It absolutely is Linux, and yes the JVM could absolutely run on something else. But it is Linux and you can run Linux binaries directly on it - that just isn’t how it is used by end users.
No you cannot, the NDK has a specific set of oficial APIS, and the Android team feels in the right to kill any application that doesn't follow the law of Android land.
Some folks like the termux rebels, occasionally find out there is a sherif in town.
> As documented in the Android N behavioral changes, to protect Android users and apps from unforeseen crashes, Android N will restrict which libraries your C/C++ code can link against at runtime. As a result, if your app uses any private symbols from platform libraries, you will need to update it to either use the public NDK APIs or to include its own copy of those libraries. Some libraries are public: the NDK exposes libandroid, libc, libcamera2ndk, libdl, libGLES, libjnigraphics, liblog, libm, libmediandk, libOpenMAXAL, libOpenSLES, libstdc++, libvulkan, and libz as part of the NDK API. Other libraries are private, and Android N only allows access to them for platform HALs, system daemons, and the like. If you aren’t sure whether your app uses private libraries, you can immediately check it for warnings on the N Developer Preview.
https://android-developers.googleblog.com/2016/06/improving-...
These stable APIs,
The JVM has nothing to do with Android. There is no JVM running android apps.
There was Dalvik VM at one point but now it’s just the Android Runtime.