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virt-v2v(1) Virtualization Support virt-v2v(1)


virt-v2v - Convert a guest to use KVM


 virt-v2v [-i mode] [other -i* options]
          [-o mode] [other -o* options]
 virt-v2v --in-place
          [-i mode] [other -i* options]


Virt-v2v converts a single guest from a foreign hypervisor to run on KVM. It can read Linux and Windows guests running on VMware, Xen, Hyper-V and some other hypervisors, and convert them to KVM managed by libvirt, OpenStack, oVirt, Red Hat Virtualisation (RHV) or several other targets. It can modify the guest to make it bootable on KVM and install virtio drivers so it will run quickly.

There is also a companion front-end called virt-p2v(1) which comes as an ISO, CD or PXE image that can be booted on physical machines to virtualize those machines (physical to virtual, or p2v).

Input and Output

You normally run virt-v2v with several -i* options controlling the input mode and also several -o* options controlling the output mode. In this sense, "input" refers to the source foreign hypervisor such as VMware, and "output" refers to the target KVM-based management system such as oVirt or OpenStack.

The input and output sides of virt-v2v are separate and unrelated. Virt-v2v can read from any input and write to any output. Therefore these sides of virt-v2v are documented separately in this manual.

Virt-v2v normally copies from the input to the output, called "copying mode". In this case the source guest is always left unchanged. In-place conversion (--in-place) only uses the -i* options and modifies the source guest in-place. (See "In-place conversion" below.)

Other virt-v2v topics

virt-v2v-support(1) — Supported hypervisors, virtualization management systems, guests.

virt-v2v-input-vmware(1) — Input from VMware.

virt-v2v-input-xen(1) — Input from Xen.

virt-v2v-output-local(1) — Output to local files or local libvirt.

virt-v2v-output-rhv(1) — Output to oVirt or RHV.

virt-v2v-output-openstack(1) — Output to OpenStack.

virt-v2v-release-notes-1.42(1) — Release notes for this release.

virt-v2v-copy-to-local(1) — Deprecated tool to handle Xen guests using host block device storage.


Convert from VMware vCenter server to local libvirt

You have a VMware vCenter server called "", a datacenter called "Datacenter", and an ESXi hypervisor called "esxi". You want to convert a guest called "vmware_guest" to run locally under libvirt.

 virt-v2v -ic vpx:// vmware_guest

In this case you will most likely have to run virt-v2v as "root", since it needs to talk to the system libvirt daemon and copy the guest disks to /var/lib/libvirt/images.

For more information see virt-v2v-input-vmware(1).

Convert from VMware to RHV/oVirt

This is the same as the previous example, except you want to send the guest to a RHV Data Domain using the RHV REST API. Guest network interface(s) are connected to the target network called "ovirtmgmt".

 virt-v2v -ic vpx:// vmware_guest \
   -o rhv-upload -oc \
   -os ovirt-data -op /tmp/ovirt-admin-password -of raw \
   -oo rhv-cafile=/tmp/ca.pem -oo rhv-direct \
   --bridge ovirtmgmt

In this case the host running virt-v2v acts as a conversion server.

For more information see virt-v2v-output-rhv(1).

Convert from ESXi hypervisor over SSH to local libvirt

You have an ESXi hypervisor called "" with SSH access enabled. You want to convert from VMFS storage on that server to a local file.

 virt-v2v \
   -i vmx -it ssh \
   "ssh://" \
   -o local -os /var/tmp

The guest must not be running. Virt-v2v would not need to be run as root in this case.

For more information about converting from VMX files see virt-v2v-input-vmware(1).

Convert disk image to OpenStack

Given a disk image from another hypervisor that you want to convert to run on OpenStack (only KVM-based OpenStack is supported), you can run virt-v2v inside an OpenStack VM (called "v2v-vm" below), and do:

 virt-v2v -i disk disk.img -o openstack -oo server-id=v2v-vm

See virt-v2v-output-openstack(1).

Convert disk image to disk image

Given a disk image from another hypervisor that you want to convert to run on KVM, you have two options. The simplest way is to try:

 virt-v2v -i disk disk.img -o local -os /var/tmp

where virt-v2v guesses everything about the input disk.img and (in this case) writes the converted result to /var/tmp.

A more complex method is to write some libvirt XML describing the input guest (if you can get the source hypervisor to provide you with libvirt XML, then so much the better). You can then do:

 virt-v2v -i libvirtxml guest-domain.xml -o local -os /var/tmp

Since guest-domain.xml contains the path(s) to the guest disk image(s) you do not need to specify the name of the disk image on the command line.

To convert a local disk image and immediately boot it in local qemu, do:

 virt-v2v -i disk disk.img -o qemu -os /var/tmp --qemu-boot


Display help.
Some input methods are able to limit the network bandwidth they will use statically or dynamically. In the first variant this sets the bandwidth limit statically in bits per second. Formats like "10M" may be used (meaning 10 megabits per second).

In the second variant the bandwidth is limited dynamically from the content of the file (also in bits per second, in the same formats supported by the first variant). You may use both parameters together, meaning: first limit to a static rate, then you can create the file while virt-v2v is running to adjust the rate dynamically.

