Is there a way to lock command line?

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http://unix.stackexchange.com – For example, in X session, I can use Ctrl-Alt-L to lock the screen, so it would ask for password to unlock and prevent somebody from messing with mine computer. But if I have an open terminal session on one of the tty's (which I can access with Ctrl-Alt-F1, for example) - then it is not locked, and somebody can still use it to do some harm. Is there a way to 'lock' that command line (with some background processes running in it, maybe)? (HowTos)