Making Armbian Live Distro Tutorial

tutorial.txt

Mirrored from https://drive.google.com/file/d/0B9rkZNVvi3bIaks1N2pQWEh3S1k/view
mentioned on https://forum.armbian.com/index.php?/topic/4176-debian-live-boot-with-armbian/

Making Armbian Live Distro Tutorial


Introduction
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Linux live distros are designed to be able to start a whole operating system from a read-only media, but to behave as if the media was read-write. The example - Debian Live. It can be burned on a CD and you can boot a full featured debian system from it, even without a hard drive. You can edit and save files, the system is writing logs, etc. After a reboot, everything is lost, since all changes are "copyonwrited" in RAM.
A live distro has some nice properties for an arm board running linux:
    - The media (sd card or emmc flash) can not be broken by write operations
    - The file system can not be messed up by a misbehaving application
    - The system can always reboot into a working state
    - The boot is faster, since all writes are in RAM
    - The media image size is small, since the file system is strongly compressed.

Write operations however use RAM. So, if you write too much, the RAM may be exhausted. In most cacses this is not a problem though.


- Debian Live overview
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A debian live distribution basically has the following components:
     - a linux kernel with support for squashfs and overlayfs (aufs)
     - a filesystem.squashfs compressed filesystem image containing all files in /. May be created by debootstrap, or from an existing non-live system, e.g. the available Armbian images.
     - an initrd image which mounts the squashed filesystem via overlayfs, that makes the read-only squashfs writable, all writes are done in RAM, no changes are made to the squashfs.
     - a bootloader, which passes the necessary parameters to the kernel and initrd


- Armbian live ditro for BPI M2+ : installing packages and modifying bootloader
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As a starting point, I compiled a standard Armbian os image: Armbian_5.27_Bananapim2plus_Debian_jessie_default_3.4.113.img
The process is well documented, so I will spare the compilation details here. I used the vendor kernel 3.4 and the only customization was to switch on the zram staging driver. Zram can be used as a compressed RAM swap device, to increase RAM capacity, but is not vital for the process. So you can skip zram, skip Armbian compilation and start with an image which is already available. You have to write the image on an SD-card.

The first thing to do is to boot the SD-card on the BPI M2+, setup root password and users and then install live-boot:

apt-get update
apt-get install live-boot

The live-boot package modifies and updates the initrd image. 
After installing live-boot, you need to modify the bootloader a bit. Change the bootargs line to this:

setenv bootargs "boot=live live-boot-path=/live union=overlayfs ${consoleargs} hdmi.audio=EDID:0 disp.screen0_output_mode=${disp_mode} consoleblank=0 loglevel=${verbosity} ubootpart=${partuuid} ubootsource=${devtype} ${extraargs} ${extraboardargs}"

you have to recompile the bootloader config with:

mkimage -C none -A arm -T script -d /boot/boot.cmd /boot/boot.scr

The modified bootargs tells to the initrd that it has to start live. live-boot-path tells where to find the filesystem.squashfs. union=overlayfs tells the initrd to use overlayfs instead of aufs (which was default for jessie). Aufs has been abandoned in newer systems, and it is not present in kernel 3.4. Overlayfs however does the same job and is present.


- Armbian live ditro for BPI M2+ : fixing initrd
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Now, you have to shutdown the BPI and mount the SD-card partition mmcblk0p1 on your PC somewhere, eg. /imagemnt

First you need to fix a small bug in the initrd created by live-boot in the jessie distribution. It happens when you try to use overlayfs. In order to fix it, you need to uncompress the initrd from the sdcard, modify a file, compress it again. That is how it is done:

tail -c+65 < /imagemnt/boot/uInitrd-3.4.113-sun8i > /tmp/out.gz
cd /tmp
mkdir initrd
cd initrd
gunzip /tmp/out.gz
cpio -i < /tmp/out
nano scripts/init-bottom/udev

change 'mount -n -o move /dev ${rootmnt}/dev' to 'mount -n --move /dev ${rootmnt}/dev'

find . -print0 | cpio --null -ov --format=newc | gzip -9 > /tmp/initramfs.cpio.gz
mkimage -A arm -T ramdisk -C none -n uInitrd -d /tmp/initramfs.cpio.gz /imagemnt/boot/uInitrd-3.4.113-sun8i


- Armbian live ditro for BPI M2+ : preparing the squashfs image and the root file system
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Now we are ready to make the filesystem.squashfs file. You need the squashfs-utils for this:

mksquashfs /imagemnt /tmp/filesystem.squashfs
mkdir /imagemnt/live
mv /tmp/filesystem.squashfs /imagemnt/live

Now, since the filesystem is already in the squashfs, we can remove everything from the image except /boot and /live:

cd /imagemnt
rm -rf bin  dev  etc  home  lib  media  mnt  opt  proc  root  run  sbin  selinux  srv  sys  tmp  usr  var
umount /imagemnt


The image/sd-card is now ready to boot live. You may shrink the mmcblk0p1 partition, since the squashed filesystem occupies only a fraction of the original size. 

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Notes:
    - you can also manipulate the image without writing it to an SD-card and booting it. You can use losetup and kpartx to mount the mmcblk0p1 partition. You can chroot into it afterwards. But since this is arm distro, you need to copy qemu-arm-static into /usr/bin of the image first, see debian howto on cross platform chrooting.
    - you should remove log2ram from the live distro, logs are now written to ram anyway
    - fstab may be (has to be) empty, initrd mounts everything. You have to remove the swap and tmpfs entires from the original Armbian image. If you need some extra mounts (e.g. additional usb disk, etc.), you may add them of course.
    - you may write the whole image to the emmc flash, the device will boot live the same way.
    - if you use zram, it has to be compiled into the kernel, selecting it as a module won't work.
    - zram can approximately double your RAM capacity
    - you can unsquash the filesystem.squashfs file, chroot into it, make changes, squash it again and copy it in the /live folder. This is the only modification you need to change your system.
    - if you want to change the kernel image, you have to overwrite the vmlinuz file in the /boot folder, and eventually you have to update /lib/modules/xxx inside the filesystem.squashfs image

Hello,
I have followed the steps to make an Armbian Live Distro (for an Orange Pi Zero in my case).
Unfortunately, if I remove any directory (one of bin, dev, etc, ...), my image/sd-card is not ready to boot alive.
The only thing that differs from instructions is that I've replaced "setenv bootargs "boot=live live-boot-path=/live ..." with "export bootargs "boot=live live-boot-path=/live " within my /boot/boot.cmd file.
Could you please provide me some help with this?
Thanks in advance

Hi,
These instructions are for the older release with 3.14 kernel. In latest releases (4.x kernel) the initrd problems are fixed and you only need to modify the boot.cmd. Don't forget mkimage