4 How to Build Erlang/OTP on Windows

Table of Contents

4.1  Introduction

This file describes how to build the Erlang emulator and the OTP libraries on Windows. The instructions apply to versions of Windows supporting the Cygwin emulated gnuish environment for Windows or the Msys ditto. We've built on the following platforms: Windows 2003 server, Windows XP Home/Professional, Windows Vista and Windows 7 (32 and 64 bit). You can probably build on Windows 2000, but you will not be able to install the latest Microsoft SDK, so you have to go back to some earlier compiler. Any Windows95'ish platform will surely get you into trouble, what I'm not sure of, but it certainly will...

The procedure described uses either Cygwin or Msys as a build environment, you run the bash shell in Cygwin/Msys and use gnu make/configure/autoconf etc to do the build. The emulator C-source code is, however, mostly compiled with Microsoft Visual C++™, producing a native Windows binary. This is the same procedure as we use to build the pre-built binaries. The fact that we use VC++ and not gcc is explained further in the FAQ section.

I describe the build procedure to make it possible for open source customers to build the emulator, given that they have the needed tools. The binary Windows releases is still a preferred alternative if one does not have Microsoft's development tools and/or don't want to install Cygwin or Msys.

To use Cygwin/Msys, one needs basic experience from a Unix environment, if one does not know how to set environment variables, run programs etc in a Unix environment, one will be quite lost in the Cygwin os Msys ditto. I can unfortunately not teach all the world how to use Cygwin and bash, neither how to install Cygwin nor perform basic tasks on a computer. Please refer to other documentation on the net for help, or use the binary release instead if you have problems using the tools.

However, if you feel comfortable with the environment and build system, and have all the necessary tools, you have a great opportunity to make the Erlang/OTP distribution for Windows better. Please submit any suggestions and patches to the appropriate mailing lists to let them find their way into the next version of Erlang. If making changes to the build system (like makefiles etc) please bear in mind that the same makefiles are used on Unix/VxWorks, so that your changes don't break other platforms. That of course goes for C-code too, system specific code resides in the $ERL_TOP/erts/emulator/sys/win32 and $ERL_TOP/erts/etc/win32 directories mostly. The $ERL_TOP/erts/emulator/beam directory is for common code.

Before the R9C release of Erlang/OTP, the Windows release was built partly on a Unix (Solaris) box and partly on a Windows box, using Perl hacks to communicate and sync between the two machines. R9C was the first release ever built solely on Windows, where no Unix machine is needed at all. Now we've used this build procedure for a couple of releases, and it has worked fine for us. Still, there might be all sorts of troubles on different machines and with different setups. I'll try to give hints wherever I've encountered difficulties, but please share your experiences by using the erlang-questions mailing list. I cannot of course help everyone with all their problems, please try to solve the problems and submit solutions/workarounds. Remember, it's all about sharing, not about demanding...

Starting with R15B, our build system runs both on Cygwin and Msys (MinGW's fork of an early cygwin version). Msys is a smaller package to install and may on some machines run slightly faster. If Cygwin gives you trouble, try Msys instead, and v.v. Beginning with R15B there is also a native 64bit version of Erlang for 64bit Windows 7 (only). These instructions apply to both the 32bit VM and the 64bit ditto.

Note that even if you build a 64bit VM, most of the directories and files involved are still named win32. You can view the name win32 as meaning any windows version not beeing 16bit. A few occurences of the name Win64 are however present in the system, for example the installation file for a 64 bit windows version of Erlang is by default named otp_win64_<version>.exe.

Lets go then, I'll start with a little FAQ, based on in house questions and misunderstandings.

4.2  Frequently Asked Questions

  • Q: So, now I can build Erlang using GCC on Windows?

    A: No, unfortunately not. You'll need Microsoft's Visual C++ still, a Bourne-shell script (cc.sh) wraps the Visual C++ compiler and runs it from within the Cygwin environment. All other tools needed to build Erlang are free-ware/open source, but not the C compiler. The Windows SDK is however enough to build Erlang, you do not need to buy Visual C++, just download the SDK (SDK version 7.1 == Visual studio 2010).

  • Q: Why haven't you got rid of VC++ then, you ******?

    A: Well, partly because it's a good compiler - really! Actually it's been possible in late R11-releases to build using mingw instead of visual C++ (you might see the remnants of that in some scripts and directories). Unfortunately the development of the SMP version for Windows broke the mingw build and we chose to focus on the VC++ build as the performance has been much better in the VC++ versions. The mingw build will possibly be back, but as long as VC++ gives better performance, the commercial build will be a VC++ one.

