On Fri, May 08, 2009 at 08:39:53PM -0400, Andres Salomon wrote:
> Package: e2fsprogs
> Version: 1.41.3-1
>
> If I attempt to shrink an ext3 filesystem while mounted (even if
> read-only) via "resize2fs /dev/hda1 8G", it refuses with:
>
> "Filesystem at /dev/hda1 is mounted on /; on-line resizing required
> On-line shrinking from $foo to $bar not supported."
>
> I don't know if this is a necessary restriction or not, but it's pretty
> annoying. If it is safe to do when the fs is mounted read-only, it
> would be nice if '-f' allowed one to bypass the check.
Well, it could cause the system to panic and reboot while resize2fs is
in the middle of resizing the filesystem --- is that unsafe enough? :-)
That's pretty extreme, and it's a pretty low-probability event, but
it's definitely within the realm of possibility. If you have the
filesystem set up to reboot if a filesystem corruption is detected,
it's even more likely.
Also note that if you are short on memory, and the system is paging,
any program currently running on the system which you are shrinking
(possibly including resize2fs itself) could end up reading in trash
blocks, which could cause that program to crash. And while resize2fs
tries very hard not to leave the filesystem corrupted if it or the
system crashes while it is running, there are certain operations which
could lead to data loss.
> Furthermore, if one boots into an initramfs (booting with 'break=mount')
> in order to resize the filesystem, mounts /dev/hda1, copies resize2fs
> and associated libs into the initramfs root, unmounts /dev/hda1, and
> then attempts to shrink the filesystem, one gets:
>
> "ext2fs_check_mount_point: No such file or directory while determining
> whether /dev/hda1 is mounted."
>
> Even using '-f' doesn't allow it to continue. This is amazingly
> unhelpful. The code in lib/ext2fs/ismounted.c checks /proc/mounts for
> the filesystem, doesn't find anything interesting, attempts to
> check /etc/mtab (which doesn't exist because we're in an initramfs),
> and returns ENOENT.
>
> Please consider the following patch to allow the administrator to
> override the failed mount point check using the -f option. It would be
> even better if that check could be made to not happen at all w/ -f (or
> some other argument).
So I'm extremely uncomfortable with this. I would much rather have
initramfs create a zero-length /etc/mtab file in the inital ramdisk
image, or better yet, have a fully supported and supportable system
which allows users to shrink the root filesystem.
For example, we could have a script fragment that checks for the
existence of a file which matches the pattern /on-initrd-*.tar.gz, and
if one or more such files exists, they are copied to the initrd, and
then the root filesystem is unmountd, and one by one, the
on-initrd-*.tar.gz files are unpacked and the /on-initrd script
contained in the tar.gz file is executed.
This could be used to perform an off-line shrink of the root
partition, by having the user request such a thing, and then
rebooting, and having it happen automatically. It could also be used
to add or remove a journal safely, as well as repack and optimize
directories (e2fsck -fD).
Another approach would be to resize the filesystem using a rescue CD.
The reason why I suggest these is they are in the long-term much more
supportable. If a user doesn't know enough to work around the
"ext2fs_check_mount_point: No such file or directory while determining
whether /dev/hda1 is mounted" error by using "touch /etc/mtab", do we
really want to trust him or her with using resize2fs -f? What if they
use it when they shouldn't, and end up trashing their own filesystem?
I've already had a bug filed by an Ubuntu user who saw this error message:
/dev/ssd/root is mounted.
WARNING!!! Running e2fsck on a mounted filesystem may cause
SEVERE filesystem damage.
Do you really want to continue (y/n)?
... and they were clueless enough to answer yes, and then when his
filesystem was severly damanged (as promised) he filed a bug
complaining about the fact. "Resize2fs -f" is even easier for said
user to screw up.
If I did anything at all, I'd be severly tempted to make the user type
something like:
Warning! An attempt to resize /dev/XXX while it is mounted
may cause your system to crash and your filesystem to be
destroyed. To continue please type: 'I ACCEPT ALL LIABILITY
FOR TRASHING MY FILESYSTEM AND PROMISE NOT TO FILE A BUG'. Or,
if your /etc/mtab file is in error or missing, type ^C, fix it
by hand, and rerun re2size2fs: "
... and only continue if the user types the required string. :-)
- Ted
--
To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org
with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
