A preliminary understanding of the file system structure and guiding process of Android

1. Structure of the android File System
After the android source code is compiled, the system. IMG, ramdisk. IMG, and userdata. IMG image files are obtained. Ramdisk. IMG is the file system of emulator. IMG includes the main packages, libraries, and other files, userdata. IMG includes some user data. After the emulator loads these three image files, it loads system and userdata to the system and userdata directories in the ramdisk file system respectively. Therefore, we can copy all the files in ramdisk. IMG and decompress system. IMG and userdata. IMG to the system and userdata directories in the ramdisk file system.

2. Separate the android File System
The system. IMG, ramdisk. IMG, and userdata. IMG image files are packaged using cpio and compressed using gzip. You can run the file command to verify that:
File ramdisk. IMG, output:
Ramdisk. IMG: gzip compressed data, from UNIX, last modified: Wed mar 18 17:16:10 2009
After the android source code is compiled, in addition to system. IMG and userdata. IMG, the system and userdata folders are generated, so you do not need to decompress them. After the android source code is compiled, the root folder is generated. In fact, the files under root are the same as those in ramdisk. IMG. But here we will introduce how to decompress ramdisk. IMG:
Copy ramdisk.imgto another directory, change its name to ramdisk.img.gz, and run the command
Gunzip ramdisk.img.gz
Create a folder named ramdisk.
Cpio-I-f ../ramdisk. img
Now you can see and operate the content in ramdisk.
Copy the files in system and userdata generated after compiling the android source code to ramdisk/system and ramdisk/userdata. In this way, a file system is obtained.

3. Mount the android File System Using a Network File System
Therefore, we need to create the/nfsroot directory, create the/nfsroot/androidfs directory, change the android File System to androidfs, and link to/nfsroot/androidfs.

4. Android kernel boot file system
After mounting the android kernel/nfsroot/androidfs, initialize and load the system library and program according to init. RC and init. Goldfish. RC until the boot is complete. The init. RC Script includes many file system initialization and loading processes. The main work of init. RC is:
1) set some environment variables
2) create directories such as system, sdcard, data, and Cache
3) mount some file systems to some directories, for example, Mount tmpfs/sqlite_stmt_journals
4) set user groups and permissions for some files
5) set some thread parameters
6) set the TCP cache size