I am using ubuntu in andriod phone. I have img file and it runs via terminal when I execute sh file. Problem is when I start terminal and try to install anything using apt-get I got permission denied. When I type su it ask for password. I know one password when I log in via vnc but that doesn't work. What should I do?

With Ubuntu root doesn't work like that.
You need an admin account and use the admin accounts password.

Root password is locked, you need to use sudo "command" then enter the admins user password.

I think you can use "sudo passwd" to set root password

That isn't advised.
https://help.ubuntu.com/community/RootSudo

Sudo passwd
Permission denied


How do I create or log into admin account?

Please note I am running ubuntu in an andriod phone

When I type "sudo"

Permission denied

If you dont know, you dont need it

From where, with what, etc, etc, etc, did you install Ubuntu ?

Correct usage is

sudo <command> <arguments>

If that doesnt work, something is screwed with whatever, however, whereever you installed Ubuntu.

I use Linux on Android . I just tried to run ubuntu in a desktop environment on my phone. Opened a terminal and ran sudo apt-get update. It then asked for password. In this case the preset password is ubuntu. Hope this helps.

sudo apt-get update gives permission denied

Can you post link for your img file Ubuntu Linux and sh file.