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

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