How to detect if running under WSL?

[AgnerF]

How do you detect if running under WSL?

C compilers in Mingw and Cygwin have preprocessing defines that allow you to identify the system. Is there a WSL preprocessing define or some other method for identifying the system? If not, please make a preprocessing define that gives a WSL version number.

You may claim that this is a genuine Linux (Ubuntu or whatever), but it is not. The floating point control word is set to reduced precision, and this causes a lot of problems. (Why has issue #830 never been fixed?). Also, of course, there is no GUI in WSL.

[floodkoff]

I think your question should be addressed to the gcc or clang compiler team not WSL

[benhillis]

The Windows version is present in our kernel command line (/proc/version, or uname -a).

[xtremeperf]

if [[ $(grep Microsoft /proc/version) ]]; then
echo "Bash is running on WSL"
fi

[AgnerF]

Thanks for the comments. I would like to detect WSL from a preprocessing directive when compiling a program. Something like #ifdef __ WSL __. There are special versions of gcc for Mingw and Cygwin, but as I understand it, there is no special version of gcc for WSL. Is there any way that a __ WSL __ define can be added automatically when the compiler is running under WSL?

[floodkoff]

@AgnerF it is a kind of define that you can do yourself. You don't need compiler support for that. Just generate config.h file using the build system of your choice. Here is how to do it in meson for example:
meson.build file

# meson.build
grep = find_program('grep')
runcmd = run_command(grep, '-q', 'Microsoft', '/proc/version')

confdata = configuration_data()
if runcmd.returncode() != 0
    confdata.set('WTL', 0)
else
    confdata.set('WTL', 1)
endif

configure_file(
    input : 'config.h.in',
    output : 'config.h',
    configuration : confdata)

config.h.in file

#mesondefine WTL

Meson will generate config.h with the following contents:

#define WTL 1

WTL define will be 1 under WTL and 0 under any other linux.

[therealkenc]

#423

[b-hayes]

Is there a way to determine WSL1 vs WSL2. I normally use the uname -a and check for Linux and Microsoft but both will say that.

[mirabilos]

@AgnerF the idea here is that unmodified Linux binaries run on WSL (and that binaries compiled on WSL are unmodified Linux binaries), so you’ll have to do a run-time check, not a compile-time check.