Other Stack Exchange users have already answered this question in posts elsewhere.
t0mm13b writes that, while displaying your carrier's shutdown animation:
- Android is safely shutting down vital parts of the runtime.
- The OS is also broadcasting intents to tell apps and services to gracefully close. These, in turn, flush their caches of all data and shared preferences, save what-nots to the sqlite database, et cetera.
In other words, apps and services are given a chance to do their cleanup systematically.
[Commands such as
adb reboot] are harsher. They actually bypass the safety mechanisms for a graceful shutdown.
Elsewhere, Yury offers another explanation of what Android does during a graceful shutdown:
- It shuts down ActivityManager. I think shutting down ActivityManager means that all activities will pass necessary lifecycle and, thus, the states of activities will be stored. But I'm not sure. I did not check.
- Then, Android turns off the cellular radio interface.
- After that, it turns off Bluetooth.
- Finally, it tries to shut MountService down.
adb reboot is faster because it skips some or all of the above.
