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DOS Subsystem for Linux (github.com/charliesome)
328 points by geocar on Sept 22, 2020 | hide | past | favorite | 180 comments

Since it's not entirely clear: this works by loading a Linux kernel into unused memory, saving the current state of DOS, turning over control of the computer to Linux, then having the init process start a new that uses the vm86 system call to resume execution of DOS.

That is actually not far from how the kernel of the Win9x series (and also Win3.x on a 386) is structured --- a "hypervisor"-like kernel runs DOS and Win32 applications in "virtual machines" using the V86 mode of the processor. In Win386/9x, that kernel is known as VMM32. In this case, it's the Linux kernel. It's very interesting to see these "chimeric" OSs appear.

Here's a bit more detail from The Old New Thing blog about Windows 3.11: https://devblogs.microsoft.com/oldnewthing/20100517-00/?p=14...

It includes:

> As you might suspect from its name, the virtual machine manager created virtual machines. Inside the first virtual machine ran a copy of Standard mode Windows. ... The other virtual machines each ran a copy of MS-DOS and were responsible for your MS-DOS sessions. ... It’s kind of stunning to realize that Enhanced mode Windows was really a completely new operating system with multiple virtual machines, pre-emptively multi-tasked with virtual memory.

I think it's quite interesting that, on that version of Windows, all the Windows programs were only cooperatively multitasked while all the DOS programs were pre-emptively multitasked.

By the way, I get the impression that Windows 95 onwards worked a bit differently, with Windows itself more tightly integrated in managing virtual machines rather than running in one itself (more like a type 2 hypervisor). For example, this post seems to suggest that: https://devblogs.microsoft.com/oldnewthing/20071224-00/?p=24...

If I recall correctly, there was at one time a Linux boot loader that ran from DOS, which could make use of DOS device drivers. I recall using Yggdrasil Linux which had an option to boot this way, which used the DOS driver for my SCSI card and CDROM drive to make it available under Linux.

That was LOADLIN. When coupled with a Linux filesystem called umsdos, it allowed you to boot Linux without repartitioning your disk or clobbering your MBR. Fun times.

Umsdos overlaid a POSIX file system on top of an MS-DOS file system, using a scheme somewhat similar to Windows long filenames (but created before that became a feature of Windows). Basically, every directory would have a magic file called --LINUX-.--- that contained POSIX file data, including full filenames and permissions.

Brings back old memories. My first Linux experience was with PhatLinux and WinLinux2000. We only had one family computer and I didn't want to risk nuking the disk, which I now know would have inevitably happened.

Still is: http://distro.ibiblio.org/baslinux/

I'm using it currently on a 386SX with 8MB of RAM (not to post this, however).

Edit: Ah, this doesn't do the driver bit. But it works pretty well in itself.

Well, if you were connected by ssh or even telnet to some pubnix, you could post there through lynx :D

I used to use that when I had a sound card that was not supported in Linux. I would load the drivers from DOS which provided Sound Blaster compatibility, then boot Linux from there.

Netware servers used to use DOS as a bootloader too.

There are a ton of comments here that seem to be misunderstanding what this software is. This creates a WSL-like environment on a DOS host system. It does not create a DOS environment on a Linux host. I'm not sure where this misunderstanding even comes from; the name is perfectly analogous to WSL.

I would imagine it's because WSL is a terribly confusing name itself for a lot of people.

There are two ways to read "Windows Subsystem for Linux":

1. This is a subsystem that runs on Windows that enables Linux binaries.

2. This is a subsystem that runs on Linux that enables Windows binaries.

The confusion comes in the fact that when I write those two sentences, I naturally want to write "This is a subsystem FOR Windows..." or "This is a subsystem FOR Linux... ." I had to consciously avoid using "for" in that sentence to highlight the problem.

So when someone who doesn't know what the thing does reads "Windows Subsystem for Linux" they may walk away with the false impression that the subsystem allows Windows binaries to run on Linux. Likewise, what you're seeing now is that people are seeing "DOS Subsystem for Linux" and thinking that this enables you run DOS on Linux.

The WSL terminology really only makes sense if you are aware that Windows has the concept of subsystems - and which is why swapping other labels makes even less sense. I.e. the run-Windows-on-Linux thing would probably not be called Linux Subsystem for Windows, because what is a "Linux Subsystem"?

And of course WSL2 isn't a subsystem anymore, but is stuck with the product name. ¯\_(ツ)_/¯

A "Linux subsystem" is a Linux system that is a part of a bigger system. And "Linux audio subsystem" is an audio system that is a part of Linux. And if you swap the words, you get "audio Linux subsystem" which doesn't make sense, not really.

So the proper name would be "Windows Linux subsystem", but I concede that it does sound really weird (because both Windows and Linux are the same kind of things, they're OSes).

And of course, if it was named "Windows's Subsystem for Linux", there would be much less confusion, but apparently the English for some reason doesn't use the possessive case here (although that's the perfect place for it) and prefer to use the noun as a possessive adjective.

