Termux is an Android terminal app and Linux environment.
Mono is an implementation of .Net Framework on various platforms, including Android.
MSBuild is the default build system in Mono (and .Net).
Skip Build Mono from source and Install MSBuild if you want to use the prebuilt binaries from Releases.
There is no pre-compiled binary for Mono on Termux now, except for prooted Arch Linux and Ubuntu. (40)
Here I describe a process to cross-compile Mono 6.12 from source on Linux.
Termux now defaults to Android 7.0 (API Level 24, /data/data/com.termux/files/usr/include/android/api-level.h). I cross-compile on Ubuntu 20.04 x86_64 and target Android 7.0.
# at first, make sure you have mono installed on the host machine
# https://www.mono-project.com/download/stable/#download-lin
sudo apt install wget perl python3 cmake unzip git ninja-build g++
# get Android NDK from https://developer.android.com/ndk/downloads for Linux
# say android-ndk-r22-linux-x86_64.zip
unzip android-ndk-r22-linux-x86_64.zip
wget https://download.mono-project.com/sources/mono/mono-6.12.0.122.tar.xz
# compile mono for PC with .Net Class Libraries
mkdir mono-6.12.0.122-PC
tar xf mono-6.12.0.122.tar.xz -C mono-6.12.0.122-PC --strip-components=1
cd mono-6.12.0.122-PC
export CC=
export CXX=
export LDFLAGS=
./configure --disable-system-aot
make
make install "DESTDIR=$(realpath ..)/mono-6.12.0.122-bin-PC"
cd ..
# compile mono for Android without .Net Class Libraries
tar xf mono-6.12.0.122.tar.xz
cd mono-6.12.0.122
arch=aarch64 # arch can be any of aarch64, armv7a
api_level=24 # api level can be any of 21-24,26-30
# patch for log output (defaults to adb log rather than terminal)
sed -i 's|#if HOST_ANDROID|#if 0|g' mono/eglib/goutput.c
sed -i 's/#if defined(HOST_ANDROID) || !defined(HAVE_ATEXIT)/#if 0/g' mono/utils/mono-proclib.c
if [ "$arch" = "armv7a" ]; then
sed -i 's|#define USE_TKILL_ON_ANDROID 1||g' mono/metadata/threads.c
sed -i 's|#define USE_TKILL_ON_ANDROID 1||g' mono/utils/mono-threads-posix.c
fi
if [ "$arch" = "armv7a" ]; then
target=$arch-linux-androideabi
else
target=$arch-linux-android
fi
export CC="$(realpath ..)/android-ndk-r22/toolchains/llvm/prebuilt/linux-x86_64/bin/clang --target=$target$api_level --sysroot=$(realpath ..)/android-ndk-r22/toolchains/llvm/prebuilt/linux-x86_64/sysroot"
export CXX="$(realpath ..)/android-ndk-r22/toolchains/llvm/prebuilt/linux-x86_64/bin/clang --target=$target$api_level --sysroot=$(realpath ..)/android-ndk-r22/toolchains/llvm/prebuilt/linux-x86_64/sysroot"
if [ "$api_level" -ge "24" ]; then
export LDFLAGS="-lz -Wl,-rpath='\$\$ORIGIN/../lib' -Wl,--enable-new-dtags"
else
export LDFLAGS="-lz" # see https://github.com/termux/termux-packages/issues/2071
fi
if [ "$arch" = "armv7a" ]; then
extra_flags=--with-btls-android-ndk-asm-workaround
else
extra_flags=
fi
./configure --host=$target --prefix=/data/data/com.termux/files/usr/local --disable-mcs-build --with-btls-android-ndk="$(realpath ..)/android-ndk-r22" --with-btls-android-api=$api_level --with-btls-android-cmake-toolchain="$(realpath ..)/android-ndk-r22/build/cmake/android.toolchain.cmake" $extra_flags
make
make install "DESTDIR=$(realpath ..)/mono-6.12.0.122-bin"
cd ..
