PackageInstaller is the default application for Android to interactively install a normal package. PackageInstaller provide user interface to manage applications/packages.

How do I find package manager on Android?

getPackageManager() is a method of Context. You can use this method inside an Activity (because an Activity is a Context), but if you are calling it elsewhere, you need to pass a Context. In a fragment you may also have access to the getActivity() function, which returns the Acitivity-Context.

What is the package installer on my Android phone?

Package Installer is the Android service responsible for installing new apps, updating the apps and uninstalling the apps. Probably the installed apps are being updated or being verified on daily basis. Hence you see package installer service shown up in the History.