This is helpful, but the composition rules are weird and confusing.

It's true that a Linux Subsystem is a subsystem of Linux, but an "X for Linux" is a component of Linux or an application for Linux.

When you put them together, it seems that the "for" wins the battle. In parsing terminology, it has lower precedence (though I'm sure the actual rules of English are more complex than that indicates).

I'd love to see an actual linguist comment on why this phrase is so confusing.

I have an English degree and can confidently say the issue is the implicit understood possessive in the correct parsing. As it stands, “for” dominates mentally because the phrase obviously needs a possessive to make sense and “for” denotes possession. If it were “Window’s Subsystem for Linux” or “DOS’s Subsystem for Linux”, explicating the proper possession, the parsing trouble would disappear.

So would just saying Linux subsystem for windows.

Which was raised when this name came up but they didn't like that Linux came first so went with gymnastic language instead.

Its even more obvious with this new name.

Its a Linux subsystem for DOS.

You could use the possessive form here: "Windows' Subsystem for Linux", but that's not a thing product managers like to use in naming...

It probably had an internal name like "winix" or "lindows" - but PM took the reins and came up with a much worse name, as is tradition.

Oh yes. My favourite example is [0] (and the parent twit).

[0] https://twitter.com/ericlippert/status/1205372172534874112

Oh, true, Linux actually uses the term in that context, somehow didn't think of that.

> And of course WSL2 isn't a subsystem anymore, but is stuck with the product name

Even WSL1 is not a classic Windows NT subsystem. Its implementation (picoprocesses) is quite different from that of the classic Windows NT subsystems (Win32, OS/2, POSIX/Interix/SFU/SUA). The classic Windows NT subsystems all involve using ntdll.dll to make NT syscalls; WSL1 processes make Linux syscalls and can't actually make NT syscalls or call ntdll. There is nothing technically stopping an OS/2 1.x executable from realising that it is running on NT and start talking to the NT kernel using the normal NT API; by contrast, a Linux executable running under WSL1, even if it detects it is running under WSL1, isn't allowed to talk to the normal NT kernel interfaces.

Aren’t you describing personalities instead of subsystems?

Windows NT user mode code is divided into programs and subsystems.[1][2] Programs are the actual applications/utilities/etc you run. Subsystems are OS components executing in user mode, generally composed of DLLs and server EXEs which expose LPC services (a little bit like Unix daemons).

There are two types of subsystems – environment subsystems (which provide APIs to programs) and integral subsystems which provide services to the environment subsystems. Integral subsystems include the security subsystem (lsass.exe). (Sources are a bit unclear about whether there is one "integral subsystem" composed of multiple parts, or multiple integral subsystems – e.g. are lsass.exe and smss.exe separate integral subsystems, or two subsystems of the integral subsystem???)

There are three environment subsystems in Windows NT – Win32, POSIX and OS/2, although the latter two have been discontinued in newer versions. The design was always open to adding more (e.g. maybe an OpenVMS subsystem) but that never happened in practice. (Win32, despite its name, doesn't just run Win32, it also runs Win16 and DOS; also, in practice the POSIX and OS/2 subsystems were dependent on the Win32 subsystem and borrowed functionality from it, despite in theory being independent of it. csrss.exe, despite having "subsystem" in its name, is not a separate subsystem, but rather the primary LPC server for the Win32 environment subsystem.)

The term "personality" is sometimes used to describe the environment subsystems, but it is not the term the Windows NT developers used. The term "personality" actually comes from Mach. The idea with Mach was that existing operating systems could be ported to run on top of the Mach microkernel through layers called "personalities" which would map the existing OS API to the underlying Mach API. The original CMU Mach team built such a layer for BSD Unix – the BSD personality – and it actually survives in XNU (macOS/iOS/etc), but they never implemented any other personalities. However, IBM's abortive Workplace OS project actually did implement an OS/2 personality for Mach, which could run alongside an AIX personality, so they actually got closer to delivering on CMU's original vision (albeit the whole project was cancelled before being fully released.) Possibly, NT's environment subsystem idea took some influence from the Mach personality concept; plus, outside observers quickly noticed the similarity between NT environment subsystems and Mach personalities, and started using the term "personality" for the former; but it has never been the officially preferred terminology for Windows.

I've never heard anyone call WSL1 an "environment subsystem". Its method of implementation is very different from the classic NT environment subsystems. You might call WSL1 or WSL2 "personalities", but as I said that's never been official Windows terminology.

[1] https://en.wikipedia.org/wiki/Architecture_of_Windows_NT

[2] http://vig.pearsoned.com/samplechapter/0201791064.pdf

I was under the impression that the name arose out of trademark requirements.


Windows has had subsystems since the OS/2 era, and WSL1 was actually such a subsystem. Initrix was the Microsoft POSIX Subsystem.

