How to edit the init.rc in android

 

We have to perform the following steps to edit your init.rc successfully:

 

.      Download the BOOT (RamDisk) image from your Android device
.       Extract the boot image into RAMDISK and kernel
.       Extract the RAMDISK to get your edit init.rc to be modify
.       Edit the init.rc file
.       Re-Pack the RAMDISK
.       Re-pack the BOOT image with RAMDISK and kernel
.       Flash the BOOT image into your device
.       Restart and now your device running with your edited init.rc file

 

Requirements for perform this tasks :

 

1.       UBUNTU OS above 10.04 version ( if you are using windows machine you can use virtual Ubuntu OS like VMware, etc.)

2.       Andorid SDK for ADB connection

3.       Extract tools for extract the BOOT image and repack BOOT image.

 

Let we see detailed procedure of each steps,

 

1.Download the BOOT image from your Android device:

 

                Basically Android device have three types of partitions these are NAND, mtd, and mmcblck.

Reputed brand devices have NAND and mtd, some China brand device have mmcblk, which means OS stored in mmc (memory card) card. But in the memory card you can’t find the init.rc file and you can see other files except init.rc  if you takeout the mmc and connect to your PC over card reader.

                Let’s start the operation, connect your device with PC( windows or Ubuntu)  and check whether its discoverable by ADB or not.  Change the working directory into android SDK /platform-tools folder then execute

 

                # adb devices

 

If you can see your device, then you can proceed with further steps. If you couldn’t find your device download the ADB USB drivers and install on your PC.

Open the device shell by executing this command

 

                # adb shell

 

Then we have to find what kind of partitions your device have. It can be by this following command

 

                # cat /proc/partitions

 

Then you will get output like this       

      

cat /proc/partitions
major minor  #blocks  name

                  mtdblock0
                    mtdblock1
                      mtdblock2
                         mtdblock3
                         mtdblock4
                         mtdblock5
                   mtdblock6
                   mtdblock7
                   mtdblock8
                   mtdblock9
               mtdblock10
               mtdblock11
              mtdblock12
              mtdblock13

mtdblock shows you that your device contain mtd partitions .

If your device have NAND partitions your will get NANDA, NANDB, NANDC or NAND0, NAND1 etc. like this.

If your device have mmc partitions you will get mmcblk1, mmcblk2, etc.

Our next process is find out where our BOOT image stored among these partitions.

 

If its mtd partitions:

 

 # cat /proc/mtd
dev:  size  erasesize  name
mtd0: 00d00000  "filesystem-SF"
mtd1:   "kernel-SF"
mtd2:   "u-boot-SF"
mtd3:   "u-boot env. cfg. 1-SF"
mtd4:   "u-boot env. cfg. 2-SF"
mtd5:   "w-load-SF"
mtd6:   "logo"
mtd7:   "boot"
mtd8:   "recovery"
mtd9:   "misc"
mtd10:   "system"
mtd11:   "cache"
mtd12:   "data"
mtd13: 17b800000  "LocalDisk"

Hence our boot partition is mtd7, we have to download the BOOT image from that partitions.

 

If its NAND partitions:

 

# cat /proc/mtd
dev:  size  erasesize  name
/boot                    emmc                   /dev/block/nandc
/bootloader       emmc                   /dev/block/nanda
/cache                  ext4                       /dev/block/nandh
/data                     ext4                       /dev/block/nande
/emmc                 vfat                        /dev/block/nandi
/recovery            emmc                   /dev/block/nandg
/misc                     emmc                   /dev/block/nandf
/sdcard                 vfat                        /dev/block/mmcblk0p1                /dev/block/mmcblk0
/sd-ext                 auto                       /dev/block/mmcblk0p2
/system                               ext4                       /dev/block/nandd

 

Hence our boot partition is NANDC, we have to download the BOOT image from this partition.

 

 

Download the image from boot partitions:

 

Execute the following command to pack your boot image.

 

                # cat /dev/block/mtdx > /mnt/sdcard/boot.img

 

x- Replace the x with your boot partition number.

 

In our case this command will be

 

                # cat /dev/block/ mtdblock7  >  /mnt/sdcard/boot.img

               

                # cat /dev/block/ nandc  > /mnt/sdcard/boot.img

 

Now your boot image got ready. you can move this boot.img to your UBUNTU PC  for further action.

