After unlock an Android device, how to access it via `adb shell` with `root` permission

Question

I unlocked my Nexus 7 device, and it shows

lock state : unlocked

However, when I used adb shell to connect it, I still couldn't ls /data, and got the error opendir failed, Permission denied.

Any idea?

Answer 1

I searched a while and found the reason:

I tried sudo ls /data, it didn't work.

while a way that works is like:

su // after this, you get the root permission

ls /data