While running the react native script for the first time there might be a permission issue of ADB. Instead of giving a full permission to ADB in the android_sdk/platform tools adb in linux it might happen.
After giving the permission though it shows the permission issue while running the react native app in the mobile application.
The following issue will resolve this problem
sudo apt-get remove adb
sudo apt-get update && sudo apt-get upgrade
sudo apt-get install adb
Once successfully installed type the adb in the terminal, it will show options for adb
Once it shows options then try running the react native android app again and the permission issue will be resolved in the Ubuntu