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Re: Ext3 filesystem modified while mounted read-only



I believe this was discussed a while backon the list.  I would
dig through the archives.

Steve

Graham Bleach wrote:

I noticed that ext3 filesystems are modified if mounted read-only:

# mke2fs -j /dev/hdb1

[...]

# md5sum /dev/hdb1 > MD5SUM
# mount -t ext3 -o ro /dev/hdb1 /mnt/test1
# umount /mnt/test1
# md5sum -c MD5SUM md5sum: MD5 check failed for '/dev/hdb1'


On examination of a block-for-block copy of 'before' and 'after' images
with od and diff, I believe that the changes are the transaction number
in the journal being increased. I have also noticed that the filesystem
is not modified if mounted read-only via a loopback device.

Can anyone explain why it is necessary to increment transaction numbers
in a read-only mount? Or why this does not happen when a loopback device
is used?


Thanks
Graham







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