In the Admin console, you might see Security and Setup Warnings after upgrading to OwnCloud 8.1. Here is how I removed the two I saw.
Strict-Transport-Securty HTTP Header
The “Strict-Transport-Security” HTTP header is not configured to least “15768000” seconds. For enhanced security we recommend enabling HSTS as described in our security tips.
The instructions provided in their Harden Security Documentation is good but here is a little more.
Add the following snippet of code to the file
/etc/apache2/sites-available/owncloud-ssl.conf within this bracket
Header always add Strict-Transport-Security "max-age=15768000; includeSubDomains; preload"
Restart your apache2 server. If you get a parsing error, you need to enable Headers. Run the following in a command line:
Memory Cache #1
No memory cache has been configured. To enhance your performance please configure a memcache if available. Further information can be found in our documentation.
According to the documentation, you need to install APCu and enable it. Funny thing is that getting the correct version of APCu was confusing. You need to uninstall the old version and then install the newer version. Follow the instruction on this github issue. As of now, you should use the 4.0.6 version of APCu.
Following the OwnCloud documentation now, add to /var/www/owncloud/config/config.php the follow option:
'memcache.local' => '\OC\Memcache\APCu',
Restart apache2 and you are good to go with no more warnings!
Memory Cache #2
APCu below version 4.0.6 is installed, for stability and performance reasons we recommend to update to a newer APCu version.
This means you need to follow the instructions in Memory Cache #1. Uninstall the older version of APCu and install version 4.0.6 or newer.