place if  /srv/data/var/php/www is where index.php is located. It is wise to put session storage outside a site's public accessible folders. You should consider creating a different folder. Perhaps /srv/data/var/php/sessions/. The owner should be www-data and with permissions set to 0700. If you were to create what was just described then you would use

PHP Code:

$config['sess_save_path'] = "/srv/data/var/php/sessions"; 


I tried your solution but always the same issue, after a short time the session expires...
I don't get it