This is only supported for:

  • input from Xen
  • input from VMware VMX when using the SSH transport method
  • input from VDDK
  • -i libvirtxml when using HTTP or HTTPS disks
  • input from VMware vCenter server

The options are silently ignored for other input methods.

See --network below.
Use ANSI colour sequences to colourize messages. This is the default when the output is a tty. If the output of the program is redirected to a file, ANSI colour sequences are disabled unless you use this option.
Write a compressed output file. This is only allowed if the output format is qcow2 (see -of below), and is equivalent to the -c option of qemu-img(1).
Save the overlay file(s) created during conversion. This option is only used for debugging virt-v2v and may be removed in a future version.
When prompting for keys and passphrases, virt-v2v normally turns echoing off so you cannot see what you are typing. If you are not worried about Tempest attacks and there is no one else in the room you can specify this flag to see what you are typing.

Note this options only applies to keys and passphrases for encrypted devices and partitions, not for passwords used to connect to remote servers.

Set the input method to disk.

In this mode you can read a virtual machine disk image with no metadata. virt-v2v tries to guess the best default metadata. This is usually adequate but you can get finer control (eg. of memory and vCPUs) by using -i libvirtxml instead. Only guests that use a single disk can be imported this way.

Set the input method to libvirt. This is the default.

In this mode you have to specify a libvirt guest name or UUID on the command line. You may also specify a libvirt connection URI (see -ic).

Set the input method to libvirtxml.

In this mode you have to pass a libvirt XML file on the command line. This file is read in order to get metadata about the source guest (such as its name, amount of memory), and also to locate the input disks. See "Minimal XML for -i libvirtxml option" below.

This is the same as -i disk.
Set the input method to ova.

In this mode you can read a VMware ova file. Virt-v2v will read the ova manifest file and check the vmdk volumes for validity (checksums) as well as analyzing the ovf file, and then convert the guest. See virt-v2v-input-vmware(1).

Set the input method to vmx.

In this mode you can read a VMware vmx file directly or over SSH. This is useful when VMware VMs are stored on an NFS server which you can mount directly, or where you have access by SSH to an ESXi hypervisor. See virt-v2v-input-vmware(1).

Specify a libvirt connection URI to use when reading the guest. This is only used when -i libvirt.

Only local libvirt connections, VMware vCenter connections, or RHEL 5 Xen remote connections can be used. Other remote libvirt connections will not work in general.

See also virt-v2v-input-vmware(1), virt-v2v-input-xen(1).

For -i disk only, this specifies the format of the input disk image. For other input methods you should specify the input format in the metadata.
Do not create an output virtual machine in the target hypervisor. Instead, adjust the guest OS in the source VM to run in the input hypervisor.

This mode is meant for integration with other toolsets, which take the responsibility of converting the VM configuration, providing for rollback in case of errors, transforming the storage, etc.

See "In-place conversion" below.

Conflicts with all -o * options.

Set input option(s) related to the current input mode or transport. To display short help on what options are available you can use:

 virt-v2v -it vddk -io "?"
Set the VDDK library directory. This directory should contain subdirectories called include, lib64 etc., but do not include lib64 actually in the parameter.

In most cases this parameter is required when using the -it vddk (VDDK) transport. See virt-v2v-input-vmware(1) for details.

Set the thumbprint of the remote VMware server.

This parameter is required when using the -it vddk (VDDK) transport. See virt-v2v-input-vmware(1) for details.

When using VDDK mode, these options are passed unmodified to the nbdkit(1) VDDK plugin. Please refer to nbdkit-vddk-plugin(1). Do not use these options unless you know what you are doing. These are all optional.
Supply a file containing a password to be used when connecting to the target hypervisor. If this is omitted then the input hypervisor may ask for the password interactively. Note the file should contain the whole password, without any trailing newline, and for security the file should have mode 0600 so that others cannot read it.
When using -i vmx, this enables the ssh transport. See virt-v2v-input-vmware(1).
Use VMware VDDK as a transport to copy the input disks. See virt-v2v-input-vmware(1). If you use this parameter then you may need to use other -io vddk* options to specify how to connect through VDDK.
Specify a key for LUKS, to automatically open a LUKS device when using the inspection. "ID" can be either the libguestfs device name, or the UUID of the LUKS device.
Use the specified "KEY_STRING" as passphrase.
Read the passphrase from FILENAME.
Read key or passphrase parameters from stdin. The default is to try to read passphrases from the user by opening /dev/tty.

If there are multiple encrypted devices then you may need to supply multiple keys on stdin, one per line.

Note --keys-from-stdin only applies to keys and passphrases for encrypted devices and partitions, not for passwords used to connect to remote servers.

Map source NIC MAC address to a network or bridge.

See "Networks and bridges" below.

Force a particular interface (controlled by its MAC address) to have a static IP address after boot.

The fields in the parameter are: "ipaddr" is the IP address. "gw" is the optional gateway IP address. "len" is the subnet mask length (an integer). The final parameters are zero or more nameserver IP addresses.

This option can be supplied zero or more times.

You only need to use this option for certain broken guests such as Windows which are unable to preserve MAC to static IP address mappings automatically. You don't need to use it if Windows is using DHCP. It is currently ignored for Linux guests since they do not have this problem.

