WSL2Compactor

WSL2Compactor is an interactive Windows console application for compacting WSL2 ext4.vhdx files.

It guides the WSL and Windows compaction steps in order.

Download

Download WSL2Compactor-win-x64.exe from the latest GitHub Release and run it as Administrator.

How It Works

• Finds WSL2 distributions with an existing ext4.vhdx.
• Shows Linux filesystem usage, Windows host allocation, and VHDX file length.
• Runs fstrim inside selected distros.
• Runs wsl.exe --shutdown so Windows can compact the VHDX file.
• Compacts with the Windows VirtDisk API.

The app offers two compact modes:

• No zero scan: uses COMPACT_VIRTUAL_DISK_FLAG_NO_ZERO_SCAN.
• Zero scan: calls CompactVirtualDisk without that flag.

Displayed Values

Column	Meaning
Linux used	df-style filesystem space used inside the distro.
Ext4 overhead	Exact ext4 structural overhead when available; otherwise -.
Linux footprint	Linux used + Ext4 overhead, shown only when both values are available.
Host allocated	Windows host disk space allocated by ext4.vhdx, read with GetCompressedFileSizeW.
File length	Logical Windows file length of ext4.vhdx.
Saved	Actual host allocation delta after compaction: max(0, host allocated before - host allocated after).

The app does not show a pre-run savings estimate because that cannot be computed from Linux used, Host allocated, and File length alone.

Build

Requirements:

• .NET 10 SDK
• Windows 10/11 x64 target

The app is a Windows x64 executable. End users should download the self-contained executable from Releases; building from source requires the .NET 10 SDK.

From Windows PowerShell:

dotnet build .\WSL2Compactor.slnx -c Release

dotnet publish .\src\WSL2Compactor\WSL2Compactor.csproj `
  -c Release `
  -r win-x64 `
  --self-contained true `
  -p:PublishSingleFile=true `
  -p:EnableCompressionInSingleFile=true `
  -p:PublishTrimmed=true `
  -p:PublishReadyToRun=false `
  -o .\.build\publish

The published executable is written to .build/publish/WSL2Compactor.exe.

For release checks, run:

dotnet build .\WSL2Compactor.slnx -c Release
dotnet format .\WSL2Compactor.slnx --verify-no-changes

License

MIT