How to make android device always in wake mode?

Question

After successful root of device. Now, I need to make device always in wake state i.e. always visibility of UI and no black screen or any daydream screens. To do so I think I've to accomplish following :

1. No lock screen - turned off
2. Sleep set to “never”
3. Daydream set to “off”

What I found is all about application layer i.e. there are some applications which can do above tasks. But since my mobile is rooted I want to achieve with system files so that even if some other applications try to change above functionalities then they should not be able to do so.

Answer 1

1. Activate developer mode
2. go to Developer options
3. turn on "Stay awake"

Answer 2

Your main use case appears to be as follows (from your question)

Even if some other applications try to change above functionalities then they should not be able to do so

You can write a system service to trigger the PowerManager.WakeLock at regular intervals. (Source)

PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, "My Tag");
wl.acquire();

// screen and CPU will stay awake during this section

wl.release();

To optimize the service you can also try setting the screen timeout the the maximum possible again at regular intervals so that even if changed manually it gets reset. (not sure how much max is allowed, you'll need to check with trial and error)

  /**
   * set screen off timeout
   * @param screenOffTimeout int 0~6
   */
private void setTimeout(int screenOffTimeout) {
    int time;
    switch (screenOffTimeout) {
    case 0:
        time = 15000;
        break;
    case 1:
        time = 30000;
        break;
    case 2:
        time = 60000;
        break;
    case 3:
        time = 120000;
        break;
    case 4:
        time = 600000;
        break;
    case 5:
        time = 1800000;
        break;
    default:
        time = -1;
    }
    android.provider.Settings.System.putInt(getContentResolver(),
            Settings.System.SCREEN_OFF_TIMEOUT, time);
}

(Source)