  • Q: OK, you need VC++, but now you've started to demand a very recent (and expensive) version of Visual studio, not the old and stable VC++ 6.0 that was used in earlier versions. Why?

    A: Well, it's not expensive, it's free (as in free beer). Just download and install the latest Windows SDK from Microsoft and all the tools you need are there. The included debugger (WinDbg) is also quite usable, it's what I used when porting Erlang to 64bit Windows. Another reason to use the latest Microsoft compilers is DLL compatibility. DLL's using a new version of the standard library might not load if the VM is compiled with an old VC++ version, why we should aim to use the latest freely available SDK and compiler.

  • Q: Can/will I build a Cygwin binary with the procedure you describe?

    A: No, the result will be a pure Windows binary, and as far as I know, it's not possible to make a Cygwin binary yet. That is of course something desirable, but there are still some problems with the dynamic linking (dynamic Erlang driver loading) as well as the TCP/IP emulation in Cygwin, which, I'm sure of, will improve, but still has some problems. Fixing those problems might be easy or might be hard. I suggest you try yourself and share your experience. No one would be happier if a simple ./configure && make would produce a fully fledged Cygwin binary. Ericsson does however not pay me to do a Cygwin port, so such a port would have to happen in spare time, which is a limited resource...

  • Q: Hah, I saw you, you used GCC even though you said you didn't!

    A: OK, I admit, one of the files is compiled using Cygwin's or MinGW's GCC and the resulting object code is then converted to MS VC++ compatible coff using a small C hack. It's because that particular file, beam_emu.c benefits immensely from being able to use the GCC labels-as-values extension, which boosts emulator performance by up to 50%. That does unfortunately not (yet) mean that all of OTP could be compiled using GCC, that particular source code does not do anything system specific and actually is adopted to the fact that GCC is used to compile it on Windows.

  • Q: So now there's a MS VC++ project file somewhere and I can build OTP using the nifty VC++ GUI?

    A: No, never. The hassle of keeping the project files up to date and do all the steps that constitute an OTP build from within the VC++ GUI is simply not worth it, maybe even impossible. A VC++ project file for Erlang/OTP will never happen, at least I will never make one. Clicking around in super-multi-tab'd dialogs to add a file or compiler option when it's so much easier in a makefile is simply not my style.

  • Q: So how does it all work then?

    A: Cygwin or Msys is the environment, which closely resembles the environments found on any Unix machine. It's almost like you had a virtual Unix machine inside Windows. Configure, given certain parameters, then creates makefiles that are used by the Cygwin/Msys gnu-make to built the system. Most of the actual compilers etc are not, however, Cygwin/Msys tools, so I've written a couple of wrappers (Bourne-shell scripts), which reside in $ERL_TOP/etc/win32/cygwin_tools and $ERL_TOP/etc/win32/msys_tools. They all do conversion of parameters and switches common in the Unix environment to fit the native Windows tools. Most notable is of course the paths, which in Cygwin/Msys are Unix-like paths with "forward slashes" (/) and no drive letters, the Cygwin specific command cygpath is used for most of the path conversions in a Cygwin environment, other tools are used (when needed) in the corresponding Msys environment. Luckily most compilers accept forward slashes instead of backslashes as path separators, but one still have to get the drive letters etc right, though. The wrapper scripts are not general in the sense that, for example, cc.sh would understand and translates every possible gcc option and passes correct options to cl.exe. The principle is that the scripts are powerful enough to allow building of Erlang/OTP, no more, no less. They might need extensions to cope with changes during the development of Erlang, that's one of the reasons I made them into shell-scripts and not Perl-scripts, I believe they are easier to understand and change that way. I might be wrong though, cause another reason I didn't write them in Perl is because I've never liked Perl and my Perl code is no pleasant reading...

    In $ERL_TOP, there is a script called otp_build. That script handles the hassle of giving all the right parameters to configure/make and also helps you set up the correct environment variables to work with the Erlang source under Cygwin.

  • Q: You use and need Cygwin, but then you haven't taken the time to port Erlang to the Cygwin environment but instead focus on your commercial release, is that really ethical?

    A: No, not really, but see this as a step in the right direction. I'm aiming at GCC compiled emulators and a Cygwin version, but I really need to do other things as well... In time, but don't hold your breath...

  • Q: Can I build something that looks exactly as the commercial release?

    A: Yes, we use the exactly same build procedure.

  • Q: Which version of Cygwin/Msys and other tools do you use then?

