I should have explained that when using the <Ctrl Alt Delete> method of exiting from Linux , as recommended by one source as a safe way to shut down, you have to press the computer's power button as soon as you see the computer start to boot back up. Otherwise, the computer just reboots. That source doesn't even mention 'shutdown -h now'.
The command cd . (single period) is described in one of my resources as 'change directory to current directory' . Why use such a command? Nothing in my man cd page about this.