Thought experiment - root anytime and any device topic

Hi there,
I would like to ask the following question although I think it will fail due to some reason, but perhaps it's interesting to get the answer - at least for me! Okay, I'm not very familiar with android but I know UNIX / Linux for quite a long time - since the 1980s ;) What I do know is:

1. root user id is always 0 on any UNIX system (also on android)


2. a UNIX filesystem mounted on an UNIX system will accept the user permissions set on the mounted filesystem


3. an executable file, owned by root and the "sticky bit" set, will run under root permission


4. only thing to do is to change from effective user id to real user id during this executable is running

with this the question comes up. Why isn't it possible to have an external UNIX filesystem (e.g. SD card) mounted where an executable binary file is placed, owned by root and sticky bit is set? Then you only would have to mount this FS and run the binary to get root permission on any android device, without having special app breaking into your device ?

I'm quite sure, this won't work - otherwise this would be done every time, cause it would be so easy. So the question is not - does this work, the question would be - why would this not work out?

- And thanks for keepin' me away from friggeling around with life Linux CDs trying to set up an external filesystem 'n stuff, 'cause I do not have a Linux up and running anymore- I'm just a user - hackin' times have passed quite a time ago for me :angel: