Libguestfs - Feb 2015 - Re: Mounting disk images with ext2 filesystems on RHEL7

On Wed, Feb 18, 2015 at 6:52 AM, Richard W.M. Jones <rjones@redhat.com>
wrote:
> On Tue, Feb 17, 2015 at 01:37:55PM -0500, Leonard Basuino wrote:
> > I get the following debug info:
> >
> > mount -o /dev/sda1 /
> > [ <time> ] EXT4-fs (sda1): mounting ext2 file system using the
ext4
> > subsystem
> > [ <time> ] EXT4-fs (sda1): bad geometry: block count 104388
exceeds size
> of
> > device (103408 blocks)
> > mount: wrong fs type, bad option, bad superblock on /dev/sda1
>
> It looks as if the image is properly corrupt.  My suggestion
> is to try 'virt-rescue' on it.
>
> virt-rescue --suggest -a <image>
Inspecting the virtual machine or disk image ...

This disk contains one or more filesystems, but we don't recognize any
operating system.  You can use these mount commands in virt-rescue (at
the
><rescue> prompt) to mount these filesystems.
# /dev/sda1 has type 'ext2'
mount /dev/sda1 /sysroot

So I tried ...
><rescue> mount /dev/sda1 /sysroot
[<time>] EXT4-fs (sda1): mounting ext2 filesystem using the ext4 subsystem
[<time>] EXT4-fs (sda1): bad geometry: block count 104388 exceeds size of
device (103408 blocks)
mount: wrong fs type, bad option, bad superblock on /dev/sda1,
           missing codepage or helper program, or other error

          In some cases useful info is found in syslog - try
          dmesg | tail

I don't think the image is corrupt because a colleague is able to mount it
with guestfish on a RHEL 6 box.

> > This has me wondering because the debug messages from guestfish -v -x
> > indicate it is mouting ext2 with ext4.
> > EXT4-fs (sdb): mounting ext2 filesystem using the ext4 subsystem
>
> This is just the way that RHEL 7 works. ie. CONFIG_EXT4_USE_FOR_EXT23=y
> is now always used.  http://lwn.net/Articles/378913/
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-top is 'top' for virtual machines.  Tiny program with many
> powerful monitoring features, net stats, disk stats, logging, etc.
> http://people.redhat.com/~rjones/virt-top
>

On Wed, Feb 18, 2015 at 09:41:52AM -0500, Leonard Basuino
wrote:
> On Wed, Feb 18, 2015 at 6:52 AM, Richard W.M. Jones
<rjones@redhat.com>
> wrote:
> 
> > On Tue, Feb 17, 2015 at 01:37:55PM -0500, Leonard Basuino wrote:
> > > I get the following debug info:
> > >
> > > mount -o /dev/sda1 /
> > > [ <time> ] EXT4-fs (sda1): mounting ext2 file system using
the ext4
> > > subsystem
> > > [ <time> ] EXT4-fs (sda1): bad geometry: block count 104388
exceeds size
> > of
> > > device (103408 blocks)
> > > mount: wrong fs type, bad option, bad superblock on /dev/sda1
> >
> > It looks as if the image is properly corrupt.  My suggestion
> > is to try 'virt-rescue' on it.
> >
> > virt-rescue --suggest -a <image>
> 
> Inspecting the virtual machine or disk image ...
> 
> This disk contains one or more filesystems, but we don't recognize any
> operating system.  You can use these mount commands in virt-rescue (at the
> ><rescue> prompt) to mount these filesystems.
> 
> # /dev/sda1 has type 'ext2'
> mount /dev/sda1 /sysroot
> 
> So I tried ...
> 
> ><rescue> mount /dev/sda1 /sysroot
> [<time>] EXT4-fs (sda1): mounting ext2 filesystem using the ext4
subsystem
> [<time>] EXT4-fs (sda1): bad geometry: block count 104388 exceeds
size of
> device (103408 blocks)
> mount: wrong fs type, bad option, bad superblock on /dev/sda1,
>            missing codepage or helper program, or other error
> 
>           In some cases useful info is found in syslog - try
>           dmesg | tail
> 
> I don't think the image is corrupt because a colleague is able to mount
it
> with guestfish on a RHEL 6 box.
This is pretty strange, and may, I suppose, indicate a kernel bug of
some kind.  I imagine it's possible that (a) the ext4 driver doesn't
understand some very obscure ext2 feature, and (b) since hardly anyone
uses ext2, this bug has never been discovered before.  Or it may be as
Pino says that the filesystem is really truncated and ext4.ko is
correctly moaning about that, but ext2.ko in RHEL 6 ignored it.

