Changelog:

20150121:

1. Initial version

20150131:

1. Added the missing automount of /media/boot
2. Fixed the date (image was 20140121)
3. Added optional step to allow root login via ssh (included on the image)

20161102:

1. Updated to Ubuntu 16.04

—-

To this you'll need:

• PC running Linux Ubuntu 16.04 64 Bits
• MicroSD or eMMC to write the new image

This guide will cover the process to recreate the official Ubuntu Minimal image. Tested and written on a Ubuntu 16.04 64Bits x86 Machine.

1. Tools:
   Basic set of tools that we will need to create our image.

   sudo apt-get install debootstrap qemu-user-static

2. Work folder
   Create a workspace

   mkdir ~/ubuntu
   cd ubuntu
   export ubuntu=`pwd`

3. Empty image (4GB)
   Create a image with 4096 1Mbyte blocks (4Gbyte image)

   dd if=/dev/zero of=./image.img bs=1M count=4096

4. Image partitioning
   Create the two needed partitions, one fat32 for kernel+initramfs+boot script and another ext4 for the OS

   fdisk image.img
   n
   p
   1
   <return>
   +128M
   t
   c
   n
   p
   2
   <return>
   <return>
   w

5. Formatting and setting up partitions
   Setup loopback and format the partitions.
   Also change the UUID and disable journaling.

   sudo losetup /dev/loop0 ./image.img
   sudo partprobe /dev/loop0
   sudo mkfs.vfat -n boot /dev/loop0p1
   sudo mkfs.ext4 -L rootfs /dev/loop0p2
   sudo tune2fs /dev/loop0p2 -U e139ce78-9841-40fe-8823-96a304a09859
   sudo tune2fs -O ^has_journal /dev/loop0p2

6. Bootloaders
   Download a pre-built version of U-Boot for C1 and fuse to our image.

   wget https://raw.githubusercontent.com/mdrjr/c1_uboot_binaries/master/bl1.bin.hardkernel
   wget https://raw.githubusercontent.com/mdrjr/c1_uboot_binaries/master/u-boot.bin
   wget https://raw.githubusercontent.com/mdrjr/c1_uboot_binaries/master/sd_fusing.sh
   chmod +x sd_fusing.sh
   sudo ./sd_fusing.sh /dev/loop0

7. Deboostrap
   Mount the partitions, copy qemu to enable chroot to arm and start debootstrap

   mkdir -p target
   sudo mount /dev/loop0p2 target
   sudo mkdir -p target/media/boot
   sudo mount /dev/loop0p1 target/media/boot
   sudo mkdir -p target/usr/bin
   sudo cp /usr/bin/qemu-arm-static target/usr/bin
   sudo debootstrap --variant=buildd --arch armhf xenial target http://ports.ubuntu.com

8. Preparations via chroot
   Will add hardkernel keys and repositories, fix ubuntu respository list and install the basic set of tools for a minimal image

   sudo chroot target
   cat << EOF > /etc/apt/sources.list
   deb http://ports.ubuntu.com/ubuntu-ports/ xenial main universe restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial main universe restricted
   
   deb http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main universe restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main universe restricted
   
   deb http://ports.ubuntu.com/ubuntu-ports/ xenial-backports main restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-backports main restricted
   
   deb http://ports.ubuntu.com/ubuntu-ports/ xenial-security main restricted
   deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-security main restricted
   deb http://ports.ubuntu.com/ubuntu-ports/ xenial-security universe
   deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-security universe
   deb http://ports.ubuntu.com/ubuntu-ports/ xenial-security multiverse  
   deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-security multiverse
   EOF
   
   apt-get update
   apt-get install software-properties-common u-boot-tools isc-dhcp-client ubuntu-minimal ssh
   
   apt-key adv --keyserver keyserver.ubuntu.com --recv-keys D986B59D
   echo "deb http://deb.odroid.in/c1/ xenial main" > /etc/apt/sources.list.d/odroid.list
   apt-get update
   
   apt-get install linux-image-c1 bootini

   At this point.. You'll have several errors, That's fine.
   You can ignore it right now.

   cp /boot/uImage* /media/boot/uImage

9. Setup ethernet as DHCP and create the loopback interface

   cat << EOF > /etc/network/interfaces.d/lo
   auto lo
   iface lo inet loopback
   EOF
   
   cat << EOF > /etc/network/interfaces.d/eth0
   auto eth0
   iface eth0 inet dhcp
   EOF

10. Setup fstab

    echo "LABEL=boot /media/boot vfat defaults 0 0" >> /etc/fstab
    echo "UUID=e139ce78-9841-40fe-8823-96a304a09859 / ext4 errors=remount-ro,noatime 0 1" >> /etc/fstab

11. Setting a root password

    passwd root

12. (Optional) Allow root login via ssh

    sed -i s/"PermitRootLogin without-password"/"PermitRootLogin yes"/g /etc/ssh/sshd_config

13. Clean ups and preparation to test the image.

    exit
    sudo umount target/media/boot
    sudo umount target
    sudo sync
    sudo losetup -d /dev/loop0

14. Flashing your image

    dd if=image.img of=/dev/sdX bs=1M

15. After your first boot, install the u-boot package to get updates.

    sudo apt-get install u-boot