This option is used to make the output more machine friendly when being parsed by other programs. See "Machine readable output" below.
Map network (or bridge) called "in" to network (or bridge) called "out". If no "in:" prefix is given, all other networks (or bridges) are mapped to "out".

See "Networks and bridges" below.

Don’t copy the disks. Instead, conversion is performed (and thrown away), and metadata is written, but no disks are created. See also discussion of -o null below.

This is useful in two cases: Either you want to test if conversion is likely to succeed, without the long copying process. Or you are only interested in looking at the metadata.

This option is not compatible with -o libvirt since it would create a faulty guest (one with no disks).

This option is not compatible with -o glance for technical reasons.

This is the same as -o local.
This is a legacy option. You should probably use -o openstack instead.

Set the output method to OpenStack Glance. In this mode the converted guest is uploaded to Glance. See virt-v2v-output-openstack(1).

Set the output method to json.

In this mode, the converted guest is written to a local directory specified by -os /dir (the directory must exist), with a JSON file containing the majority of the metadata that virt-v2v gathered during the conversion.

See virt-v2v-output-local(1).

Set the output method to libvirt. This is the default.

In this mode, the converted guest is created as a libvirt guest. You may also specify a libvirt connection URI (see -oc).

See virt-v2v-output-local(1).

Set the output method to local.

In this mode, the converted guest is written to a local directory specified by -os /dir (the directory must exist). The converted guest’s disks are written as:


and a libvirt XML file is created containing guest metadata:


where "name" is the guest name.

Set the output method to null.

The guest is converted and copied (unless you also specify --no-copy), but the results are thrown away and no metadata is written.

Set the output method to OpenStack. See virt-v2v-output-openstack(1).
This is the same as -o rhv.
This is the same as -o rhv-upload.
Set the output method to qemu.

This is similar to -o local, except that a shell script is written which you can use to boot the guest in qemu. The converted disks and shell script are written to the directory specified by -os.

When using this output mode, you can also specify the --qemu-boot option which boots the guest under qemu immediately.

This is the same as -o rhv.
Set the output method to rhv.

The converted guest is written to a RHV Export Storage Domain. The -os parameter must also be used to specify the location of the Export Storage Domain. Note this does not actually import the guest into RHV. You have to do that manually later using the UI.

See virt-v2v-output-rhv(1).

Set the output method to rhv-upload.

The converted guest is written directly to a RHV Data Domain. This is a faster method than -o rhv, but requires oVirt or RHV ≥ 4.2.

See virt-v2v-output-rhv(1).

Set the output method to vdsm.

This mode is similar to -o rhv, but the full path to the data domain must be given: /rhv/data-center/<data-center-uuid>/<data-domain-uuid>. This mode is only used when virt-v2v runs under VDSM control.

Set the output file allocation mode. The default is "sparse".
Specify a connection URI to use when writing the converted guest.

For -o libvirt this is the libvirt URI. Only local libvirt connections can be used. Remote libvirt connections will not work. See virt-v2v-output-local(1) for further information.

When converting the guest, convert the disks to the given format.

If not specified, then the input format is used.

Rename the guest when converting it. If this option is not used then the output name is the same as the input name.
Set output option(s) related to the current output mode. To display short help on what options are available you can use:

 virt-v2v -o rhv-upload -oo "?"
For -o openstack (virt-v2v-output-openstack(1)) only, set a guest ID which is saved on each Cinder volume in the "virt_v2v_guest_id" volume property.
For -o openstack (virt-v2v-output-openstack(1)) only, this can be used to disable SSL certification validation when connecting to OpenStack by specifying -oo verify-server-certificate=false.
For -o openstack (virt-v2v-output-openstack(1)) only, set optional OpenStack authentication. For example -oo os-username=NAME is equivalent to "openstack --os-username=NAME".
For -o rhv-upload (virt-v2v-output-rhv(1)) only, the ca.pem file (Certificate Authority), copied from /etc/pki/ovirt-engine/ca.pem on the oVirt engine.
For -o rhv-upload (virt-v2v-output-rhv(1)) only, set the RHV Cluster Name. If not given it uses "Default".
For -o rhv-upload (virt-v2v-output-rhv(1)) only, if this option is given then virt-v2v will attempt to directly upload the disk to the oVirt node, otherwise it will proxy the upload through the oVirt engine. Direct upload requires that you have network access to the oVirt nodes. Non-direct upload is slightly slower but should work in all situations.
For -o rhv-upload (virt-v2v-output-rhv(1)) only, verify the oVirt/RHV server’s identity by checking the server‘s certificate against the Certificate Authority.
For -o openstack (virt-v2v-output-openstack(1)) only, set the name of the conversion appliance where virt-v2v is running.
If -o vdsm and the output format is qcow2, then we add the qcow2 compat=0.10 option to the output file for compatibility with RHEL 6 (see

If -oo vdsm-compat=1.1 is used then modern qcow2 (compat=1.1) files are generated instead.

Currently -oo vdsm-compat=0.10 is the default, but this will change to -oo vdsm-compat=1.1 in a future version of virt-v2v (when we can assume that everyone is using a modern version of qemu).

