android的init.rc文件的语法

 android的启动脚本（init.rc）文件的语法，参考资料：

 http://www.kandroid.org/android_pdk/bring_up.html

Android初始化语言（Android Init Language）

Android初始化脚本语言包含四种类型的语句：

• 动作（Actions）
• 指令（Commands）
• 服务（Services）
• 选项（Options）

该语言的语法包括下列约定：

• 所有类型的语句都是基于行（line-oriented）的， 一个语句包含若干个tokens，token之间通过空格字符分隔. 如果一个token中需要包含空格字符，则需要通过C语言风格的反斜线（'\'）来转义，或者使用双引号把整个token引起来。反斜线还可以出现在一行的末尾，表示下一行的内容仍然属于当前语句。
• 以'#'开始的行是注释行。
• 动作（Actions）和服务（Services）语句隐含表示一个新的段落（section）的开始。 所有的指令（commands）和选项（options）归属于上方最近的一个段落。在第一个段落之前的指令（commands）和选项（options）是无效的。
• 动作（Actions）和服务（Services）拥有唯一性的名字。如果出现重名，那么后出现的定义将被作为错误忽略掉。

动作（Actions）

动作（Actions）是一个有名字的指令（commands）序列。每个动作（Actions）都定义一个触发条件（trigger），用于指示什么时候执行这个动作。当与动作的触发器匹配的事件发生时，该动作将被添加到一个即将被执行的队列的队尾（除非它已经在队列中）。

队列中的每一个动作被依次取出执行，动作中的每一个指令也将依次执行。初始化程序（Init）在执行一个动作的各项指令的期间，还需要处理其它操作（比如，设备创建/销毁，属性设置，进程重启）。

一个动作定义的形式如下：

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

服务（Services）

服务是初始化程序需要启动的一些程序，初始化程序还有可能会在这些程序退出之后重启它们。Services take 一个服务定义的形式如下：

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

选项（Options）

选项将影响控制初始化程序运行服务的时机和方法。可能的选项如下表。

选项	说明
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 group default 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.

触发器（Triggers）

触发器是一个字符串，用于匹配特定的事件，这些事件将触发触发器所属动作（Actions）的执行。

触发器	说明
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).

属性（Properties）

初始化程序（Init）可以根据需要修改一些系统的属性。

属性	说明
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