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Applies to SUSE Linux Enterprise Server 15 SP2

18 libguestfs

Virtual Machines consist of disk images and definition files. Manually accessing and manipulating these guest components (outside of normal hypervisor processes) is possible, but inherently dangerous and risks compromising data integrity. libguestfs is a C library and a corresponding set of tools designed for safely accessing and modifying Virtual Machine disk images—outside of normal hypervisor processes, but without the risk normally associated with manual editing.


Using libguestfs tools is fully supported on the AMD64/Intel 64 architecture only.

18.1 VM Guest Manipulation Overview

18.1.1 VM Guest Manipulation Risk

As disk images and definition files are simply another type of file in a Linux environment, it is possible to use many tools to access, edit and write to these files. When used correctly, such tools can be an important part of guest administration. However, even correct usage of these tools is not without risk. Risks that should be considered when manually manipulating guest disk images include:

  • Data Corruption: Concurrently accessing images, by the host machine or another node in a cluster, can cause changes to be lost or data corruption to occur if virtualization protection layers are bypassed.

  • Security: Mounting disk images as loop devices requires root access. While an image is loop mounted, other users and processes can potentially access the disk contents.

  • Administrator Error: Bypassing virtualization layers correctly requires advanced understanding of virtual components and tools. Failing to isolate the images or failing to clean up properly after changes have been made can lead to further problems once back in virtualization control.

18.1.2 libguestfs Design

libguestfs C library has been designed to safely and securely create, access and modify virtual machine (VM Guest) disk images. It also provides additional language bindings: for Perl, Python, PHP (only for 64-bit machines), and Ruby. libguestfs can access VM Guest disk images without needing root and with multiple layers of defense against rogue disk images.

libguestfs provides many tools designed for accessing and modifying VM Guest disk images and contents. These tools provide such capabilities as: viewing and editing files inside guests, scripting changes to VM Guests, monitoring disk used/free statistics, creating guests, doing V2V or P2V migrations, performing backups, cloning VM Guests, formatting disks, and resizing disks.

Warning: Best Practices

You must not use libguestfs tools on live virtual machines. Doing so will probably result in disk corruption in the VM Guest. libguestfs tools try to stop you from doing this, but cannot catch all cases.

However most command have the --ro (read-only) option. With this option, you can attach a command to a live virtual machine. The results might be strange or inconsistent at times but you will not risk disk corruption.

18.2 Package Installation

libguestfs is shipped through 4 packages:

  • libguestfs0: which provides the main C library

  • guestfs-data: which contains the appliance files used when launching images (stored in /usr/lib64/guestfs)

  • guestfs-tools: the core guestfs tools, man pages, and the /etc/libguestfs-tools.conf configuration file.

  • guestfs-winsupport: provides support for Windows file guests in the guestfs tools. This package only needs to be installed to handle Windows guests, for example when converting a Windows guest to KVM.

To install guestfs tools on your system run:

> sudo zypper in guestfs-tools

18.3 Guestfs Tools

18.3.1 Modifying Virtual Machines

The set of tools found within the guestfs-tools package is used for accessing and modifying virtual machine disk images. This functionality is provided through a familiar shell interface with built-in safeguards which ensure image integrity. Guestfs tools shells expose all capabilities of the guestfs API, and create an appliance on the fly using the packages installed on the machine and the files found in /usr/lib64/guestfs.

18.3.2 Supported File Systems and Disk Images

Guestfs tools support various file systems including:

  • Ext2, Ext3, Ext4

  • Xfs

  • Btrfs

Multiple disk image formats are also supported:

  • raw

  • qcow2

Warning: Unsupported File System

Guestfs may also support Windows* file systems (VFAT, NTFS), BSD* and Apple* file systems, and other disk image formats (VMDK, VHDX...). However, these file systems and disk image formats are unsupported on SUSE Linux Enterprise Server.

18.3.3 virt-rescue

virt-rescue is similar to a rescue CD, but for virtual machines, and without the need for a CD. virt-rescue presents users with a rescue shell and some simple recovery tools which can be used to examine and correct problems within a virtual machine or disk image.

