From: rrezaian@austral.chi.il.us (Russell Rezaian)
Newsgroups: chi.mail
Subject: Re: clout closed
Date: 21 Jan 93 21:04:31 GMT
Distribution: chi
Organization: D.O.C. Data Processing Systems

In article <C10rDt.GoE@ddsw1.mcs.com> karl@ddsw1.mcs.com (Karl Denninger) writes:
>In article <1993Jan17.001105.7415@austral.chi.il.us> rrezaian@austral.chi.il.us (Russell Rezaian) writes:
>>Before that we had a remote reboot hang due to a memory error. This has
>>happened about 3 times in the past few months.  We haven't traced the
>>cause of our little memory parity error, but I suspect it might have
>>something to do with line glitches, cosmic rays, heat, or malignant beings
>>from the spirit world.
>
>Or bad memory :-)

That had occurred to me also...  :-)

>Seriously, do you have the RAM test enabled on the machine?  The PROM
>default is to check only the first meg (not very useful!)  Then again, these
>"ram tests" are frequently not useful anyway, but they are better than
>nothing!

Yup, we have the default RAM test on a powerup set, and after the second
time I went into the PROM diags and ran all of the memory tests there.
Nothing, all of the ram tested clean.

>Filled virtual space will prevent the inode cache from being properly
>managed, and can manifest as no available inodes.  Of course, you'll also be
>getting complaints about other things (like no swap space), and processes 
>will refuse to start (since there is no backing store or RAM for them 
>available)

That pretty much was what happened, and it's didn't take us much time to
trace the problem.  Of course the i-node messages did rather tend to
confuse the issue for a while, but considering they were with respect to
the root partition it wasn't really likely that we were actually out of
i-nodes.  Dead giveaway that the problem's elsewhere.

>In the extreme case, this can completely lock you out - unless you get lucky
>and something exits just as you're trying to log on.

It did lock us out, someone rebooted the machine and things were fine.

>>Now, during this time clout has had problems with spool space, including
>>two instances of the mailbombing of a local client site.  NOT ONCE has
>>this required a physical reboot of clout, and at least three times that I
>>remember it hasn't even had any effect on the function of the clout
>>machine.
>
>It should not, IF you have parititioned your disks correctly.  It will,
>however, cause mail to be dumped on the floor unceremoniously.

Actually, no it won't.  At least not for sites in chi.il.us.  While the
clout machine won't be able to accpet mail, all of the site in chi.il.us
that depend on clout have at least one secondary MX site so the mail can
go there.  In fact, on those ocasions when clout has been out of commision
this is exactly what has happened.  It's really neat when something works
the way it's supposed to.

>Anyone who runs a system with the mail spool on the root partition deserves 
>what they get.  They will get it.  The pat answer to this is "don't do
>that".

We don't.  We're not that stupid.  Anyone with a spool of any kind on the
root partiton is asking for trouble, and IMHO anyone with /tmp on the root
partiton is asking for trouble too...

>In general, there are several items which will hose you every time:
>
>1)	Running out of virtual space (RAM + page).  This will, on occasion,
>	crash systems (or it might just lock them up)  It is always bad news.

Bingo.  This has happened a few times lately, and we are currently looking
for more RAM.  Depending on how bad things get we might try adding some
swap sace to the system, but I want to put as much real RAM in as possible
before stealing even more of our limited disk space.

>2)	Running out of disk space on root (frequently prevents anyone from
>	signing on; ergo, you have a bitch of a time fixing the problem).
>	Some machines also crash under this kind of stress.

We haven't had this problem, luckily.  And I hope we don't.  Root is a bt
tight, but that's just my opinion, I know people who as a matter of course
run with less space on root partitons than we now have.

>3)	NIS problems can cause service failures or a completely locked up
>	system (its not really locked, but system calls which attempt to do
>	name <> uid mapping hang, so it appears locked).  NIS should NEVER
>	be run unless you have TWO servers on EACH subnet.  NO EXCEPTIONS.
>	Further, NIS should NEVER be run on a machine which is visible from
>	"hostile" locations -- if it is, you're asking for someone to 
>	download your password file and crack the passwords.

Only if your password file is available via NIS, ours isn't.

>	Filtering on 
>	routers is only marginally useful in combatting this; even if you 
>	prevent contact with the portmapper, people can still get through 
>	by creative port guessing.  (This is less true for "secure" NIS, 
>	but even that isn't very secure)  Run the Sun security (shadow 
>	password and more) package instead, and get rid of NIS.

Shadow password isn't too helpful if you don't have any users on a system.
Since we don't have any users on clout there's not much point.  Not to
mention that shadow password files are horribly over-rated.  Adding more
of the Sun C2 package might not be too bad an idea though, we should look
into it!

>This is a good start.  CLOUT seems to be missing a few of these points ;-)

Well, we've cleaned up the big NIS problem, as a quick fix, and over the
long term I am going to be isolating what ever it is that still wants NIS
and pulling that.  (There may come a time when we want NIS again, but not
yet...)

Other than that, the only serious problem that we have discussed that
really applies is memory.  And we're looking!  Somehow it always
comes down to this, all our problems seem to devolve to space.  At least
there's hope on the disk front.
--
Russell Rezaian			|  rrezaian@austral.chi.il.us
  rrezaian@clout.chi.il.us	|  rrezaian@zed.chi.il.us
Newsgroups: chi.eats