Update /etc/nginx/nginx.conf to have sendfile off;
Then find the location of opcache.so (/usr/lib/php5/20131226/opcache.so):
sudo find / -name 'opcache.so'
Add the following to opcache.ini:
sudo nano /etc/php5/mods-available/opcache.ini
zend_extension=/usr/lib/php5/20131226/opcache.so
opcache.memory_consumption=128
opcache.interned_strings_buffer=8
opcache.max_accelerated_files=4000
opcache.revalidate_freq=0
opcache.validate_timestamps=on
opcache.fast_shutdown=1
Update the timezone:
sudo dpkg-reconfigure tzdata
Update the time so it's older than the host OS. For example your Host OS is at 10:01:00, then set your VM to:
sudo date --set 10:00:50
sudo service nginx restart