I think this time you must reboot. But there are some things you can do
for next time.

> I got pppd set up ok I thought, but then I realized that I haven't been
> logging errors (they've been coming through the console), about 6 different
> errors (I can't give the specifics, and I'll getting to why I can't).
> 
> At the same time I got pppd mostly working, I was trying to connect with
> eXodus 6.0.1 with no luck, some error about "incorrect login" with any of
> the users I'd set up.  Telnet works, ftp works, but no remote X.  I saw the
> post about http://macaroni.cs.wits.ac.za/xsetup.html and I followed those
> instructions, however I followed them verbatim, thinking if there was
> something that was supposed to be customized for a particular setup that I
> neglected I could go back and fix it.

What error? Please tell us more details.

> Then I experienced two things - I had disconnected from PPP on the MacOS
> side, tried to reconnect, and found I couldn't (looks like pppd has quit
> after a successful session?  perhaps I have to explicity tell it to
> re-launch after it closes down?)  So then I went to the Mac II itself to
> login, and faced with the nice xdm login screen, I assumed everything was
> ok, but when I enter a username and password, the screen goes white with
> the little black cursor at the bottom (back at the console for a moment?),
> then grey X, then back to the login screen!

Yes, pppd will just end after a successful session. How had you started
it in the first place? From the unix console?

One thing you could do is set /etc/ttys up to always run pppd on that serial
port, but I'm not certain how to do this exactly. Another option is to
run a getty on the other tty, and flag it as secure. Thus you can either use
two cables to hook the two serial ports together, or you can switch the
cable around. But you can get a serial session with a normal prompt. By
making it secure, root can log in. :-)

> Right now I can think of no way to get into MacBSD, so my Mac II just sits
> there.
> 
> I'll probably just end up force-rebooting, then logging in by ppp, and then
> fix the files... if only I knew what I did wrong.  (For future reference,
> is there a way to stop xdm from loading at startup if its misconfigured the
> way I must have?)  Where did I go wrong?

Why not just boot single user, fsck, mount r/w, and then clean things up?

Take care,

Bill