Android initialization Language

Android initialization Language

The init. rc file is not a common configuration file, but a file written by a script called "Android Init Language" (AIL.

AIL consists of the following four parts:

1. Actions)

2. Command (Commands)

3. Services)

4. Options)

These four parts are line-oriented code, that is, the line breaks are used as the separator for each statement. Each line of code is represented by multiple symbols (Tokens. You can use the backslash escape character to insert spaces in the Token. Double quotation marks can combine multiple Tokens separated by spaces into one Tokens. If a row cannot be written, you can add a backslash at the end of the row to connect to the next row. That is to say, you can use a backslash to connect multiple lines of code into one line of code.

AIL comments and a line of many Shell scripts, starting.

AIL needs to be divided into multiple sections during writing, and Actions or Services must be specified at the beginning of each part. That is to say, each Actions or Services determines a Section. All Commands and Options can only belong to the recently defined Section. If Commands and Options are defined before the first Section, they are ignored.

The names of Actions and Services must be unique. If two or more actions or services have the same name, init will throw an error when executing them and ignore these actions and services.

Next let's take a look at how to set Actions, Services, Commands, and Options.

The syntax format of Actions is as follows:

On

 

That is to say, Actions starts with the keyword on, followed by a trigger, followed by several commands. For example, the following is a standard Action.

On boot

Ifup lo

Hostname localhost

Domainname localdomain

Among them, boot is the trigger, and the following three lines are command

So what triggers does init. rc support? Currently, init. rc supports the following five types of triggers.

1. boot

This is the first Trigger triggered after init is executed, that is, the Trigger is executed after/init. rc is loaded.

2. =

When the attribute Set Is triggered. For example,

On property: vold. decrypt = trigger_reset_main

Class_reset main

3. device-added-

Triggered when a device node is added

4. device-removed-

Added when the device node is removed

5. service-exited-

Will be triggered when a specific service exits

After Actions, several commands are required. These commands are as follows:

1. exec [] *

Create and execute a program ( ). Before the program is fully executed, init will be blocked. Because it is not a built-in command, try to avoid using exec, which may cause init execution timeout.

2. export

In the global environment Set the variable value . (This will be inherited by all processes running after this command)

3. ifup

Start Network Interface

4. import

Specify other configuration files to be parsed. It is often used for expansion of the current configuration file.

5. hostname

Set Host Name

6. chdir

Change working directory

7. chmod

Change File Access Permissions

8. chown

Change the file owner and group

9. chroot

Change the processing root directory

10. class_start

Start all services not running under the specified service class.

11 class_stop

Stop all running services under the specified service class.

12. domainname

Set Domain Name

13. insmod

Load Specified Driver Module

14. mkdir [Mode] [owner] [group]

Create a directory You can select mode, owner, and group. If not specified, the default permission is 755 and belongs to the root user and root group.

15. mount

[ ] *

 

Try

Mount the specified device. You can specify an mtd block device in the form of mtd @ name. Including ro, rw, and re

 

16. setkey

Reserved, unavailable for the moment

17. setprop

Set System Properties Is set .

18. setrlimit

Set (Resource restrictions)

19. start

Start the specified service (if the service is not running ).

20. stop

Stop the specified service (if the service is running ).

21. symlink

Create a point Soft connection .

22. sysclktz

Set the system clock benchmark (0 indicates that the clock tick is based on the Greenwich Mean Time (GMT)

23. trigger

Trigger an event. Used for Action queuing

24. wait [ ]

Wait for a file to exist. If the file exists, return immediately or Returned after the specified timeout. The default timeout value is 5 seconds.

25. write [ ] *

Direction The specified file is written into one or more strings.

A service is a program that is started during initialization and restarted upon exit (optional ). Services are as follows:

Service [] *

 

 

For example, the following is a standard Service usage

Service servicemanager/system/bin/servicemanager

Class core

User system

Group system

Critical

Onrestart restartzygote

Onrestart restartmedia

Onrestart restartsurfaceflinger

Onrestart restartdrm

The Service option is the modifier of the service, which can affect how and how the service runs. The Service supports the following options:

1. critical

This indicates that this is a very important service. If the service exits more than 4 times in four minutes, the system restarts and enters the Recovery (Recovery) mode.

2. disabled

This indicates that the service cannot be automatically started with the trigger. The service must be explicitly started by name.

3. setenv

When the process starts, set the environment variable Set .

4. socket [ [ ]

Create a unix domainsocketnamed/dev/socket/ And pass

Its fd to thelaunchedprocess. Must bedgram, stream or seqpacket.

User and group default to0.0.

Create a unix domain named/dev/socket/ And pass its file descriptor to the started process. It must be dgram, stream, or seqpacket. The default value of user and group is 0.

5. user

Change the User Name of the service before starting the service. The default value is root.

6. group [ ] *

Change the group name of the service before starting the service. Except (required) The first group name, the attached group name is usually used to set the supplemental group of the process (through the setgroups function), and the file is root by default.

7. oneshot

Do not restart when the service exits.

8. class

Specify a service class. All services of the same category can be started and stopped at the same time. If a class is not specified through the class option, the default class service is used by default.

9. onrestart

When the service is restarted