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Thread: nbd in knoppix 6.7.1 (boot: knoppix64)

  1. #1
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    nbd in knoppix 6.7.1 (boot: knoppix64)

    I would like to mount a kvm qcow2 image (Windows XP) via nbd, but 'modprobe nbd' returns nil. Nothing obvious (to me ) in debian package repository for the missing kernel module. Pointers (instructions, reading materials) on how to achieve the image mount would be greatly appreciated. thanks in advance.

  2. #2
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    If you look inside the the kernel's configuration file, you will see that the support for network block devices was already compiled into the Knoppix kernel. There is no need to load a kernel module using modprobe. The device names are /dev/nbd[0..15].

    I do not use network block devices myself, but I found a short tutorial on the Debian Administration web site: Working with network block devices

  3. #3
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    Thank you very much Klaus for the details on nbd, and also the tutorial (which would help bridge the gaps in my knowledge and get me going). Very much appreciated.

  4. #4
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    Continuing on getting nbd to work in Knoppix 6.7.1 (boot:knoppix64) - now with the knowledge that kernel has nbd -

    the nbd server appears to start OK ("kvm-nbd -c /dev/nbd0 xp-disk.qcow2"), and fdisk shows partition 1 (as expected for the disk image xp-disk.qcow2). however, the device fails to mount ~ "mount /dev/nbd0p1 /mnt/xp-disk" gives the error message "mount: special device /dev/nbd0p1 does not exist").

    A quick search points to the max_part parameter for nbd devices: "cat /sys/module/nbd/parameters/max_part" gives 0 (thus the failed mount). Had nbd been compiled as a module, it is said that "rmmod nbd" followed by "modprobe nbd max_part=16" would re-set the max_part parameter for mount to proceed. Given that nbd is compiled into the kernel in x86_64 in Knoppix 6.7.1, is it possible to change the parameter, and how? (it couldn't be editing directly the file in /sys/module/nbd/parameters/ - could it?)

  5. #5
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    Quote Originally Posted by boryeu.mao View Post
    Had nbd been compiled as a module, it is said that "rmmod nbd" followed by "modprobe nbd max_part=16" would re-set the max_part parameter for mount to proceed. Given that nbd is compiled into the kernel in x86_64 in Knoppix 6.7.1, is it possible to change the parameter, and how?
    You can set the parameter using this "nbd.max_part=16", and this can be specified when you are prompted at boot parameter (in the exact same manner as you specify a cheatcode ), or you can specify it inside the file /mnt-system/boot/syslinux/syslinux.cfg.

    Have fun with nbd, though I haven't used it before !

  6. #6
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    Thanks much for the solution(s) - and the help in improving my knowledge on all things kernel. It makes sense to have to reboot since the parameter is meant for the kernel. My first encounter with nbd as well. PS - correcting myself, max_part ought to be 15 (and not 16).

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