title: How to run Android system app without root permission?
body: <p>Is there any way to run Android system app without root permission? I can execute system app via adb such as:</p>
  
  <blockquote>
    <p>adb shell /system/bin/screencap -p /sdcard/screen.png</p>
  </blockquote>
  
  <p>In my own application, I wanna run a shell command like that without "su" command. Is there any way? How does android prevent user apps to execute system app?</p>