Let's clarify ths
Then Unroot. As it has been said, you cannot add a password to Root.
Okay, *****cat, let's see why you're noob
I used linux as a developer and administrator of a huge system for the last ten years, but I have to tell that I use android for 3 days, and never had before.
Through these 3 mere days I discovered that android is fundamentally an _exact_ linux and, as such, it does impiles the possibility of using unix user accounts and passwords.
The former (user accounts) is a natural part of the system, every app installed to the droid is given an exclusive one. (i must stop here to admit this is a strike of genius, a beautiful way to separate applications' workspace and permissions in such a way as we usually do on web servers hosting multiple domains, virtual hosts). It must be mentioned, that the files which control user accounts under linux (like /etc/passwd) are absent under android, because there is a stub for mapping the android_id to passwd structure. So there are no physical files for this purpose, the stub should populate the values. BUT this behaviour may be altered (i wouldn't like to describe how, it's your fight to figure out).
The latter one is a bit tricky, because android has no system authentication method (like PAM, or such) built in it, hence the only way to change the UID or EUID is to call the corresponding kernel call from a C program. BUT you are welcome to these C programs (including PAM itself), from any of the linux distros around, and after a (really-really) minimal modification they will work on android perfectly.
Thank you for your kind attention
