How are msys, msys2, and msysgit related to each other?

Git 2.8 (March 2016) includes a very detailed commit which explains the importance of msys2 for the new git-for-windows which replaced msysgit in early 2015.

See commit df5218b (13 Jan 2016) by Johannes Schindelin (dscho).
^{(Merged by Junio C Hamano -- gitster -- in commit 116a866, 29 Jan 2016)}

For a long time, Git for Windows lagged behind Git's 2.x releases because the Git for Windows developers wanted to let that big jump coincide with a well-needed jump away from MSys to MSys2.

To understand why this is such a big issue, it needs to be noted that many parts of Git are not written in portable C, but instead Git relies on a POSIX shell and Perl to be available.

To support the scripts, Git for Windows has to ship a minimal POSIX emulation layer with Bash and Perl thrown in, and when the Git for Windows effort started in August 2007, this developer settled on using MSys, a stripped down version of Cygwin.
Consequently, the original name of the project was "msysGit" (which, sadly, caused a lot of confusion because few Windows users know about MSys, and even less care).

To compile the C code of Git for Windows, MSys was used, too: it sports two versions of the GNU C Compiler:

• one that links implicitly to the POSIX emulation layer,
• and another one that targets the plain Win32 API (with a few convenience functions thrown in).

Git for Windows' executables are built using the latter, and therefore they are really just Win32 programs. To discern executables requiring the POSIX emulation layer from the ones that do not, the latter are called MinGW (Minimal GNU for Windows) when the former are called MSys executables.

This reliance on MSys incurred challenges, too, though:

• some of our changes to the MSys runtime -- necessary to support Git for Windows better -- were not accepted upstream, so we had to maintain our own fork.
• Also, the MSys runtime was not developed further to support e.g. UTF-8 or 64-bit, and apart from lacking a package management system until much later (when mingw-get was introduced), many packages provided by the MSys/MinGW project lag behind the respective source code versions, in particular Bash and OpenSSL.

For a while, the Git for Windows project tried to remedy the situation by trying to build newer versions of those packages, but the situation quickly became untenable, especially with problems like the Heartbleed bug requiring swift action that has nothing to do with developing Git for Windows further.

Happily, in the meantime the MSys2 project (https://msys2.github.io/) emerged, and was chosen to be the base of the Git for Windows 2.x.
Just like MSys, MSys2 is a stripped down version of Cygwin, but it is actively kept up-to-date with Cygwin's source code.
Thereby, it already supports Unicode internally, and it also offers the 64-bit support that we yearned for since the beginning of the Git for Windows project.

MSys2 also ported the Pacman package management system from Arch Linux and uses it heavily. This brings the same convenience to which Linux users are used to from yum or apt-get, and to which MacOSX users are used to from Homebrew or MacPorts, or BSD users from the Ports system, to MSys2: a simple pacman -Syu will update all installed packages to the newest versions currently available.

MSys2 is also very active, typically providing package updates multiple times per week.

It still required a two-month effort to bring everything to a state where Git's test suite passes, many more months until the first official Git for Windows 2.x was released, and a couple of patches still await their submission to the respective upstream projects. Yet without MSys2, the modernization of Git for Windows would simply not have happened.

This commit lays the ground work to supporting MSys2-based Git builds.

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In the comments, the question was asked in January 2016:

Since Git for Windows is already based on MSYS2, have the binaries that don't depend on the emulation layer been made available as an MSYS2 package?

Ray Donnelly answered at the time:

We haven't fully merged yet, no. We're working on it though.

But... madz points out that during early 2017, that effort did not pan out.
See:

• Alexpux/MSYS2-packages PR 786
• git-for-windows/git issue 284

The problem is that I cannot contribute changes that will result in a new msys2-runtime in a timely manner.
Not a big problem, though: I'll just keep the fork of Git for Windows running indefinitely.

The wiki therefore mentions now (2018):

Git for Windows created some patches for msys2-runtime that have not been sent upstream. (This had been planned, but it was determined in issue #284 that it would probably not be happening.)
This means that you have to install Git for Windows customized msys2-runtime to have a fully working git inside MSYS2.

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Note that, since commit aeb582a9 (Git 2.22, Q2 2019), the Git for Windows project started the upgrade process to a MSYS2 runtime version based on Cygwin v3.x.

mingw: allow building with an MSYS2 runtime v3.x

Recently the Git for Windows project started the upgrade process to a MSYS2 runtime version based on Cygwin v3.x.

This has the very notable consequence that $(uname -r) no longer reports a version starting with "2", but a version with "3".

That breaks our build, as df5218b (config.mak.uname: support MSys2, 2016-01-13, Git v2.8.0-rc0) simply did not expect the version reported by uname -r to depend on the underlying Cygwin version: it expected the reported version to match the "2" in "MSYS2".

