How do I get back unused disk space from Ubuntu on WSL2?

Question

I'm using Ubuntu 20.04 on WSL2 on Windows 10, and I noticed that after removing files on Ubuntu I was not getting the space back that was taken up by the removed files. For example: Before I deleted files on Ubuntu it showed on Windows explorer that my free space on the (C:) drive was around 46GB. Then after I deleted around 10GB of files, which in my case where some temporary Gatsby sites, it resulted in even less free space, around 45GB, which I thought was very weird.

So how can I get back those unused bits? Is there some terminal command which I can use or can I do something via the windows GUI or something?

Answer 1

There's a WSL Github issue open on this topic. WSL will automatically grow the virtual disk (ext4.vhdx), but shrinking it to reclaim unused space is something that must currently be done manually.

The first thing you'll need to do is know the location of your ext4.vhdx. For a default Ubuntu installation, it should be in something like %PROFILE%\AppData\Local\Packages\CanonicalGroupLimited.UbuntuonWindows_79rhkp1fndgsc\LocalState\

Then there are several techniques that you can use to remove the unused space. I recommend you start with a wsl --shutdown and copy the vhdx as a backup to start. If you are running Docker Desktop, also shut it down, otherwise it may inadvertently attempt to restart WSL after your --shutdown.

• If you are on Windows Professional or higher, you can install Hyper-V and use the Optimize-VHD commandlet as described in the original issue. .

• On Windows Home (and higher) you can use diskpart as described in this comment.

• Exporting the WSL distro and re-importing it into a new WSL instance (as in this comment) will also reclaim the space. Note that you will need to reset the default username after an import. See here.

I have tested and confirmed both the second and third techniques personally.

Answer 2

• Activate Hyper-V module in windows features (control-panel -> Turn windows features on or off -> activate Hyper-v -> restart). This is required to activate optimize-vhd command.
• Open windows powershell as admin: First, press Windows+R to open Run, and then type “powershell” in the text box. Next, press Ctrl+Shift+Enter. Windows PowerShell will open in admin mode. In powershell, run following commands.
• wsl.exe --shutdown
• cd into ext4.vhdx folder that typically is cd C:\Users\<user>\AppData\Local\Packages\CanonicalGroupLimited.Ubuntu20.04onWindows_79rhkp1fndgsc\LocalState\
• optimize-vhd -Path .\ext4.vhdx -Mode full (Make sure the ext4.vhdx is not clicked on by mouse, because that would lead to the error of the the file is being used by another process in powershell)

Answer 3

When the command let optimize-vhd is not available in your system do the following:

Shutdown the wsl before managing its disk

wsl --shutdown

Save the following script as compact-disk.txt

select vdisk file="C:\Users\%username%\AppData\Local\Packages\CanonicalGroupLimited.Ubuntu20.04onWindows_79rhkp1fndgsc\LocalState\ext4.vhdx"
attach vdisk readonly
compact vdisk
detach vdisk

Open prompt as Administrator and run the saved script above

diskpart /s <SAVED_SCRIPT_FOLDER_PATH>\compact-disk.txt

Answer 4

With this Self-elevate script you can compact multiple vhdx at once.

# Self-elevate the script if required
if (-Not ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole] 'Administrator')) {
    if ([int](Get-CimInstance -Class Win32_OperatingSystem | Select-Object -ExpandProperty BuildNumber) -ge 6000) {
        $CommandLine = "-File `"" + $MyInvocation.MyCommand.Path + "`" " + $MyInvocation.UnboundArguments
        Start-Process -FilePath PowerShell.exe -Verb Runas -ArgumentList $CommandLine
        Exit
    }
}

#Full Path of vhdx file
$d1 = #Ex: "E:\Docker\wsl\data\ext4.vhdx"
$d2 = ""
$d3 = ""
$d4 = ""
$d5 = ""
$d6 = ""

$paths = $d1, $d2, $d3, $d4, $d5, $d6

foreach ($file in $paths) {
    echo ""
    echo "Befor Shrinking File sizes in MB"
    Get-ChildItem -Path $file | Select-Object FullName, @{Name = "Size"; E = { $_.Length / 1MB } }
    echo ""
    echo "---------"
    echo "Shrinking $file"
    echo "---------"

    wsl --shutdown
    Optimize-VHD -Path $file -Mode Full

    echo ""
    echo "After Shrinking File sizes in MB"
    Get-ChildItem -Path $file | Select-Object FullName, @{Name = "Size"; E = { $_.Length / 1MB } }
    echo ""
    echo ""
    echo ""
    echo ""
}

Read-Host -Prompt "Press Enter to exit"

btw, With a little tweak you can also run it on startup ("Start Docker when you login" should be disabled)

Answer 5

You can use wslcompact utility.

It doesn't require an elevated prompt and ensures minimum size, about 2% more than what df / reports inside the WSL distro. It compacts way more than DISKPART or Optimize-Vhd commands.