There was a POSIX subsystem in Windows NT before Microsoft acquired Interix (which became Windows Services for Unix).

Yes, but the name "Linux Subsystem for Windows" would have been much less confusing.

WSL1 isn't actually an NT subsystem like Interix was.

Could they have just called it the Windows Linux Subsystem?

I assumed it was marketing. They didn't want to put the other guy's name first.

And if you think "Windows Subsystem for Linux" is bad, the subsystem that enables the Win32 API is csrss or "Client/Server Runtime Subsystem" and it makes you think: why does that subsystem not mention Windows but the Linux one does?

I have to assume the answer to that question is marketing. They really want to hammer into you that you're running Linux on Windows.

Agreed. "Linux on Windows" is more clear to me.

The "on Windows" part makes it clear that Windows is the host OS.

Many Microsoft's past products used "for $PLATFORM" in the product name. For example:

Microsoft Word for Windows

Microsoft Word for DOS

Microsoft Word for Mac

It makes it clear that it was the version of the product FOR a given platform.

At first glance "Windows Subsystem for Linux" seems like Microsoft's version of WINE.

Maybe we'll get a real "Windows Subsystem for Linux" when the desktop version of Microsoft Linux arrives.

Better choice would have been "Subsystem for Linux on Windows". Its all indeed a big naming confusion

It still doesn't even make sense when you know about Windows subsystems though. True, it is a "Windows subsystem" in Windows terminology, but from my native-English speaker point of view, it's not "for" Linux in the way that the word "for" is used in standard English.

It does work if you assume it's a shortening of something like "Windows Subsystem for Running Linux Applications (on Windows)"

But I get that naming it is a tricky problem, because even a technically accurate name like "Windows Linux Subsystem" (after the old 'Microsoft POSIX Subsystem' name) is still confusing.

It doesn't matter at all if you write 'for', as the possession is totally unclear.

"Windows Subsystem for Linux"


Is the 'windows subsystem' for linux?

or is the 'subsystem for linux' a windows branded feature?

If you asked most people they would probably choose incorrectly.

As bad as the original name was, "Bash on Ubuntu on Windows", I think it was still better than WSL.

It's worse because it can run other distros and shells. hell.

It's really confusing. Windows Linux Subsystem would be more clear. Windows Subsystem for Linux always hinted me to a Vine competitor. Then I know what it is so I read this DOS Subsystem for Linux in the right way (and right to left!)

Also, why linux? Linux is the kernel, which is not what is being run, more like everything on a gnu/linux system apart from linux.

As I pointed out when WSL came out, the name always includes the thing that is being replaced by the Windows NT kernel: be that OS/2 or Linux.

* https://news.ycombinator.com/item?id=11417059

* https://news.ycombinator.com/item?id=18948258

WSL1 emulated Linux kernel syscalls. GNU was run on top of it unmodified, but could be used without GNU. on WSL2 the actual kernel is what is being run, in a thin VM wrapped by lots of wrappers to provide a native-like experience.

Why not use "in"/"on"?

Linux Subsystem on Windows

Linux Subsystem in Windows

I expect Microsoft doesn't want to have "Linux" come first in the name from a branding perspective.

I saw a discussion that it was mostly concerns about the Linux trademark when WSL1 didn't actually use a Linux Kernel with the leading part of the name/term.

Yep - the sentence "X subsystem for Y" reads to me like you're adding an X thing to your Y - i.e. you're adding some Windows thing to your Linux, but what Microsoft means by it is the other way around.

Windows (Subsystem for Linux)

- vs -

Windows Subsystem (for Linux)

((Windows Subsystem) for Linux)

is probably closest to WSL1’s intent.

It was a Windows subsystem (the first new one in years), and its goal was to let you run Linux apps.

"Windows Linux-ABI Subsystem" would have been crystal-clear.

Microsoft has a tradition with these confusing backwards names.

They used to have a product called Windows Services for UNIX [1] which was, you guessed it, UNIX Services for Windows: NFS, Telnet, cron, rsh, etc.

[1] https://en.wikipedia.org/wiki/Windows_Services_for_UNIX

My understanding, especially with WSL1, was that there was a concern about the Linux trademark if MS used the name "Linux Subsystem for Windows" which would have been a better name, since WSL1 didn't actually use a Linux kernel. WSL2 does though.

"Windows' Linux Subsystem" might have been better as well (WLS), using it as a posessive statement, or "Windows' Subsystem of/with Linux" which would keep the same WSL abbreviation.

Perhaps the confused commenters should read the post before commenting. Crazy as that sounds.

It makes sense as "A windows subsystem for Linux". Unfortunately, dropping the "A" makes it ambigious.

They're both phrased unnaturally, IMO.

The suffix "for Linux" strongly implies it's software for use on Linux. It's like the "4j" and "4win" suffixes, implying software built for the Java and Windows environments, respectively.

