[TUHS] was turmoil, moving to rm -rf /

Dan Cross crossd at gmail.com
Wed Apr 26 01:28:21 AEST 2017


On Tue, Apr 25, 2017 at 10:18 AM, Clem Cole <clemc at ccc.com> wrote:

> Problem was /etc has been burned too...  so the mknod command is off the
> table.
>

Either boot into standalone media like some kind of miniroot (that
hopefully has a copy of mknod) or look for some kind of shell builtin?
E.g., if the shell provides some mechanism to make a raw system call, you
can do it. E.g., an escape hatch to syscall() or indir(). If a copy of
`mkdir` survived, then on older systems where directory creation was done
by calling mknod(), one might be able to modify `mkdir` enough to create
device file for a tape device to launch a restore off of. I thought some
systems came with a syscall(1) utility, but it does't seem to be current
anymore and I can't find any references to it so perhaps I'm misremembering.

I once messed up a NeXT machine by "mv"'ing the system shared libraries to
an unexpected path. Oops. I had to boot off the CD to fix it, but that's
child's play compared to some of the esoterica you guys are talking about.

        - Dan C.


On Tue, Apr 25, 2017 at 10:08 AM, Larry McVoy <lm at mcvoy.com> wrote:
>
>> Whoever was the genuis that put mknod in /etc has my gratitude.
>> We had other working Masscomp boxen but after I screwed up that
>> badly nobody would let me near them until I fixed mine :)
>>
>> And you have to share who it was, I admitted I did it, I think
>> it's just a thing many people do..... Once :)
>>
>> On Tue, Apr 25, 2017 at 10:02:26AM -0400, Clem Cole wrote:
>> > Larry,
>> >
>> > I had to laugh when I read that because what you don't know is it was
>> part
>> > of my old Unix wizards test which was left over from a the day when one
>> of
>> > our hackers (whom I think you would later get to know so I'll not name
>> him)
>> > accidentally typed: rm -rf . as root from his / on his workstation.
>> >
>> > Because /bin/rmdir had been lost, he started getting errors when rmdir
>> was
>> > forked.  So he hit  ^C, but he had already lost:  /bin, /dev, /etc,
>> /lib,
>> > most of /usr.  He was a developer in the networking group so he was
>> working
>> > on network code which we could not trust would not panic (in fact we
>> > disconnected the node from the ethernet immediately just in case).
>>  But we
>> > did have pretty much everything in /usr/bin/[s-z]* -- that is we think
>> it
>> > was deleting files in /usr/bin when he stopped it.
>> >
>> > We obviously had another working Masscomp box just like it. And of
>> course
>> > the shell was working on the machine that was in trouble.   We recovered
>> > the system as it was.   Hint the key item is you have to start by
>> putting
>> > /dev back together and the solution to that problem has had been
>> discussed
>> > on this list.
>> >
>> > Clem
>> >
>> > On Mon, Apr 24, 2017 at 7:59 PM, Larry McVoy <lm at mcvoy.com> wrote:
>> >
>> > > This is gonna seem like I'm tooting my own horn, and I am a little,
>> but
>> > > here's an rm -rf / story.
>> > >
>> > > Clem will be amused because I was a junior or senior in college and a
>> sys
>> > > admin for a Masscomp with a 40MB disk with 20 users.  And I did some
>> > > version
>> > > of rm -rf /, realized part way through that I screwed up, and killed
>> it.
>> > > But /bin and /dev were gone so putting things back together was hard.
>> > >
>> > > But I did it and wrote up this little note for the people who came
>> after
>> > > me, if I was stupid enough to do this someone else would, was my
>> thinking.
>> > > You can get a sense of how scared I was in it if you read it
>> carefully.
>> > > It was a very long night.
>> > >
>> > > For an undergrad, I think it's not bad?  Maybe?  I dunno, I look at
>> how
>> > > much I needed to have understood to get the system back up, that's a
>> lot
>> > > of reading, playing, experience.  Love that Geophysics department,
>> they
>> > > pushed me.
>> > >
>> > > And it was during my (brief) foray into the *roff -me macros (I went
>> > > -ms and never looked back).  Roff source on request to anyone who is
>> > > twisted enough to want it.
>> > >
>> > > http://mcvoy.com/lm/masscomp-restore.pdf
>> > >
>> > > Complete with all the typos.
>> > >
>> > > --lm
>> > >
>>
>> --
>> ---
>> Larry McVoy                  lm at mcvoy.com
>> http://www.mcvoy.com/lm
>>
>
>
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