if you use kde you should get a nice "K" icon at lower left corner, klick that and chose exit then shutdown on the menu that pops upp.
if you are in a console there are several (each work by themselves no need to type them all)
Code:
sudo init0
Code:
sudo halt
Code:
sudo shutdown -h now
should all work.
for rebooting
Code:
sudo reboot
Code:
sudo init 6
Code:
sudo  shutdown -r now
should work.