Apparently OLD security prefs made it possible to lock all prefs and demand a password.
In Mountain Lion that option no longer exists.
And the startup disk pref in mountain lion seems to have fallen through the cracks.
I select my startup disk, close the lock, restart,
and, whether the computer does startup from the correct internal boot drive or whether it fails and just gives me a gray screen, once I do get in, the dratted lock on that particular preference is always open.
I have two attached external drives. My time machine drive doesn't have an on-off switch so I have to remember to unplug it before I turn on the computer in order to avoid the problem of the gray screen.
I can't seem to make that preference stay locked and demand a password to open it, tho most other preferences DO demand a password.
I do an automatic login, but I don't think that has anything to do with it.
Is there a terminal command that will fix this bug?