    A: For Cygwin and Msys alike, we try to use the latest releases available when building. What versions you use shouldn't really matter, I try to include workarounds for the bugs I've found in different Cygwin/Msys releases, please help me add workarounds for new Cygwin/Msys-related bugs as soon as you encounter them. Also please do submit bug reports to the appropriate Cygwin and/or Msys developers. The GCC we used for 17 was version 4.7.0 (MinGW 64bit) and 4.3.4 (Cygwin 32bit). We used VC++ 10.0 (i.e. Visual studio 2010), Sun's JDK 1.5.0_17 (32bit) and Sun's JDK 1.7.0_1 (64bit), NSIS 2.46, and Win32 OpenSSL 0.9.8r. Please read the next section for details on what you need.

  • Q: Can you help me setup X in Cygwin?

    A: No, unfortunately I haven't got time to help with Cygwin related user problems, please read Cygwin related web sites, newsgroups and mailing lists.

  • Q: Why is the instruction so long? Is it really that complicated?

    A: Partly it's long because I babble too much, partly because I've described as much as I could about the installation of the needed tools. Once the tools are installed, building is quite easy. I also have tried to make this instruction understandable for people with limited Unix experience. Cygwin/Msys is a whole new environment to some Windows users, why careful explanation of environment variables etc seemed to be in place. The short story, for the experienced and impatient is:

    • Get and install complete Cygwin (latest) or complete MinGW with msys

    • Install Microsofts Windows SDK 7.1 (and .Net 4)

    • Get and install Sun's JDK 1.5.0 or higher

    • Get and install NSIS 2.01 or higher (up to 2.46 tried and working)

    • Get, build and install OpenSSL 0.9.8r or higher (up to 1.0.0a tried & working) with static libs.

    • Get the Erlang source distribution (from http://www.erlang.org/download.html) and unpack with Cygwin's tar.

    • Set ERL_TOP to where you unpacked the source distribution

    • $ cd $ERL_TOP

    • Get (from http://www.erlang.org/download/tcltk85_win32_bin.tar.gz) and unpack the prebuilt TCL/TK binaries for windows with cygwin tar, standing in $ERL_TOP

    • Modify PATH and other environment variables so that all these tools are runnable from a bash shell. Still standing in $ERL_TOP, issue the following commands:

      $ eval `./otp_build env_win32`
      $ ./otp_build autoconf
      $ ./otp_build configure
      $ ./otp_build boot -a
      $ ./otp_build release -a
      $ ./otp_build installer_win32
      $ release/win32/otp_win32_17 /S

    Voila! Start->Programs->Erlang OTP 17->Erlang starts the Erlang Windows shell.

4.3  Tools you Need and Their Environment

You need some tools to be able to build Erlang/OTP on Windows. Most notably you'll need Cygwin or Msys and Microsofts Windows SDK, but you also might want a Java compiler, the NSIS install system and OpenSSL. Well' here's the list:

  • Cygwin, the very latest is usually best. Get all the development tools and of course all the basic ditto. In fact getting the complete package might be a good idea, as you'll start to love Cygwin after a while if you're accustomed to Unix. Make sure to get jar and also make sure not to install a Cygwin'ish Java... The Cygwin jar command is used but Sun's Java compiler and virtual machine...

    If you are going to build a 64bit Windows version, you should make sure to get MinGW's 64bit gcc installed with cygwin. It's in one of the development packages.

    URL: http://www.cygwin.com

    Get the installer from the web site and use that to install Cygwin. Be sure to have fair privileges. If you're on a NT domain you should consider running mkpasswd -d and mkgroup -d after the installation to get the user databases correct. See their respective manual pages.

    When you start you first bash shell, you will get an awful prompt. You might also have a PATH environment variable that contains backslashes and such. Edit $HOME/.profile and $HOME/.bashrc to set fair prompts and set a correct PATH. Also do a export SHELL in .profile. For some non-obvious reason the environment variable $SHELL is not exported in bash. Also note that .profile is run at login time and .bashrc when sub shells are created. You'll need to explicitly source .bashrc from .profile if you want the commands there to be run at login time (like setting up aliases, shell functions and the like). I personally usually do like this at the end of .profile:

    export ENV
    . $ENV

    You might also, if you're a hard core type of person at least, want to setup X-windows (XFree86), that might be as easy as running startx from the command prompt and it might be much harder. Use Google to find help...

    If you don't use X-windows, you might want to setup the Windows console window by selecting properties in the console system menu (upper left corner of the window, the Cygwin icon in the title bar). Especially setting a larger screen buffer size (lines) is useful as it gets you a scrollbar so you can see whatever error messages that might appear...

    If you want to use (t)csh instead of bash you're on your own, I haven't tried and know of no one that has. I expect that you use bash in all shell examples.

  • Alternatively you download MinGW and Msys. You'll find the latest installer at:

    URL: http://sourceforge.net/projects/mingw/files/Installer/mingw-get-inst/

    Make sure to install everything they've got.

