[Libguestfs] Mounting disk images with ext2 filesystems on RHEL7

[Leonard Basuino]

On Mon, Feb 16, 2015 at 6:10 PM, Richard W.M. Jones <rjones at redhat.com>
wrote:

> On Mon, Feb 16, 2015 at 06:00:06PM -0500, Leonard Basuino wrote:
> > Hope someone can point me in the right direction.  I don't know if what I
> > am trying to do should work or not.
> >
> > I have 2 disk images.  One is a VM with an ext2 boot filesystem and ext4
> > filesystems with the OS loaded.  I am amble to guestmount this with no
> > issue and am able to see the files that are on the ext2 file system.
> >
> > I can also run guestfish on the image, mount the ext2 filesystem, and
> list
> > the files.
> >
> > However, the second image I have is only a boot disk image with just an
> > ext2 filesystem.
> >
> > guestmount complains that there is no OS and won't mount.
>
> What you really need to do is run:
>
>   virt-filesystems -a second-disk.img --all --long -h
>
> which will tell you what filesystems (etc) are available in the second
> image.
>


> The only filesystem is /dev/sda1 of type ext2



> > guestfish complains "...wrong fs type, bad option, bad superblock...".
>
> Try using guestfish -v -x flags to provide extra information about
> this error.  See:
>
> http://libguestfs.org/guestfs-faq.1.html#debug
>

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
....

also, trying to mount the image with:
mount -t ext2 <image> <mount point>
returns:
mount: wrong fs type, bad option, bad superblock on /dev/loop0
...
the end of dmesg has:
[<time>] EXT4-fs (loop0): VFS: Can't find ext4 filesystem

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

So is the problem that there is no ext4 filesystem in the image and RHEL 7
is having issues with it?


> Also, what version of libguestfs and where did you get it from?
>
> version 1.22.6-22, came with RHEL 7


> > Should I be able to mount a boot disk image with guestmount?
>
> Yes, libguestfs aims to be able to access any disk image, and mostly
> we have achieved that.  Whether it is bootable or not wouldn't
> normally matter.
>
> > I suspect I'll have to use the -m (mount) option and not -i (as I did for
> > the image with an OS), but that failed too even though I passed in the fs
> > type of ext2,
>
> `-i' invokes inspection:
>
> http://libguestfs.org/guestfs.3.html#inspection
>
> Inspection is an optional convenience feature, and you can access disk
> images without it, but then you need to know what filesystems you want
> to mount (eg. using 'virt-filesystems' -- see above).
>
> > Why would I be able to mount, via guestfish, the ext2 in the first image
> > (with other filesystems of type ext4) but not the disk image with only an
> > ext2 filesystem?
>
> I've no idea, but for more information you can enable debugging at run
> time:
>
> http://libguestfs.org/guestfs-faq.1.html#debug
>
> Rich.
>
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-p2v converts physical machines to virtual machines.  Boot with a
> live CD or over the network (PXE) and turn machines into KVM guests.
> http://libguestfs.org/virt-v2v
>
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