Windows Subsystem for Linux (known as WSL)

This article has been written to complete the presentation and to deal in depth with the subject in detail.

---

• Windows Subsystem for Linux (known as WSL)
  • What is the WSL and how it works ?
    • WSL is not a virtual machine !
    • WSL 1 vs WSL 2
    • The limits of WSL
  • Install WSL on Windows
    • Requirements
    • Download WSL
    • WSL distributions available at this time
  • Some useful WSL features
    • Mount an EXT file system on Windows (or other filesystem)
      • Mount an entire disk
      • Mount a partition from a disk
    • Add a desktop environment to your WSL
    • Some useful commands
  • Appendix - Sources and References

What is the WSL and how it works ?

The WSL for Windows Subsystem for Linux is a compatibility layer developed by Microsoft for running Linux binaries natively (ELF format) in a console environment on Windows 10 and Windows 11. This ingenious technology provides a Linux-compatible kernel interface and can interact directly with the Windows operating system with performances very close to a native Linux distribution. Moreover, it allows a user to choose a Linux distribution to install directly from the Microsoft Store (more info in below).

WSL is not a virtual machine !

Oh my god, I have heard so many times "WSL ? Yeah it's like a virtual machine on your Windows" but no. It's not as simple... Although WSL uses virtualization technologies in some cases (more information in the next section), it does not work in a partitioned environment on your Windows system like a classic virtual machine on VMware or VirtualBox.

It's important to know that all your storage devices that have an assigned letter by the Windows operating system (for example C:, D:, E:, ...) are reachable in the /mnt directory. As an example, the famous C: partition of your Windows system is in /mnt/c and this is same thing for the others.

The NTFS and FAT partitions are directly mounted on the /mnt directory but it's necessary to execute some commands to mount EXT4 ones (more information below).

Therefore, the WSL can access to your storage devices and it may have some consequences. Indeed, if you try to delete your Document folder for example, you will notice that it will be permanently removed from your computer. You can also create a new file with a text editor like vim or nano and be able to edit it with a Windows text editor (like notepad for example).

For the curious ones, we tried to do a rm -fr /mnt/c command with the WSL and the root privileges, to delete all the files in the C:\ directory. It seems that the WSL can only delete the files in the user folder in C:\Users<name_of-the_user>. However, the windows system becomes quite unstable and slow.

WSL 1 vs WSL 2

The first thing to know is that WSL 2 isn't only an simple evolution of the first version. The entire architecture has been redesigned and the operation is not the same.

First of all, let's see how the architecture of WSL 1 looks like :

As you can see, WSL 1 is a simple layer between the linux distribution and the Windows kernel. The Linux syscalls are converted into Windows syscalls with bridges.

Actually, we can compare the WSL 1 with the well known Wine software that permits to execute Windows applications on Linux systems by converting Windows API calls on Linux API calls.

However, we can notice in the architecture of the WSL 2 that there is a whole Linux kernel virtualized :

The Virtual Machine Platform is a less powerful version of Hyper-V that still enables a hypervisor. Note that Microsoft if very vague on what the actual differences are between the Virtual Machine Platform and Hyper-V.

As we can see, the WSL 2 is based on a Linux kernel virtualized with the Virtual Machine Platform. This version has an increased I/O performance and a full system call compatibility. Indeed, initial versions of WSL 2 run up to 20 times faster compared to WSL 1 when unpacking a zipped tar archive, and around 2-5 times faster when using file intensive operations like git clone, apt upgrade, etc. Besides, unlike the WSL 1, it supports 32-bits applications.

However, if you are using files stored in storage devices on /mnt in your Windows file system, the WSL 1 will be faster than then second version. It has a lighter architecture and it does not need a hypervisor layer. But if you are using files stored in the root directory ( / ), WSL 2 will be even faster because file operations are moved on a VHD (Virtual Hardware Disk). You can access to this virtual disk with the windows explorer if you enter the command explorer.exe in your home directory or directly with the windows explorer by specifying the path \\wsl$\<name_of_the_distro>.

The limits of WSL

First of all, hardware acceleration isn't supported so the graphic performances are quite poor and well known graphic standards, like the CUDA technology, are not implemented. Regarding the audio, it's not natively supported but it can be remedied by installing a network-capable sound server like PulseAudio.

Currently, a better integrated desktop oriented WSL is still in development and its named WSLg. At this time, according to Microsoft, it only works on Windows 11 (build 22000+) or Windows 11 Insider Preview (builds 21362+). If you want more information, check the references section below.

Moreover, networking on WSL isn't fully reliable. WSL allows you to communicate with a network, but it may be less efficient because it needs to pass through a few layers in order to do work. This implies a considerable loss of performance when executing processes that operate at a low network level.

As Microsoft says in its documentation, WSL has been designed for the developers. So, if you want to host a Web service or sharing storages locally for example, it's better and more convenient to use a full Linux virtual machine in a classic hypervisor.

Install WSL on Windows

Requirements

First, you must be running Windows 10 64bits version 2004 or higher (Build 19041 or higher) or Windows 11 64bits.

To check your Windows version and build number, select Windows logo key + R, type winver and select OK.

If you have an older version, update your system with Windows Update.

