Shrink, optimise and expand an existing QCOW2 image

A virtual disk image is a block device in a file. There are a number of different disk image formats to choose from when setting up a virtual machine. QEMU Copy On Write version 2 (QCOW2) is the default virtual disk image format for the Quick Emulator (QEMU). Features such as thin provisioning, snapshots and compression make QCOW2 one of the most versatile virtual disk formats available.

These instructions specifically target Debian 12 with a GNOME desktop as the host, but they should also be applicable to other Linux distributions such as Ubuntu or Linux Mint. The guest in this particular example is a Windows 11 virtual machine that has run out of space.

The overall objective is to shrink and optimise the 64 GiB disk image for random read and write operations before expanding it to a desired size of 128 GiB.

With thanks to Fam Zheng.

Before you begin

Shut down the virtual machine and delete all existing snapshots from the image file.

Never modify images currently in use by a running virtual machine.

Step 1

On the host, install the necessary tools for working with virtual disk images.

$ sudo apt-get install --yes libguestfs-tools gnome-disk-utility

Step 2

Only root can access the host directory /var/lib/libvirt/images. Use the following command to obtain the necessary privileges.

$ sudo su

Step 3

Continue by creating a directory in which to keep your virtual machine backups.

# mkdir /var/lib/libvirt/backups

Step 4

Now create a backup of the virtual machine with the name windows by copying its QCOW2 image file to the backups directory.

# cp /var/lib/libvirt/images/windows.qcow2 /var/lib/libvirt/backups/windows-backup.qcow2

Step 5

Sparsify the image file to convert any free space within the disk image to free space on the host.

# virt-sparsify --in-place /var/lib/libvirt/images/windows.qcow2

Step 6

Rename the sparsified image file.

# mv /var/lib/libvirt/images/windows.qcow2 /var/lib/libvirt/images/windows-sparsified.qcow2

Step 7

Check the disk size of the sparsified image file.

# qemu-img info /var/lib/libvirt/images/windows-sparsified.qcow2

The disk size should be smaller than the virtual size. In this particular case, the disk size is 33.7 GiB and the virtual size 64 GiB.

image: /var/lib/libvirt/images/windows-sparsified.qcow2
file format: qcow2
virtual size: 64 GiB (68719476736 bytes)
disk size: 33.7 GiB
cluster_size: 65536
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: true
refcount bits: 16
corrupt: false
extended l2: false

Step 8

Determine which partition to resize by obtaining more detailed information about the contents of the sparsified disk image.

# virt-filesystems --long -h --all -a /var/lib/libvirt/images/windows-sparsified.qcow2

On the virtual device /dev/sda, the partition /dev/sda3 is equivalent to the Local Disk (C:) of the Windows 11 virtual machine.

Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1 filesystem vfat - - 96M -
/dev/sda3 filesystem ntfs - - 63G -
/dev/sda4 filesystem ntfs - - 768M -
/dev/sda1 partition - - - 100M /dev/sda
/dev/sda2 partition - - - 16M /dev/sda
/dev/sda3 partition - - - 63G /dev/sda
/dev/sda4 partition - - - 768M /dev/sda
/dev/sda device - - - 64G -

Step 9

Load the network block device (NBD) kernel module.

# modprobe nbd max_part=8

Step 10

Connect the sparsified image.

# qemu-nbd --connect=/dev/nbd9 /var/lib/libvirt/images/windows-sparsified.qcow2

Step 11

The partition /dev/sda3 listed in Step 8 is equivalent to /dev/nbd9p3 connected as a network block device. Use GNOME Disks to shrink /dev/nbd9p3 to its Minimal Size.

Use a graphical utility to minimise the risk of introducing errors.

This image has an empty alt attribute; its file name is disks-options-825x586.png
Select the correct partition and from the pop-up menu, choose the option Resize…
This image has an empty alt attribute; its file name is resize-volume.png
Select Minimal Size and resize the partition.

Step 12

Disconnect the resized image.

