What happens in the system if it receives a push notification from an app that is not currently running?

If an iOS app is not running (i.e., it is inactive or completely terminated from memory), and the system receives a push notification, the behavior depends on the type of notification:

• Regular push notification with a visible message (alert): iOS will display the notification to the user in the Notification Center and on the lock screen. The app will not launch automatically, but if the user taps on the notification, the system will launch the app.

• Silent push (background notification): if the app is not running, the system may launch it in the background to handle such a notification, but this is not guaranteed and depends on the device state, power management policies, and other factors. Silent push is used to update content without user intervention.

Thus, receiving a push notification can either lead to launching the app in the background (for silent push) or simply displaying the notification without launching the app (for regular notifications).