= Boot Process
include::_support/common.inc[]

“How does Mobile NixOS boot?”

This is what this documentation topic tries to describe. This is for end-users.

For developers, see in-depth topics.


== Booting Mobile NixOS

Most devices targeted by Mobile NixOS are intended to boot only one kernel at
a time, with one stage-1, and one system.

NixOS, in turn, shines when a system can choose a _generation_, which has its
own kernel, stage-1, and system build.

Mobile NixOS, at this point in time, sits on the halfway point. The user cannot
choose which generation a kernel and stage-1 comes from, but can boot a
specific generation.


== Booting a specific generation

This is done through booting in "recovery mode". This will stop the stage-1
process before it jumps into the default generation, and will allow you to
select a system to boot into.

The method to enter recovery mode depends on your device

=== Android-based devices

Android-based devices can be booted in their respective recovery mode.

When the device is a _"Boot as recovery"_ system, no other setup than flashing
the boot partition is required. _"Boot as recovery"_ systems are generally newer
Android-based devices.

When the device is not a _"Boot as recovery"_, or still uses a recovery
partition, you will need to flash a recovery image to the recovery partition.

....
 $ nix-build --argstr device $DEVICE -A build.android-recovery
 $ fastboot flash recovery result
....

=== All other devices

_Including the default boot partition for Android-based devices._

When the boot process is about to switch to the system, if any of the following
keys are held, it will instead show the recovery menu.

* Volume up
* Volume down
* Left shift
* Right shift
* Left control
* Right control
* Escape

== Testing the boot GUI

The simulator can be launched using the following commands:

....
 $ nix-build --argstr device qemu-x86_64 -A pkgs.boot-gui-simulator
 $ result/bin/simulator --resolution 1080x1920
....