the needn't and the haven't

[josé ángel madrid gómez]

Apart from the applications I use, I'm sure {at least my /usr/bin is
full of them} there are hundreds of command-line applications, or even
X-apps I have installed and I don't know. Sure there are some other apps
which are just installed, as daemons or so, which are running the whole
time.
And I'm sure that I don't really need some of them.
For example: Postfix? I'm not using my pc as a mail server, do I need
postfix?
Mutt? I just read the mail and news in thunderbird, do i need mutt?
aptitude? If I have Synapctic...
In conclusion, is there a way to know what can I make disappear in my
Ubuntu instalation? {I mean, apart from try+error way}
Of course, maybe I don't need them now, but I can need them in a future,
 so, unless there is no way to download them, they should stay.

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I keep on learning