This is pretty common problem. I’ve encountered it on recent version of the Debian operating system. When you see something like that:
Notice: session_start(): ps_files_cleanup_dir: opendir(/var/lib/php5/sessions) failed: Permission denied (13) in /mnt/www-data/htdocs/raportMNW/inc/bryanjhv/slim-session/src/Slim/Middleware/Session.php on line 110
You can fix that easily with following Linux commands:
sudo nano /etc/php5/apache2/php.ini
Now use CTRL+W to find following string session.save_path and configure it like that:
session.save_path = "/tmp"
Save your file using CTRL+X and restart Apache2 service:
sudo service apache2 restart
And voilà!