[Experimental] Dual Boot and above Discussion

karandpr · Jan 8, 2015

Alright so I have achieved Dual Boot :victory:
THIS IS NOT KEXEC .

It's a simple hack or probably an elegant one.
We can probably achieve multiboot but that is not important.

There are some other things which will be ironed out but thats for later.

Thread Rules :
No Thank you or How Do I do it or nooby questions.
This thread is exclusively for Developers, Enthusiasts and/or Professionals.
Knowledge of Linux and Terminal is MANDATORY.
Dual Partitioned SD card. Second partition preferably
Linux Installed on your computer.

Rubbish posts will be removed .
Save some pride by not being a n00b.

Currently I have planned two types in my mind.

Type 1: Dual Booting ROMs with Same Boot Images - Completed

This hack works across ROMs which use same kernel with same ramdisk... ICS ROMs series , LXP ROMs who use the LXP kernels.. If there is even slight difference in the ramdisk (esp. the init.rc) ,you wont be able to boot ROMs.

Type 2: Dual Booting ROMs with Same kernels but different Ramdisks- Therotically completed.

Post 1: Intro
Post 2: Prepare SD Card and Images
Post 3: Prepare Ramdisk and ROM Installations
Post 4: Installation and switching ROMs
Post 5:Ramdisk Mod
Post 6 : Multiple Mounts/ MultiBoot
Post 7: FAQ

karandpr · Jan 9, 2015

Problems :
Partitioning SD card is annoying and not fruitful
Second SD card partition might be used as second SD card on First ROM.

Solution"
Use loop Images.

I WOULD RECOMMEND USING ANY LINUX DISTRO FOR MAKING A LOOP IMAGE. Because LINUX !!!

Preparation:

Dump Images and formatting.

Make dump images

Code:

dd if=/dev/zero of=system.kdpr bs=4096 count=100000

Will you give you 400 MB image

Code:

dd if=/dev/zero of=data.kdpr bs=4096 count=200000

Will you give you 800 MB image.

Mount Images (as root)

Code:

losetup /dev/loop0 system.kdpr

Code:

losetup /dev/loop1 data.kdpr

Format images(as root)

Code:

sudo mkfs.ext4 -T ext4 -b 4096 -m 0 -J size=4 -O ^huge_file,^has_journal,^resize_inode,^ext_attr /dev/loop0
sudo mkfs.ext4 -T ext4 -b 4096 -m 0 -J size=4 -O ^huge_file,^has_journal,^resize_inode,^ext_attr /dev/loop1
tune2fs -c 100 -i 100d -m 0 /dev/loop0
tune2fs -c 100 -i 100d -m 0 /dev/loop1

You have two ext4 formatted images system.kdpr and data.kdpr ready.
Copy those images to sd-ext folder.You can mount /dev/mmcblk0p2 on a folder and directly push these images via adb push
OR copy images to SD card and copy to second partition.
Either way the system.kdpr and data.kdpr should be in root of the second SD card partition.

Assuming you have mounted second sd card partition on /data/sd-ext.

Run this command

Code:

touch flag_kdpr

The Images are now ready and loaded :victory:

karandpr · Jan 6, 2015

Now is the time to hack the boot image.
Unpack Boot image and navigate to ramdisk folder

Navigate to the lines in init.rc where partitions are mounted .
Comment off or remove the lines mounting system and data
For stock ICS it is in init.semc.rc

Code:

 #mount yaffs2 [email protected] /system
    #mount yaffs2 [email protected] /system rw remount
    #mount yaffs2 [email protected] /data nosuid node

v

add a line

Code:

exec /sbin/mount_fs.sh

now create a bash script named mount_fs.sh as follows

Bash:

#!/sbin/sh

mount /dev/block/mmcblk0p2 /res/sdext
flag_boot=`cat /res/sdext/flag_kdpr`

if [ ${flag_boot} -eq 1 ]
then
mount /res/sdext/system.kdpr /system
mount -o remount,rw /res/sdext/system.kdpr /system 
mount /res/sdext/data.kdpr /data
else
mount /dev/block/mtdblock0 /system
mount -o rw,remount /system
mount /dev/block/mtdblock1 /data
fi

make a folder named /res/sdext or choose mount point of your choice

We will be controlling the mount point and boot via the file flag_kdpr.
Using this flag we can also achieve MultiBoot

Repack the boot image.

karandpr · Jan 6, 2015

Installing Secondary ROM

Open the zip and extract the updater script .
Remove the lines for mounting/formatting system and data.
Repack the zip

Mount sd-ext
Run these commands in terminal

Code:

mount /sd-ext/system.kdpr /system
mount /sd-ext/data.kdpr /data

Install the zip ROM.
ROM will be installed in the dump images.