> virt-rescue -a sles.qcow2
Welcome to virt-rescue, the libguestfs rescue shell.

Note: The contents of / are the rescue appliance.
You need to mount the guest's partitions under /sysroot
before you can examine them. A helper script for that exists:
mount-rootfs-and-do-chroot.sh /dev/sda2

[   67.194384] EXT4-fs (sda1): mounting ext3 file system
using the ext4 subsystem
[   67.199292] EXT4-fs (sda1): mounted filesystem with ordered data
mode. Opts: (null)
mount: /dev/sda1 mounted on /sysroot.
mount: /dev bound on /sysroot/dev.
mount: /dev/pts bound on /sysroot/dev/pts.
mount: /proc bound on /sysroot/proc.
mount: /sys bound on /sysroot/sys.
Directory: /root
Thu Jun  5 13:20:51 UTC 2014
(none):~ #

You are now running the VM Guest in rescue mode:

(none):~ # cat /etc/fstab
devpts  /dev/pts          devpts  mode=0620,gid=5 0 0
proc    /proc             proc    defaults        0 0
sysfs   /sys              sysfs   noauto          0 0
debugfs /sys/kernel/debug debugfs noauto          0 0
usbfs   /proc/bus/usb     usbfs   noauto          0 0
tmpfs   /run              tmpfs   noauto          0 0
/dev/disk/by-id/ata-QEMU_HARDDISK_QM00001-part1 / ext3 defaults 1 1

18.3.4 virt-resize

virt-resize is used to resize a virtual machine disk, making it larger or smaller overall, and resizing or deleting any partitions contained within.

Procedure 18.1: Expanding a Disk

Full step-by-step example: How to expand a virtual machine disk

  1. First, with virtual machine powered off, determine the size of the partitions available on this virtual machine:

    > virt-filesystems --long --parts --blkdevs -h -a sles.qcow2
    Name       Type       MBR  Size  Parent
    /dev/sda1  partition  83   16G   /dev/sda
    /dev/sda   device     -    16G   -
  2. virt-resize cannot do in-place disk modifications—there must be sufficient space to store the resized output disk. Use the truncate command to create a file of suitable size:

    > truncate -s 32G outdisk.img
  3. Use virt-resize to resize the disk image. virt-resize requires two mandatory parameters for the input and output images:

    > virt-resize --expand /dev/sda1 sles.qcow2 outdisk.img
    Examining sles.qcow2 ...
    Summary of changes:
    /dev/sda1: This partition will be resized from 16,0G to 32,0G.  The
        filesystem ext3 on /dev/sda1 will be expanded using the 'resize2fs'
    Setting up initial partition table on outdisk.img ...
    Copying /dev/sda1 ...
    ◐ 84%
    ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒════════⟧ 00:03
    Expanding /dev/sda1 using the 'resize2fs' method ...
    Resize operation completed with no errors.  Before deleting the old
    disk, carefully check that the resized disk boots and works correctly.
  4. Confirm the image was resized properly:

    > virt-filesystems --long --parts --blkdevs -h -a outdisk.img
    Name       Type       MBR  Size  Parent
    /dev/sda1  partition  83   32G   /dev/sda
    /dev/sda   device     -    32G   -
  5. Bring up the VM Guest using the new disk image and confirm correct operation before deleting the old image.

18.3.5 Other virt-* Tools

There are guestfs tools to simplify administrative tasks—such as viewing and editing files, or obtaining information on the virtual machine. virt-filesystems

This tool is used to report information regarding file systems, partitions, and logical volumes in a disk image or virtual machine.

> virt-filesystems -l -a sles.qcow2
Name       Type        VFS   Label  Size         Parent
/dev/sda1  filesystem  ext3  -      17178820608  - virt-ls

virt-ls lists file names, file sizes, checksums, extended attributes and more from a virtual machine or disk image. Multiple directory names can be given, in which case the output from each is concatenated. To list directories from a libvirt guest, use the -d option to specify the name of the guest. For a disk image, use the -a option.

