问题
I want to change the init.rc file of an android pad. But after I change it and reboot the system, the original init.rc comes back.
How can I make the change to the init.rc persistently without rebuild the system (since I don't have the source code of the system)? Or is there any way to work around?
回答1:
Unpack the uramdisk using following command in host PC(Linux)
mkdir /tmp/initrc cd /tmp/initrd
sudo mount /dev/sdb1 /mnt
sdb1 is partion where uramdisk/uInitrd resides.
dd bs=1 skip=64 if=/mnt/uInitrd of=initrd.gz
gunzip initrd.gz
At this point running the command file initrd should show:
mkdir fs
cd fs
cpio -id < ../initrd
Make changes to init.rc
Pack uramdisk using following commands:
find ./ | cpio -H newc -o > ../newinitrd
cd ..
gzip newinitrd
mkimage -A arm -O linux -C gzip -T ramdisk -n "My Android Ramdisk Image" -d newinitrd.gz uInitrd-new
回答2:
A number of Android devices include code to prevent root modifications to the system files. The way this is done is by using the recovery partition. On reboot, they basically restore the system partition using the recovery image. If your system is doing that then you cannot make persistent changes - the best you could do would be to hook up something to run after reboot to re-apply your change. In CyanogenMod they had hooks in the init.rc to run sdcard scripts if found. Perhaps you can create an app or widget to then launch a script to make the mods required using a setuid root script from the data partition. Without building your own ROM you are quite restricted in this area.
Possibly you could fetch the recovery image and try unpacking that, making your changes and repacking and flashing it. But make sure you can recover with fastboot before you try this.
回答3:
Try this site: http://bootloader.wikidot.com/linux:boot:android Read the section at the bottom: •The Android boot image: boot.img ◦Unpack, re-pack boot image: http://android-dls.com/wiki/index.php?title=HOWTO:_Unpack%2C_Edit%2C_and_Re-Pack_Boot_Images#Background
回答4:
When an android system boots, uboot unpacks a special compressed ball of files in your boot partition called 'uRamdisk' to RAM, and defines those files to comprise the root directory of the system. uRamdisk normally contains a bunch of directories (system, data, media, etc.) that serve as mountpoints for partitions that contain the files that go in them, but also has some very basic files vital to your system, including the init binary and startup scripts like init.rc.
when you edit the init.rc, you've actually just edited the unpackaged copy of init.rc that resides in your RAM. To really change it then, you have to copy your uRamdisk, extract it, edit the init.rc from there, repackage uRamdisk and then replace the new one with the old one in /boot.
Try looking up the 'xuramdisk' and 'mkuramdisk' scripts, these make the process very simple.
回答5:
Your root partition (where /init.rc lives) is a ramdisk which is unpacked from an initrd file and mounted every time your device boots. Any changes you make are to the ramdisk only, and will be lost on the next reboot.
If you can get the initrd file, you can mount it on your Linux host system, modify the files there, unmount it, and write it back to your Android.
The initrd file exists in its own partition on the device. If you can figure out which partition it is, you can grab it from the device onto your host, mount it, modify it, and write it back to the device. This is what tripler was talking about above.
In general, modifying boot.img is something that only system developers do. If you're building the entire Android system, you'll have access to the necessary source code. My workflow for this looks like this:
# Modify init.rc
m -j8 bootimage_signed
adb reboot bootloader
fastboot flash boot $OUT/boot.img
fastboot reboot
回答6:
I don't know if you are still trying to do this but without knowing your exact device nobody can give you an exact answer.
Try taking a dd image of all your internal partitions and use some scripts like those included with android kitchen on xda forums. Your recovery and boot partitions will both have a ram disk but odds are you want to modify the init.rc in the boot.img not recovery, unless you only want the changes present in recovery mode.
The unyaffs thing doesn't apply to all devices and most devices have different partition layouts so you have to figure out which is boot and what type of fs it is. Maybe if you give your device specs you can get a better answer.
回答7:
Please note that it may be easier for you to use an app like Scripter to run a script at boot time than modify this file.
Before following @tripler's instructions above you need a file called boot.img which can be extracted by (run on rooted Android device, untested without root):
dd if=/dev/block/platform/<someplatform>/by-name/boot of=/sdcard/boot.img
Then connect your Android to your computer and copy the boot.img file from there.
Script:
http://linuxclues.blogspot.ca/2012/11/split-bootimg-python-android.html
Here is a modified, easier to see version of tripler's instructions (assuming boot.img is in tmp):
cd /tmp
mkdir fs
# Now use the linked script above to split the boot.img file into ramdisk.gz and kernel
python split_boot_img.py -i boot.img -o parts
cd fs
gunzip -c ../parts/ramdisk.gz | cpio -id
# make changes to init.rc
At that point you will have to rebuild the boot.img back together before reflashing, which will be device-specific. Can't help you with that, sorry!
回答8:
You have to edit/change the init.rc before building your Android pad file system. This is the preferred way, and always works.
来源：https://stackoverflow.com/questions/9768103/make-persistent-changes-to-init-rc