    To be able to build the 64bit VM, you will also need the 64bit MinGW compiler from:

    URL: http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Automated%20Builds/

    The latest version should do it. Make sure you download the mingw-w64-bin_i686-mingw_<something>.zip, not a linux version. You unzip the package on top of your MinGW installation (c:\MinGW) and that's it.

    Setting up your environment in Msys is similar to setting it up in Cygwin.

  • Microsofts Windows SDK version 7.1 (corresponding to VC++ 10.0 and Visual Studio 2010). You'll find it here:

    URL: http://www.microsoft.com/download/en/details.aspx?id=8279

    but before you install that, you need to have .Net 4 installed, you'll find that here:

    URL: http://www.microsoft.com/download/en/details.aspx?id=17851

    Use the web installer for the SDK, at least when I tried downloading the whole package as an image, I got SDK 7.0 instead, which is not what you want...

    There will be a Windows command file in %PROGRAMFILES%\Mirosoft SDKs\Windows\v7.1\Bin\SetEnv.cmd that set's the appropriate environment for a Windows command prompt. This is not appropriate for bash, so you'll need to convert it to bash-style environments by editing your .bash_profile. In my case, where the SDK is installed in the default directory and %PROGRAMFILES% is C:\Program Files, the commands for setting up a 32bit build environment (on a 64bit or 32bit machine) look like this (in cygwin):

    # Some common paths
    PRG_FLS=$C_DRV/Program\ Files
    # nsis
    # java
    ## MS SDK
    MVS10="$PRG_FILES/Microsoft Visual Studio 10.0"
    WIN_MVS10="C:\\Program Files\\Microsoft Visual Studio 10.0"
    SDK10="$PRG_FILES/Microsoft SDKs/Windows/v7.1"
    WIN_SDK10="C:\\Program Files\\Microsoft SDKs\\Windows\\v7.1"
    $SDK10/Bin/NETFX 4.0 Tools:\

    If you're using Msys instead, the only thing you need to change is the C_DRV setting, which would read:


    And of course you might need to change C:\Program Files etc if you're using a non-english version of Windows (XP). Note that in later versions of Windows, the national adoptions of the program files directories etc are not on the file system but only in the explorer, so even if explorer says that your programs reside in e.g. C:\Program, they might still reside in C:\Program Files in reality...

    If you are building a 64 bit version of Erlang, you should set up PATHs etc a little differently. I use the following script to make things work in both Cygwin and Msys:

            if [ "$IN_CYGWIN" = "true" ]; then 
               cygpath -d "$P"
               (cd "$P" && /bin/cmd //C "for %i in (".") do @echo %~fsi")
            if [ "$IN_CYGWIN" = "true" ]; then 
               cygpath "$P"
               echo "$P" | /bin/sed 's,^\([a-zA-Z]\):\\,/\L\1/,;s,\\,/,g'
     # Some common paths
     if [ -x /usr/bin/msysinfo ]; then
        # Without this the path conversion won't work
        export MSYSTEM COMSPEC
        export CYGWIN
     if [ "$IN_CYGWIN" = "true" ]; then 
     if [ "$IN_CYGWIN" = "true" ]; then 
     PRG_FLS64=$C_DRV/Program\ Files
     PRG_FLS32=$C_DRV/Program\ Files\ \(x86\)
     VISUAL_STUDIO_ROOT32=$PRG_FLS32/Microsoft\ Visual\ Studio\ 10.0
     MS_SDK_ROOT64=$PRG_FLS64/Microsoft\ SDKs/Windows/v7.1
     # Okay, now mangle the paths and get rid of spaces by using short names
     WIN_VCROOT32=`make_winpath "$VISUAL_STUDIO_ROOT32"`
     VCROOT32=`make_upath $WIN_VCROOT32`
     WIN_SDKROOT64=`make_winpath "$MS_SDK_ROOT64"`
     SDKROOT64=`make_upath $WIN_SDKROOT64`
     WIN_PROGRAMFILES32=`make_winpath "$PRG_FLS32"`
     WIN_PROGRAMFILES64=`make_winpath "$PRG_FLS64"`
     # nsis
     # java
     ## The PATH variable should be Unix'ish
     ## Microsoft SDK libs
     # Put nsis, c compiler and java in path
     # Make sure LIB and INCLUDE is available for others

    All this is derived from the SetEnv.cmd command file mentioned earlier. The bottom line is to set the PATH so that NSIS and Microsoft SDK is found before the Msys/Cygwin tools and that Java is last in the PATH.

