[electroly]

Technically correct by some estimation, perhaps, but Cygwin is a crazy approach, was slow (contrary to the implication of the "low cruft" claim), was not as compatible as these other approaches, required recompilation, and was widely disliked at most points in its life. There's a lot of crazy voodoo stuff happening in cygwin1.dll to make this work; it totally qualifies as "hacking in some foreign Linux plumbing", it's just happening inside your process. Just picture how fork() is implemented inside cygwin1.dll without any system support.

Cygwin doesn't work at all in Windows AppContainer package isolation; too many voodoo hacks. MSYS2 uses it to this day, and as a result you can't run any MSYS2 binaries in an AppContainer. Had to take a completely different route for Claude Code sandboxing because of this: Claude Code wants Git for Windows, and Git for Windows distributes MSYS2-built binaries of bash.exe and friends. Truly native Windows builds don't do all the unusual compatibility hacks that cygwin1.dll requires; I found non-MSYS2-built binaries of the same programs all ran fine in AppContainer.

[skissane]

> but Cygwin is a crazy approach, was slow

A lot of this is issues Microsoft could fix if they were sufficiently motivated

e.g. Windows lacks a fork() API so cygwin has to emulate it with all these hacks

Well, technically the NT API does have the equivalent of fork, but the Win32 layer (CSRSS.EXE) gets fatally confused by it. Which again is something Microsoft could potentially fix, but I don’t believe it has ever been a priority for them

Similarly, Windows lacks exec(), as in replace the current process with new executable. Windows only supports creating a brand new process, which means a brand new PID. So Cygwin hacks it by keeping its own PID numbers; exec() changes your Windows PID but not your Cygwin PID. Again, something Microsoft arguably could fix if they were motivated

[electroly]

> A lot of this is issues Microsoft could fix if they were sufficiently motivated...

They did fix it, in a sense, with WSL1 picoprocesses. Faster and more compatible than Cygwin. Real fork and exec on the Windows NT kernel. Sadly, WSL2 is even faster and more compatible while being much less interesting. WSL1 was pretty neat, at least, and is still available.

In any event, this diversion doesn't change my analysis of Cygwin. Cygwin still sucks regardless of whose fault it is. I intentionally left this stuff out of my post because I thought it was obvious that Cygwin is working around Windows limitations to hack in POSIX semantics; it's the whole point of the project. None of us can change Windows or Cygwin and they're both ossified from age and lack of attention. We have to live with the options we've actually got.

If you need a Windows build of a Linux tool in 2026 and can't use WSL, try just building it natively (UCRT64, CLANG64, MSVC, your choice) without a compatibility layer. Lots of tools from the Linux ecosystem actually have Windows source compatibility today. Things were different in the 90s when Cygwin was created.