So let's invert that test case to test for anything else than a version starting with "1" (for MSys).
That should safeguard us for the future, even if Cygwin ends up releasing versions like 314.272.65536.

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Git 2.22 (Q2 2019) will future-proof a test against an update to MSYS2 runtime v3.x series.

See commit c871fbe (07 May 2019) by Johannes Schindelin (dscho).
^{(Merged by Junio C Hamano -- gitster -- in commit b20b8fe, 19 May 2019)}

t6500(mingw): use the Windows PID of the shell

In Git for Windows, we use the MSYS2 Bash which inherits a non-standard PID model from Cygwin's POSIX emulation layer: every MSYS2 process has a regular Windows PID, and in addition it has an MSYS2 PID (which corresponds to a shadow process that emulates Unix-style signal handling).

With the upgrade to the MSYS2 runtime v3.x, this shadow process cannot be accessed via OpenProcess() any longer, and therefore t6500 thought incorrectly that the process referenced in gc.pid (which is not actually a real gc process in this context, but the current shell) no longer exists.

Let's fix this by making sure that the Windows PID is written into gc.pid in this test script so that git.exe is able to understand that that process does indeed still exist.

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Git 2.37.3 (Q3 2022) illustrates how msys2 is used, through conditionally allow building Python interpreter on Windows:

See commit 2f0623a, commit 7934c74, commit 49d279f (29 Jul 2022) by Johannes Schindelin (dscho).
^{(Merged by Junio C Hamano -- gitster -- in commit 8dfa09f, 08 Aug 2022)}

mingw: remove unneeded NO_CURL directive

^{Signed-off-by: Johannes Schindelin}

In df5218b ("config.mak.uname: support MSys2", 2016-01-13, Git v2.8.0-rc0 -- merge listed in batch #4), we introduced support for building Git for Windows in the then-brand new Git for Windows v2.x build environment that was based off of MSYS2.

To do that, we split the non-msysGit part (that targeted MSys1) in two, and instead of sharing the NO_CURL = YesPlease setting with MSys1, we overrode it for MSYS2 with the empty value because we very much want to build Git for Windows with libcurl.

But that was unnecessary: we never set that variable beforehand, therefore there is no need to override it.

Let's just remove that unnecessary line.

Disclaimer: I am an MSYS2 developer

While MSYS isn't dead, I would say it's not looking very healthy either. It is a project started by the MinGW team many years ago as a fork of Cygwin that never kept up with Cygwin.

msysgit is a fork of a slightly older version of MSYS with some custom patches, old versions of Bash and Perl and a native port of Git.

MSYS2 is a project started by Alexey Pavlov of the mingw-builds team (who are the official packagers for MinGW-w64 toolchains) as a recent fork of Cygwin which tracks the latest Cygwin closely so that it doesn't end up out of date. Alexey forward ported the old MSYS patches and added some of his own.

As well as providing the necessary Unix tools with which to compile native software - the stated goal of MSYS - we ported the Pacman package manager from Arch Linux. Pacman is more than just about managing binary packages (though it does that very well). It has a software building infrastructure called makepkg that allows the creation of recipes (PKGBUILD and patch files) for building software.

IMHO, the adoption of Pacman changes things significantly for open source development on Windows. Instead of everyone hacking on their own bespoke shell scripts to build software in a hodge-podge, incompatible way, packages can now depend on other packages and PKGBUILD files and associated patches can be used as a reference for constructing new PKGBUILDs. It's as close to a Linux system as a (native) Windows can get (Arch Linux in particular) and allows for simple updating of all the installed packages.

We target Windows XP SP3 as a minimum and support both 32-bit and 64-bit Windows. We would ask that you never mix MSYS2 with msys or msysgit. Pacman is used to manage the whole system and as such, files from the other systems will cause conflicts.

We also try to upstream our patches to the projects we build and actively solicit contributions from other open source projects. We hope others find it easy to work with us.

Our main website is on SourceForge, and it contains links to our PKGBUILD repositories. We also have a more user friendly installer site on GitHub.

Feel free to join us on IRC (oftc #msys2) if you want more information.

My understanding on the connections between them is

• Cygwin offers POSIX emulation on top of windows
• msys tried to simplify Cygwin but is obsolete from 2010
• msysGit - allowed Git up to 1.9.4 on Windows (could be called git-for-windows-1.X), based on an old version of msys.
• msys2 - a simplified Cygwin, forked from it, with changes from msys and kept in sync with features from Cygwin, integrated with Pacman
• MinGW - initial MinGW, abandoned from 2010
• MinGW-w64 - a faster and better integration with windows, without POSIX
• git-for-windows-2.x - offers Git from 2.X for Windows using MinGW-64, MinGW-32 and when is not possible with a fallback to msys2

Fiddle with complete graph definition in mermaid.