You need to have a Windows functionality installed before using WSL. To install it, select Windows Logo key, type Windows Features and enter. This window should open :

Make sure to install Virtual Machine Platform. After this, you must restart your Windows system.

Or you can type this command in a prompt with administrator privileges to install it :

dism.exe /online /enable-feature /featurename:VirtualMachinePlatform /all /norestart

Make sure to restart the system afterwards.

Download WSL

You can install the WSL feature with the same procedure described before by selecting the Windows Subsystem for Linux or with the following Powershell command as an administrator :

wsl --install

According to Microsoft, this command will activates the required optional components, downloads the latest Linux kernel, sets WSL 2 as default and installs a Linux distribution for you (Ubuntu by default)

or

dism.exe /online /enable-feature /featurename:Microsoft-Windows-Subsystem-Linux /all /norestart

This command will only install WSL.

WSL distributions available at this time

At this moment (when this article was written), you can install these distributions :

• Ubuntu
• Debian
• Kali Linux
• openSUSE
• Alpine Linux
• Pengwin (more information about it in Presentation.md)
• Fedora Remix

You can install the distribution you want directly on the Windows Store !

Or you can install it via a console with the command :

wsl --install --distribution DistribName

Some useful WSL features

Mount an EXT file system on Windows (or other filesystem)

First, you must be running Windows 11 Build 22000 or higher and have admin privileges. This procedure only works on the WSL 2 and it is non-peristent, the filesystem will be unmounted after WSL shutdown.

Mount an entire disk

To mount an entire disk, we first need to identify the physical disk.

In a windows console :

GET-CimInstance -query "SELECT * from Win32_DiskDrive"

This command should return a list of physical drives in this format :

\\.\PHYSICALDRIVEX X : number of the physical drive

Then we can mount it with the command :

wsl --mount \\.\PHYSICALDRIVEX

Default filesystem is ext4, we can specify the type of filesystem with the argument t. We can list the available filesystem with cat /proc/filesystems

The mounted disk should be now accessible via the Explorer in \\wsl$\Distro\mnt\PHYSICALDRIVEX

Or directly in the distro used : /mnt/PHYSICALDRIVEX

Mount a partition from a disk

To mount only a partition from a disk, we first need to identify the physical disk as before. In a windows console :

GET-CimInstance -query "SELECT * from Win32_DiskDrive"

Then mount the physcial disk :

wsl --mount \\.\PHYSICALDRIVEX

Now we are going to list the available partitions with :

lsblk

It should return something like this :

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdb      8:16   0    1G  0 disk
├─sdb2   8:18   0   50M  0 part
├─sdb3   8:19   0  873M  0 part
└─sdb1   8:17   0  100M  0 part
sdc      8:32   0  256G  0 disk /
sda      8:0    0  256G  0 disk

We can now mount the partition we want by specifying only the number of the partition. For instance if it's sdb1, we specify 1 :

wsl --mount \\.\PHYSICALDRIVEX --partition 1 --type <Filesystem>

Add a desktop environment to your WSL

This procedure only works on the WSL 2. WSL 2 allows us to run linux applications with GUI by default.

You could run a complete desktop environnement but we need a X server. There are plenty of tutos about that.

X11 server with Xfce

If you are in the kali team, they have built a nice tool called Win-KeX which provides a Kali Desktop Experience for WSL 2.

In the kali console you can install the tool with :

sudo apt install -y kali-win-kex

To launch it in Window mode with sound support :

kex --win -s

To launch it in Enhanced Session Mode :

kex --esm --ip -s

Some useful commands

Update WSL :

wsl --update

Stop WSL :

wsl --shutdown

Export a distro (Backup) :

wsl --export distro filename.tar 

Import a distro (Restore) :

wsl --import distro install_location filename.tar

List distros and version :

wsl -l -v

List available distros to install :

wsl --list --online

Set WSL default version to 2 :

wsl --set-default-version 2

Set WSL default version to 2 :

wsl --set-default-version 2

Appendix - Sources and References

You can find here all the references that we used to write this article and the presentation :

https://docs.microsoft.com/en-us/windows/wsl/about

https://www.whitewaterfoundry.com/what-is-wsl

https://docs.microsoft.com/en-us/windows/wsl/install

https://docs.microsoft.com/en-us/windows/wsl/compare-versions

https://docs.microsoft.com/en-us/virtualization/api/hypervisor-platform/hypervisor-platform

https://en.wikipedia.org/wiki/Windows_Subsystem_for_Linux

https://www.howtogeek.com/426749/how-to-access-your-linux-wsl-files-in-windows-10/

https://www.it-connect.fr/wsl-comment-acceder-aux-fichiers-linux-depuis-windows-10/

https://www.kali.org/docs/wsl/win-kex/

Official GitHub repositories of the WSL projects :

WSL 1 (only for issue reporting) : https://github.com/microsoft/WSL

WSL 2 : https://github.com/microsoft/WSL2-Linux-Kernel

WSLg : https://github.com/microsoft/wslg

Lists of different compatibles softwares that work or not on WSL :

https://github.com/ethanhs/WSL-Programs

https://github.com/davatron5000/can-i-subsystem-it

---

Updated : 03/03/2022, Authors : Xen0rInspire, AnthonyF