1. Opcache warning

Nextcloud sometimes gives a opcache warning in the admin settings when it checks the security and setup.

You may see something like this: 

Opcache is not properly configured 
Security & setup warnings
It is important for the security and performance of your instance that everything is configured correctly. To help you with that we are doing some automatic checks. Please see the Tips & Ticks section and the documentation for more information.
The PHP Opcache is not properly configured. For better performance we recommend to use following settings in the php.ini:
Please double check the installation guides, and check for any errors or warnings in the log.

In my case this Nextcloud 13 and CentOS 6 x64.

After much trouble-shooting and test tweaks with no success, I ran across this thread;
Post 14/26 suggests the module should be located in /usr/lib/php. I did not have that folder, but I did have /usr/lib64/php/modules/
I decided to create a symbolic link in /usr/lib/php.

cd /usr/lib/php
ln -s /usr/lib64/php/modules/
service httpd restart

And hey presto, the warning disappeared!

Upon reading through the rest of the thread, I found at the very end a post regarding CentOS 7.
You might want to start with that suggestion there first, instead of whacking php like I did...


2. Update

If the problem persists on your CentOS 6-installation, and you have the opcache set in /etc/php.ini, have a look at /etc/php.d/10-opcache.ini also. Are the opcache-statements seen above set there?
If not, add them as root and restart the httpd daemon, then check the Nextcloud settings page again for the warnings. They should be gone.

# nano /etc/php.ini
# nano /etc/php.d/10-opcache.ini