on fedora, at least, you can change the runlevel by editing the following file:
that’s it, you’re now running multiuser mode with no GUI. on our machines, this seems to have helped stability and call quality, to a small but measurable degree.
as far as what NEEDS to be running for asterisk - not much. as long as you have network connectivity and can get asterisk to launch, i think you’d be good to go.
i’ve gotten asterisk to install successfully on minimal install of fedora, and it runs great. i’m sure there are linux/asterisk gurus out there who know exactly what is needed and how to get a box set up that way, but i’m not one of them…
good luck, and i hope this helps.