Here is by far the easiest way to install Arch Linux on a Cubox -i4 Pro. These directions below are cut and pasted from here. Be sure and click the “Installation” tab on the page to get to the directions.

Install to a micro SD card Remember this device has no built in storage or flash, U-Boot is on early sectors of the SD card. Replace sdX in the following instructions with the device name for the SD card as it appears on your computer.
  1. Zero out the first few MB of the card to remove any previous U-Boot environment:
    dd if=/dev/zero of=/dev/sdX bs=1M count=4
  2. Start fdisk to partition the SD card:
    fdisk /dev/sdX
  3. At the fdisk prompt, create the new partitions:
    1. Type n, then p for primary, 1 for the first partition on the drive, 8192 for the starting sector, and +20M for the ending sector.
    1. Type t to set the type, then c to set it to FAT.
    1. Type n, then p for primary, 2 for the second partition, 49152 for the first sector, and press ENTER twice to accept default values.
    1. Exit by typing w.
  1. Create and mount the vfat filesystem:
    mkfs.vfat /dev/sdX1
  2. mkdir boot
  3. mount /dev/sdX1 boot
  4. Create and mount the ext4 filesystem:
    mkfs.ext4 /dev/sdX2
  5. mkdir root
  6. mount /dev/sdX2 root
  7. Download and extract the root filesystem:
    wget http://archlinuxarm.org/os/ArchLinuxARM-imx6-cubox-latest.tar.gz
  8. tar -xf ArchLinuxARM-imx6-cubox-latest.tar.gz -C root
  9. Move boot files to the boot partition:
    mv root/boot/* boot
  10. Install the U-Boot bootloader:
    dd if=boot/SPL of=/dev/sdX bs=512 seek=2
  11. dd if=boot/u-boot.img of=/dev/sdX bs=1K seek=42
  12. Unmount the partitions:sync
  13. umount boot root
  14. Insert the SD card into the Cubox-i contacts uppermost, connect ethernet, and apply 6-12V power.
  15. Use the serial console (CN6 micro USB connector) or SSH to the IP address given to the board by your router. The default root password is 'root'.

Use USB as a root device
  1. Make sd card as above, then extract rootfs to the ext4 formatted USB storage, edit the file on the fat partion called uEnv.txt to reflect where rootfs is (probably /dev/sda1)
  2. Note the kernel stays on the card (uImage) and there is an fstab entry to take care of that.

How to install latest kernel (xbmc does not work with this)
pacman -Sy linux-imx6-cubox-dt uboot-cubox-i
*******This step here above was problematic for me. It failed saying that SPL and u-boot.img were already present. You can get around this by doing this (as root):
cd /boot
mv SPL SPL.old
mv u-boot.img u-boot.img.old
Then run the command again:
pacman -Sy linux-imx6-cubox-dt uboot-cubox-i

When you reboot check your kernel version by typing:
uname -a
To install X and a Window Manager type the following:
pacman -Sy
pacman -Su
pacman -S lxde xf86-video-fbturbo xorg-xinit

Start X by typing

xinit /usr/sbin/lxsession