[wired14]

most of the time i have at least 80-90 proccesses running. DO i need all of them? how can i get a list of what is running and how do i kill the ones i do not want?

Also, how can i know their purpose?

[Christoph]

ps aux will show you every process on your computer (running/sleeping/waiting/whatever). It will usually be a long list (mine was 156 lines just now), but it's easy to filter through it with grep. The man and info pages will tell you what most of the stuff does.
I've got a neat little script called ws (for what started...) that tells you the PID and starting command for any process that matches the input string.

#!/bin/bash
PSAUX=~/.psauxtmp
ps aux>$PSAUX
for ps in $(pgrep $1)
do
..#the format of ps' output is
..#root 3849 0.0 0.0 0 0 ? SW 21:04 0:00 [nfsd]
..#Strip out everything before the name of what was executed by looking for
..#the last 2 times (ie 21:04 0:00)
..echo -n $ps": " && cat $PSAUX|grep $ps|sed 's;.*[0-9]*:[0-9]* [0-9]*:[0-9]* ;;g'
done
rm $PSAUX

edit: Don't forget to replace the invisible dots with spaces (or nothing) if you copy and paste.

[Arkaine23]

Odds are there are service running you may not need. It depends on your distro exactly how to go about disabling them.

[Christoph]

I should emphasize that my script will only kill a running process. If you want a service not to start, you have to play with your distro's init scripts, which are somewhat distro-dependent. Your distro's online docs should tell you what you need to know.

edit: I shouldn't emplasize.

[tamasrepus]

80-90 processes for a Linux system is not much. Keep in mind many of those are probably duplicate processes, which do not take much memory. Several kernel user-space daemons also get run as processes, and you would have no control over them.

Probably the best list is your own computer. Take each running process, and `man thatprocess` to see what it does and whether you need it. There's always your favorite search engine too.