Booting to secondary ROM:
In the recovery or first ROM run this command

Code:

echo 1 > /sd-ext/flag_kdpr

OR

Code:

echo 1 > /res/sdext/flag_kdpr

and reboot

Booting to primary ROM:
In the recovery or first ROM run this command

Code:

echo 0 > /sd-ext/flag_kdpr

OR

Code:

echo 0 > /res/sdext/flag_kdpr

and reboot

karandpr · Jan 8, 2015

Stage 2 : Ramdisk Mod .

This is actually theoretical, but it should work anyway. @nobodyAtall 's recovery for locked bootloader works in a similar fashion.
This is for LXP+ kernels or kernels who use init.sh to load the ramdisk archives.

Steps .
Preparation :
SD Card

Add a folder named ramdisk in root of second SD card

Code:

mkdir ramdisk

Add ramdisks in this folder

Add a flag for ramdisk

Code:

touch flag_ramdisk

Make a script mount ramdisk.sh

Bash:

#!/sbin/busybox sh

flag_ramdisk=`cat /sdext/flag_ramdisk`

if [ ${flag_ramdisk} -eq 1 ]
then

busybox cpio -i < /sdext/ramdisk/abc_ramdisk.cpio

elif [ ${flag_ramdisk} -eq 2 ]
then

busybox cpio -i < /sdext/ramdisk/pqr_ramdisk.cpio

else

busybox cpio -i < /sbin/ramdisky.cpio
fi

Ramdisk of Primary kernel

Edit init.sh
create directory

Code:

mkdir -m 755 -p /sdext

Mount second SD card partition before loading the ramdisk

Code:

mount /dev/block/mmcblk0p2 /sdext

Comment or delete the line loading kernel.
Replace/add with

Code:

busybox sh /sdext/ramdisk.sh

Unmount Second sd card

Ramdisk will "theoretically" load.

karandpr · Jan 8, 2015

Handling Multiple Ramdisks and Multiple Mounts.

Multiple Ramdisk mod is useful when.

You have to test a new ramdisk
You have to run alternative ROM on a same kernel(e.g MIUI)
Load custom recovery for alternative mount points (CM12 ,Secondary ROM)

Dual/Multi ROM is useful for

Alpha/Beta testing
For the lulz

Both of these mods are independent of each other.

You can use Primary Ramdisk with Ramdisk mod and Secondary Ramdisks with mount mods

Multi Boot is similarly implemented. Except you need lot of space in second partition ,each around 1-1.5 GB per system-data combo.

karandpr · Jan 15, 2015

Some "friendlier" ways to dual Boot.

Method 1

Method 2

karandpr · Jan 15, 2015 at 6:41 AM

Lagfix after a while.
After 5-7 boots , Secondary ROM starts lagging.
fsck is needed to be performed from the reccovery to fix lag.

Commands :

Code:

e2fsck /res/sdext/data.kdpr
e2fsck /res/sdext/system.kdpr

Or just add it to mount scripts before mounting.

ryanrinaldhi · Apr 2, 2014 44 5 0

@karandpr,is there any possibility to dualboot some roms with different kernel layout or version (like multiboot on newer phone)?

karandpr · Apr 11, 2016 at 5:59 PM

ryanrinaldhi said:
@karandpr,is there any possibility to dualboot some roms with different kernel layout or version (like multiboot on newer phone)?

Nope. On fly layout change is impossible.
Even when you change layout ,you need a fastboot erase ,or the consequences can be weird.

Version change is possible.
anonymous had a kernel which can boot ICS , CM9 ,CM 10 & MIUI JB.
Multiboot off his hybrid kernel is very possible.

I am exploring the possibility of Kitkat and lollipop since both are versions 3.4 . Not sure if it can happen but worth a risk.

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[Experimental] Dual Boot and above Discussion

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