raspberry pi 3b+ boots download (@23Aug18) image.
Comes up with OSMC screen
Error message: Cannot mount bootfs
and fails to install…
Install to where?
Edit: While the answer to above question still matters I have read this again and actually believe your mean you are booting the installer from USB instead of SD Card, correct? AFAIK a plain USB boot is currently not supported by the OSMC installer
You are better off booting from an SD card and using the USB drive for the system (USB install in the installer). See here: Boot OSMC from USB mass storage RPi3B+ - #13 by grahamh
Just to be clear: OSMC supports having the boot partition on SD card (250MB) and the rest of the system on USB. The installer does not support having both the boot partition and the system partition on USB. It can be done but you need to know what you are doing.
My preference is to use USB for many different reasons including ease of use and run speed.
My experience is that the USB booting and running works well.
If there are any instruction for installing OSMC onto the usb (boot & rootfs) it would be helpful.
Automatic is preferred but semi manual install is not a problem.
Obviously handling updates to USB as normal is an essential.
As previously stated, there is no way to boot without a minimal install on a SD card. Think of the SD card as where the BIOS is installed. The rest of the install can be on a USB drive.
That requirement would probably kill it. The updater could bork your system at any time.
If you really really want to try, you have to clone an entire SD card (both partitions) to your USB stick, then edit cmdline.txt to point to the linux system partition eg root=/dev/sda2 and edit /etc/fstab to point to /dev/sda1.
Problem is, if you have more than one USB drive, the order in which they are recognised is not guaranteed. I think you can use labels or UUIDs to get round that.
HOW TO BOOT FROM A USB MASS STORAGE DEVICE ON A RASPBERRY PI 3
NB the scary part:
Before a Raspberry Pi 3 will boot from a mass storage device, it needs to be booted from an SD card with a config option to enable USB boot mode. This will set a bit in the OTP (One Time Programmable) memory in the Raspberry Pi SoC that will enable booting from a USB mass storage device. Once this bit has been set, the SD card is no longer required. Note that any change you make to the OTP is permanent and cannot be undone.
Edit: This is for the Pi 3. I believe the Pi 3+ doesn’t need this treatment.