i have already root my nexus4,but why it shows “shell@mako:/ $ ”when i enter command“adb shell” Should not shell@mako:/ $ be shell@mako:/ #? 
Or I haven't root successfully yet? 
How to check whether my nexus4 have root successfully?

Thanks!
Rooted or not: Logging in via adb shell first brings you to a user-prompt only (connected with the "shell" account). In order to work with root, you need to "escalate" your permissions by invoking su:

&gt; adb shell
shell@mako:/ $ su
#


Apart from that, there are a few root checker apps available as well...