> virt-ls -h -lR -a sles.qcow2 /var/log/
d 0755        776 /var/log
- 0640          0 /var/log/NetworkManager
- 0644        23K /var/log/Xorg.0.log
- 0644        23K /var/log/Xorg.0.log.old
d 0700        482 /var/log/YaST2
- 0644        512 /var/log/YaST2/_dev_vda
- 0644         59 /var/log/YaST2/arch.info
- 0644        473 /var/log/YaST2/config_diff_2017_05_03.log
- 0644       5.1K /var/log/YaST2/curl_log
- 0644       1.5K /var/log/YaST2/disk_vda.info
- 0644       1.4K /var/log/YaST2/disk_vda.info-1
[...] virt-cat

virt-cat is a command line tool to display the contents of a file that exists in the named virtual machine (or disk image). Multiple file names can be given, in which case they are concatenated together. Each file name must be a full path, starting at the root directory (starting with '/').

> virt-cat -a sles.qcow2 /etc/fstab
devpts /dev/pts devpts mode=0620,gid=5 0 0
proc   /proc    proc   defaults        0 0 virt-df

virt-df is a command line tool to display free space on virtual machine file systems. Unlike other tools, it not only displays the size of disk allocated to a virtual machine, but can look inside disk images to show how much space is actually being used.

> virt-df -a sles.qcow2
Filesystem                           1K-blocks       Used  Available  Use%
sles.qcow2:/dev/sda1                  16381864     520564   15022492  4% virt-edit

virt-edit is a command line tool capable of editing files that reside in the named virtual machine (or disk image). virt-tar-in/out

virt-tar-in unpacks an uncompressed TAR archive into a virtual machine disk image or named libvirt domain. virt-tar-out packs a virtual machine disk image directory into a TAR archive.

> virt-tar-out -a sles.qcow2 /home homes.tar virt-copy-in/out

virt-copy-in copies files and directories from the local disk into a virtual machine disk image or named libvirt domain. virt-copy-out copies files and directories out of a virtual machine disk image or named libvirt domain.

> virt-copy-in -a sles.qcow2 data.tar /tmp/
virt-ls -a sles.qcow2 /tmp/
data.tar virt-log

virt-log shows the log files of the named libvirt domain, virtual machine or disk image. If the package guestfs-winsupport is installed it can also show the event log of a Windows virtual machine disk image.

> virt-log -a windows8.qcow2
<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"><System><Provider Name="EventLog"></Provider>
<EventID Qualifiers="32768">6011</EventID>
<TimeCreated SystemTime="2014-09-12 05:47:21"></TimeCreated>
<Security UserID=""></Security>


18.3.6 guestfish

guestfish is a shell and command line tool for examining and modifying virtual machine file systems. It uses libguestfs and exposes all of the functionality of the guestfs API.

Examples of usage:

> guestfish -a disk.img <<EOF

Welcome to guestfish, the guest filesystem shell for
editing virtual machine filesystems and disk images.

Type: 'help' for help on commands
      'man' to read the manual
      'quit' to quit the shell

><fs> add sles.qcow2
><fs> run
><fs> list-filesystems
/dev/sda1: ext3
><fs> mount /dev/sda1 /
 cat /etc/fstab
devpts  /dev/pts          devpts  mode=0620,gid=5 0 0
proc    /proc             proc    defaults        0 0
sysfs   /sys              sysfs   noauto          0 0
debugfs /sys/kernel/debug debugfs noauto          0 0
usbfs   /proc/bus/usb     usbfs   noauto          0 0
tmpfs   /run              tmpfs   noauto          0 0
/dev/disk/by-id/ata-QEMU_HARDDISK_QM00001-part1 / ext3 defaults 1 1

18.3.7 Converting a Physical Machine into a KVM Guest

Libguestfs provides tools to help converting Xen virtual machines or physical machines into KVM guests. The Xen to KVM conversion scenario is covered by the Xen to KVM Migration Guide. The following section will cover a special use case: converting a bare metal machine into a KVM one.

