Apache

 Apache  is widely deployed open source web server software.

HTTP 406 Not Acceptable Error
In some cases, Apache returns HTTP 406 when fetched from a client that does not include  in the Accept header. This is due to a common misconfiguration where PHP is enabled by using the  declaration instead of a proper solution.


 * https://stackoverflow.com/a/24598848/712641
 * https://stackoverflow.com/a/41793472/712641

This error surfaced when XRay was unable to fetch posts on adactio.com because XRay does not include  in its Accept header. The fix was to remove the  declaration and include the below instead.

 MultiviewsMatch Any 

Permissions
Summary (from serverfault thread):


 * Apache usually runs as the www-data, which will at the very least need read access to files
 * “Application” files (e.g. *.php) don’t need execute permissions as they’re not directly executed by the web server, they only need read permissions
 * Your user should own the files
 * The www-data user should own the group, which should have read and execute (why execute?) permissions
 * Any files or folders which will be changed by apache need to have write (+w) permissions for the group owner
 * Run  to set the default permissions for newly created files.   sets permissions to read+write for owner and group, no permissions for others, which is a sensible default

wikipedia has a clear explanation of the unix permissions shorthand.