android的啟動腳本（init.rc）文件的語法，參考資料：
http://www.kandroid.org/android_pdk/bring_up.html
Android初始化腳本語言包含四種類型的語句：
該語言的語法包括下列約定：
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(fā)條件（trigger），用于指示什么時候執(zhí)行這個動作。當與動作的觸發(fā)器匹配的事件發(fā)生時，該動作將被添加到一個即將被執(zhí)行的隊列的隊尾（除非它已經在隊列中）。
隊列中的每一個動作被依次取出執(zhí)行，動作中的每一個指令也將依次執(zhí)行。初始化程序（Init）在執(zhí)行一個動作的各項指令的期間，還需要處理其它操作（比如，設備創(chuàng)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）
服務是初始化程序需要啟動的一些程序，初始化程序還有可能會在這些程序退出之后重啟它們。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序運行服務的時機和方法?？赡艿倪x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 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. |
觸發(fā)器（Triggers）
觸發(fā)器是一個字符串，用于匹配特定的事件，這些事件將觸發(fā)觸發(fā)器所屬動作（Actions）的執(zhí)行。
| 觸發(fā)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> | 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）
初始化程序（Init）可以根據(jù)需要修改一些系統(tǒng)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
