android init.rc 语法分析
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system/core/init/readme.txt（此文也是对init.rc 的解释）内容不同：
socket [ [ ] ]
Debugging notes
---------------
By default, programs executed by init willdrop stdout and stderr into
/dev/null. To help with debugging, you canexecute your program via the
Andoird program logwrapper. This willredirect stdout/stderr into the
Android logging system (accessed vialogcat).
For example
service akmd /system/bin/logwrapper/sbin/akmd
---------------
By default, programs executed by init willdrop stdout and stderr into
/dev/null. To help with debugging, you canexecute your program via the
Andoird program logwrapper. This willredirect stdout/stderr into the
Android logging system (accessed vialogcat).
For example
service akmd /system/bin/logwrapper/sbin/akmd
sysclktz
Setthe system clock base (0 if system clock ticks in GMT)
注3：triggers
boot
Thisis the first trigger that will occur when init starts
(after /init.conf is loaded)
=
Triggers of this form occur when the property is set
tothe specific value .
device-added-
device-removed-
Triggers of these forms occur when a device node isadded
orremoved.
service-exited-
Triggers of this form occur when the specified serviceexits.
=
device-added-
device-removed-
service-exited-
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init 由如下四种类型语句组成：
- Actionn
：行为 - Commands
- Services
- Options
- 每一个语句占据一行，并且各个关键字被空格分开。c规范中的（如 \n）反斜杠将被忽略(backslashescapes)而被认为是一个空格，双引号用来保证空格不会把一个文字串分分为多个关键字。行最后的反斜杠用作续行。
- 由 # （前面允许有空格）开始的行都是注释行(comment)
- 一个actions 或 services 的开始隐含声明了一个新的段，所有commands 或 options属于最近的声明。在第一个段之前的 commands 或 options 都会被忽略
- 每一个actions 和 services都有不同的名字。后面与前面发生重名的，那么这个后面重名的将被忽略或被认为是一个错误
Actions其实就是一组被命名的命令序列。actions都有一个触发条件，触发条件决定了action何时执行。当一个事件发生如果匹配action的触发条件，那么这个action将会被添加到预备执行队列的尾部（除非它已经在队列当中）
每一个action中的命令将被顺序执行。init进程负责在其它activities（如：设备创建/销毁，属性设置，进程重启）之间执行这些命令序列。
Services
Options
options 是service的修饰符，用来告诉init 怎样及何时启动service。
disabledThis service will not automatically start with its class. Itmust be explicitly started by name.socket [ [ ] ]Create a unix domain socket named /dev/socket/ andpass its fd to the launched process. Valid dgram andstream. user and groupdefault to 0.(type 实际中是放在name之后)
userChange to username before exec'ing this service. Currentlydefaults to root.group [ ]*Change to groupname before exec'ing this service. setgroups()). Currently defaults toroot.capability [ ]+Set linux capability before exec'ing this serviceoneshotDo not restart the service when it exits.classSpecify a class name for the service.
Triggers are strings used to match certain kinds of events thatcause an action to occur.
bootThis is the first trigger that occurs when init starts (after/init.conf is loaded).=Triggers of this form occur when the property is set to thespecific value .device-added-
device-removed-Triggers of these forms occur when a device node is added orremoved.service-exited-Triggers of this form occur when the specified serviceexits.
Commands
exec [ ]*Fork and execute a program (). This will block until theprogram completes execution. Try to avoid exec. Unlike thebuiltin commands, it runs the risk of getting init"stuck".export Set the environment variable equal to in the global environment(which will be inherited by all processes started after thiscommand is executed).ifupBring the network interface online.importParse an init config file, extending the currentconfiguration.hostnameSet the host name.class_startStart all services of the specified class if they are notalready running.class_stopStop all services of the specified class if they are currentlyrunning.domainnameSet the domain name.insmodInstall the module at .mkdirMake a directory at .mount]*. This may be of the form mtd@name tospecify a mtd block device by name.
setkey- currenlty undefined -setprop Set system property to .setrlimit Set the rlimit for a resource.startStart a service running if it is not already running.stopStop a service from running if it is currently running.symlink Create a symbolic link at with the value .write [ ]*Open the file at and write one or more strings to it withwrite(2).Properties
what it's doing:
init.actionEqual to the name of the action currently being executed or ""if none.init.commandEqual to the command being executed or "" if none.init.svc.State of a named service ("stopped", "running", or"restarting").
setprop ro.FOREGROUND_APP_MEM 1536
setprop ro.VISIBLE_APP_MEM 2048
on property:ro.kernel.qemu=1
start adbd
setprop用于设置属性，onproperty可以用于判断属性，这里的属性在整个Android系统运行中都是一致的。
exam init.rc
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on init
sysclktz 0
loglevel 3
# setup the global environment
# Backward compatibility
# create mountpoints and mount tmpfs on sqlite_stmt_journals
#{{ added by FriendlyARM
#}}
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# Create cgroup mount points for process groups
# mount mtd partitions
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