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Resize disks in VirtualBox with Snapshots

It is quite straightforward to resize a disk in VirtualBox as stated here and there. It becomes tricky though if the virtual machine,aka VM, has snapshots attached. The virtual disk thus is persisted across multiple VHD files, and the old trick will generally take not effect. This is also a known bug hanging there for more than three years.

The suggested approach is to delete all snapshots and wait patiently for VirtualBox Manager to merge all the VHD files for you. It is a painfully lengthy process, so I decide to take a shortcut.

  1. First, shutdown the VM and backup the whole virtual machine folder.
  2. Then modify the size of all .vdi files in the root of the VM and Snapshots subdirectory.
VBoxManage modifyhd "Windows 8.1.vdi" --resize 81920
for x in Snapshots/*.vdi ; do VBoxManage modifyhd $x --resize 81920 ; done

Startup the VM, and you will see the unallocated space in the Disk Management utility.

Resize .vmdk disk on Linux

Convert .vmdk format to .vdi and then resize. You can change format back after the resizing.

VBoxManage clonehd "ubuntu-xenial-16.04-cloudimg.vmdk" "ubuntu-xenial-16.04-cloudimg.vdi"  --format vdi  #.vmdk -> .vdi
VBoxManage clonehd "ubuntu-xenial-16.04-cloudimg.vdi"  "ubuntu-xenial-16.04-cloudimg.vmdk" --format vmdk #.vdi  -> .vmdk

Resize .vdi disk on Windows

cd "C:\Program Files\Oracle\VirtualBox"
VBoxManage.exe modifyhd "C:\Users\piotr\VirtualBox VMs\vm-ubuntu64\vm-ubuntu64.vdi" --resize 20480

Note it also can resize VHD (Hyper-V) file formats.

Vagrant note

  • OS: Ubuntu 16.04 LTS
  • Vagrant version 2.1.1
  • VirtualBox: 5.1.34_Ubuntu

Steps I have taken to resize Vagrant Ubuntu disk

  1. Stopped VM
  2. In settings removed attached drive "ubuntu-xenial-16.04-cloudimg.vmdk"
  3. Converted .vmdk into .vdi
  4. Attached "ubuntu-xenial-16.04-cloudimg.vdi" making sure that
    • Controller: SCSI Controller
    • Hard disk is attached to: SCSI Port 0, otherwise may throw error "no bootable medium found"

Shrink unused space on virtual drive

Hypervisor: Virtualbox, VMware

Virtual disks can be shrink as long as they are ext3 or ext4 file systems.

$ vagrant ssh
$ sudo dd if=/dev/zero of=wipefile bs=1024x1024; rm wipefile

The above command is simply writing zero bytes to the wipefile in chunks of 1024 bytes until there is no disk space left in your VM’s disk. Then it is removing the wipefile. This basically leaves all those excess bytes zero’d out.


This is necessary because the shrink/compaction tools provided by either VMWare or VirtualBox both have no way of identifying space they can free up in the disks unless they are zero’d out.


With VirtualBox the only way I was able to shrink the disk image was to clone it to a smaller copy using the following command:

$ VboxManage clonehd name-of-original-vm.vdi name-of-clone-vm.vdi

Once you have cloned the vdi you can then import it into the VM through VirtualBox and get rid of the original vdi.


With VMware you can shrink the vmdk disk by doing the following:

$ vmware-vdiskmanager -d /path/to/main.vmdk
$ vmware-vdiskmanager -k /path/to/main.vmdk

Installing Virtualbox guest additions

Be sure to install DKMS(Dynamic Kernel Module System) before installing the Linux Guest Additions

sudo apt-get install dkms


Additional packages if dkms was not enough

sudo apt-get install linux-headers-$(uname -r) build-essential dkms #if above not work
sudo apt-get install perl make gcc #was required for Ubuntu 18.04 LTS


In the "Devices" menu in the virtual machine's menu bar, VirtualBox has a handy menu item named "Insert Guest Additions CD image", which mounts the Guest Additions ISO file inside your virtual machine. Then change directory to your CD-ROM and issue following command:

sh ./VBoxLinuxAdditions.run

Generalize Windows

If you wish to re use your Windows VM image it needs to be generalized:

C:\Windows\System32\Sysprep
sysprep.exe /oobe /generalize /shutdown /mode:vm