    Make a simple hello world (maybe one that prints out sizeof(void *)) and try to compile it with the cl command from within bash. If that does not work, your environment needs fixing. Also remember to fix up the PATH environment, especially old Erlang installations might have inserted quoted paths that Cygwin/Msys does not understand. Remove or correct such paths. There should be no backslashes in your path environment variable in Cygwin bash, but LIB and INCLUDE should contain Windows style paths with semicolon, drive letters and backslashes.

  • Sun's Java JDK 1.5.0 or higher. Our Java code (jinterface, ic) is written for JDK 1.5.0. Get it for Windows and install it, the JRE is not enough. If you don't care about Java, you can skip this step, the result will be that jinterface is not built.

    URL: http://java.sun.com

    Add javac LAST to your path environment in bash, in my case this means:

    `PATH="$PATH:/cygdrive/c/Program Files/Java/jdk1.5.0_17/bin"`

    No CLASSPATH or anything is needed. Type javac at the bash prompt and you should get a list of available Java options. Make sure by typing type java that you use the Java you installed. Note however that Cygwin's jar.exe is used, that's why the JDK bin-directory should be added last in the PATH.

  • Nullsoft NSIS installer system. You need this to build the self installing package. It's a free open source installer that's much nicer to use than the commercial Wise and Install shield installers. This is the installer we use for commercial releases as well from R9C an on.

    URL: http://www.nullsoft.com/free/nsis

    Install the lot, especially the modern user interface components, as it's definitely needed. Put makensis in your path, in my case:

    PATH=/cygdrive/c/Program\ Files/NSIS:$PATH

    type makensis at the bash prompt and you should get a list of options if everything is OK.

  • OpenSSL. This is if you want the SSL and crypto applications to compile (and run). There are prebuilt binaries available, but I strongly recommend building this yourself. It's quite easy.

    First get the source from

    URL: http://openssl.org/source/

    I would recommend using 0.9.8r.

    Download the tar file and unpack it (using your bash prompt) into a directory of your choise.

    You will need a Windowish Perl for the build. ActiveState has one:

    URL: http://www.activestate.com/activeperl/downloads

    Download and install that. Disable options to associate it with the .pl suffix and/or adding things to PATH, they are not needed.

    Now fire up the Microsoft Windows SDK command prompt in RELEASE mode for the architecture you are going to build. The easiest is to copy the shortcut from the SDKs start menu item and edit the command line in the shortcut (Right click->Properties) to end with /Release. Make sure the banner when you double click your shortcut (the text in the resulting command window) says Targeting Windows XP x64 Release if you are going to do a 64 bit build and Targeting Windows XP x86 Release if you are building a 32 bit version.

    Now cd to where you unpacked the OpenSSL source using your Release Windows command prompt (it should be on the same drive as where you are going to install it if everything is to work smothly).

    C:\> cd <some dir>

    Add ActiveState (or some other windows perl, not cygwins) to your PATH:

    C:\...\> set PATH=C:\Perl\bin;%PATH%

    Or if you installed the 64bit perl:

    C:\...\> set PATH=C:\Perl64\bin;%PATH%

    Configure OpenSSL for 32 bit:

    C:\...\> perl Configure VC-WIN32 --prefix=/OpenSSL

    Or for 64 bit:

    C:\...\> perl Configure VC-WIN64A --prefix=/OpenSSL-Win64

    Do some setup (for 32 bit):

    C:\...\> ms\do_ms

    The same for 64 bit:

    C:\...\> ms\do_win64a

    Then build static libraries and install:

    C:\...\> nmake -f ms\nt.mak
    C:\...\> nmake -f ms\nt.mak install

    That's it - you now have your perfectly consistent static build of openssl. If you want to get rid of any possibly patented algorithms in the lib, just read up on the OpenSSL FAQ and follow the instructions.

    The installation locations chosen are where configure will look for OpenSSL, so try to keep them as is.

  • Building with wxWidgets. Download wxWidgets-2.8.9 or higher patch release (2.9.* is a developer release which currently does not work with wxErlang).

    Install or unpack it to DRIVE:/PATH/cygwin/opt/local/pgm.

    edit: C:\cygwin\opt\local\pgm\wxMSW-2.8.11\include\wx\msw\setup.h enable wxUSE_GLCANVAS, wxUSE_POSTSCRIPT and wxUSE_GRAPHICS_CONTEXT

    build: From a command prompt with the VC tools available (See the instructions for OpenSSL build above for help on starting the proper command prompt in RELEASE mode):

    C:\...\> cd C:\cygwin\opt\local\pgm\wxMSW-2.8.11\build\msw
    C:\...\> nmake BUILD=release SHARED=0 UNICODE=1 USE_OPENGL=1 USE_GDIPLUS=1 DIR_SUFFIX_CPU= -f makefile.vc
    C:\...\> cd C:\cygwin\opt\local\pgm\wxMSW-2.8.11\contrib\build\stc
    C:\...\> nmake BUILD=release SHARED=0 UNICODE=1 USE_OPENGL=1 USE_GDIPLUS=1 DIR_SUFFIX_CPU= -f makefile.vc