Note this option only affects -o vdsm output. All other output modes (including -o rhv) generate modern qcow2 compat=1.1 files, always.

If this option is available, then "vdsm-compat-option" will appear in the --machine-readable output.

Normally the RHV output mode chooses random UUIDs for the target guest. However VDSM needs to control the UUIDs and passes these parameters when virt-v2v runs under VDSM control. The parameters control:
  • the image directory of each guest disk (-oo vdsm-image-uuid) (this option is passed once for each guest disk)
  • UUIDs for each guest disk (-oo vdsm-vol-uuid) (this option is passed once for each guest disk)
  • the OVF file name (-oo vdsm-vm-uuid).
  • the OVF output directory (default current directory) (-oo vdsm-ovf-output).

The format of UUIDs is: "12345678-1234-1234-1234-123456789abc" (each hex digit can be "0-9" or "a-f"), conforming to OSF DCE 1.1.

These options can only be used with -o vdsm.

This option controls the format of the OVF generated at the end of conversion. Currently there are two possible flavours:
The OVF format used in RHV export storage domain.
The OVF format understood by oVirt REST API.

For backward compatibility the default is rhvexp, but this may change in the future.

Supply a file containing a password to be used when connecting to the target hypervisor. Note the file should contain the whole password, without any trailing newline, and for security the file should have mode 0600 so that others cannot read it.
The location of the storage for the converted guest.

For -o libvirt, this is a libvirt directory pool (see "virsh pool-list") or pool UUID.

For -o json, -o local and -o qemu, this is a directory name. The directory must exist.

For -o rhv-upload, this is the name of the destination Storage Domain.

For -o openstack, this is the optional Cinder volume type.

For -o rhv, this can be an NFS path of the Export Storage Domain of the form "<host>:<path>", eg:

The NFS export must be mountable and writable by the user and host running virt-v2v, since the virt-v2v program has to actually mount it when it runs. So you probably have to run virt-v2v as "root".

Or: You can mount the Export Storage Domain yourself, and point -os to the mountpoint. Note that virt-v2v will still need to write to this remote directory, so virt-v2v will still need to run as "root".

You will get an error if virt-v2v is unable to mount/write to the Export Storage Domain.

Print the estimated size of the data which will be copied from the source disk(s) and stop. One number (the size in bytes) is printed per disk, and a total:

 $ virt-v2v --print-estimate
 disk 1: 100000
 disk 2: 200000
 total: 300000

With the --machine-readable option you get JSON output which can be directed into a file or elsewhere:

 $ virt-v2v --print-estimate --machine-readable=file:estimates
 $ cat estimates
  "disks": [ 100000, 200000 ],
  "total": 300000

When using this option you must specify an output mode. This is because virt-v2v has to perform the conversion in order to print the estimate, and the conversion depends on the output mode. Using -o null should be safe for most purposes.

When this option is used along with --machine-readable you can direct the output to an alternate file.

Print information about the source guest and stop. This option is useful when you are setting up network and bridge maps. See "Networks and bridges".
When using -o qemu only, this boots the guest immediately after virt-v2v finishes.
This disables progress bars and other unnecessary output.
Choose the root filesystem to be converted.

In the case where the virtual machine is dual-boot or multi-boot, or where the VM has other filesystems that look like operating systems, this option can be used to select the root filesystem (a.k.a. "C:" drive or /) of the operating system that is to be converted. The Windows Recovery Console, certain attached DVD drives, and bugs in libguestfs inspection heuristics, can make a guest look like a multi-boot operating system.

The default in virt-v2v ≤ 0.7.1 was --root single, which causes virt-v2v to die if a multi-boot operating system is found.

Since virt-v2v ≥ 0.7.2 the default is now --root ask: If the VM is found to be multi-boot, then virt-v2v will stop and list the possible root filesystems and ask the user which to use. This requires that virt-v2v is run interactively.

--root first means to choose the first root device in the case of a multi-boot operating system. Since this is a heuristic, it may sometimes choose the wrong one.

You can also name a specific root device, eg. --root /dev/sda2 would mean to use the second partition on the first hard drive. If the named root device does not exist or was not detected as a root device, then virt-v2v will fail.

Note that there is a bug in grub which prevents it from successfully booting a multiboot system if virtio is enabled. Grub is only able to boot an operating system from the first virtio disk. Specifically, /boot must be on the first virtio disk, and it cannot chainload an OS which is not in the first virtio disk.

Enable verbose messages for debugging.
Display version number and exit.
Enable tracing of libguestfs API calls.


Xen paravirtualized guests

Older versions of virt-v2v could turn a Xen paravirtualized (PV) guest into a KVM guest by installing a new kernel. This version of virt-v2v does not attempt to install any new kernels. Instead it will give you an error if there are only Xen PV kernels available.

