There is no tool to create the startup drive under Linux/Ubuntu. I'm therefore following the manual install method. It however fails on the make bootable script.
$ sudo ./make_bootable_linux
INFO: make_bootable_linux v1.3
INFO: The following device appears to be the unRAID USB Flash drive: /dev/mmcblk0p
Permit UEFI boot mode [Y/N]: Y
INFO: unRAID USB Flash drive currently mounted to /tmp/UNRAID_TMP_MOUNT, copying temporary installer files to /tmp/UNRAID
To continue you may need to enter your admin password
FAIL: Invalid block device /dev/mmcblk0p
$ sudo bash ./make_bootable_linux
INFO: make_bootable_linux v1.3
INFO: The following device appears to be the unRAID USB Flash drive: /dev/mmcblk0p
INFO: Temporarily mounting unRAID USB Flash drive to /tmp/UNRAID_TMP_MOUNT
Permit UEFI boot mode [Y/N]: Y
INFO: unRAID USB Flash drive currently mounted to /tmp/UNRAID_TMP_MOUNT, copying temporary installer files to /tmp/UNRAID
To continue you may need to enter your admin password
FAIL: Invalid block device /dev/mmcblk0p
I looks like the script detects the device as `/dev/mmcblk0p`, omitting the partition number 1 after it.