# copy .Net Class Libraries
cp -rf mono-6.12.0.122-bin-PC/usr/local/lib/mono mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/lib/
# Some libraries may use libc.so.6, which doesn't exist on Android. We can create a symbol link to libc.so.
if [ "$arch" = "armv7a" ]; then
ln -s /system/lib/libc.so mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/lib/libc.so.6
else
ln -s /system/lib64/libc.so mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/lib/libc.so.6
fi
Don't try to build MSBuild from source, it depends on a .Net Core version which is not shipped with Visual Studio and is very difficult to compile both on Windows or on Linux. Just download the pre-compiled binary from Mono. It contains only portable .Net binaries.
sudo apt install p7zip-full
wget http://download.mono-project.com/repo/ubuntu/pool/main/m/msbuild/msbuild_16.6+xamarinxplat.2021.01.15.16.11-0xamarin1+ubuntu2004b1_all.deb
7z x msbuild_16.6+xamarinxplat.2021.01.15.16.11-0xamarin1+ubuntu2004b1_all.deb
tar xf data.tar
cp -R usr/* mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/
rm -rf data.tar usr
Modify the path of msbuild command.
sed -i 's|/usr/bin|/data/data/com.termux/files/usr/local/bin|g' mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/bin/msbuild
sed -i 's|/usr/lib|/data/data/com.termux/files/usr/local/lib|g' mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/bin/msbuild
Roslyn is buggy on Mono on arm64 as it assumes the legacy x86/x86_64 memory model which guarantees memory access order in some situations on the metal.
- https://preshing.com/20120930/weak-vs-strong-memory-models/
- dotnet/roslyn#24932
- mono/mono#12632
- https://xamarin.github.io/bugzilla-archives/56/56546/bug.html
- https://news.ycombinator.com/item?id=14318877
This problem can not really be fixed in Mono, as there is a huge performance penalty. To workaround this problem, we have to force Roslyn to run single-threaded.
sed -i 's|"@(Compile)"|"@(Compile);/parallel-"|g' mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/lib/mono/msbuild/Current/bin/Roslyn/Microsoft.CSharp.Core.targets
sed -i 's|"@(Compile)"|"@(Compile);/parallel-"|g' mono-6.12.0.122-bin/data/data/com.termux/files/usr/local/lib/mono/msbuild/Current/bin/Roslyn/Microsoft.VisualBasic.Core.targets
In spite of the huge performance penalty, mono has implemented legacy x86/x86_64 memory model (total store order). The preceding patch is not necessary.
Pack all files.
cd mono-6.12.0.122-bin/data/data/com.termux/files/usr
tar cfJ mono-termux.6.12.0.122-arm64-android24.tar.xz local
Transfer file to /data/data/com.termux/files/usr on device.
Extract files on device.
cd /data/data/com.termux/files/usr
tar xf mono-termux.6.12.0.122-arm64-android24.tar.xz
Add usr/local/bin to system environment variable PATH if it isn't already there.
echo export PATH=/data/data/com.termux/files/usr/local/bin:$PATH >> ~/.bash_profile
# only do this if you use a version built for Api Level < 24
# echo export LD_LIBRARY_PATH=/data/data/com.termux/files/usr/local/lib:$LD_LIBRARY_PATH >> ~/.bash_profile
For our binaries to run faster, we can build AOT cache for some system libraries on device.
cd /data/data/com.termux/files/usr/local/lib/mono/4.5
mono --aot csc.exe
mono --aot mcs.exe
mono --aot Microsoft.CodeAnalysis.CSharp.dll
mono --aot Microsoft.CodeAnalysis.dll
mono --aot mscorlib.dll
mono --aot System.Collections.Immutable.dll
mono --aot System.Reflection.Metadata.dll
To use SSL, a certificate store is required.
Android provides a system certificate store at /system/etc/security/cacerts with read-only access.
Mono can use Android system certificate store, but requires Mono for Android (Xamarin Android).
But we can also use a separate certificate store like on Linux. Just copy /usr/share/.mono from a Linux device with Mono installed to ~/.config/.mono on the Android device.
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