How to debug an android application started from 'adb shell am start -D '?

Question

I need to debug an android application that is already installed on a phone. I am able to start the application in debug mode but I can't connect to the process using JDWP. I have try two different ways that both fail. (see following sections)

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Command line attempt

1- Start the application

[...]sdk\platform-tools>adb -d shell am start -D -n "package/package.SomeActivity"

The application starts and a alert display "/!\ Waiting for debugger".

2- Open a JDWP port

[...]sdk\platform-tools>adb forward tcp:8000 jdwp:7602

3- Attempt to connect using jdb

[...]sdk\platform-tools>jdb -attach 127.0.0.1:8000
    java.io.IOException: shmemBase_attach failed:
        at com.sun.tools.jdi.SharedMemoryTransportService.attach0(Native Method)
        at com.sun.tools.jdi.SharedMemoryTransportService.attach(SharedMemoryTransportService.java:108)
        at com.sun.tools.jdi.GenericAttachingConnector.attach(GenericAttachingConnector.java:116)
        at com.sun.tools.jdi.SharedMemoryAttachingConnector.attach(SharedMemoryAttachingConnector.java:63)
        at com.sun.tools.example.debug.tty.VMConnection.attachTarget(VMConnection.java:519)
        at com.sun.tools.example.debug.tty.VMConnection.open(VMConnection.java:328)
        at com.sun.tools.example.debug.tty.Env.init(Env.java:63)
        at com.sun.tools.example.debug.tty.TTY.main(TTY.java:1066)
Fatal error:
Unable to attach to target VM.

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IntelliJ attempt

I have configure my local project to start the default Activity and uncheck the "Deploy application".

I also get the application started with the same alert but unfortunately the IDE doesn't connect to the remote process.

Target device: 42f7cc14e2acbfab
Launching application: ********/********.SomeActivity.
DEVICE SHELL COMMAND: am start -D -n "********/********.SomeActivity"
Starting: Intent { cmp=********/********.SomeActivity }

Waiting for process: ********

Answer 1

1. Root the phone

2. Open a root shell

   (computer)$ adb shell 
   (phone)$ su
   (phone)#
   

3. Run am command

   # am start -D -n "package/package.SomeActivity"
   

This way you can debug any app, no matter if it has android:debuggable set or not.

Answer 2

The deployed application was configured with the debuggable attribute set to false. The prompt given on the mobile phone was simply misleading.