Re: fsck in background?

On Mar 31, 2003  21:14 +0400, Hans Reiser wrote:
> Oleg Drokin wrote:
> 
> >On Mon, Mar 31, 2003 at 12:30:37PM +0200, myciel wrote:
> >>so I'm curious if maybe fscking in background is planned? - idea is not new
> >>and bsd guys say that they have it  for freebsd 5.0 in ffs.
> >>    
> >>
> >
> >This is not possible for reiserfs, I think.
> >reiserfs have non-constant metadata location , so while you can certainly
> >check fs consistency of some snapshot, you cannot fix it because all the
> >real data might have ben shifted to other blocks, old blocks might have
> >been already freed and so on.
>
> It can be done, but I don't have the funding/staff for it.

I wrote a script to do this once, using LVM snapshots.  Attached here.
I haven't used it in a long time, and didn't do much other than write
it and test it out a bit, but it likely works OK.

It obviously doesn't actually fix any problems that it detects, but
for systems that run a long time it avoids the need to do a shutdown
to verify large filesystems are intact.  For ext2/3 it also resets the
"last checked" count/time so that ext3 will not do gratuitous full fscks
if the system has been up over 6 months (assuming you run the script
periodically while the system is running).

Cheers, Andreas
============================= lvm-fsck =============================
#!/bin/sh
# Automatically checks ext2/ext3 filesystems that are currently mounted
# and also residing on LVM logical volumes, so that we can snapshot them.
# You need to have the LVM VFS locking patch applied for this to work.
#
# (C) Andreas Dilger, 2001
#
# Licensed under the GNU General Public License, version 2 or later

#set -vx

# Use the PATH to find any installed fsck programs
PATH=$PATH:/sbin:/usr/sbin:/usr/local/sbin
PROG=`basename $0`

FSCKLV=lvfsck
lvscan | grep ACTIVE | while read LVSCAN DASH ACTIVE LV LV2 SIZE; do
        [ "$LV" = "Snapshot" ] && continue
        if [ "$LV" = "Original" ]; then
                LV=`echo $LV2 | tr -d \"`
        else
                LV=`echo $LV | tr -d \"`
        fi
        VG="`dirname $LV`"
        LVS="$VG/$FSCKLV"
        # This could be smarter (i.e. removing old snapshot after checking if
        # another lvm-fsck is running, but we don't want to do concurrent fscks
        # if it takes a really long time to run, or if the script has problems.
        # Sadly, lvdisplay does not return an error code if $LVS doesn't exist
        if [ "`lvdisplay $LVS 2> /dev/null`" ]; then
                echo "$LVS exists!  Unable to check $LV"
                continue
        fi

        # Check if this LV is mounted and has a fsck-able filesystem on it
        AWKLV="`echo $LV | tr / .`"
        FSTYPE=`mount | awk "/^$AWKLV/ { print \\$5 }"`
        FSCK="`which fsck.$FSTYPE 2> /dev/null`"
        [ "$FSCK" ] || continue

        echo "$PROG: running read-only $FSCK on $LV"
        # Just a guess at how much snapshot space we need
        SIZE="`df -P $LV | tail +2 | awk '{ print $2 / 500 }'`"
        lvcreate -s -L ${SIZE}k -n $FSCKLV $LV > /dev/null
        rc=$?
        if [ $rc -ne 0 ]; then
                echo "Creating snapshot of $LV at $LVS failed with rc=$rc" 1>&2
                continue
        fi
        case $FSTYPE in
        ext2|ext3) $FSCK -f -n $LVS; rc=$?
                if [ $rc -eq 0 ]; then
                        tune2fs -C 0 $LV > /dev/null
                        tune2fs -T now $LV > /dev/null 2>&1
                        ;;
        reiserfs) echo Yes | $FSCK --check $LVS; rc=$? ;;
        *) echo "Don't know how to check $FSTYPE filesystems passively"; rc=$1;;
        esac
        [ $rc -ne 0 ] && echo "$FSCK of $LV failed with rc=$rc" 1>&2
        lvremove -f $LVS > /dev/null
        rc=$?
        [ $rc -ne 0 ] && echo "lvremove of $LVS failed with rc=$rc" 1>&2
done
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/