I want to know how to clear the history of the command I typed
and is there a way to see the serial key which it activate the Unix ?
History is shell-dependent, but usually goes into $HISTFILE = ~/.shell_hist or the like; see your shell's man page. You can zap the fille and start a new shell. Just removing one command or line is a bit more difficult. It sounds hacker-esque. History is great! Don't ever put passwords on the command line, generally. Put them in env vars, in piped streams, but not where ps can report them and $HISTFILE records them.
All keys are serial, UNIX does not need activation, so I am getting confused.
He wants to know if there is a way to show the installation key serial numbers and activation keys, and hide the fact that he found them.
Well ever hacker nows there is a way, usually if you get in there first with trojans and loggers. Might be simpler to go to LINUX.