I have one emulator actively running at the moment but I see two emulators running when I run the app. One of them is an Unknown Emulator.
When I choose the Unknown emulator, the console shows this error:
Error: Could not access the Package Manager. Is the system running?
How do I terminate this Unknown Simulator? I think it's using my system's resources and degrading the performance.
Well, it was the BlueStacks emulator running in the background. Android Studio automatically detects it. The unknown simulator was there because BlueStacks was running in the background at the Notification Tray in my windows 8.1
When I closed BlueStacks from the Notification Tray, the Unknown emulator vanished for good.
First reason if your emulator in offline. To resolve this you need to run command kill-server from adb.
Open Command prompt->navigate to android sdk-> go to platform-tools-> adb kill-server -> adb start-server
You need to run above command to remove unknown
Second reason if your project configuration not match with emulator configuration
Change your emulator configuration with your project requirement. May be your application version not match with emulator configuration
It was very simple to fix for my case :) Just need to type the following 2 commands using CMD:
adb kill-server
adb start-server
Make sure that the windows PATH variable contains "adb.exe" file's directory location. Normally, it should be:
YOUR_PATH_TO_SDK\platform-tools
//For example: D:\sdk\platform-tools
来源：https://stackoverflow.com/questions/27615127/android-studio-unknown-emulator-running-and-cant-be-terminated