    Or - if building a 64bit version:

    C:\...\> cd C:\cygwin\opt\local\pgm\wxMSW-2.8.11\build\msw
    C:\...\> nmake TARGET_CPU=amd64 BUILD=release SHARED=0 UNICODE=1 USE_OPENGL=1 USE_GDIPLUS=1 DIR_SUFFIX_CPU= -f makefile.vc
    C:\...\> cd C:\cygwin\opt\local\pgm\wxMSW-2.8.11\contrib\build\stc
    C:\...\> nmake TARGET_CPU=amd64 BUILD=release SHARED=0 UNICODE=1 USE_OPENGL=1 USE_GDIPLUS=1 DIR_SUFFIX_CPU= -f makefile.vc
  • The Erlang source distribution (from http://www.erlang.org/download.html). The same as for Unix platforms. Preferably use tar from within Cygwin to unpack the source tar.gz (tar zxf otp_src_17.tar.gz).

    set the environment ERL_TOP to point to the root directory of the source distribution. Let's say I stood in $HOME/src and unpacked otp_src_17.tar.gz, I then add the following to .profile:

    export $ERL_TOP
  • The TCL/TK binaries. You could compile Tcl/Tk for windows yourself, but you can get a stripped down version from our website which is suitable to include in the final binary package. If you want to supply tcl/tk yourself, read the instructions about how the tcl/tk tar file used in the build is constructed under $ERL_TOP/lib/gs/tcl. The easy way is to download http://www.erlang.org/download/tcltk85_win32_bin.tar.gz and unpack it standing in the $ERL_TOP directory. This will create the file win32.tar.gz in $ERL_TOP/lib/gs/tcl/binaries.

    One last alternative is to create a file named SKIP in the $ERL_TOP/lib/gs/ after configure is run, but that will give you an erlang system without gs (which might be okay as you probably will use wx anyway).

    Note that there is no special 64bit version of TCL/TK needed, you can use the 32bit program even for a 64bit build.

4.4  The Shell Environment

So, if you have followed the instructions above, when you start a bash shell, you should have an INCLUDE environment with a Windows style path, a LIB environment variable also in Windows style, and finally a PATH that let's you reach cl, makensis, javac etc from the command prompt (use which cl etc to verify from bash).

You should also have an ERL_TOP environment variable that is Cygwin style, and points to a directory containing, among other files, the script otp_build.

A final massage of the environment is needed, and that is done by the script $ERL_TOP/otp_build. Start bash and do the following, note the "back-ticks" (`), can be quite hard to get on some keyboards, but pressing the back-tick key followed by the space bar might do it...

$ cd $ERL_TOP
$ eval `./otp_build env_win32`

If you're unable to produce back-ticks on your keyboard, you can use the ksh variant:

$ cd $ERL_TOP
$ eval $(./otp_build env_win32)

If you are building a 64 bit version, you supply otp_build with an architecture parameter:

$ cd $ERL_TOP
$ eval `./otp_build env_win32 x64`

This should do the final touch to the environment and building should be easy after this. You could run ./otp_build env_win32 without eval just to see what it does, and to see that the environment it sets seems OK. The path is cleaned of spaces if possible (using DOS style short names instead), the variables OVERRIDE_TARGET, CC, CXX, AR and RANLIB are set to their respective wrappers and the directories $ERL_TOP/erts/etc/win32/cygwin_tools/vc and $ERL_TOP/erts/etc/win32/cygwin_tool are added first in the PATH.

Try now a type erlc. That should result in the erlc wrapper script (which does not have the .sh extension, for reasons best kept untold...). It should reside in $ERL_TOP/erts/etc/win32/cygwin_tools or $ERL_TOP/erts/etc/win32/msys_tools. You could also try which cc.sh, which ar.sh etc.

Now you're ready to build...

4.5  Building and Installing

Now it's assumed that you have executed eval `./otp_build env_win32` or eval `./otp_build env_win32 x64` for this particular shell...

Building is easiest using the otp_build script. That script takes care of running configure, bootstrapping etc on Windows in a simple way. The otp_build script is the utility we use ourselves to build on different platforms and it therefore contains code for all sorts of platforms. The principle is, however, that for non-Unix platforms, one uses ./otp_build env_<target> to set up environment and then the script knows how to build on the platform "by itself". You've already run ./otp_build env_win32 in the step above, so now it's mostly like we build on any platform. OK, here are then steps; Assuming you will want to build a full installation executable with NSIS, you can omit <installation directory> and the release will be copied to $ERL_TOP/release/win32: and there is where the packed self installing executable will reside too.

