Launch Windows programs from "Bash on Ubuntu on Windows" (WSL)

main features:

• Win32 command line tools in the console, invoked from WSL
• Win32 command line tools with redirections to WSL (stdin/stdout/stderr to or from pipe/file)
• suspend/resume propagation (Ctrl-Z suspends the Win32 processes, fg resumes them)
• exit codes propagation
• launch "detached" GUI Windows programs (uses start of cmd)

Using cbwin breaks the WSL security model (access control within WSL using Linux accounts): Windows programs are not subject to extra WSL security checks, so the capability to run a Windows program is equivalent to being root in WSL. If you are only using separation between the WSL root and user to avoid casual mistakes and not for strong security purposes this is not an issue. (Note that being root under WSL does not give you any Windows administrator rights.)

WSL is currently vulnerable to a form of UAC bypass when running elevated WSL processes, see this issue. Elevated instances of outbash.exe do not allow non-elevated callers to launch processes, but it is easy for non-elevated WSL processes to force elevated ones (present and future) to do anything, including accessing protected Windows files and talking with outbash.exe. Therefore, I do not recommend launching an elevated "Bash On Windows" (with or without outbash.exe) in an hostile environment, in order not to reduce the effectiveness of UAC.

Note that outbash.exe listens on 127.0.0.1, but validates that processes that establish a connection are running as the same user as outbash.exe (this check is implemented starting with version v0.7). Therefore, it can be used on multi-user computers.

Binary releases:

1. In the unpacked binary archive, launch outbash.exe
2. Do: sudo ./install.sh
3. In Windows, copy outbash.exe where you want, usually somewhere in your %PATH%
4. In WSL sessions launched by outbash.exe, you can now call Windows programs with the wrun, wcmd, and wstart commands.

Or from source:

1. Build outbash.exe with Visual C++ 2015 and use it instead of bash.exe
2. In caller/, build wrun, wcmd, and wstart (with ./build.sh)
3. Install wrun, wcmd, and wstart in /usr/local/bin (with sudo ./install.sh)
4. In WSL sessions launched by outbash.exe, you can now call Windows programs with the wrun, wcmd, and wstart commands.

wcmd launches a command with cmd. wrun launches the command line directly with CreateProcess, without using cmd. wstart launches a detached command (with start of cmd).

Windows processes and their children launched with wcmd or wrun are handled in a Windows Job, and suspending the WSL caller process (wcmd or wrun) results in the suspension of all the Windows processes in the corresponding Job. Also, when the launched process terminates, all its direct and indirect children are killed. This means that trying to manually do e.g. wcmd start notepad won't yield useful results, because notepad will be killed just after having been launched -- wstart must be used in this case.

If in doubt use wcmd to launch Win32 command line tools, and wstart to launch graphical applications.

xilun@WINWIN:/mnt/c/Users$ uname -a
Linux WINWIN 3.4.0+ #1 PREEMPT Thu Aug 1 17:06:05 CST 2013 x86_64 x86_64 x86_64 GNU/Linux
xilun@WINWIN:/mnt/c/Users$ wcmd dir
 Le volume dans le lecteur C n’a pas de nom.
 Le numéro de série du volume est CZTX-666H

 Répertoire de c:\Users

22/04/2016  20:00    <DIR>          .
22/04/2016  20:00    <DIR>          ..
22/04/2016  20:20    <DIR>          Default.migrated
22/04/2016  20:00    <DIR>          Public
27/04/2016  01:15    <DIR>          xilun
               0 fichier(s)                0 octets
               5 Rép(s)  43 126 734 848 octets libres
xilun@WINWIN:/mnt/c/Users$ wstart notepad
xilun@WINWIN:/mnt/c/Users$ 

You can redirect input and output (avoid doing that with wstart, it would behave weirdly):

xilun@WINWIN:/mnt/c/Users$ wcmd dir | grep xilun
15/05/2016  05:09    <DIR>          xilun
xilun@WINWIN:/mnt/c/Users$ wcmd dir > xilun/foobar
xilun@WINWIN:/mnt/c/Users$ wc xilun/foobar
 12  50 457 xilun/foobar
xilun@WINWIN:/mnt/c/Users$ echo dir | wrun cmd | grep 'c:\\Users'
c:\Users>dir
 Répertoire de c:\Users
c:\Users>
xilun@WINWIN:/mnt/c/Users$ 

The environment block for launched processes is the one outbash.exe was started with, but it can be modified for individual commands. The --env option allows to set environment variables for the command. Parameters after this option are interpreted as environment variable definitions until one starts with "--" or a parameter does not contain an "=" character. An empty value erases the variable. Remaining command line arguments are used to compose the Windows command line. All the options interpreted by the launcher must be given at the start, before the Windows command line.

xilun@WINWIN:/mnt/c/Users$ wcmd --env TITI=TOTO TATA=TUTU set
[...]
SystemRoot=C:\WINDOWS
TATA=TUTU
TEMP=C:\Users\xilun\AppData\Local\Temp
TITI=TOTO
TMP=C:\Users\xilun\AppData\Local\Temp
[...]
xilun@WINWIN:/mnt/c/Users$ wcmd --env TEMP= set
[...]
SystemRoot=C:\WINDOWS
TMP=C:\Users\xilun\AppData\Local\Temp
[...]

Other example to launch msbuild to rebuild outbash.exe, which shows that return codes are propagated (running from another copy of outbash.exe, its impossible to overwrite it when in use):

xilun@WINWIN:/mnt/c/Users/xilun/Documents/Projects/cbwin/vs$ wcmd '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64 && msbuild /t:Rebuild /p:Configuration=Release /m cbwin.sln'
Microsoft (R) Build Engine, version 14.0.25123.0
Copyright (C) Microsoft Corporation. Tous droits réservés.

La génération a démarré 30/04/2016 15:46:15.

[...]

    La génération a réussi.
    0 Avertissement(s)
    0 Erreur(s)

Temps écoulé 00:00:04.61
xilun@WINWIN:/mnt/c/Users/xilun/Documents/Projects/cbwin/vs$ echo $?
0
xilun@WINWIN:/mnt/c/Users/xilun/Documents/Projects/cbwin/vs$ wcmd '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64 && msbuild /t:Rebuild /p:Configuration=Release /m does_not_exist.sln'
Microsoft (R) Build Engine, version 14.0.25123.0
Copyright (C) Microsoft Corporation. Tous droits réservés.

MSBUILD : error MSB1009: Le fichier projet n'existe pas.
Commutateur : does_not_exist.sln
xilun@WINWIN:/mnt/c/Users/xilun/Documents/Projects/cbwin/vs$ echo $?
1
xilun@WINWIN:/mnt/c/Users/xilun/Documents/Projects/cbwin/vs$ 

For now running interactive Win32 console tools in the same console as a WSL bash session (for example: wrun cmd or wcmd python) does not work well. The main problems seem to be related to the console switching internal modes (charset, but not only) between the Win32 and the WSL world. I don't know yet if something nice enough to use in that regard can be achieved without some changes from MS about how their stuff works. (This might be somehow related to WSL not working well, for now, with ConEmu or Bitvise SSH Server - but I'm not really sure about that)

It is an unfinished work in progress. There are various stuff not-implemented and maybe tons of bugs.