Therefore before conversion you should check that a regular kernel is installed. For some older Linux distributions, this means installing a kernel from the table below:

 RHEL 3         (Does not apply, as there was no Xen PV kernel)
 RHEL 4         i686 with > 10GB of RAM: install 'kernel-hugemem'
                i686 SMP: install 'kernel-smp'
                other i686: install 'kernel'
                x86-64 SMP with > 8 CPUs: install 'kernel-largesmp'
                x86-64 SMP: install 'kernel-smp'
                other x86-64: install 'kernel'
 RHEL 5         i686: install 'kernel-PAE'
                x86-64: install 'kernel'
 SLES 10        i586 with > 10GB of RAM: install 'kernel-bigsmp'
                i586 SMP: install 'kernel-smp'
                other i586: install 'kernel-default'
                x86-64 SMP: install 'kernel-smp'
                other x86-64: install 'kernel-default'
 SLES 11+       i586: install 'kernel-pae'
                x86-64: install 'kernel-default'
 Windows        (Does not apply, as there is no Xen PV Windows kernel)

Enabling virtio

"Virtio" is the name for a set of drivers which make disk (block device), network and other guest operations work much faster on KVM.

Older versions of virt-v2v could install these drivers for certain Linux guests. This version of virt-v2v does not attempt to install new Linux kernels or drivers, but will warn you if they are not installed already.

In order to enable virtio, and hence improve performance of the guest after conversion, you should ensure that the minimum versions of packages are installed before conversion, by consulting the table below.

 RHEL 3         No virtio drivers are available
 RHEL 4         kernel >= 2.5.9-89.EL
                lvm2 >= 2.02.42-5.el4
                device-mapper >= 1.02.28-2.el4
                selinux-policy-targeted >= 1.17.30-2.152.el4
                policycoreutils >= 1.18.1-4.13
 RHEL 5         kernel >= 2.6.18-128.el5
                lvm2 >= 2.02.40-6.el5
                selinux-policy-targeted >= 2.4.6-203.el5
 RHEL 6+        All versions support virtio
 Fedora         All versions support virtio
 SLES 11+       All versions support virtio
 SLES 10        kernel >=
 OpenSUSE 11+   All versions support virtio
 OpenSUSE 10    kernel >=
 Debian 6+      All versions support virtio
 Ubuntu 10.04+  All versions support virtio
 Windows        Drivers are installed from the ISO or directory pointed
                to by "VIRTIO_WIN" environment variable if present

RHEL 4: SELinux relabel appears to hang forever

In RHEL ≤ 4.7 there was a bug which causes SELinux relabelling to appear to hang forever at:

 *** Warning -- SELinux relabel is required. ***
 *** Disabling security enforcement.         ***
 *** Relabeling could take a very long time, ***
 *** depending on file system size.          ***

In reality it is waiting for you to press a key (but there is no visual indication of this). You can either hit the "[Return]" key, at which point the guest will finish relabelling and reboot, or you can install policycoreutils ≥ 1.18.1-4.13 before starting the v2v conversion. See also

Debian and Ubuntu

"warning: could not determine a way to update the configuration of Grub2"

Currently, virt-v2v has no way to set the default kernel in Debian and Ubuntu guests using GRUB 2 as bootloader. This means that virt-v2v will not change the default kernel used for booting, even in case it is not the best kernel available on the guest. A recommended procedure is, before using virt-v2v, to check that the boot kernel is the best kernel available in the guest (for example by making sure the guest is up-to-date).

"vsyscall attempted with vsyscall=none"

When run on a recent Debian host virt-v2v may fail to convert guests which were created before 2013. In the debugging output you will see a crash message similar to:

 vsyscall attempted with vsyscall=none ip:...
 segfault at ...

This is caused because Debian removed support for running old binaries which used the legacy vsyscall page to call into the kernel.

You can work around this problem by running this command before running virt-v2v:

 export LIBGUESTFS_APPEND="vsyscall=emulate"

For more information, see


Windows ≥ 8 Fast Startup is incompatible with virt-v2v

Guests which use the Windows ≥ 8 "Fast Startup" feature (or guests which are hibernated) cannot be converted with virt-v2v. You will see an error:

 virt-v2v: error: unable to mount the disk image for writing. This has
 probably happened because Windows Hibernation or Fast Restart is being
 used in this guest. You have to disable this (in the guest) in order
 to use virt-v2v.

As the message says, you need to boot the guest and disable the "Fast Startup" feature (Control Panel → Power Options → Choose what the power buttons do → Change settings that are currently unavailable → Turn on fast startup), and shut down the guest, and then you will be able to convert it.

For more information, see: "WINDOWS HIBERNATION AND WINDOWS 8 FAST STARTUP" in guestfs(3).

Boot failure: 0x0000007B

This boot failure is caused by Windows being unable to find or load the right disk driver (eg. viostor.sys). If you experience this error, here are some things to check:

  • First ensure that the guest boots on the source hypervisor before conversion.
  • Check you have the Windows virtio drivers available in /usr/share/virtio-win, and that virt-v2v did not print any warning about not being able to install virtio drivers.

    On Red Hat Enterprise Linux 7, you will need to install the signed drivers available in the "virtio-win" package. If you do not have access to the signed drivers, then you will probably need to disable driver signing in the boot menus.

  • Check that you are presenting a virtio-blk interface (not virtio-scsi and not ide) to the guest. On the qemu/KVM command line you should see something similar to this:

     ... -drive file=windows-sda,if=virtio ...

    In libvirt XML, you should see:

     <target dev='vda' bus='virtio'/>
  • Check that Windows Group Policy does not prevent the driver from being installed or used. Try deleting Windows Group Policy before conversion.
  • Check there is no anti-virus or other software which implements Group Policy-like prohibitions on installing or using new drivers.
  • Enable boot debugging and check the viostor.sys driver is being loaded.