Converting a physical machine into a KVM one is not yet supported in SUSE Linux Enterprise Server. This feature is released as a technology preview only.

Converting a physical machine requires collecting information about it and transmitting this to a conversion server. This is achieved by running a live system prepared with virt-p2v and kiwi tools on the machine.

Procedure 18.2: Using virt-p2v
  1. Install the needed packages with the command:

    > sudo zypper in virt-p2v kiwi-desc-isoboot

    These steps will document how to create an ISO image to create a bootable DVD. Alternatively, you can create a PXE boot image instead; for more information about building PXE images with KIWI NG, see man virt-p2v-make-kiwi.

  2. Create a KIWI NG configuration:

    > virt-p2v-make-kiwi -o /tmp/p2v.kiwi

    The -o defines where to create the KIWI NG configuration.

  3. Edit the config.xml file in the generated configuration if needed. For example, in config.xml adjust the keyboard layout of the live system.

  4. Build the ISO image with kiwi:

    > kiwi --build /tmp/p2v.kiwi1 \
         -d /tmp/build2 \
         --ignore-repos \
         --add-repo http://URL/TO/SLE/REPOSITORIES3 \
         --type iso


    The directory where the KIWI NG configuration was generated in the previous step.


    The directory where KIWI NG will place the generated ISO image and other intermediary build results.


    The URLs to the package repositories as found with zypper lr -d.

    Use one --add-repo parameter per repository.

  5. Burn the ISO on a DVD or a USB stick. With such a medium, boot the machine to be converted.

  6. After the system is started, you will be asked for the connection details of the conversion server. This server is a machine with the virt-v2v package installed.

    If the network setup is more complex than a DHCP client, click the Configure network button to open the YaST network configuration dialog.

    Click the Test connection button to allow moving to the next page of the wizard.

  7. Select the disks and network interfaces to be converted and define the VM data like the amount of allocated CPUs, memory and the Virtual Machine name.


    If not defined, the created disk image format will be raw by default. This can be changed by entering the desired format in the Output format field.

    There are two possibilities to generate the virtual machine: either using the local or the libvirt output. The first one will place the Virtual Machine disk image and configuration in the path defined in the Output storage field. These can then be used to define a new libvirt-handled guest using virsh. The second method will create a new libvirt-handled guest with the disk image placed in the pool defined in the Output storage field.

    Click Start conversion to start it.

18.4 Troubleshooting

18.4.1 Btrfs-related Problems

When using the guestfs tools on an image with Btrfs root partition (the default with SUSE Linux Enterprise Server) the following error message may be displayed:

> virt-ls -a /path/to/sles12sp2.qcow2 /
virt-ls: multi-boot operating systems are not supported

If using guestfish '-i' option, remove this option and instead
use the commands 'run' followed by 'list-filesystems'.
You can then mount filesystems you want by hand using the
'mount' or 'mount-ro' command.

If using guestmount '-i', remove this option and choose the
filesystem(s) you want to see by manually adding '-m' option(s).
Use 'virt-filesystems' to see what filesystems are available.

If using other virt tools, multi-boot operating systems won't work
with these tools.  Use the guestfish equivalent commands
(see the virt tool manual page).

This is usually caused by the presence of snapshots in the guests. In this case guestfs does not know which snapshot to bootstrap. To force the use of a snapshot, use the -m parameter as follows:

> virt-ls -m /dev/sda2:/:subvol=@/.snapshots/2/snapshot -a /path/to/sles12sp2.qcow2 /

18.4.2 Environment

When troubleshooting problems within a libguestfs appliance, the environment variable LIBGUESTFS_DEBUG=1 can be used to enable debug messages. To output each command/API call in a format that is similar to guestfish commands, use the environment variable LIBGUESTFS_TRACE=1.

18.4.3 libguestfs-test-tool

libguestfs-test-tool is a test program that checks if basic libguestfs functionality is working. It will print a large amount of diagnostic messages and details of the guestfs environment, then create a test image and try to start it. If it runs to completion successfully, the following message should be seen near the end:

===== TEST FINISHED OK =====

18.5 External References