What's more, Windows or DOS as an adjective of subsystem bind more tightly than "for Linux". So if you were to start dropping parts of the name, you'd drop "for Linux" first. Except you can't, because then it's just the Windows Subsystem.

LSW would have been a much more natural name. In a conversation about Windows subsystems, you could refer to it as the Linux Subsystem. If other operating systems picked up on the idea, they would have their own Linux subsystems, e.g. Linux Subsystem for macOS. If you wanted to check if your OS had anything like it, you could search "is there a Linux subsystem for FreeBSD?" Which might turn up results about the Linux ABI in FreeBSD. Speaking of which, imagine if it had been named the FreeBSD ABI for Linux. What an awful pattern! You can't even repeat the pattern unless both modifiers are proper nouns! Could you have called the VFS Subsystem the "FreeBSD Subsystem for VFS"?

They're both phrased unnaturally, IMO.

This is why we teach sentence diagramming in elementary school.

Maybe the person who came up with "WSL" wasn't a native English-speaker?

Something that should come up early in sentence diagramming but often isn't explained well enough is that sentence diagrams aren't context free, often can be ambiguous, and depend on the context of the speaker to determine referents. Sentence diagrams in the real world are rarely as easy as elementary school examples.

In this case, the context known to the speaker but often missed when trying to "sentence diagram" WSL involves the part "Windows Subsystem". That referent, to which the original author was quite familiar, is invoked in WSL as a single noun in part of the larger noun phrase, and while you could continue to sentence diagram break "Windows Subsystem" into constituent parts here, it is important to remember it as a single connected "atom" to which "for Linux" modifies in the overall noun phrase of "(Windows Subsystem) for Linux". Given that context/referent, the sentence diagram here is unambiguous to the original team/"speaker". It's the audience with much less familiarity with the referent/context in question that has ambiguity problems in trying to "sentence diagram" the noun phrase.

It follows the same naming convention as SFU (Windows Subsystem for Unix) [1] which was equally confusing.

My belief (!!), back then, was that it was intentionally named confusing. Back when it came around, Microsoft was under scrutiny for monopoly behavior. They didn't want Windows to be compatible with Unix in any way; they wanted the world to run Windows (9x, NT) only. That was my belief/theory, as it is now I don't have anything to back it up as it is though. Your theory might equally be viable.

[1] https://en.wikipedia.org/wiki/Windows_Services_for_UNIX

It's Microsoft. They came up with Xbox, Xbox 360, Xbox One, Xbox One X, and now Xbox Series X. WSL is a drop in the bucket of stupid naming schemes.

I expect it's branding. I'm having trouble coming up with a name that sounds unambiguous while keeping "Windows" as the first word. And I doubt Microsoft's branding people would be happy if "Linux" appeared in the title before "Windows".

It's amusing to imagine a stodgy company like Microsoft naming it something indie like "tux4win".

They completely missed the opportunity to call it LinuxFTW

And then one learns Shakespeare in secondary school where all that 'sensible' diagramming and rigidity jumps out of the window.

"<X> <services|subsystem> on <Y>" strikes me as unambiguous.

But it might have the problem of branding the product as a “Linux subsystem” and they want to sell it as a “windows subsystem”, that runs Linux code

The poor naming convention goes back ~20 years or so to (at least) "Windows Services for UNIX" (SFU) [0]. The naming was not intuitive then and it still isn't today.

The "problem" is that these products are not what you automatically assume they are!

To illustrate: SFU provided NFS and NIS servers, a cron daemon, a telnet server, and various CLI "utilities" (i.e., standard "services" provided by "UNIX") running on Windows -- not Windows services that run on UNIX!

Once you know that, the "Windows Services for UNIX" name kinda makes sense and helps to understand what the "Windows Subsystem for Linux" and, now, the "DOS Subsystem for Linux" actually are.


[0]: https://en.wikipedia.org/wiki/Windows_Services_for_UNIX

I know what it means and what way round it is now due to repetition, but WSL struck me as a weird name and confused me at first.

Usually, saying "for Linux" or "for Windows" about something means there's a thing that is for (or "to run on") Linux or Windows, not that the thing is "of" Linux or to enable the use of Linux. I appreciate there are two ways to look at the semantics, but the one they picked for WSL seems the least common one to me.

Grammatically, I read the title and thought "yes! finally a way to run those Dell firmware updaters instead of using FreeDOS boot sticks" and then read the comments to find out it's backwards in nature. The phrase is "bad English" in a colloquial sense.

Next up is Microsoft's browser: Windows Subsystem for HTML

Have you heard of the HTML5 supercomputer? https://twitter.com/Html5Nikola

If it's an HTML5-based device that runs Windows[1] then it's "HTML5 Subsystem for Windows" going by Microsoft's phrase structure.

[1] https://copy.sh/v86/?profile=windows98

Maybe he should be in charge of naming at Microsoft, can't do worse

It's because the WSL name is also confusing.