Come out from your terminal window and pull the boot.img file to your PC over ADB

 

                # adb pull /mnt/sdcard/boot.img  <PC destination location> 

 

But all devices wouldn’t show this message for this command, Its works for mtd partitions. some devices only show the following information

 

                # cat /proc/mtd

                dev:  size  erasesize  name

 

Hence we need to go for other choice. The other choice is below            

 

                # mount

 

rootfs on / type rootfs (rw)

tmpfs on /dev type tmpfs (rw,nosuid,relatime,mode=755)

devpts on /dev/pts type devpts (rw,relatime,mode=600)

proc on /proc type proc (rw,relatime)

sysfs on /sys type sysfs (rw,relatime)

tmpfs on /mnt/asec type tmpfs (rw,relatime,mode=755,gid=1000)

tmpfs on /mnt/obb type tmpfs (rw,relatime,mode=755,gid=1000)

/dev/block/mmcblk0p5 on /system type ext2 (rw,relatime)

/dev/block/mmcblk0p6 on /data type ext2 (rw,nosuid,nodev,relatime,errors=continu

e)

/dev/block/mmcblk0p7 on /cache type ext2 (rw,nosuid,nodev,relatime,errors=contin

ue)

none on /proc/bus/usb type usbfs (rw,relatime,devmode=666)

/dev/block/vold/179:1 on /mnt/sdcard type vfat (rw,dirsync,nosuid,nodev,noexec,r

 

        From the output you can see some partitions name and its file system purpose.  Hence you can omit this partitions because its allotted for filesystem not for boot image. And then we have to try trail and error method. which means you have convert other possible partitions as part1.img, part2.img etc like this. Then we can find which one is boot image while we extracting the boot images by extract tool.

 

 

2.Extract the boot image into RAMDISK and kernel

 

                You can download the extract tools below. In the attachment copy the unmkbootimg file to your boot.img location and execute the following command

 

                # ./unmkbootimg boot.img

 

This command will extract your boot.img into ramdisk and kernel and another one important thing is after extracting you will get the command for recreate the boot.img with this ramdisk and kernel  in terminal so please note it.

 

If you are not using unmkbootimg file for extracting the boot image means you have to do one important work that is, you have to note your boot image BASE address its very important to recreate your boot image with edited init.rc. If you recreate the boot image with wrong BASE address your device won’t get boot So be careful.

 

Now you have ramdisk in your hand 

 

 

3.Extract the RAMDISK to get your edit init.rc to be modify

 

               Now the time for extract your ramdisk to get init.rc. 

According to this do the following things

                create the folder name it as newramdisk

                Inside the newramdisk folder create another folder and name it as oldramdisk.

                Copy your ramdisk into your oldramdisk folder

                Goto the oldramdisk in terminal

                Execute the following commands to extract your ramdisk

 

                # gzip –dc initramfs.cpio.gz | cpio –i

 

                                Now you can find extracted files including init.rc, in same directory. Now you can edit init.rc and other files if you need.

 

4.Re-Pack the RAMDISK

               

                After edit the init.rc you have to re-pack the ramdisk. Execute the following commands to re-pack the ramdisk. Before you giving this command you have to delete your initramfs.cpio.gz  file, because the following command compress the all files inside the folder.

               

                # find . | cpio –o –H newc | gzip > ../initramfs.cpio.gz

 

                This command create your new ramdisk into your newramdisk folder. You can check this in newramdisk location.

 

Now you have new edited ramdisk file in your hand.

 

5.Re-pack the boot image.

 

                Now you have newramdisk + kernel file + command  to create the boot image for your device.

Create the final folder and place the newramdisk and kernel file and change the working directory into this folder. Then you have to give the mkbootimg command to create your boot image.

              Before you giving this command you have to install mkbootimg binary in your UBUNTU host system. This binary is attached with extract tools.

 

                # mkbootimg  --kernel kernel.gz –ramdisk initramfs.cpio.gz –o new_boot.img

 

Note: its just a example command execute the command which one you got while extracting the boot image because that command only generated with your BASE address

 

This command create the boot image to your device with your BASE address.

 

 

6.Flash the BOOT image into your device

 

              Now you have create the boot image with edited init.rc and its ready to flash into your device.

Push the new_boot.img file into your device over ADB

 

              # adb push <source_location/new_boot.img> /mnt/sdcard

 

Then you can see the new_boot.img file into your /mnt/sdcard location

Next step is final step, that is flash the image into your device

 

              # cat /mnt/sdcard/new_boot.img  > /dev/block/nandc

 

Note: nandc is your boot partition, from where you got your boot image. Replace the nandc with your boot partition name.

 

Now you had edited your init.rc then reboot the device. Enjoy with your modified init.rc

 

Attachments: 

Download the Extract Tools..!!

 

If you happen to face any problem during this process feel free to comment here...

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