shutdown on BSD and Linux

[Joerg Sonnenberger]

On Thu, Sep 07, 2006 at 11:50:20AM +0000, Rahul Siddharthan wrote:
> If you include ports/pkgsrc, it IS a "distro".  And decidedly flaky,
> at that, compared to most linux distros.  No BSD comes with Apache or
> PostgreSQL in the base system, and only NetBSD includes Postfix, to
> give the three examples in Ubuntu's teardown wiki article.

OpenBSD has had Apache 1.3 in base for ages. Apache behaves graceful, as
does PostgreSQL. In fact, even killing is not very problematic for both,
as long as the disks are correctly flushed. Postfix doesn't really care
either.

> I'd have taken that seriously at one time -- in fact I did -- but one
> too many crashes that completely trashed my UFS+softupdates filesystem
> changed my mind.  When I reported that on FreeBSD, the answer is yeah,
> ATA does write-caching and lies about it and sucks generally, tough,
> use SCSI.  (And I'm not the only one to have had trashed filesystems,
> there are plenty of "unexpected softupdates inconsistency" errors
> reported on lists.  Some bugs were found and fixed by Matt, IIRC, but
> it looks like only Kirk McKusick really understands softupdates.)

I know of one such issue (reference count of the root directory being
sometimes wrong), but yes -- most of the issues are ATA write cache
related.

> Yes, I use cheap ATA hardware, and don't always notice when my laptop
> battery is going to die, and sometimes plug in unstable devices, so I
> have occasional crashes and unclean poweroffs.  On Linux ext3, held in
> near-universal scorn by BSD types, I have NEVER had a trashed
> filesystem, and only ever lost data in a couple of open files (usually
> system logs).  In fact, the only problem I ever remember having on
> linux is poor VM behaviour, exhibited when a runaway process eats all
> available RAM.  And these days that's much better too.

I had a completely trashed ext3 once, on *SCSI* disks. ATA write caching with
reordering can kill journaling as well, BTW. The chances are just
smaller.

> >Sounds more like a CPU-fan or HDD spun UP, not down, as needed in a burst of
> >intensive activity (putting stuff away properly before shutdown..)
> 
> Nope... if the burst of activity happens while (as I said) the machine
> is powering off, something is seriously amiss.  On linux, the sounds
> die away and the machine is silent for a second or two BEFORE poweroff.

It might issue a stop command to ATA drives before calling the powerdown
function. Not sure. But drives are supposed to handle that themselve and
almost all do.

Joerg