OpenStack and Windows reactivation

OpenStack does not offer stable device / PCI addresses to guests. Every time it creates or starts a guest, it regenerates the libvirt XML for that guest from scratch. The libvirt XML will have no <address> fields. Libvirt will then assign addresses to devices, in a predictable manner. Addresses may change if any of the following are true:

  • A new disk or network device has been added or removed from the guest.
  • The version of OpenStack or (possibly) libvirt has changed.

Because Windows does not like "hardware" changes of this kind, it may trigger Windows reactivation.

This can also prevent booting with a 7B error [see previous section] if the guest has group policy containing "Device Installation Restrictions".

Support for SHA-2 certificates in Windows 7 and Windows Server 2008 R2

Later versions of the Windows virtio drivers are signed using SHA-2 certificates (instead of SHA-1). The original shipping Windows 7 and Windows Server 2008 R2 did not understand SHA-2 certificates and so the Windows virtio drivers will not install properly.

To fix this you must apply SHA-2 Code Signing Support from: before converting the guest.

For further information see:

Networks and bridges

Guests are usually connected to one or more networks, and when converted to the target hypervisor you usually want to reconnect those networks at the destination. The options --network, --bridge and --mac allow you to do that.

If you are unsure of what networks and bridges are in use on the source hypervisor, then you can examine the source metadata (libvirt XML, vCenter information, etc.). Or you can run virt-v2v with the --print-source option which causes virt-v2v to print out the information it has about the guest on the source and then exit.

In the --print-source output you will see a section showing the guest’s Network Interface Cards (NICs):

 $ virt-v2v [-i ...] --print-source name
     Network "default" mac: 52:54:00:d0:cf:0e

Bridges are special classes of network devices which are attached to a named external network on the source hypervisor, for example:

 $ virt-v2v [-i ...] --print-source name
     Bridge "br0"

To map a specific source bridge to a target network, for example "br0" on the source to "ovirtmgmt" on the target, use:

 virt-v2v [...] --bridge br0:ovirtmgmt

To map every bridge to a target network, use:

 virt-v2v [...] --bridge ovirtmgmt

Fine-grained mapping of guest NICs

The --mac option gives you more control over the mapping, letting you map single NICs to either networks or bridges on the target. For example a source guest with two NICs could map them individually to two networks called "mgmt" and "clientdata" like this:

 $ virt-v2v [...] \
    --mac 52:54:00:d0:cf:0e:network:mgmt \
    --mac 52:54:00:d0:cf:0f:network:clientdata

Note that virt-v2v does not have the ability to change a guest’s MAC address. The MAC address is part of the guest metadata and must remain the same on source and target hypervisors. Most guests will use the MAC address to set up persistent associations between NICs and internal names (like "eth0"), with firewall settings, or even for other purposes like software licensing.

Resource requirements


The most important resource for virt-v2v appears to be network bandwidth. Virt-v2v should be able to copy guest data at gigabit ethernet speeds or greater.

Ensure that the network connections between servers (conversion server, NFS server, vCenter, Xen) are as fast and as low latency as possible.

Disk space

Virt-v2v places potentially large temporary files in $VIRT_V2V_TMPDIR (usually /var/tmp, see also "ENVIRONMENT VARIBLES" below). Using tmpfs is a bad idea.

For each guest disk, an overlay is stored temporarily. This stores the changes made during conversion, and is used as a cache. The overlays are not particularly large - tens or low hundreds of megabytes per disk is typical. In addition to the overlay(s), input and output methods may use disk space, as outlined in the table below.

This temporarily places a full copy of the uncompressed source disks in $VIRT_V2V_TMPDIR (or /var/tmp).
This temporarily places a full copy of the output disks in $VIRT_V2V_TMPDIR (or /var/tmp).
You must ensure there is sufficient space in the output directory for the converted guest.

See also "Minimum free space check in the host" below.

VMware vCenter resources

Copying from VMware vCenter is currently quite slow, but we believe this to be an issue with VMware. Ensuring the VMware ESXi hypervisor and vCenter are running on fast hardware with plenty of memory should alleviate this.

Compute power and RAM

Virt-v2v is not especially compute or RAM intensive. If you are running many parallel conversions, then you may consider allocating one CPU core and 2 GB of RAM per running instance.

Virt-v2v can be run in a virtual machine.


Virt-v2v attempts to optimize the speed of conversion by ignoring guest filesystem data which is not used. This would include unused filesystem blocks, blocks containing zeroes, and deleted files.

To do this, virt-v2v issues a non-destructive fstrim(8) operation. As this happens to an overlay placed over the guest data, it does not affect the source in any way.

If this fstrim operation fails, you will see a warning, but virt-v2v will continue anyway. It may run more slowly (in some cases much more slowly), because it is copying the unused parts of the disk.

Unfortunately support for fstrim is not universal, and it also depends on specific details of the filesystem, partition alignment, and backing storage. As an example, NTFS filesystems cannot be fstrimmed if they occupy a partition which is not aligned to the underlying storage. That was the default on Windows before Vista. As another example, VFAT filesystems (used by UEFI guests) cannot be trimmed at all.

fstrim support in the Linux kernel is improving gradually, so over time some of these restrictions will be lifted and virt-v2v will work faster.

