Android 初始化語言(Android Init Language 

Android初始化腳本語言包含四種類型的語句:

  • 動作(Actions
  • 指令(Commands
  • 服務(Services
  • 選項(Options

該語言的語法包括下列約定:

  • 所有類型的語句都是基於行(line-oriented)的, 一個語句包含若干個tokenstoken之間通過空格字元分隔. 如果一個token中需要包含空格字元,則需要通過C語言風格的反斜線('\')來轉義,或者使用雙引號把整個token引起來。反斜線還可以出現在一行 的末尾,表示下一行的內容仍然屬於當前語句。
  • '#'開始的行是注釋行。
  • 動作(Actions)和服務(Services)語句隱含表示一個新的段落(section)的開始。 所有的指令(commands)和選項()歸屬于上方最近的一個段落。在第一個段落之前的指令(commands)和選項()是無效的。
  • 動作(Actions)和服務(Services)擁有唯一性的名字。如果出現重名,那麼後出現的定義將被作為錯誤忽略掉。

動作(Actions

動作(Actions)是一個有名字的指令(commands)序列。每個動作 Actions)都定義一個觸發條件(trigger),用於指示什麼時候執行這個動作。當與動作的觸發器匹配的事件發生時,該動作將被添加到一個即將 被執行的佇列的隊尾(除非它已經在佇列中)。

佇列中的每一個動作被依次取出執行,動作中的每一個指令也將依次執行。初始化程式(Init)在執行一個動作的各項指令的期間,還需要處理其他操作(比如,設備創建/銷毀,屬性設置,進程重啟)。

一個動作定義的形式如下:

on <trigger>
  <command>
  <command>
  <command>

服務(Services

服務是初始化程式需要啟動的一些程式,初始化程式還有可能會在這些程式退出之後重啟它們。Services take 一個服務定義的形式如下:

  service <name> <pathname> [ <argument> ]*
  <option>
  <option>
  ...

選項(Options

選項將影響控制初始化程式運行服務的時機和方法。可能的選項如下表。

選項

說明

disabled

This service will not automatically start with its class. It must be explicitly started by name.

socket <name><type>  <perm> [ <user> [ <group> ] ]

Create a unix domain socket named /dev/socket/<name> and pass its fd to the launched process. Valid <type> values include dgram and stream. user and groupdefault to 0.

user <username>

Change to username before exec'ing this service. Currently defaults to root.

group <groupname> [ <groupname> ]*

Change to groupname before exec'ing this service.  Additional  groupnames beyond the first, which is required, are used to set additional groups of the process (with setgroups()). Currently defaults to root.

capability [ <capability> ]+

Set linux capability before exec'ing this service

oneshot

Do not restart the service when it exits.

class <name>

Specify a class name for the service.  All services in a named class must start and stop together. A service is considered of class "default" if one is not specified via the class option.

 

觸發器(Triggers

觸發器是一個字串,用於匹配特定的事件,這些事件將觸發觸發器所屬動作(Actions)的執行。

 

觸發器

說明

boot

This is the first trigger that occurs when init starts (after /init.conf is loaded).

<name>=<value>

Triggers of this form occur when the property <name> is set to the specific value <value>.

device-added-<path>
device-removed-<path>

Triggers of these forms occur when a device node is added or removed.

service-exited-<name>

Triggers of this form occur when the specified service exits.


指令(Commands

Command

Description

exec <path> [ <argument> ]*

Fork and execute a program (<path>). This will block until the program completes execution. Try to avoid exec. Unlike the builtin commands, it runs the risk of getting init "stuck".

export <name> <value>

Set the environment variable <name> equal to <value> in the global environment (which will be inherited by all processes started after this command is executed).

ifup <interface>

Bring the network interface <interface> online.

import <filename>

Parse an init config file, extending the current configuration.

hostname <name>

Set the host name.

class_start <serviceclass>

Start all services of the specified class if they are not already running.

class_stop <serviceclass>

Stop all services of the specified class if they are currently running.

domainname <name>

Set the domain name.

insmod <path>

Install the module at <path>.

mkdir <path>

Make a directory at <path>.

mount <type> <device> <dir> [ <mountoption> ]*

Attempt to mount the named device at the directory <dir> <device>. This may be of the form mtd@name to specify a mtd block device by name.

setkey

- currenlty undefined -

setprop <name> <value>

Set system property <name> to <value>.

setrlimit <resource> <cur> <max>

Set the rlimit for a resource.

start <service>

Start a service running if it is not already running.

stop <service>

Stop a service from running if it is currently running.

symlink <target> <path>

Create a symbolic link at <path> with the value <target>.

write <path> <string> [ <string> ]*

Open the file at <path> and write one or more strings to it with write(2).

 

屬性(Properties

初始化程式(Init)可以根據需要修改一些系統的屬性。 

屬性

說明

init.action

Equal to the name of the action currently being executed or "" if none.

init.command

Equal to the command being executed or "" if none.

init.svc.<name>

State of a named service ("stopped", "running", or "restarting").

 

init.rc文件示例

on boot
  export PATH /sbin:/system/sbin:/system/bin
  export LD_LIBRARY_PATH /system/lib

  mkdir /dev
  mkdir /proc
  mkdir /sys


  mount tmpfs tmpfs /dev
  mkdir /dev/pts
  mkdir /dev/socket
  mount devpts devpts /dev/pts
  mount proc proc /proc
  mount sysfs sysfs /sys


  write /proc/cpu/alignment 4


  ifup lo


  hostname localhost
  domainname localhost


  mount yaffs2 mtd@system /system
  mount yaffs2 mtd@userdata /data


  import /system/etc/init.conf


  class_start default


service adbd /sbin/adbd
  user adb
  group adb


service usbd /system/bin/usbd -r
  user usbd
  group usbd
  socket usbd 666


service zygote /system/bin/app_process -Xzygote /system/bin --zygote
  socket zygote 666


service runtime /system/bin/runtime
  user system
  group system


on device-added-/dev/compass
  start akmd


on device-removed-/dev/compass
  stop akmd


service akmd /sbin/akmd
  disabled
  user akmd
  group akmd

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