3 questions

[Alex <radsky ncia net>]

<Ctrl Alt Del>     or   ' shutdown -h now'-------   Which is the
preferred way of exiting from Linux?  They seem to produce the same
shutdown action.

' ls'  or  'dir'     These seem to produce the same listing.   Is there
a circumstance when one is preferred over the other?

'cd .'   What's with this command?  When should it be used?