Hey guys, I know you are here because you want to install your little hackbox in sdcard. But unfortunately it's not possible.l :(
So why did I created this post ?
Because many of you guys are crawling Google to know the trick and I am here to stop your time wast crawling. You deserve the truth.
Well why is it not possible ?
It's because your sdcard is mounted as FAT with noexec flag ( noexec means no execution ) which prevents execution of any file or binary. But in older versions of android like lolipop we can remount our sdcard without noexec flag but remember that it will only work in some old devices but wait .. why it will not work in new devices and Android versions ? It's because of the new protected file system i.e FUSE. Just search it on Google and you will get it.
It's not possible to install termux in sdcard , at least it's true for new devices and Android versions.