# qemu-nbd -d /dev/nbd9

Step 13

Unload the NBD kernel module.

# modprobe -r nbd

Step 14

Create a target image larger than the resized source image. In this example, the size of the target image is 128G and its format QCOW2 with full preallocation and a cluster size of 2M.

# qemu-img create -f qcow2 -o preallocation=full -o cluster_size=2M /var/lib/libvirt/images/windows-target.qcow2 128G

Step 15

Copy the source image to the target image. Specify the correct partition which to expand in the process.

# virt-resize --expand /dev/sda3 /var/lib/libvirt/images/windows-sparsified.qcow2 /var/lib/libvirt/images/windows-target.qcow2

Step 16

Confirm the size of the target image.

# qemu-img info /var/lib/libvirt/images/windows-target.qcow2

The overall disk size is now 128 GiB in total.

image: /var/lib/libvirt/images/windows-target.qcow2
file format: qcow2
virtual size: 128 GiB (137438953472 bytes)
disk size: 128 GiB
cluster_size: 2097152
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: false
refcount bits: 16
corrupt: false
extended l2: false

Step 17

Obtain more detailed information about the contents of the target disk image.

# virt-filesystems --long -h --all -a /var/lib/libvirt/images/windows-target.qcow2

The partition /dev/sda3 of the virtual device /dev/sda is now 127G in size.

Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1 filesystem vfat - - 96M -
/dev/sda3 filesystem ntfs - - 127G -
/dev/sda4 filesystem ntfs - - 768M -
/dev/sda1 partition - - - 100M /dev/sda
/dev/sda2 partition - - - 16M /dev/sda
/dev/sda3 partition - - - 127G /dev/sda
/dev/sda4 partition - - - 768M /dev/sda
/dev/sda device - - - 128G -

Step 18

Rename the target image file.

# mv /var/lib/libvirt/images/windows-target.qcow2 /var/lib/libvirt/images/windows.qcow2

All done!

You can also modify format specific options for an existing image without having to create a target disk image. Or alternatively expand into a target image that uses a format compatible with other hypervisors, such as RAW, VMDK, VDI, VHD, VHDX or QED.

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Following these instructions, Espanso 2.2.1 for Wayland will be installed on your system and enabled for the current user.

Compiling Espanso from source code

Side-step any dependency problems by compliling Espanso from source and moving the binary into place.

Step 1

Install the required C/C++ compiler and some additional tools.

$ sudo apt-get install --yes build-essential curl git wl-clipboard libxkbcommon-dev libdbus-1-dev libwxgtk3.*-dev libssl-dev

Step 2

Install the required Rust compiler, which is managed by the rustup tool.

$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh&&source ~/.bashrc

Press [Enter] to proceed with the installation.

Current installation options:

1) Proceed with instalation (default)
2) Customize installation
3) Cancel installation
>

Install cargo-make, which is required during the build process.

$ cargo install --force cargo-make --version 0.34.0

Step 3

Get the source code by cloning the Espanso repository to the local directory ~/.local/src/espanso.

$ git clone --progress https://github.com/federico-terzi/espanso ~/.local/src/espanso

Step 4

Compile the Espanso binary as a Wayland-only build in release mode.

$ cargo make --cwd ~/.local/src/espanso --profile release --env NO_X11=true build-binary

Move the resulting binary to the /usr/local/bin directory.

$ sudo mv ~/.local/src/espanso/target/release/espanso /usr/local/bin/

Step 5

Give Espanso the permissions required for operation.

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Check to see if the Espanso binary was installed successfuly.

$ espanso --version

Step 6

Register Espanso as a systemd service.

$ espanso service register

Launch Espanso.

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Step 7

GNOME desktop only: remove the conflicting default shortcut for activating the window menu.

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Use [Alt + Space] to open Espanso’s Search bar.

All Done!

Experimental support for Wayland

Espanso has some known limitations under Wayland. Most notably, “there is currently no support for App-specific configurations”.

Big ‘Thank you’ to Federico Terzi for creating Espanso!

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