[Fedora-xen] Createing/working with disk images
Andrew Cathrow
acathrow at redhat.com
Tue Mar 27 21:58:46 UTC 2007
Run kpartx to create the devices - will be created in /dev/mapper
kpartx -a /dev/loop0
On Tue, 2007-03-27 at 15:32 -0600, Lamont Peterson wrote:
> All,
>
> I need to create some images that pygrub can boot (on FC6 & RHEL5). IIUC,
> that means that the image file must be a disk image complete with partition
> table.
>
> The trouble I'm running into is figuring out how to access the "partition"
> within the disk image file as a block device. This is necessary in order to
> format or mount the filesystems and run mkswap for the disk image's swap
> partition.
>
> Here's what I have so far.
>
> 1. Create the disk image file, ala "dd if=/dev/zero
> of=/var/lib/xen/images/someVM/sda bs=1k seek=4608k count=1"
>
> 2. Create partitions with fdisk (this requires setting the number of
> cylinders, but that's easy).
>
> 3. losetup /dev/loop0 /var/lib/xen/images/someVM/sda
>
> At this point, I can run "fdisk -l /dev/loop0" and get:
>
> Disk /dev/loop0: 4831 MB, 4831839232 bytes
> 255 heads, 63 sectors/track, 587 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
>
> Device Boot Start End Blocks Id System
> /dev/loop0p1 1 523 4200966 83 Linux
> /dev/loop0p2 524 588 522112+ 82 Linux swap /
> Solaris
>
> However, there is no /dev/loop0p1 or /dev/loop0p2 devices and I'm not sure
> what to do to make those accessible. I need to be able
> to "mke2fs -j /dev/loop0p1" and "mkswap /dev/loop0p2" or equivalent. Then I
> need to mount /dev/loop0p1 to copy files to it.
>
> How can I access partitions inside a disk image as block devices? Should I be
> using something other than losetup here?
> --
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> Fedora-xen at redhat.com
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