Orange Pi 3: moving the system to eMMC
My Orange Pi 3 has 8GB of eMMC flash installed so microSD is unnecessary. Well, it's necessary for the first boot and then the system can be moved to eMMC. Armbian installer can do that but I prefer to do everything myself.

eMMC is accessible via /dev/mmcblk2. Also, there are /dev/mmcblk2boot0 and /dev/mmcblk2boot1. I don't know what the latter twos are for. They aren't writable.
Armbian microSD has MBR and system partition starting from sector 8192. The 4MB gap is reserved for uboot.
The move begins from creating system partition on the eMMC:
fdisk /dev/mmcblk2
Everyone knows how to use fdisk
so I have nothing more to say.
Format created partition and copy the system on it:
mkfs -t ext4 /dev/mmcblk2p1 mkdir /mnt/emmc mount /dev/mmcblk2p1 /mnt/emmc mkdir /mnt/root mount /dev/mmcblk0p1 /mnt/root rsync -rltvWpog --specials --devices /mnt/root/ /mnt/emmc/
Write UUID of the new partition to /mnt/emmc/boot/armbianEnv.txt and /mnt/emmc/etc/fstab.
Copy uboot (the second command copies MBR bootloader):
dd if=/dev/mmcblk0 of=/dev/mmcblk2 bs=512 seek=1 skip=1 count=8191 dd if=/dev/mmcblk0 of=/dev/mmcblk2 bs=432 count=1
That's all. Power it down shutdown now
, pull microSD out and turn on again. Is it working? No? Game over then.