What can prevent root from modifying or deleting a file when SELinux is disabled?

Issue

• A certain file cannot be modified or deleted, even by the root user Errors "Operation not permitted"

Example:

    chmod: changing permissions of '/etc/passwd': Operation not permitted

• When directory has immutable attribute set while trying to delete the underlying files you get "Permission denied" error.

Example:

lsattr -R /etc/dhcp
---------------- /etc/dhcp/dhclient.d

rm -rf /etc/dhcp/dhclient.d
rm: cannot remove ‘/etc/dhcp/dhclient.d’: Permission denied