> Using 9front and set "service=cpu" but rio doesn't start.

This is expected.  CPU servers typically don't have any reason to run
rio.  Mine don't even have monitors attached (usually).

> I've tried adding screenrc to /rc/bin/cpurc and /cfg/$sysname/cpustart
> but gives me errors on /dev/draw.

If you compare /rc/bin/cpurc and /rc/bin/termrc you'll see that the
vga device (#v) is bound only in /rc/bin/termrc.  You can arrange
this in /rc/bin/cpustart, before you include /rc/bin/screenrc, like so:

bind -a '#v' /dev >/dev/null >[2=1]

--
Cheers,
Alex Musolino