... else setenv bootpart 1; fi part uuid ${devtype} ${devnum}:${bootpart} uuid setenv bootargs "console=ttyS0 console=${console} root=PARTUUID=${uuid} rw rootwait" if load ${devtype} ${devnum}:${bootpart} ${kernel_addr_r} /boot/zImage; then gpio set 54 echo fdt: ${fdtfile} if ...

... how to change it. /boot/boot.txt you should be able to add to a line line near the beginning: setenv bootargs console=${console},${baudrate} root=PARTUUID=${uuid} rw rootwait change to: setenv bootargs console=tty0 console=${console},${baudrate} root=PARTUUID=${uuid} rw rootwait and the "tty0" ...

Oh yes, in the initrd you should have enough commands to see why the root file system wasn't loaded. My guess it it couldn't find the PARTUUID. Probably because it could only see the sd card and not the eMMC.

What disk boots depends on uboot. If you look in /boot/boot.txt you can see its sets root=PARTUUID=${uuid} and uuid is set via part uuid ${devtype} ${devnum}:${bootpart} uuid So you could just rewrite that to point at the sD card. Now can't rember how clever the BBB ...

... kernel, only has limited methods of recognizing partitions. I don't recall if the label is allowed. IIRC the preferred method these days is PARTUUID. Think you get that using blkid . Am at work right now - I'll check when I get home what I have. It look like the one for the HDD is ce291bb3-01 ...

If you set root via PARTUUID then it should boot the usb even with the hdd in place...

... /boot/zImage Device Tree: load ide 0:1 ${fdtaddr} /boot/dtbs/kirkwood-goflexnet.dtb Set up the root location part uuid ide 0:1 uuid setenv root PARTUUID=${uuid} setenv bootargs console=${console} ${mtdparts} root=${root} rw rootwait ${optargs} ${ncargs} Initrd: load ide 0:1 ${rdaddr} /boot/initramfs-linux-img ...

... and so the root and boot partitions can be ext4 formatted. The root parameter for uboot in these devices is set in /boot/uEnv.txt, mine is: root=PARTUUID=94a2dc27-01 mtdparts=mtdparts=orion_nand:0xC0000(uboot),0x40000(uboot_env),0x80000(old_uboot_env),0x80000(key_store),0x80000(info),0xA00000(etc),0xA00000(kernel_1),0x2FC0000(rootfs1),0xA00000(kernel_2),0x2FC0000(rootfs2) ...

And from : https://github.com/torvalds/linux/blob/master/init/do_mounts.c this is why we use PARTUUID: /* * Convert a name into device number. We accept the following variants: * * 1) <hex_major><hex_minor> device number in hexadecimal represents itself * no leading 0x, ...

... else setenv bootpart 1; fi part uuid ${devtype} ${devnum}:${bootpart} uuid setenv bootargs "console=tty0 console=${console} root=PARTUUID=${uuid} rw rootwait" if load ${devtype} ${devnum}:${bootpart} ${kernel_addr_r} /boot/zImage; then gpio set 54 echo fdt: ${fdtfile} if ...