Post-conversion tasks

Guest network configuration

Virt-v2v cannot currently reconfigure a guest’s network configuration. If the converted guest is not connected to the same subnet as the source, its network configuration may have to be updated. See also virt-customize(1).

Converting a Windows guest

When converting a Windows guests, the conversion process is split into two stages:

Offline conversion.
First boot.

The guest will be bootable after the offline conversion stage, but will not yet have all necessary drivers installed to work correctly. These will be installed automatically the first time the guest boots.

N.B. Take care not to interrupt the automatic driver installation process when logging in to the guest for the first time, as this may prevent the guest from subsequently booting correctly.

Free space for conversion

Free space in the guest

Virt-v2v checks there is sufficient free space in the guest filesystem to perform the conversion. Currently it checks:

Minimum free space: 100 MB
Minimum free space: 50 MB

This is because we need to build a new initramfs for some Enterprise Linux conversions.

Windows "C:" drive
Minimum free space: 100 MB

We may have to copy in many virtio drivers and guest agents.

Minimum free space: 10 MB

In addition to the actual free space, each filesystem is required to have at least 100 available inodes.

Minimum free space check in the host

You must have sufficient free space in the host directory used to store large temporary overlays (except in --in-place mode). To find out which directory this is, use:

 $ df -h "`guestfish get-cachedir`"
 Filesystem        Size  Used Avail Use% Mounted on
 /dev/mapper/root   50G   40G  6.8G  86% /

and look under the "Avail" column. Virt-v2v will refuse to do the conversion at all unless at least 1GB is available there. You can change the directory that virt-v2v uses by setting $VIRT_V2V_TMPDIR.

See also "Resource requirements" above and "ENVIRONMENT VARIABLES" below.

Running virt-v2v as root or non-root

Nothing in virt-v2v inherently needs root access, and it will run just fine as a non-root user. However, certain external features may require either root or a special user:

When using -o rhv -os server:/esd virt-v2v has to have sufficient privileges to NFS mount the Export Storage Domain from "server".

You can avoid needing root here by mounting it yourself before running virt-v2v, and passing -os /mountpoint instead, but first of all read the next section ...

RHV-M cannot read files and directories from the Export Storage Domain unless they have UID:GID 36:36. You will see VM import problems if the UID:GID is not correct.

When you run virt-v2v -o rhv as root, virt-v2v attempts to create files and directories with the correct ownership. If you run virt-v2v as non-root, it will probably still work, but you will need to manually change ownership after virt-v2v has finished.

When using -o libvirt, you may need to run virt-v2v as root so that it can write to the libvirt system instance (ie. "qemu:///system") and to the default location for disk images (usually /var/lib/libvirt/images).

You can avoid this by setting up libvirt connection authentication, see Alternatively, use -oc qemu:///session, which will write to your per-user libvirt instance.

Because of how Cinder volumes are presented as /dev block devices, using -o openstack normally requires that virt-v2v is run as root.
This does not need root (in fact it probably won’t work), but may require either a special user and/or for you to source a script that sets authentication environment variables. Consult the Glance documentation.
This normally requires root. See the next section.

Writing to block devices

Some output modes write to local files. In general these modes also let you write to block devices, but before you run virt-v2v you may have to arrange for symbolic links to the desired block devices in the output directory.

For example if using -o local -os /dir then virt-v2v would normally create files called:

 /dir/name-sda     # first disk
 /dir/name-sdb     # second disk
 /dir/name.xml     # metadata

If you wish the disks to be written to block devices then you would need to create /dir/name-sda (etc) as symlinks to the block devices:

 # lvcreate -L 10G -n VolumeForDiskA VG
 # lvcreate -L 6G -n VolumeForDiskB VG
 # ln -sf /dev/VG/VolumeForDiskA /dir/name-sda
 # ln -sf /dev/VG/VolumeForDiskB /dir/name-sdb

Note that you must precreate the correct number of block devices of the correct size. Typically -of raw has to be used too, but other formats such as qcow2 can be useful occasionally so virt-v2v does not force you to use raw on block devices.

Minimal XML for -i libvirtxml option

When using the -i libvirtxml option, you have to supply some libvirt XML. Writing this from scratch is hard, so the template below is helpful.

Note this should only be used for testing and/or where you know what you're doing! If you have libvirt metadata for the guest, always use that instead.

 <domain type='kvm'>
   <name> NAME </name>
     <boot dev='hd'/>
     <disk type='file' device='disk'>
       <driver name='qemu' type='raw'/>
       <source file='/path/to/disk/image'/>
       <target dev='hda' bus='ide'/>
     <interface type='network'>
       <mac address='52:54:00:01:02:03'/>
       <source network='default'/>
       <model type='rtl8139'/>

In-place conversion

It is also possible to use virt-v2v in scenarios where a foreign VM has already been imported into a KVM-based hypervisor, but still needs adjustments in the guest to make it run in the new virtual hardware.

