You can now run Linux apps on Windows thanks to a feature called Windows Subsystem for Linux ("WSL" for short). But what is it, exactly? Is it an emulation layer like Wine? Is it a VM like VirtualBox? Is it dual-booting like Boot Camp? It's none of the above—it's something pretty unique and hard to explain.
👇
Next: Let me try to explain it anyway!
## Ubuntu as a Windows app
To get Linux working on Windows, you first need to install Linux. Not from an ISO... but from the Microsoft Store (think: Windows's version of the Mac App Store). A full guide to installing WSL is available from Microsoft.
Linux distributions are available as apps. To be specific, they're command-line apps, just like git
or vim
.
Next: To understand WSL, let's first look at how the Windows command line works.
## Command-line apps
Windows has support command line interface (CLI) apps, just like Linux. In fact, many built-in system utilities are CLI apps.
💡 Try this: press Win
+ R
, then run ping 8.8.8.8
. It will open a new window.
👇 Next: Let's see what makes this window work.
## Windows console host
CLI apps are ran inside the Windows console host. The console host, or conhost.exe, is a GUI app that draws a terminal inteface in a graphical window.
💡Try this: open the task manager (Ctrl
+ Shift
+ Esc
). Now run ping -t 8.8.8.8
. You'll see a new application in the task manager called TCP/IP Ping Command. Under this group are 2 processes:
- ping.exe—the command you just ran; and
- conhost.exe—also known as Console Window Host, the GUI that shows ping's output.
In Linux terms: Think of conhost.exe as a terminal emulator, like XTerm might be for Linux. It's a graphical UI that shows terminal output. ping.exe runs on conhost.exe in the same way /usr/bin/ping runs inside Xterm.
👇 Next: Let's see how the Windows Command Prompt works.
## Cmd.exe on Conhost
All CLI apps open in conhost.exe. This includes the Windows Command Prompt, or cmd.exe—which is a CLI app, just like ping.exe!
💡 Try this: Go to Win
+ R
and run cmd.exe
. You'll see this open in the same Windows console host window that ping.exe
opened.
In Linux terms: Think of cmd.exe like the Bash shell. A terminal window in Linux will run Bash, and will close the window when Bash exits. cmd.exe (the shell) and conhost.exe (the terminal GUI) works the same way.
Next: This may be the case for the Command Prompt, but why does Powershell's window look different?
## Powershell's blue window
If you open Powershell, you'll notice that the window is blue. It's not a different app, it's still the same conhost.exe with different settings! You'll notice it has the same menus as cmd.exe.
Powershell.exe
is a CLI app, too—just like cmd.exe
. Conhost simply lets you choose different settings per app. It simply comes with different color settings for Powershell by default.
In Linux terms: Most terminal emulators on Linux would support different profiles, and you may be assigning different profiles per command. Windows's conhost.exe has a different profile for Powershell that has its Screen Background set to blue.
Next: Is WSL just like cmd.exe and Powershell then?
## The WSL launcher: `wsl.exe`
Yes! You can think of WSL as another CLI application just like cmd.exe and powershell.exe. Just like other CLI apps, you can run wsl.exe
. This is the WSL Launcher, which boots up the WSL platform and drops you into the bash (your user's shell by default).
💡 Try this: Try running wsl.exe
via Win
+ R
. This should get you a Linux bash prompt running inside a conhost.exe window. Seems very similar to Cmd and Powershell, doesn't it?
Next: Let's try mixing all these together.
## Shells inside shells
Windows's cmd.exe and powershell.exe can run command line applications. You can use it to run ping.exe
, chkdsk.exe
, or—wouldn't you know it—even wsl.exe
.
💡 Try this: Try running wsl.exe
or bash.exe
from within a Command Prompt (cmd.exe). In fact, try running wsl.exe
inside powershell.exe
inside cmd.exe
, or any combination above! Typing exit
will bring you one level out.
In Linux terms: Think of them just like shells. Windows's Cmd might be like Bash, and Powershell might be Fish or Zsh. wsl.exe
works the same way.
Next: Why do the backslashes (\
) in Windows appear as forward slashes (/
) in WSL?
## The WSL filesystem
WSL has its own filesystem! If you do ls /
inside WSL, you'll find /usr
, /bin
and the other usual suspects in a Linux filesystem. This is a full POSIX-compliant filesystem managed by WSL, away from the limitations of your Windows's NTFS.
💡 Try this: Go to your Linux's home directory with cd
. Create two files with the same filename, but different case: touch xyz.txt XYZ.TXT
. These two files can't co-exist in Windows's case-insensitive filesystem, can it? They will live happily inside WSL just fine.
In Linux terms: Think of WSL as a separate Linux system—a bit like a VirtualBox VM. It has its own filesystem, processes, /dev
devices. Running wsl.exe
will tunnel you into this Linux subsystem.
Next: So is it a virtual machine?
