A couple of days ago I had a problem with VirtualBox, I couldn’t start one of my VMs because it was displaying an error message saying: “VERR_SUPLIB_OWNER_NOT_ROOT”
Searching on the internet I found this bug. and they suggested to run:

chown -R root:root /usr/lib/virtualbox
chmod 4711 /usr/lib/virtualbox/VirtualBox

This didn’t fix my issue, so I started to dig deeply into the issue and I found a log file on ~/.VirtualBox/Machines/VM/Logs/VBox.log with the following message:

00:00:00.448 pdmR3LoadR0U: pszName="VMMR0.r0" rc=VERR_SUPLIB_OWNER_NOT_ROOT szErr="The owner is not root: '/usr'"

I took a quick look at /usr permissions and I found that for some weird reason, it had uid:gid 500:500
# ls -ld /usr
drwxrwxr-x. 13 500 500 4096 Aug 3 2006 /usr

Solution:
chown root:root /usr