$ ./otp_build autoconf # Ignore the warning blob about versions of autoconf
$ ./otp_build configure <optional configure options>
$ ./otp_build boot -a
$ ./otp_build release -a <installation directory>
$ ./otp_build installer_win32 <installation directory> # optional

Now you will have a file called otp_win32_R12B.exe in the <installation directory>, i.e. $ERL_TOP/release/win32.

Lets get into more detail:

  • $ ./otp_build autoconf - This step rebuilds the configure scripts to work correctly in the cygwin environment. In an ideal world, this would not be needed, but alas, we have encountered several incompatibilities between our distributed configure scripts (generated on a Linux platform) and the cygwin environment over the years. Running autoconf on cygwin ensures that the configure scripts are generated in a cygwin-compatible way and that they will work well in the next step.

  • $ ./otp_build configure - This runs the newly generated configure scripts with options making configure behave nicely. The target machine type is plainly win32, so a lot of the configure-scripts recognize this awkward target name and behave accordingly. The CC variable also makes the compiler be cc.sh, which wraps MSVC++, so all configure tests regarding the C compiler gets to run the right compiler. A lot of the tests are not needed on Windows, but I thought it best to run the whole configure anyway. The only configure option you might want to supply is --with-ssl, which might be needed if you have built your own OpenSSL distribution. The Shining Lights distribution should be found automatically by configure, if that fails, add a --with-ssl=<dir> that specifies the root directory of your OpenSSL installation.

  • $ ./otp_build boot -a - This uses the bootstrap directory (shipped with the source, $ERL_TOP/bootstrap) to build a complete OTP system. It first builds an emulator and sets up a minimal OTP system under $ERL_TOP/bootstrap, then starts to compile the different OTP compilers to make the $ERL_TOP/bootstrap system potent enough to be able to compile all Erlang code in OTP. Then, all Erlang and C code under $ERL_TOP/lib is built using the bootstrap system, giving a complete OTP system (although not installed). When this is done, one can run Erlang from within the source tree, just type $ERL_TOP/bin/erl and you should have a prompt. If you omit the -a flag, you'll get a smaller system, that might be useful during development. Now exit from Erlang and start making a release of the thing:

  • $ ./otp_build release -a - Builds a commercial release tree from the source tree, default is to put it in $ERL_TOP/release/win32, you can give any directory as parameter (Cygwin style), but it doesn't really matter if you're going to build a self extracting installer too. You could of course build release to the final directory and then run ./Install.exe standing in the directory where the release was put, that will create a fully functional OTP installation. But let's make the nifty installer:

  • $ ./otp_build installer_win32 - Create the self extracting installer executable. The executable otp_win32_17.exe will be placed in the top directory of the release created in the previous step. If no release directory is specified, the release is expected to have been built to $ERL_TOP/release/win32, which also will be the place where the installer executable will be placed. If you specified some other directory for the release (i.e. ./otp_build release -a /tmp/erl_release), you're expected to give the same parameter here, (i.e. ./otp_build installer_win32 /tmp/erl_release). You need to have a full NSIS installation and makensis.exe in your path for this to work of course. Once you have created the installer, you can run it to install Erlang/OTP in the regular way, just run the executable and follow the steps in the installation wizard. To get all default settings in the installation without any questions asked, you run the executable with the parameter /S (capital S) like in:

    $ cd $ERL_TOP
    $ release/win32/otp_win32_17 /S


    $ cd $ERL_TOP
    $ release/win32/otp_win64_17 /S

    and after a while Erlang/OTP-17 will have been installed in C:\Program Files\erl6.4\, with shortcuts in the menu etc.

    The necessary setup of an Erlang installation is actually done by the program Install.exe, which resides in the release top. That program creates .ini-files and copies the correct boot scripts. If one has the correct directory tree (like after a ./otp_build release -a), only the running of Install.exe is necessary to get a fully functional OTP. What the self extracting installer adds is (of course) the possibility to distribute the binary easily, together with adding shortcuts to the Windows start menu. There is also some adding of entries in the registry, to associate .erl and .beam files with Erlang and get nifty icons, but that's not something you'll really need to run Erlang. The registry is also used to store uninstall information, but if one has not used the self extracting installer, one cannot (need not) do any uninstall, one just scratches the release directory and everything is gone. Erlang/OTP does not need to put anything in the Windows registry at all, and does not if you don't use the self extracting installer. In other words the installer is pure cosmetics.