It’s because the WSL is confusing and doesn’t follow english naming conventions. “X subsystem for y” reads left to right as X is an adjective describing the subsystem, and for seems to indicate y is the platform that X subsystem is for.

Instead it’s seemingly meant to be parsed inside-out with “subsystem for Linux” as one noun indicating a subsystem that runs Linux apps, and DOS as an adjective describing that noun. Maybe wsl did it to keep the windows brand first? Are there many other “windows subsystems for Y” out there and this is a Microsoft-universe term? I don’t know but it’s very strange.

Indeed, this confused me as a Linux user who hasn't used Windows in over a decade (and therefore is unfamiliar with the terminology). Thank you. I was reading this as a potential DOS Box alternative to run on Fedora.

If the project maintainer is reading, it would be super helpful to put that at the top of your REMADME.md. I'll even send you a PR. FTR it's not your fault the terminology is confusing :-)

Why not compare it with Wine instead?

Besides, latest WSL is not like that anymore, it's a hypervisor running a VM now.

It says "DOS subsystem for Linux". The way I'm reading it:

1. It's for Linux (so Linux is the host).

2. It creates some subsystem that runs DOS (either emulated, virtualized or translated like Wine is doing for Windows on Linux).

That can allow running DOS games on Linux for example, instead of using DOSbox for it.

"WSL" is Windows Subsystem for Linux is obviously from the old Services for Unix used to bait-and-switch people to NT, and the grammar in the latter is irrelevant, the meaning of "SFU" is clear.

The misunderstanding comes from choosing a name for it that stongly implies it is not the thing that it is.

Would prefer me some LSD to be honest.

Maybe it's wishful thinking that the embracing and extending can be recursively embraced. :)

i think the confusion comes from the phrase "for those who prefer a DOS environment".

maybe it could be phrased as "for those who want linux but need to run DOS as their main OS"

Yeah, I got that too. It was clear that the name was a parody of WSL.

Wuts WSL?

I've been fielding these questions all day. Saying the same thing. It's for "DOS" so you can run _bash_. Ok? People got all excited for Prince of Persia... smh. +1

Just wondering. Since "Windows subsystem for Linux" is running Linux on Windows, shouldn't it be named "Linux subsystem for DOS"?

No, because this is running Linux on DOS.

Thanks, I thought it is running DOS under Linux before I saw you comments.

It is, actually. It just happens to be the same DOS that was running before Linux was started.

> running DOS under Linux

What about DOSBox?

DOSBox would be the "Linux Subsystem for DOS" using this contorted naming scheme. Aren't we having fun now? :-)

Windows naming is wrong :D

NT != DOS :)

The abbreviation would make sense, if it weren't for workplace restrictions on use of controlled substances.

On a more serious note, the hack described by the author [0] is quite ingenious.

[0] https://news.ycombinator.com/item?id=24556801

EDIT: I stand corrected. A closer look at TFA confirmed that it is indeed DSL. I was confused by the screenshot which at first glance just shows DOS running in QEMU on Linux. But it goes deeper!

Yes, that is correct. Windows Subsystem for Linux means it's one of Windows' subsystems which provides linux.

This should be called Linux Subsystem for DOS.

This is a thing you execute under DOS to run linux commands. it provides Linux. (or at least pretends to do it that way around)

Misunderstandings aside (I am fully up to speed on that), why do this and WSL each use "for" to mean "provides"? In most software contexts, the noun after the word "for" is the thing you already had, like "Word for Windows" et al.

I assume this uses it purely to make fun of Windows.

Windows has the concept of subsystems - technically the Win32 API is also just a subsystem around the NT kernel that provides the "Windows API". Windows NT also had one providing an OS/2 API, and one providing POSIX API - the latter later evolved into/was replaced by "Windows Services for UNIX" - assume there and with WSL the intent is to read it as "for Linux/UNIX applications".

But why specifically this confusion phrasing is unclear, maybe they wanted to keep the "Windows" brand attached to the thing - i.e. treat "Windows Subsystem" and "Windows Services" as one term?

Windows subsystem for Linux is a thing you execute under Windows to run linux commands. It provides Linux.

So what's different?

This one runs on DOS.

Right, but I mean naming wise, shouldn't it indeed be DOS Subsystem for Linux?

E: Ah I see, I misinterpreted the comment chain depth. Thanks all.

Yes, it should be DOS Subsystem for Linux. It also is DOS Subsystem for Linux.

right, and the comment I replied to said it should be the other way around, so I pointed out (what I assumed to be) their point of misunderstanding.

This used to be the best way to try Linux before live CDs became a thing. The first Linux distro I ever used (DragonLinux) was 'installed' by unzipping an 8mb zip file and running a BAT file. You could 'uninstall' it by deleting the directory it created next time you booted into DOS.

