Q:

adb install system app

I am aware that using adb install command installs an app in the /data/app folder. Also I know the in order to install an app as a system app I need to push it directly to the system. Is it possible to use adb install directly to the /system/priv-app/ on rooted phones?

A:

if I got your question, this should do the work:
adb root
adb remount
adb push apk-filename-here /system/app/
adb shell chmod 644 /system/app/apk-filename-here
adb reboot

See this or this link for more info.

