# init.rc changes
init.rc changes to run any script
Can be used to start any android application, service
```
on property:dev.bootcomplete=1
    exec - system system -- /system/bin/sh <custom script path>
    # exec - system system -- /system/bin/sh /data/local/bootscript/testservice.sh
```
Script can contains applications start, stop commands
/system/bin/am startservice com.example.android.testservice/.MyService
/system/bin/am stopservice com.example.android.testservice/.MyService
/system/bin/am start/kill/force-stop com.example.android.testservice/.MainActivity


# Get the image - Extracting Existing Kernel + Ramfs

Enter the machine using `adb shell`
Identify the partition either using
Run `cat /proc/partitions` OR
parted utility


Dump the partition to a file using dd

```
dd if=/dev/block/mmcblk0p6 of=/data/kernel_ramfs.img
```

Extract it to your linux system `adb pull /data/kernel_ramfs.img`


# Install abootimg

Run `sudo apt-get install abootimg`


# Check the Kernel Dump

Run `abootimg -i kernel_ramfs.img`. It need to show

```
Android Boot Image Info:

* file name = kernel_ramfs.img

* image size = 16777216 bytes (16.00 MB)
  page size  = 2048 bytes

* Boot Name = ""

* kernel size       = 9797076 bytes (9.34 MB)
  ramdisk size      = 2017625 bytes (1.92 MB)

* load addresses:
  kernel:       0x40008000
  ramdisk:      0x41000000
  tags:         0x40000100

* empty cmdline
* id = 0x7c37c0d4 0xcefde745 0xe81b85ba 0xf05275ba 0xbe7de0ad 0x00000000 0x00000000 0x00000000
```

That means you dump the correct kernel+ramfs

# Extract Kernel Dump

```
abootimg -x kernel_ramfs.img
```

It will extract `zImage` and also `initrd.img`

# Extract Ramdisk, Modify And Repack

```
mkdir initrd
cd initrd
cat ../initrd.img | gunzip | cpio -vid
```

Modify the ramdisk accordingly (e.g. you modify init.rc or add another additonal files)
Then repack accordingly

```
cd initrd
find . | cpio --create --format='newc' | gzip > ../myinitrd.img
```

# Repacking Boot.Img

```
cd ..
abootimg --create myboot.img -f bootimg.cfg -k zImage -r myinitrd.img
```
Repacking might fail due to size issue, remove unnecessary comments, files from ramdisk image and try again after recreating initrd image.

# Reflash
Enter in fastboot mode
```
adb reboot-bootloader
sudo fastboot devices -l            # To check whether device entered in fastboot mode
sudo fastboot erase boot            # Erase existing boot image
sudo fastboot flash boot boot.img   # Flash new image
sudo fastboot reboot                # To come out from fastboot mode
```

# Verify the changes
Verify init.rc for changes
Verify dmesg, logcat(Any init.rc script invokation error will come in dmesg)


Another way
Download the Extract Tools..!! - https://drive.google.com/file/d/0B4fizJM7V7pPMUNkNzNEV01Sb28/view

1) Get boot.img file

2) unpack boot.img file
~/Downloads/Extract\ Tolls/unmkbootimg boot.img

3) Extract ramdisk (initramfs)
gzip -dc initramfs.cpio.gz | cpio -i

4) Re-pack ramdisk
find . | cpio -o -H newc | gzip > ../initramfs.cpio.gz     # From the extracted folder

5) Re-pack boot img
~/Downloads/Extract\ Tolls/mkbootimg --kernel kernel.gz --ramdisk ../initramfs.cpio.gz -o new_boot.img

References: 

http://droidcore.blogspot.in/2012/12/how-to-edit-initrc-in-android.html

https://github.com/135f2l/AndroidNativeDaemon

https://android.stackexchange.com/questions/184074/selinux-prevents-my-init-rc-exec-command-to-execute