the "bs=512 skip=63" depents on the size of boot sectors. It is not the same in all cases.

Under Linux you can check the consistens of your image. For example the command "file foo.dat" should detect your file as "filesystem data" and should print the used filesystem (ext3, Reisser or so). Remember, that ReisserFs and ext4 is not compiled in in all coLinux kernels. So it can be your problem here. Rootfilesystems for coLinux should be formated with ext3

Second check: You can mount the file as loop:

    mount -o loop,ro foo.dat /mnt

If that works, your Image file is ok.
If the loop does not mount, then the image file is corrupt.

A safer way to create such image:

Create an additional big disk (vdi), that is 10% or more than the disk you wand to copy.
Run Xubuntu
Format the new disk with ext2 (ext2 has less overhead as ext3/4 or Reisser)
Reboot Xubuntu in a maintaince text mode or single user mode. I don't know exactly how it is named in Ubuntu. But it should be a mode with less of all startup and no X11 running.
Mount your new disk, for example to mount point /mnt.
Try to mount the root filesystem to readonly. If that not can it is no big problem. But it would be better.
Now make a raw backup from your root filesystem. Is your rootfilesystem is on device /dev/sda1, you shoult run a comman like:
    dd if=/dev/sda1 of=/mnt/MyRawImage.img
This make a while. Wait to finish, and copy the file "MyRawImage.img" to your Windows.
If you not have enough disk space, you can compress the image file:
    dd if=/dev/sda1 | bzip2 > /mnt/MyRawImage.img.bz2


On 05.02.2011 18:22, 卍\(^o^)/卐 wrote:
Hello, I'm a new baby to coLinux. Thanks for your wonderful job!
 now, i have some trouble in creating disk image!
 here is my steps:
 first, I installed a xubuntu system in VirtualBox(my host OS is Windows7)
 second, I turn off the Virtual machine, using VBoxManage.exe covert the "vdi" disk file to RAW format
 third, I use dd coverting the RAW image with para "bs=512 skip=63"
 could you tell me whether these steps has something wrong? And How to make rootfs image?
 wish to hear from you !
 Happy new year!
 Err info:
 VFS: Mounted root (ext2 filesystem) on device1:0.                                                                                                              ===========================================================================     # This process will install (if necessary) the coLinux modules for the          # coLinux kernel.                                                               input: AT Translated Set 2 keyboard as /devices/serio0/input/input0             ===========================================================================                                                                                     Determining /, Found.                                                           Mounting /                                                                      EXT3-fs (cobd0): error: can't find ext3 filesystem on dev cobd0.                EXT2-fs (cobd0): error: can't find an ext2 filesystem on dev cobd0.             EXT4-fs (cobd0): VFS: Can't fi
nd ext4 filesystem                                ISOFS: Unable to identify CD-ROM format.                                        mount: Mounting /dev/cobd0 on /mnt/linux failed: Invalid argument               List of all partitions:                                                         7500         4194272 cobd0 (driver?)                                            No filesystem could mount root, tried:  ext3 ext2 ext4 iso9660                  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(117,0)Pid: 1, comm: swapper Not tainted #1                          Call Trace:                                            
 [<c122f6af>] ? printk+0x18/0x21                                                 [<c122f681>] panic+0x4e/0x64                                                    [<c12eea9c>] mount_block_root+0x242/0x254                                       [<c108dac7>] ? sys_mknod+0x27/0x30                                              [<c12ee0c7>] ? kernel_init+0x0/0xea                                             [<c12eeb07>] mount_root+0x59/0x5f                                               [<c12ef66f>] initrd_load+0x277/0x38c                                            [<c12ee0c7>] ? kernel_init+0x0/0xea                                             [<c12eebcb>] prepare_namespace+0xbe/0x183                                       [<c1080d40>] ? sys_access+0x20/0x30