## Linux in a box
Not only does WSL have its own filesystem, it's a full Linux system that runs as an app in Windows! It may be easy to think it's like VirtualBox, but it's not a VM.
Why is it not a VM? There's no CPU or hardware emulation involved like in a VM. A whole Linux system runs like any other app in Windows.
💡 Try this: Run htop
inside WSL (you may need to install it first), and view it as a tree (shift-T
). It has a whole process tree, even with an /init
process! You'll see your machine's full CPU and memory capacity—it's not pre-allocated, unlike a VM. It shares these hardware resources just as any other Windows app would.
In Linux terms: On a typical system, Linux's entry point would be in /boot/vmlinuz-linux, which is fired by a bootloader like GRUB. Think of WSL as a version of this packaged as a wsl.exe file. The whole Linux subsystem will be running as a process inside Windows.
Note about WSL2: There are two versions of WSL. The new experimental version, WSL2, actually works as a Virtual Machine.
Next: If WSL is a separate subsystem from your Windows environment, how do they share files?
## Windows files inside WSL
Your Windows files are visible inside WSL under /mnt/c
.
💡 Try these: Here are some experiments you can try inside WSL:
Case insensitive files: In WSL, try
cd /mnt/c/Windows
andcd /mnt/c/WINDOWS
. They'll both work! The Windows filesystem you're accessing in/mnt/c
is case-insensitive.Check mount points: Run
findmnt
. You'll see/mnt/c
is mounted as drvfs, just as how you would mount a drive in Linux.Two home directories: Look at
/mnt/c/Users
. You'll see you have 2 home directories: your WSL/Linux one in/home
, and your Windows one in/mnt/c/Users
.Permissions won't work: Try to make a file in
/mnt/c
and runchmod
to change its permissions. It won't work—the filesystem these files live on is NTFS, which doesn't support UNIX-style permissions.
Next: We can see Windows files in WSL. Can we see WSL files in Windows?
## WSL files from Windows
WSL exposes your files as a network resource in \\wsl$
. (The actual files live somewhere in C:\Windows
, though it's not a good idea to use them directly.)
💡 Try this: Open Windows Explorer. In the location bar, type in \\wsl$\Ubuntu
. This should get you access to the WSL filesystem as a network folder.
In Linux terms: \\wsl$\Ubuntu
is called a UNC path, which is Windows's way of accessing network resources. Think of it like smb://wsl/Ubuntu
.
## Running Windows apps in WSL
You can run Windows *.exe
programs inside WSL. It will simply open them in Windows, just as you would have ran those programs from Windows itself.
💡 Try this: In WSL, type notepad.exe
. In fact, you can even try running cmd.exe
—this should get you a Windows command prompt! To see how this works, try which notepad.exe
, which shows that it's simply running /mnt/c/WINDOWS/system32/notepad.exe
.
user@desktop ~$ notepad.exe
In Linux terms: Linux can run ELF binaries (ie, Linux's native executable format). Once it finds a PE32+ binary (ie, Windows's format), it'll simply tell Windows to open it outside of WSL. Also, Windows's %PATH%
carries over into Bash's $PATH
, making the system .exe
files available anywhere in WSL.
## Running WSL apps in Windows
Linux apps can be ran from Windows using wsl.exe
, the WSL launcher. This starts up the WSL subsystem (if it hasn't been yet) and runs a command from within it.
Try this: Open a command prompt (Win
+R
to run cmd.exe
), then type: wsl ls /
Microsoft Windows [Version 10.0.18985.1]
(c) 2019 Microsoft Corporation. All rights reserved.
C:\>wsl ls /
bin/ dev/ home/ lib/ lost+found/ mnt/ proc/ run/
boot/ etc/ init* lib64/ media/ opt/ root/ sbin/
...
Next: Can we replace conhost?
## Alternatives to _conhost_
You don't need to use conhost.exe to run CLI apps. You can run them in third party terminal emulators. There's wsltty (based on Cygwin's mintty), Terminus (an Electron-basde terminal), Conemu (supports tabs and panes), and a few more.
Any of these apps can run any CLI application. They often usually come with built-in shortcuts for cmd, Powershell, WSL, and possibly a few others.
In Linux terms: Just like XTerm has many alternatives, conhost has its own alternatives as well.
Next: Let's recap what we know so far.
## Recap
Ubuntu is a command-line app. It's installed from the Microsoft Store.
Windows provides
wsl.exe
that launches an installed Linux distribution (Ubuntu in this case). This is a command-line program that brings you to a Bash prompt. There's alsobash.exe
, which does the same thing (it's like an alias for "wsl.exe bash").CLI apps: are ran inside
conhost.exe
, the built-in Windows terminal. There are alternatives to this that developers might like better.Environments:
cmd.exe
,powershell.exe
, andwsl.exe
WSL launcher:
wsl.exe
runs the WSL subsystem and drops you into a Bash prompt. It's just a CLI app.
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