Slackware had "ZipSlack" which would fit on a 100Mb Zip disk, or could be installed (read: copied) into a DOS directory and run from there: https://en.wikipedia.org/wiki/ZipSlack

So does this run DOS on Windows? Or DOS on Linux? Or Linux on DOS? Or DOS on Linux on Windows? Would be nice if there were an explanation in the README.

This runs Linux "inside" of DOS, allowing you to exec Linux i686 binaries "inside" of a DOS terminal

I put inside in quotes because how this actually works is quite amusing (and apparently is actually how Windows 95 also works)

Is this explained somewhere? I'd love to read how it works (without trying to understand the source code).

Author here. I am planning to do an in depth write up of how this works, but it seems Hacker News found it sooner :)

When DSL is first invoked at the command line it boots up the Linux kernel which takes over control of the computer from DOS.

Now here’s the trick: DSL makes use of a processor feature called VM8086 which allows for a 32 bit operating system to run legacy 16 bit code mostly natively. This feature is how early Windows, DOS extenders, etc worked. The Linux kernel also supports VM86, although it is largely undocumented and not really used these days. I think dosemu is the only major user of VM86 on Linux.

DSL then returns to DOS, which has essentially been flipped inside out and is now unknowingly running inside a VM8086 task. Helpfully Linux does not appear to clobber DOS’s memory during its own boot process.

DSL does just enough emulation of hardware like the keyboard to make things work, allowing DOS raw hardware access for everything else. This situation of running two operating systems at the same time on the same hardware is extremely fragile and unsafe of course, but it does seem to work surprisingly well anyway!

Wow you weren't kidding about "largely undocumented". https://man7.org/linux/man-pages/man2/vm86.2.html

Would be really cool if someone contributed a proper man page, I bet it would be a fascinating read.

> Helpfully Linux does not appear to clobber DOS’s memory during its own boot process.

Is that just a coincidence or intentional somehow?

I guess DOS can only access the first 1MB (err... plus 65520 HMA bytes?), so if Linux just avoids using that space then DOS can keep running happily... I was curious if there's actually a mechanism to tell Linux to avoid that space.

DOS memory management fascinates me in its absurdity.

With HIMEM.SYS + EMM386.EXE [0][1], you could include or exclude certain memory segments. But, DOS Subsystem for Linux uses non-standard little documented Unreal Mode [2][3] instead of traditional DOS Memory Management.

[0] http://www.mdgx.com/mem6.htm#6

[1] http://manmrk.net/tutorials/DOS/msdos7/emm386.htm

[2] https://en.m.wikipedia.org/wiki/Unreal_mode

[3] https://github.com/charliesome/doslinux/blob/master/doslinux...

Have you tried the approach of booting Linux and then creating a normal fullscreen qemu/KVM-based VM initialized with the memory state of the DOS OS, with a configuration so that the transition works correctly?

That would make the whole system fully robust and safe, and also support running XMS/EMS managers, DOS extenders, Windows and other bootloaders from the DOS VM.

I'm not sure however whether you would need to modify qemu to make it work and how hard that would be (also I guess that would have less hacky fun factor).

After not finding much of a README (yet), I poked around the source code a few minutes ago. Thanks for my actually confirming my initial "...he can't be doing it that way, surely..." :)

This is nice. It reminds me of the IPL sequence of some mainframe OS I sadly can't remember right now (might be System/i?) where the bootloader that launched the kernel was a first-class OS process that went from running the entire system to being promoted to an OS task as the kernel started up. Except in this case you're promoting the entire OS to a kernel task, while the promoted OS continues to run :D

I wonder if you could extend this to turn Linux into a replacement for HIMEM.SYS, to "properly" support the fact that HIMEM has to be disabled. :D

(Immediately after reading that I thought "wait; the two OSes are running independently, of course that won't work..." but then I realized, no, HIMEM works by trapping interrupts... so this is not only possible, but vm86 of course works by handing you interrupts to deal with.)

The extremely-confusing-but-still-positive benefit of this would be to allow you to elevate DOS to have demand-paged virtual memory, complete with swapfile.

It might be interesting to identify the oldest kernel version(s) you're prepared to put up with, to realize the smallest _in-memory_ kernel size possible, and _possibly_ enable running multi-MB applications on real systems with only 640KB of RAM (with the proviso that using an SSD via a SATA-IDE adapter would give the best results - and the rationale that both of those items will soon be cheaper than old DIMMs). The issue suggesting 2.4 is maybe a bit of a stretch, but the early 2.6 trees might be interesting.

Implementing my own extended memory support in the supervisor is indeed an interesting idea, I might try it out :)

Another idea I had after reading the dosemu source is implementing a DPMI server to allow protected mode DOS apps to run. It might even be possible to run an early version of Windows this way too.

Thanks for the explanations. Very interesting. Please add it to the README.md or the GitHub Wiki if you want to go into much more detail. Thanks!

Very cool! Can it use multiple processors under Linux or is it limited to 1 CPU because of some tricks for the DOS compatibility?

