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wsl.md

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Windows Subsystem for Linux (WSL)

What is WSL

WSL -- the Windows Subsystem for Linux, was introduced in 2016. It was called Bash on Ubuntu on Windows back then. It is a component in Windows that makes you can run Linux commmands (Linux binary executables) directly in Windows. It looks like a virtual machine but without the overhead of it.

The primary purpose of WSL is to make the Linux command-line tools can be run in Windows and interact with other Windows command-line tools.

How does WSL Work

The request for a Linux system call from any Linux applications in WSL will be translated by a Linux kernel compatibility layer into a request of Windows kernel calls. So it looks like a command-line Linux distro without the actual Linux kernel but a Linux kernel compatibility layer in Windows.

It is different from Cygwin, because Cygwin provides Cygwin runtime running in user mode to do the translation, and all Linux application needs to be rebuilt from source and linked to Cygwin runtime to be used in Windows.

Installation

Prerequisites

To use WSL, your OS must be Windows 10 version 1709 or the latest. You can check the version by running systeminfo in PowerShell or going to Settings -> System -> About.

Install WSL

Go to 'Turn Windows Features On or Off' (Control Panel -> Programs -> Programs and Features), tick on the box 'Windows Subsystem for Linux' to install WSL and reboot.

Or run the command below in PowerShell as administrator:

PS> Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux

Install a Linux Distro

Then you also need to go to Microsoft Store and search for a Linux distro (for example, Ubuntu) to install.

Usage

Launch WSL

To Launch WSL, you can launch the installed Linux distro from Windows Start menu.

You can also launch it from PowerShell (Below I use PS> to indicate PowerShell and $ to indicate Linux command line in WSL):

PS> ubuntu  # Launch Ubuntu
PS> debian  # Or launch Debian
PS> wsl     # Launch the default distro

Then you are inside WSL command line environment, where you can run Linux commands just like in a Linux machine:

$ ls -a
.  ..  .bash_history  .bash_logout  .bashrc  .profile  .sudo_as_admin_successful

Interaction with Windows

  • Other than launching and run Linux commands inside a WSL distro, you can also run the commands directly in Windows without going into the distro first:

    PS> wsl ls -a
.  ..  .bash_history  .bash_logout  .bashrc  .profile  .sudo_as_admin_successful

  • You can also feed the output from a Windows command to a Linux command, and vice versa:

    PS> ipconfig | wsl grep IPv4  # Pipeline Windows and Linux command in PowerShell
   IPv4 Address. . . . . . . . . . . : 10.168.2.39
   IPv4 Address. . . . . . . . . . . : 192.168.139.81
PS> wsl                       # Launch WSL
$ ipconfig.exe | grep IPv4    # Pipeline Windows and Linux command in WSL
   IPv4 Address. . . . . . . . . . . : 10.168.2.39
   IPv4 Address. . . . . . . . . . . : 192.168.139.81

    Note: Windows command should be appended with .exe extension if run in WSL.

GUI Applications

  1. To launch a GUI app in WSL, such as gedit, a X Server needs to be installed in Windows so that it can be shown in Windows instead of WSL, since WSL is just a command line environment. There are many X Server apps in Windows, Xming and VcXsrv are two of them.

  2. Then set the DISPLAY to tell WSL to use the X Server. For example:

    $ DISPLAY=:0 gedit

    Or you can add this into ~/.bashrc:

    export DISPLAY=:0

Misc

File System

  • In WSL, all Windows drives are mounted under /mnt. To access the files under Windows' C or D drive, you can cd /mnt/c or cd /mnt/d in WSL. To modify files in Windows from WSL, you need to run WSL as administrator other than as sudo. The mounted Windows file system is DriveFs in WSL, and the Linux file system is VolFs in WSL.

  • In Windows, all Linux file systems are in a directory like

    C:\Users\<username>\AppData\Local\Packages\CanonicalGroupLimited.UbuntuonWindows_79rhkp1fndgsc\LocalState\rootfs\

    You can also open current working directory in WSL by executing $ explorer.exe . (Note: The dot in the end of the command indicates current directory). But be aware that modifying Linux files within Windows would have side effects, because some functionalities of Linux don't have similar counterparts in Windows, such as file mode, which would lead to inconsistencies in the file attributes when modified in Windows.

Uninstallation

To uninstall one of the installed distros, you can right-click the distro in Windows Start menu to uninstall it. But then if you want to reinstall it, you need to remove the installed directory of previous installation, such as

C:\Users\<username>\AppData\Local\Packages\CanonicalGroupLimited.UbuntuonWindows_79rhkp1fndgsc\

WSL 2

WSL 2 is the second version of WSL, but with a completely different structure from WSL. Because it uses a lightweight VM to run a real Linux kernel underneath instead of a compatibility translation layer, WSL 2 makes Windows run much more Linux applications than WSL, and allows to run docker containers natively.

WSL 2 is still under development, and is only available in Windows Insider Preview.

NOTE Because Windows Insider Preview is a development version of Windows, it is not stable and you will be at high risk of having a malfunctional Windows and unable to do anything except reinstall or reverting to a previous state, as said in Windows Insider Preview Downloads:

If you want to stop using Windows 10 Insider Preview and return to your previous version of Windows, you'll need to reinstall your previous version from the recovery or installation media that came with your PC—typically a DVD. If you don't have recovery media, you might be able to create recovery media from a recovery partition on your PC using software provided by your PC manufacturer. You'll need to do this before you upgrade. Check the support section of your PC manufacturer's website for more info.

After you install Windows 10 Insider Preview, you won’t be able to use the recovery partition on your PC to go back to your previous version of Windows.

Another way of testing would be to install a Window Insider Preview ISO in a virtual machine. Though the ISO isn't the latest version, it contains WSL 2 so that you can have a try. The lowest version of Windows with WSL 2 is Windows build 18917.

To enable WSL 2 in Windows when you are Windows Insider Preview, enable 'Virtual Machine Platform' in 'Turn Windows Features On and Off' (Control Panel -> Programs -> Programs and Features) or run the command:

PS> Enable-WindowsOptionalFeature -Online -FeatureName VirtualMachinePlatform

The usage of WSL 2 is similar to WSL, but:

  1. If you want to change a WSL distro into WSL 2, you need to convert it by

    PS> wsl --set-version <distro> 2

    And the conversion may take a very long time. So if you want install a distro with WSL 2 as default, set the default version before getting the distro from Windows Store:

    PS> wsl --set-default-version 2

    If you are not sure about the version of a distro, check it by

    PS> wsl -l -v

  2. Because WSL 2 is running in a VM, communication between WSL 2 and Windows is over virtual network, thus you need to enable public network access in X Server as well as in Windows firewall to allow GUI apps being shown in Windows. And then add the IP of Windows to DISPLAY:

    $ DISPLAY=$(cat /etc/resolv.conf | grep nameserver | awk '{print $2}') gedit

    The IP of Windows relative to WSL 2 can be found in the file /etc/resolv.conf. See Reminder: For GUIs w/ WSL2 you need to allow for public access.

Reference