Mac iOS simulator starts at

1. You install the terminal list all available devices xcrun instruments -s or xcrun simctl list
2. A start-up mode:
   first start the simulator: open -a Simulator, then we will start with the default iOS system version;
   start iOS system: xcrun simctl boot "first step simctl simulator name list" or xcrun instruments -w " simulator name "the first step in the list of instruments;
3. Start way: first start iOS restart the system simulator, i.e. the reverse order of a startup mode;
4. Install the specified appxcrun simctl install booted
5. xcrun simctl launch booted
6. xcrun simctl uninstall booted