It would be cool to do the same using KVM. You can use a magic I/O port instead of an interrupt as the upcall mechanism, on the other hand trapping interrupts has to be done from the DOS side...

I look forward to your writeup, but in the meantime, thank you for your comment explaining how this works. Excellent hack!

That's hilarious. Nice hack!

From a quick skim through the code:

- it first, if not yet present, starts Linux, via normal Linux kernel load. It passes over some pointers from DOS into /init arguments so that /init can know about DOS' context when Linux was first loaded

- Linux's /init then uses VM86 [1] to call back into DOS, back to the function that was run in DOS before Linux was loaded (vm86_return). This is a bit of a 'draw the rest of the fucking owl' deal, as it has to actually emulate a lot of DOS/PC behaviour (emulate INB/OUTB, etc). It's basically a small VM, like with KVM, but for 16-bit DOS.

- when DOS wants to run a Linux command, it now uses a special new interrupt (DOSLINUX_INT) to call into the kernel. This in turn triggers a VM86 exit, jumps into the VM86 monitor in /init, executes the command, and pokes the result back into DOS, resuming VM86 emulation.

[1] - https://en.wikipedia.org/wiki/Virtual_8086_mode

Please elaborate on the owl reference!

The GIF's prety much crystal clear: it runs QEMU on Linux. And QEMU runs whatever you want, because it's a machine emulator/virtualiser, in this case it's running as x86 with MS DOS on top.

No.... QEMU is being used to run DOS, since a) who runs DOS on metal these days, and b) how would you record the screen if you were running DOS on metal (I suppose you could use a capture card). Linux is running in a WSL-like environment on the DOS host.

>who runs DOS on metal these days

freedos developers?

people updating HP bios from bootable media

people using intels ssd firmware update tool

No, qemu is only there to boot DOS. DOS then runs Linux commands via `dsl` (DOS Subsystem for Linux).

You could perhaps argue "inception" since it's Linux running a DOS VM running Linux commands. But the charitable explanation is the author just wanted a convenient environment to do DOS development rather than bare metal (think of it like a Vagrant box).

No, the interesting part is what's happening in DOS. QEMU was probably just used for screenshots and not going through the pain of installing DOS on a new machine.

This entire discussion is strong evidence that the GIF is not crystal clear at all. (-:

“Your scientists were so preoccupied with whether or not they could, they never stopped to ask if they should.”

-Dr. Ian Malcolm

I guess someone had to ask this...

Does it run under WSL?

Well, no... WSL runs Linux inside Windows. DSL runs Linux inside DOS. So there's no stacking that makes sense here.

(I think we're seeing just how confusing the "Subsystem for Linux" naming is. "Foo Subsystem for Linux" sounds like a way to run Foo under Linux, but it's the opposite...)

> I think we're seeing just how confusing the "Subsystem for Linux" naming is.


> a way to run Foo under Linux

"Under" is also confusing since "run X under Y" means the same as "run X on Y" even though it's the opposite analogy.

I suggest everyone stick to "X on Y", e.g. Linux on DOS.

Windows -> Dosbox -> DSL -> Wine?

We have to go deeper.

There was a video where someone was running a firefox browser inside another browser using wasm. It was presented as a wacky "future history" talk... I can't find it in my watch history

So this is basically the equivalent of a non-dedicated Netware 2.x server, then?

Netware 2 was an 80286 OS. (DOS was an 8086 OS.) https://en.wikipedia.org/wiki/NetWare#NetWare_286_2.x

Normally, Netware took over the whole PC, but if you ran it non-dedicated, it loaded in memory above 1MB (which DOS couldn't use anyway) and then let DOS continue running in a pre-empted box, using the screen and keyboard. So someone could use the console as a DOS PC, while the Netware server ran in the background using the rest of the server's RAM, doing file and print for all the client machines.

It worked really well... the main problem was that the user would often turn off the "PC" when they were done. >_<

More seriously -- this seems to compare well to the old Locus DOS/Merge product: https://en.wikipedia.org/wiki/Merge_(software)

Is there any benefit to DSL [argh, TLA overload, this is not Damn Small Linux] compared to DOSemu?

This remember the days when I started SuSE Linux 5.1 with loadlin

> DOS Subsystem for Linux

> A WSL alternative for users who prefer an MS-DOS environment.

Very confusing description. Is it made for Linux? So what does it have to do with WSL which is made for Windows? May be it's a Wine analog for running DOS programs on Linux then or it's actually emulating things like DosBox does?

A couple comments....this is super interesting to me. It boots into Linux from an HDD image. It also requires and uses Unreal Memory Mode [0][1] (vs. Real Mode or Protected Mode). It makes me wonder how compatible & stable this is with other DOS era software.

[0] https://en.m.wikipedia.org/wiki/Unreal_mode

[1] https://github.com/charliesome/doslinux/blob/master/doslinux...

Note: if you edit the post before the time limit passes you can fix the casing of Dos.

