How to deal with trashed fstabs

[Roy Smith]

During the process of replacing our XY-450 disk controller with a Ciprico
Rimfire, I ran into a sticky detail.  You have to change your fstab to
indicate that your disks are now rf0, rf1, etc, instead of xy0, xy1, etc.
Once you do this, there is no turning back, i.e. if you can't get the new
controller to work and want to go back to the xy, you can't.  Even if you
save a copy of your old xy-based kernal and boot it, when it comes up,
even single-user, it will read the rf-based fstab, all of which will refer
to non-existant rf disks.  Here's how I dealt with the problem.

First off, even though the entry for / in fstab is wrong, root gets
mounted anyway (I'm not quite sure if "mounting the root file system" has
any meaning, suffice it to say it's there).  Problem is, you don't even
have a /bin, because that's on /pub.MC68020, which didn't get mounted.
Fortunately, you do have a shell (that's about all you have).  You can do
something like:

	% echo '/dev/xy0a / 4.2 rw 0 0' > /etc/fstab
	% echo '/dev/xy0d /pub.MC68020 4.2 rw 0 0' >> /etc/fstab

and reboot.  The next step is to make your life a bit easier should
anything like that ever happen again.  I made a /minibin and put a
"survival kit" in it.  Ask yourself what programs you would most want if
you were stranded on a desert island with only 150 kbytes of binaries.  I
picked cat, cp, dd, ed, ls, mv, ps, rm, and stty.  It's cheap insurance.
Someday it might give you enough to work with on a badly trashed system to
avoid having to drag out the distribution tapes and doing a cold install.

-- 
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
{att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy at alanine.phri.nyu.edu
"The connector is the network"