Is it possible that only root can shutdown/ reboot the computer if multiple
users are logged in and when there is only one user that user is able to
shutdown the computer?
time ago, the question was asked at each install. There is certainly an
option "who can shut down the computer", but do not forget to hide
switches...
here:
https://www.debian.org/doc/manuals/securing-debian-howto/ch4.en.html
see
4.8 Restricting system reboots through the console
mostly:
If you want to restrict this, you must check the /etc/inittab so that
the line that includes ctrlaltdel calls shutdown with the -a switch.
(but not only, see shutdown man page)
jdd