Attempts to change the group of the file filename
to group.
Only the superuser may change the group of a file arbitrarily; other users may change the group of a file to any group of which that user is a member.
Note: This function will not work on remote files as the file to be examined must be accessible via the servers filesystem.
Note: When safe mode is enabled, PHP checks whether the files or directories you are about to operate on have the same UID (owner) as the script that is being executed.