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SubjectRe: Mount corrupts an ext2 filesystem on a RAM disk
On Tue, 16 Jul 2002, Maurice Volaski wrote:

> >It also works okay here. Maybe, just maybe, you booted with initrd,
> >but did't unmount it before you started mucking with it `umount /initrd`
> >in the script below.
> >
>
> I retested the ramdisk without executing the initial umount
> instructions you proposed and saw the problem as I expected, but when
> I first ran your umount instructions and then tested again, the fsck
> problem didn't show up!
>
> I tested this on all three of my boxes and they all behave the same.
>
> So I guess this means there is a problem somewhere else, but I don't
> know what:
>
> 1) initrd really had still been mounted though df does not detect it.
>
> 2) there is no ghost initrd mounted, but merely executing bogus
> umount instructions in some unknown way prevents the problem.
>
> If it is the first one, there are two questions: why is initrd not
> getting unmounted and why doesn't it show up in df?
> If it is the second one, then what could be going on?
> --

Depending upon the distribution, initrd may not be unmounted.
It would normally be 'transferred' to /initrd on the new root-
filesystem when that is mounted, and just left alone. It's not
going to show up in 'df' because it got mounted before /etc/mtab
existed and `df` (most versions I've seen) reads /etc/mtab. To
fix that problem, as root do:

rm /etc/mtab
ln -s /proc/mounts /etc/mtab

That will substitute /proc/mounts, which has the real information
about what actually got mounted.


Script started on Tue Jul 16 12:38:07 2002
# cat /etc/mtab
/dev/sdb1 / ext2 rw,noatime 0 0
/dev/sdc1 /alt ext2 rw,noatime 0 0
/dev/sdc3 /home/users ext2 rw,noatime 0 0
none /proc proc rw 0 0
/dev/sda1 /dos/drive_C msdos rw 0 0
/dev/sda5 /dos/drive_D msdos rw 0 0
# df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/sdb1 16603376 5906288 9853680 37% /
/dev/sdc1 6356624 1198700 4835020 20% /alt
/dev/sdc3 2253284 1768524 370300 83% /home/users
/dev/sda1 1048272 281840 766432 27% /dos/drive_C
/dev/sda5 1046224 181280 864944 17% /dos/drive_D
# rm /etc/mtab
# ln -s /proc/mounts /etc/mtab
# df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/root.old 1766 1723 0 100% /initrd
/dev/root 16603376 5906284 9853684 37% /
/dev/sdc1 6356624 1198700 4835020 20% /alt
/dev/sdc3 2253284 1768524 370300 83% /home/users
/dev/sda1 1048272 281840 766432 27% /dos/drive_C
/dev/sda5 1046224 181280 864944 17% /dos/drive_D
# ls /initrd
bin dev etc lib linuxrc sbin
# umount /initrd
# df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/root 16603376 5906284 9853684 37% /
/dev/sdc1 6356624 1198700 4835020 20% /alt
/dev/sdc3 2253284 1768524 370300 83% /home/users
/dev/sda1 1048272 281840 766432 27% /dos/drive_C
/dev/sda5 1046224 181280 864944 17% /dos/drive_D
# exit
exit
Script done on Tue Jul 16 12:39:28 2002

I don't normally set the link I demonstrated because the actual
drive name of my root file-system gets lost, it becomes /dev/root.
If I run lilo under this configuration, with the parameters
"root=current", I get something strange, failing to find the
root file-system upon boot.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).

Windows-2000/Professional isn't.

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