DVD/CD players can get dirty (internally). Which might require the lens to be cleaned. More so with smokers and/or pets in the house. Isopropyl alcohol or rubbing alcohol and a Qtip, while unplugged / off of course.
UGOA is user group other all type permissions. ls -l shows the attributes.
$ ls -l /boot/vmlinuz-4.19.0-6-amd64
Code:
-rw-r--r-- 1 root root 5262576 Sep 20 05:51 /boot/vmlinuz-4.19.0-6-amd64
-111222333 - 4444 5555 6666666 777777777777 8888888888888888888888888888
Where 1 is the owner / user Read+Write+eXecute permissions
Where 2 is the group RWX permissions
Where 3 is the other / everyone RWX permissions
Where 4 is the owner / user
Where 5 is the group
Where 6 is the file size
Where 7 is the date / timestamp
Where 8 is the file name and location in this case.
Where chmod modifies the RWX permissions
Where chown modifies the owner/user (and/or group with :group)
Where chgrp modifies the group
$ man chmod
$ man chown
$ man chgrp