nbdkit-guestfs-plugin1

Usage

Warning

Using nbdkit-guestfs-plugin in read-write mode on live virtual machines can be dangerous, potentially causing disk corruption. Use the -r (read-only) option to use this plugin safely if the disk image or virtual machine might be live.

Examples

Export the first partition inside a disk image called "disk.img", and allow writes:

 nbdkit guestfs disk=disk.img export=/dev/sda1

Export a disk image which is located inside a libvirt guest called "Guest", read-only (-r option):

 nbdkit -r guestfs domain=Guest mount=inspect export=/images/disk.img

Overview

"nbdkit-guestfs-plugin" is an nbdkit(1) plugin that lets you access the contents of disk images over NBD. There are many weird and wonderful uses for this, and this man page only covers the simpler ones.

The parameters control:

•

Which disk(s) are added to libguestfs. Specifically "disk=DISK" and "domain=DOMAIN" add a single disk or all the disks from a particular libvirt guest.

•

What, if any, filesystems inside the disk image / guest have to be mounted. Use "mount=inspect" to do this automatically (like guestfish(1) -i option), else mount individual filesystems.

•

What device or file from inside the disk image or guest you want to export over NBD. Use "export=DEVICE|FILE" to specify the thing that you want to export.

•

Use the -r option to export read-only. The default is read-write.

Parameters

connect=URI

This optional parameter specifies the libvirt connection URI. This is only used with the "domain" parameter.

debug=on

Enable full debugging of libguestfs. Note you'll probably also have to use the nbdkit(1) option -v in order to see the messages.

disk=DISK

Add the named disk image. You may specify this option multiple times.

domain=DOMAIN

Add the disk(s) from the libvirt guest called "DOMAIN".

export=DEVICE

export=FILE

Export "DEVICE" or "FILE" (from inside the disk image or guest) over NBD.

Device names are the usual libguestfs names like /dev/sda1 (meaning the first partition of the first disk), or /dev/VG/LV (a logical volume), or RAID arrays etc. The device name should not be confused with host devices.

Filenames are similarly those located inside the guest or disk image, and always start with a "/" character (even for Windows guests).

Exports are writable by default. Use the -r option to make them read-only. Exporting read-write a live disk image or virtual machine will probably cause disk corruption.

format=FORMAT

This can be used to specify the format of the disk. Use it before the "disk=DISK" argument. It works like the --format option of guestfish(1).

mount=inspect

Use guest inspection to mount disks. This is like "guestfish -i".

mount=DEV

mount=DEV:MOUNTPOINT

Mount "DEV" from inside the guest on "MOUNTPOINT" (defaults to /). This is like "guestfish -m".

trace=on

Enable tracing of libguestfs calls. Note you'll probably also have to use the nbdkit(1) option -v in order to see the messages.

Worked examples

 nbdkit guestfs disk=disk.img export=/dev/sda1

 nbdkit guestfs disk=disk.img export=/dev/VG/LV

 nbdkit -r guestfs domain=Guest export=/dev/sda1

 nbdkit -r guestfs domain=Guest export=/dev/VG/LV

 nbdkit guestfs disk=disk.img mount=/dev/sda1 export=/image

 nbdkit guestfs disk=windows.img mount=inspect \
   export=/Users/rich/AppData/image

Debugging

To debug this plugin, use the following options:

 nbdkit -f -v guestfs debug=on trace=on [...]

This enables libguestfs debugging and tracing (see guestfs-faq(1)). It also ensures that the messages are displayed by nbdkit (because of -f and -v).

Files

$plugindir/nbdkit-guestfs-plugin.so

The plugin.

Use "nbdkit --dump-config" to find the location of $plugindir.

Version

"nbdkit-guestfs-plugin" first appeared in nbdkit 1.2.