In that case it is assumed that a third-party tool has created the target VM in the supported KVM-based hypervisor based on the source VM configuration and contents, but using virtual devices more appropriate for KVM (e.g. virtio storage and network, etc.).

Then, to make the guest OS boot and run in the changed environment, one can use:

 virt-v2v -ic qemu:///system converted_vm --in-place

Virt-v2v will analyze the configuration of "converted_vm" in the "qemu:///system" libvirt instance, and apply various fixups to the guest OS configuration to make it match the VM configuration. This may include installing virtio drivers, configuring the bootloader, the mountpoints, the network interfaces, and so on.

Should an error occur during the operation, virt-v2v exits with an error code leaving the VM in an undefined state.

Machine readable output

The --machine-readable option can be used to make the output more machine friendly, which is useful when calling virt-v2v from other programs, GUIs etc.

There are two ways to use this option.

Firstly use the option on its own to query the capabilities of the virt-v2v binary. Typical output looks like this:

 $ virt-v2v --machine-readable

A list of features is printed, one per line, and the program exits with status 0.

The "input:" and "output:" features refer to -i and -o (input and output mode) options supported by this binary. The "convert:" features refer to guest types that this binary knows how to convert.

Secondly use the option in conjunction with other options to make the regular program output more machine friendly.

At the moment this means:

Progress bar messages can be parsed from stdout by looking for this regular expression:

The calling program should treat messages sent to stdout (except for progress bar messages) as status messages. They can be logged and/or displayed to the user.
The calling program should treat messages sent to stderr as error messages. In addition, virt-v2v exits with a non-zero status code if there was a fatal error.

Virt-v2v ≤ 0.9.1 did not support the --machine-readable option at all. The option was added when virt-v2v was rewritten in 2014.

It is possible to specify a format string for controlling the output; see "ADVANCED MACHINE READABLE OUTPUT" in guestfs(3).



If this directory is present, then virtio drivers for Windows guests will be found from this directory and installed in the guest during conversion.


Location of the temporary directory used for the potentially large temporary overlay file. If neither environment variable is set then /var/tmp is used.

To reliably ensure large temporary files are cleaned up (for example in case virt-v2v crashes) you should create a randomly named directory under /var/tmp, set "VIRT_V2V_TMPDIR" to point to this directory, then when virt-v2v exits remove the directory.

See the "Disk space" section above.

This can point to the directory containing data files used for Windows conversion.

Normally you do not need to set this. If not set, a compiled-in default will be used (something like /usr/share/virt-tools).

This directory may contain the following files:

(Required when doing conversions of Windows guests)

This is the RHSrvAny Windows binary, used to install a "firstboot" script in the guest during conversion of Windows guests.

See also: ""

This is a Windows binary shipped with SUSE VMDP, used to install a "firstboot" script in Windows guests. It is required if you intend to use the --firstboot or --firstboot-command options with Windows guests.

The RHV Application Provisioning Tool (RHEV APT). If this file is present, then RHEV APT will be installed in the Windows guest during conversion. This tool is a guest agent which ensures that the virtio drivers remain up to date when the guest is running on Red Hat Virtualization (RHV).

This file comes from Red Hat Virtualization (RHV), and is not distributed with virt-v2v.

This is where virtio drivers for Windows are searched for. It can be a directory or point to virtio-win.iso (CD ROM image containing drivers).

If unset, then we look for drivers in whichever of these paths is found first:

The ISO containing virtio drivers for Windows.
The exploded tree of virtio drivers for Windows. This is usually incomplete, hence the ISO is preferred.

See "Enabling virtio".

For other environment variables, see "ENVIRONMENT VARIABLES" in guestfs(3).


There are some special cases where virt-v2v cannot directly access the remote hypervisor. In that case you have to use virt-v2v-copy-to-local(1) to make a local copy of the guest first, followed by running "virt-v2v -i libvirtxml" to perform the conversion.
Variously called "engine-image-uploader", "ovirt-image-uploader" or "rhevm-image-uploader", this tool allows you to copy a guest from one oVirt or RHV Export Storage Domain to another. It only permits importing a guest that was previously exported from another oVirt/RHV instance.
This script can be used to import guests that already run on KVM to oVirt or RHV. For more information, see this blog posting by the author of virt-v2v:


virt-p2v(1), virt-customize(1), virt-df(1), virt-filesystems(1), virt-sparsify(1), virt-sysprep(1), guestfs(3), guestfish(1), qemu-img(1), virt-v2v-copy-to-local(1), virt-v2v-test-harness(1), engine-image-uploader(8),, nbdkit(1), nbdkit-vddk-plugin(1),


Matthew Booth

Cédric Bosdonnat

Tomáš Golembiovský

Shahar Havivi

Roman Kagan

Mike Latimer

Nir Soffer

Richard W.M. Jones

Pino Toscano

Tingting Zheng


Copyright (C) 2009-2020 Red Hat Inc.


This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.


To get a list of bugs against libguestfs, use this link:

To report a new bug against libguestfs, use this link:

When reporting a bug, please supply:

  • The version of libguestfs.
  • Where you got libguestfs (eg. which Linux distro, compiled from source, etc)
  • Describe the bug accurately and give a way to reproduce it.
  • Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug report.
2022-01-01 virt-v2v-1.44.2