Based on android2.3.5: How does Linux start the Andriod daemon init?

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Author: EasyWave time: 2013.07.28

Category: Android source code analysis statement: reprinted. Please keep the link

NOTE: If any error occurs, please correct it. These are my Learning Log articles ......

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1): How does Linux Andriod work?

We all know that when starting a file system in Linux, command line is usually specified in the Linux kernel, as shown below:

We can see from the figure that there is a Boot options option in the Linux Kernel configuration. After Entering, we can see a line of command like this:

Console = ttySAC0 root =/dev/mtdblock2 rootfstype = cramfs init =/linuxrc

This line is very important. To successfully start the Andriod system, you need to pay attention to init =/linuxrc. This will be explained in detail later. Now let's take a look at the kernel startup, what do you do? For details, refer to another blog:MACHINE_START and MACHINE_END
Macro defineThis section details how to start Linux. Here we only focus on this function: static noinline int init_post (void) as follows:

We can see that after the kernel is started, it will automatically find the previously specified init =/linuxrc. If it cannot be found, then he will find the following/sbin/init,/etc/init and so on. In the andriod file system, there is a linuxrc file under the root directory. How can we see it? We can decompress ramdisk by running the command. img. The procedure is as follows [taking the OK6410 Andriod system as an example]:

Enter the following command in the command line:Cp ramdisk. img ramdisk.img.gz

Create a folder, such as mkdir test, and copy ramdisk.img.gz to the new test file. Then run the command: gunzip ramdisk.img.gz to decompress the folder. The following command is used:

Cpio-I-F ramdisk. img decompress the file system, as shown below:

We can see a linuxrc file in the test folder, as shown below:

Finally, open the linuxrc file and check the content as follows:

Check whether the last line/init is correct. The Linux kernel loads linuxrc through command line, and then loads the/init Andriod daemon init in linuxrc.