Quoting Brad Campbell (lists2009@???):

> This is one I find interesting. I've never used an operating system
> where it was required to know root credentials to halt or reboot the
> machine from the login screen.

Remember, Unix is a multiuser operating system, and also one supporting
both local and remote users, who would be annoyed by someone deciding to
cut them off.

Imagine a host with hundreds of simultaneous users, such as (say) a
shared ISP machine. You would absolutely not want just anyone to be
able to shutdown or reboot the machine at will. Tberefore, the
conventional solution to this problem is to require membership in a
bespoke group for shutdown/reboot rights.

That being said, although the Linux kernel (like those of other
Unix-type OSes) can intercept hardware reboot signals (like Ctrl-Alt-Del
on x86) and control/define what that does, generally speaking anyone
with physical console access can force reboot one way or another anyway.

-- 
Cheers,                              « On donne des conseils, mais on ne 
Rick Moen                            donne point la sagesse d'en profiter. »
rick@???                                     -- La Rochefoucauld
McQ! (4x80)