Android Init Stages

.

Stages

Init stage Contents
early-init Very first stage of initialization. Used for SELinux and OOM settings
init Creates file systems, mount points, and writes kernel variables
early-fs Run just before filesystems are ready to be mounted
fs Specifies which partitions to load
post-fs Commands to run after filesystems (other than /data) are mounted
post-fs-data /data decrypted (if necessary) and mounted
early-boot Run after property service has been initialized, but before booting rest
boot Normal boot commands
charger Commands used when device is in charger mode

Adapted from Jonathan Levin’s excellent Android Internals: A Confectioner’s Cookbook, chapter 4.

Classes

Programs can be started based on init stage triggers:

service my_service /bin/mysvc
    user system
    group system
    disabled

on boot
    start my_service

But it is more common to assign a class to a service, based on which it is started:

service my_service /bin/mysvc
    class core
    user system
    group system

The service will be started based on class_start core which happens on boot.

TODO: Overview of classes

Class Comment
core Never shut down after restarting
main Shut down and then restart after the disk password is entered
late_start Does not start until after /data has been decrypted and mounted
Trigger Classes
on charger charger
on late-fs early-hal
on nonencrypted hal, core
on boot hal, core

Keywords (selection)

Keyword Action
start Starts a service, even when it’s disabled
class core Makes a service part of a group.
class_start Starts a group. Once this group is started, the service is started only if it is enabled (services can be disabled by having disabled in the service spec, or disable <service>)
enable Allows a service to be started as part of a class_start. If the class is already started, this’ll schedule the service to be started
disable Prevent a service from being started as part of class_start. This does not stop the service if it’s already running

Changes with encryption

With the introduction of system-wide encryption into Android, the init process gains a few more tricks: - vold.decrypt triggers - class early_hal for crucial services needed for decryption, e.g. keymaster and gatekeeper (TODO: Add link to AOSP init.rc for class_start) - restarting framework, reboot, minimal UI stuff - nonencrypted trigger, which, despite its name, always gets triggered and which pulls in class_start main and class_start late_start

on property:vold.decrypt=trigger_restart_min_framework
    class_start main

on property:vold.decrypt=trigger_restart_framework
    stop surfaceflinger
    start surfaceflinger
    class_start main
    class_start late_start

on property:vold.decrypt=trigger_shutdown_framework
    class_reset late_start
    class_reset main

(Gone in master/Q: Stop using trigger_reset_main)