Does running `e2fsck -n /dev/sda1' under virt-rescue show up any
errors?

Anything interesting in the output of `tune2fs -l /dev/sda1'?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

On Wed, Feb 18, 2015 at 9:47 AM, Richard W.M. Jones <rjones@redhat.com>
wrote:
> On Wed, Feb 18, 2015 at 09:41:52AM -0500, Leonard Basuino wrote:
> > On Wed, Feb 18, 2015 at 6:52 AM, Richard W.M. Jones
<rjones@redhat.com>
> > wrote:
> >
> > > On Tue, Feb 17, 2015 at 01:37:55PM -0500, Leonard Basuino wrote:
> > > > I get the following debug info:
> > > >
> > > > mount -o /dev/sda1 /
> > > > [ <time> ] EXT4-fs (sda1): mounting ext2 file system
using the ext4
> > > > subsystem
> > > > [ <time> ] EXT4-fs (sda1): bad geometry: block count
104388 exceeds
> size
> > > of
> > > > device (103408 blocks)
> > > > mount: wrong fs type, bad option, bad superblock on
/dev/sda1
> > >
> > > It looks as if the image is properly corrupt.  My suggestion
> > > is to try 'virt-rescue' on it.
> > >
> > > virt-rescue --suggest -a <image>
> >
> > Inspecting the virtual machine or disk image ...
> >
> > This disk contains one or more filesystems, but we don't recognize
any
> > operating system.  You can use these mount commands in virt-rescue (at
> the
> > ><rescue> prompt) to mount these filesystems.
> >
> > # /dev/sda1 has type 'ext2'
> > mount /dev/sda1 /sysroot
> >
> > So I tried ...
> >
> > ><rescue> mount /dev/sda1 /sysroot
> > [<time>] EXT4-fs (sda1): mounting ext2 filesystem using the ext4
> subsystem
> > [<time>] EXT4-fs (sda1): bad geometry: block count 104388
exceeds size of
> > device (103408 blocks)
> > mount: wrong fs type, bad option, bad superblock on /dev/sda1,
> >            missing codepage or helper program, or other error
> >
> >           In some cases useful info is found in syslog - try
> >           dmesg | tail
> >
> > I don't think the image is corrupt because a colleague is able to
mount
> it
> > with guestfish on a RHEL 6 box.
>
> This is pretty strange, and may, I suppose, indicate a kernel bug of
> some kind.  I imagine it's possible that (a) the ext4 driver
doesn't
> understand some very obscure ext2 feature, and (b) since hardly anyone
> uses ext2, this bug has never been discovered before.  Or it may be as
> Pino says that the filesystem is really truncated and ext4.ko is
> correctly moaning about that, but ext2.ko in RHEL 6 ignored it.
>
> Does running `e2fsck -n /dev/sda1' under virt-rescue show up any
> errors?
>
> ><rescue> e2fsck -n /dev/sda1
e2fsck 1.42.9 (28-Dec-2013)
The filesystem size (according to the superblock) is 104388 blocks
The physical size of the device is 103408 blocks
Either the superblock or the partition table is likely to be corrupt!
Abort? no

/boot contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/boot: 36/26104 files (2.8% non contiguous), 12201/104388 blocks

> Anything interesting in the output of `tune2fs -l /dev/sda1'?
>
I'm not retyping all of the output ... interesting?
Filesystem state: not clean
Block count: 104388
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-builder quickly builds VMs from scratch
> http://libguestfs.org/virt-builder.1.html
>