Bash on Ubuntu on Windows

I ran some Linux commands today. I do that a lot, but it’s the first time I’ve run most of them from a command prompt I opened in windows, and had them act on that Windows machine.

This isn’t unheard of, of course. The Cygwin project has provided Win32 builds of Linux tools for years and virtual machines provide another route to these things but they have their problems. Cygwin requires that binaries are recompiled for Windows and while they provide a dll containing much of the standard POSIX API, there’s a substantial amount of friction in getting anything new to work. Sure, that’s been done for you in a lot of cases, but even then, the results aren’t always perfect.

VMs have different problems: you have to allocate memory and disk space in large chunks and then put up with the resource overhead that running a whole OS within an OS creates. After that, you have to access them – typically you’re looking at a new IP address for the VM and ssh, VNC or some kind of proprietary access method specific to the hosting software is necessary to overcome the rigid separation between Windows and the VM. Operating on or moving data from one to the other is hard work.

This is new.

With the first anniversary update (build 1607) of Windows 10 (x64 only), comes Ubuntu, which is not something I’d have put much money on. More specifically, the user space root filesystem (including all the binaries) from Ubuntu 14.04 LTS “Trusty” can be installed inside Windows. It is quite simply a command-line only (no X) Ubuntu installation, bit for bit, with just the Linux kernel and the boot code taken out.

To make it useful, MS (with Canonical’s help) have created a new Windows subsystem that allows the NT kernel to service all the calls that would normally be made to the Linux kernel. And it’s that simple. All the Ubuntu software can behave as it normally does, making the syscalls it normally makes and getting the responses it expects to get, so nothing needs to be recompiled even though there is no Linux kernel running.

You get apt, so you can install stuff from the Ubuntu software repository, anything you like. Software (including servers) get access to Windows’ own ports and the Windows file system. You can write C in Visual Studio Code and compile it with the Ubuntu version of gcc. You get bash, but if that’s not your thing, apt-get install zsh or something more esoteric. In short, this is the perfect way to run grep and sed on your windows files.

Now, it’s not all rosy. It is currently a beta release and not everything works as it should yet. There are apparently about 350 syscalls in the API being emulated and not all of them are used, so the devs have implemented a subset based on what they believe to be useful and what has been possible, given the inevitable restrictions. There is no hardware access and no graphical implementation beyond what you get in a normal terminal. Also, the talk back in March was that 16.04 was just around the corner and, now in September, it hasn’t arrived yet.

Furthermore, everything Linuxy is done in the bash shell and you can’t run Win32 exes from there, nor can you run Linux ELFs from a normal Windows command prompt, unless you invoke the bash shell as a wrapper (and if you can pipe output from one to the other, I’ve yet to work out how). For me though, there’s so much you can do that the restrictions don’t feel like restrictions and this is still a pre-release version.

Apart from the technical details, the other aspect of this that intrigued me was the political side. MS and Canonical have never been obvious bedfellows and although the stance MS has taken on Linux and open source in general has significantly mellowed under Satya Nadella (cf Steve Ballmer making SMB changes to deliberately stop Samba working), collaboration like this is still a surprising step. In essence, The Windows Way is being side-lined for a rival. I came to the conclusion that this does make sense for both parties, but it’s really Canonical who are riding the tiger.

From Microsoft’s perspective, they’ve come to realise that Linux isn’t going to go away. Whether antagonism towards it helps or hinders their own cause is an interesting and probably nuanced question but given that people are using it, devs especially, it makes some sense for them to offer tools to those devs inside the Windows marquee that they used to have to go elsewhere for – people using Linux (and at risk of moving to Linux exclusively) now have less of a reason to do so. Is there a downside? Well, yes: devs who haven’t been exposed to Linux previously may feel more comfortable with it when server OS options are being considered. Big deal? Probably not massive.

Canonical’s position is more interesting and it may take a while to see how it’s going to play out. Their stuff is freely available, of course, and MS could have just come and taken it, but they’ve been actively engaged in this project (even showing up on panels at BUILD) and as leaders in a world where MS is frequently seen as the enemy, “selling out” is a charge that might come their way.

What’s the upside? Well, Windows devs have often dabbled in Linux for various reasons – usually server related, but also for tools that work really well at solving problems that have never been fully solved on Windows (or where the tools exist but are less at home). Those devs are now going to be doing that with Ubuntu rather than Fedora or SUSE. So what are they going to pick, familiar as they will be with Ubuntu, when they need a server for something (or even choose to use a Linux desktop)? It’s not rocket science to see this as a really, really effective advertising campaign. But what are they actually helping Microsoft do?

In the past, MS was known for its strategy of taking things like “standards” and building on them, bending them to their own way of doing things and forcing the de facto standard that resulted onto everyone else, regardless of whether it benefited the rest of the world or not. They can’t alter the Ubuntu code directly (although they could start offering pull requests for modifications), especially since Ubuntu aren’t themselves responsible for most of the most commonly used utilities.

What they could do, ultimately, is threaten a different freedom: the freedom from Windows in the server market. This "freedom" is forced (welcome or not) on projects who choose (or need) Linux tools. Soon, perhaps, there will be a server OS that can run software from both camps and at that point, it’s Linux that is being side-lined as Windows is suddenly there, wrapped around it, begging to be given some jobs to do.

So the balancing act is this: Canonical are stealing a march on their competitors and more selflessly, pushing Linux into the Windows world in an astoundingly direct way, but are they also greasing the way for Windows in spaces which would have been solely Linux enclaves previously?