Many years ago we used to run loadlin under dos to load linux and dosemu under linux to run dos. And by many I mean before Windows 95. And ofcourse if you wanted the worst of both worlds there was cygwin.

For those unfamiliar, confused, or otherwise opposed to the naming of the Windows Subsystem for Linux, I would highly suggest reading chapter 2 of Windows Internals: Seventh Edition, which describes how Windows supported POSIX and OS/2 through its "subsystem" model, and how WSL fits into that model and what additional changes were required. The naming of "Windows Subsystem for Linux" makes perfect sense in this Windows OS centric context.

So I would love to know if I could run Win98SE/ME and SSH into the native running Linux with this. Perhaps I'd actually prefer that over running Windows10 with WSL2. One problem would be modern browser support for Win98SE so I would need to use an Windows X client to start the linux based browser.

Come to think of it, perhaps you could run Wine to run dos, filemanager/explorer and control panel to emulate the Windows98SE experience.

It could be useful for DOS users who want to run Nethack 3.6.6 under Linux.

Altough running Nethack under Minix 2 would be easier.

i saw a youtube video the other day entitled "why learn asm in 2020", i guess for doing something like this.

this project looks really cool. i don't hear a whole lot of people using dos nowadays but for a tinkering around that would be awesome.

hats off to the author. it's amazing one dude could code this.

In a way, DOS was a perfect platform to learn tinkering with. .COM files were basically pure machine code, and DOS would execute them directly.

If you take the abbreviation style from Microsoft...

Windows Subsystem for Linux -> WSL

Linux Subsystem for DOS -> LSD

I like it!

Great news! When people complain about my code I can just say I wrote it on LSD.

Except that it's the DOS Sybsystem for Linux, not the other way around

I love this! It exemplifies the absurdity of making Linux a subsystem of Windows (a far less powerful OS) by doing the same thing with DOS!

Dear god I am so confused what this does now.

It seems like cropping the QEMU "chrome" from the screenshot would make it clearer that it's a DOS environment, and that the prefix "dsl" allows you to run Linux commands...

640K is enough memory for anybody, right?

Could you theoretically get forwards compatibility with the NT kernel by running Wine in this?

Apart from the naming issue, wouldn't "DOSBOX on Linux" be more useful?

This isn't "DOS on Linux" but rather "Linux on DOS" (Hence the name, DOS Subsystem for Linux, mirroring Windows Subsystem for Linux), so I don't think it has much to do with dosbox.

If someone has Linux, wouldn't they just run FreeDOS in a VM?

They don't have Linux.

Why would someone choose such a stupid name then? It's "for Linux"... which means you already have Linux, and you want to run DOS in a sub-system (a VM)

Take that, Microsoft! :D

Otherwise known as DSL?

DSL also stands for Damn Small Linux. And Digital Subscriber Line. And a few other things.

One might almost think we need a Domain-Specific Language to distinguish between all these meanings.


Serious question, simply put: why? Was this done for academic reasons, or is there an application for this technology in mind?

Might want to look at mtools.

Does it support running 16-bit real mode DOS binaries a la DOSBox?

You don't need it to run DOS binaries on DOS.

It’s not clear if this is DOS or a DOS shell that actually executes Linux binaries. The description is confusing, hence my question.

It is literally DOS, so it executes real mode binaries natively.

Okay, actually, this is more like VMWare ESX in the 4.0 days. It's kind of, uh, inside out.

Basically it's DOS, which launches Linux via DSL, which then runs a task out of init in vm86 mode that uses KVM to _continue_ the DOS that launched it as if it were the only thing running.

The DOS doesn't know anything has happened, even though the rug has been pulled out from under it, and it is now running in a KVM VM guest. You just can't tell anything is different because all the BIOS/real mode stuff is unchanged.

You get your prompt back when a native Linux binary finishes but it's the linux kernel emulating the DOS session after that first command, until you reboot.

This should come preinstalled on literally any and all Linux flavours. It would remove so many barriers for folks first trying Linux after decades of Windows.

I feel like for most Windows users, using DOS is probably as (or even more) foreign as using Linux. How many times do you think the average Windows user has used a command prompt in the past year?

Counter question: how many times do you think the average Windows user has tried installing Linux? Because it's probably fewer than those who use what they'll invariable call the "dos box" for something, so having something in place to make the transition for those Windows users who DO venture out of their comfort zone to give Linux (yet another?) try easier is great.

This is Linux under DOS and not DOS under Linux.

DOS Subsystem for Linux means exactly that, you are using a DOS subsystem in Linux. That is why it is confusing. If it is a WSL for DOS, that is what it should be called.

> should be called WSL for DOS

Windows subsystem for linux for DOS. Sounds right

Also Dick Sucking Lips

Hey, could you please stop posting unsubstantive comments to HN? It's not what this site is for, so we ban accounts that do it, and eventually the main account as well.


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