qemu-img is a powerful command-line tool that lets you create, convert, and inspect virtual machine disk images with ease.

It supports a wide range of image formats, including:

• QCOW2 – the most common format with snapshot support
• RAW – simple and fast, great for performance
• VDI – used by VirtualBox
• VMDK – VMware’s disk format
• …and many more

With qemu-img, you can:

• Create new virtual machine disks
• Convert images between different formats
• Check and repair disk images
• Resize or modify virtual machine disks

Perfect for anyone working with KVM, Proxmox, VirtualBox, or VMware environments.

Example 1: Create a New Image

Let us create an image in the default libvirt storage pool path.

sudo qemu-img create -f qcow2 /var/lib/libvirt/images/deb12.qcow2 20G

• -f qcow2: Specifies the image format (QCOW2 is a common format for QEMU/KVM).
• 20G: Creates a 20GB virtual disk.

A virtual machine that uses the disk image can be created using virt-install

sudo virt-install \
--name debian12 \
--ram 4096 \
--vcpus 2 \
--disk path=/var/lib/libvirt/images/deb12.qcow2 \
--os-variant debian12 \
--network bridge=virbr0 \
--graphics none \
--console pty,target_type=serial \
--location /var/lib/libvirt/images/debian-12.7.0-amd64-DVD-1.iso \
--extra-args 'console=ttyS0,115200n8'

Installation will start in text mode.

...
┌───────────────────────┤ [!!] Select a language ├────────────────────────┐
│ │
│ Choose the language to be used for the installation process. The │
│ selected language will also be the default language for the installed │
│ system. │
│ │
│ Language: │
│ │
│ C │
│ English │
│ │
│ <Go Back> │
│ │
└─────────────────────────────────────────────────────────────────────────┘

<Tab> moves; <Space> selects; <Enter> activates buttons

Example 2: Resize an Image

We can resize an image by adding extra 10GB to it using resize command option:

qemu-img resize /var/lib/libvirt/images/deb12.qcow2 +10G

Example 3: Inspect an Image

The qemu-img info command provides detailed information about a virtual machine disk image, including its format, size, and metadata.

qemu-img info /var/lib/libvirt/images/deb12.qcow2

Example 4: Converting between image formats

It is generally straightforward to convert images from one format to another using qemu-img:

Image format	Argument to qemu-img
QCOW2 (KVM, Xen)	qcow2
QED (KVM)	qed
raw	raw
VDI (VirtualBox)	vdi
VHD (Hyper-V)	vpc
VMDK (VMware)	vmdk

Refer to the examples below to learn how image conversion can be done from one format to the other.

Example 5: Grow image / filesystem

Get default filesystem disk size using qemu-img:

IMAGE=ubuntu-24.04-amd64.img
qemu-img info $IMAGE

In the output, we can confirm the disk size before growing it.

image: ubuntu-24.04-amd64.img
file format: qcow2
virtual size: 3.5 GiB (3758096384 bytes)
disk size: 581 MiB
cluster_size: 65536
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: false
refcount bits: 16
corrupt: false
extended l2: false
Child node '/file':
filename: ubuntu-24.04-amd64.img
protocol type: file
file length: 581 MiB (608755712 bytes)
disk size: 581 MiB

Suppose we want to grow disk size by 20GB

qemu-img resize $IMAGE +20G

Confirmation after the change:

$ qemu-img info $IMAGE
image: ubuntu-24.04-amd64.img
file format: qcow2
virtual size: 23.5 GiB (25232932864 bytes)
...

The -f format flag is optional. If omitted, qemu-img will try to infer the image format.

• Convert a raw image file to a qcow2 image file.

qemu-img convert -f raw -O qcow2 image.img image.qcow2

• convert a vmdk image file to a raw image file.

qemu-img convert -f vmdk -O raw image.vmdk image.img

• Convert a vmdk image file to a qcow2 image file.

qemu-img convert -f vmdk -O qcow2 image.vmdk image.qcow2

• Convert qcow2 to vdi

qemu-img convert -O vdi test.qcow2 test.vdi

• Convert qcow2 to raw

qemu-img convert -O raw test.qcow2 test.raw

• Convert qcow2 to vmdk

qemu-img convert -O vmdk test.qcow2 test.vmdk

🔧 The above guide is part of the comprehensive Mastering KVM Virtualization – The Ultimate eBook. Get your full copy today. Download here.