Beginning with R9C, the Windows installer does not add Erlang to the system wide path. If one wants to have Erlang in the path, one has to add it by hand.

4.6  Development

Once the system is built, you might want to change it. Having a test release in some nice directory might be useful, but you also can run Erlang from within the source tree. The target local_setup, makes the program $ERL_TOP/bin/erl.exe usable and it also uses all the OTP libraries in the source tree.

If you hack the emulator, you can then build the emulator executable by standing in $ERL_TOP/erts/emulator and do a simple

$ make opt

Note that you need to have run (cd $ERL_TOP && eval `./otp_build env_win32`) in the particular shell before building anything on Windows. After doing a make opt you can test your result by running $ERL_TOP/bin/erl. If you want to copy the result to a release directory (say /tmp/erl_release), you do this (still in $ERL_TOP/erts/emulator)

$ make TESTROOT=/tmp/erl_release release

That will copy the emulator executables.

To make a debug build of the emulator, you need to recompile both beam.dll (the actual runtime system) and erlexec.dll. Do like this

$ cd $ERL_TOP
$ rm bin/win32/erlexec.dll
$ cd erts/emulator
$ make debug
$ cd ../etc
$ make debug

and sometimes

$ cd $ERL_TOP
$ make local_setup

So now when you run $ERL_TOP/erl.exe, you should have a debug compiled emulator, which you will see if you do a:

1> erlang:system_info(system_version).

in the erlang shell. If the returned string contains [debug], you got a debug compiled emulator.

To hack the erlang libraries, you simply do a make opt in the specific "applications" directory, like:

$ cd $ERL_TOP/lib/stdlib
$ make opt

or even in the source directory...

$ cd $ERL_TOP/lib/stdlib/src
$ make opt

Note that you're expected o have a fresh Erlang in your path when doing this, preferably the plain 17 you have built in the previous steps. You could also add $ERL_TOP/bootstrap/bin to your PATH before rebuilding specific libraries, that would give you a good enough Erlang system to compile any OTP erlang code. Setting up the path correctly is a little bit tricky, you still need to have $ERL_TOP/erts/etc/win32/cygwin_tools/vc and $ERL_TOP/erts/etc/win32/cygwin_tools before the actual emulator in the path. A typical setting of the path for using the bootstrap compiler would be:

$ export PATH=$ERL_TOP/erts/etc/win32/cygwin_tools/vc\

That should make it possible to rebuild any library without hassle...

If you want to copy a library (an application) newly built, to a release area, you do like with the emulator:

$ cd $ERL_TOP/lib/stdlib
$ make TESTROOT=/tmp/erlang_release release

Remember that:

  • Windows specific C-code goes in the $ERL_TOP/erts/emulator/sys/win32, $ERL_TOP/erts/emulator/drivers/win32 or $ERL_TOP/erts/etc/win32.

  • Windows specific erlang code should be used conditionally and the host OS tested in runtime, the exactly same beam files should be distributed for every platform! So write code like:

    case os:type() of
        {win32,_} ->
        Other ->

That's basically all you need to get going.

4.7  Using GIT

You might want to check out versions of the source code from GitHUB. That is possible directly in cygwin, but not in Msys. There is a project MsysGIT:


that makes a nice Git port. The msys prompt you get from MsysGIT is however not compatible with the full version from MinGW, so you will need to check out files using MsysGIT's command prompt and then switch to a common Msys command prompt for building. Also all test suites cannot be built as MsysGIT/Msys does not handle symbolic links. To build test suites on Windows, you will need Cygwin for now. Hopefully all symbolic links will disappear from our repository soon and this issue will disappear.

4.8  Final Words

My hope is that the possibility to build the whole system on Windows will open up for free development on this platform too. There are many things one might want to do better in the Windows version, like the window-style command prompt as well as pure Cygwin porting. Although i realize it's a much larger step to start building on Windows (with all the software you need) than for instance on Linux, I sincerely hope that some of you will make the effort and start submitting Windows friendly patches.

The first build system for Erlang using Cygwin on Windows was created by Per Bergkvist. I haven't used his build system, but it's rumored to be good. The idea to do this came from his work, so credit is well deserved.

Of course this would have been completely impossible without the excellent Cygwin. The guys at Cygnus solutions and Redhat deserve a huge THANKS! as well as all the other people in the free software community who have helped in creating the magnificent software that constitutes Cygwin.

Also the people developing the alternative command prompt Msys and the MinGW compiler are worth huge THANKS! The 64bit port would have been impossible without the 64bit MinGW compiler.

Good luck and Happy Hacking, Patrik, OTP

4.9  Copyright and License

Copyright Ericsson AB 2003-2014. All Rights Reserved.

The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/.

Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License.