fsck: broken file system with background check remains broken after bootup

[Matthias Andree]

Rob <spamrefuse at yahoo.com> writes:

> I had following situation:
>
>   Someone suddenly cut the power of a FreeBSD 5.3 PC, leaving the /usr
>   filesystem in a very broken state. During next bootup, there was indeed
>   the message telling 'not properly unmounted', but boot continued with
>   background fsck after 60 seconds; although I have
>      fsck_y_enable="YES"
>   in /etc/rc.conf.

That is the one that may cause problems. The default fsck settings are
conservative so as to only make "safe" changes. fsck -y also makes more
radical changes to your file system.

OTOH, I am not convinced that fsck (particularly bgfsck) is bug-free, I
have seen file system corruption on a FreeBSD 4.10 system that went with
the write caches disabled.

> This scared me. What if /usr was such broken that even single user mode
> would hang!?!

Don't worry as long as /usr is separate from /.

> Moreover, the main user of this PC is not a Unix guru and I hoped that
> the configuration setting in /etc/rc.conf of fsck_y_enable would do an
> automatic fix at bootup, like it used to do with 4.10. However, that
> apparently does not happen anymore.
>
> What can I do to enforce an immediate fix of the filesystems at bootup
> with FreeBSD 5.3, when a filesystem is not properly unmounted at shutdown?
>
> I suppose I should not change default background_fsck ("YES"). How about
> the background_fsck_delay? Should I set this to "0"?

Setting background_fsck=NO should be safe and cause the fsck to run in
foreground - exactly your desire. I would avoid touching the
background_fsck_delay.

If, as you say, the main user of the PC is not a guru and shuts down the
machine improperly, consider disabling the write cache. For ATA drives,
place hw.ata.wc="0" into /etc/loader.conf.local and reboot, for SCSI
drives, use "camcontrol modepage da0 -m8 -e -P3" and change the figure on
the WCE: line to 0, then save and exit; repeat for all further da*
drives if you have more than one.

That will limit the potential damage on the disk to one block rather
than the whole of the cache, which is between 2 and 8 MB on the common
drives sold today.

-- 
Matthias Andree