@george

mkfs -t ext4 /dev/mmcblk0

then it success

@george I try many times booting from usb drive, when i run "sudo mkfs.ext4 /dev/mmcblk0" in shell, it alway show "/dev/mmcblk0 is apparently in used by system. will not make a file system here!", and x64 computer find no device when cm5 laptop reboot pushing power button many times, and cm5 laptop is rebooting over and over again,

is there a different way to format the mmc to help burning img from x64 computer?

@george I used a old usb drive , that I can enter ubuntu, but when i run "sure miss.ext4 /dev/mmcblk0" in shell
it seems not work.
/dev/mmcblk0 is apparently in used by system. will not make a file system here!

@george it cost about 30minutes but not enter. may it can only start from type c port by external usb drive? type a usb port is not valid?

@george i use a usb drive to boot , it works to start ubuntu, but it seems very slow, it cost about 15 minutes still not user login interface

@Rock i know the difference s between usb2 and usb3 , I just want to know how start my laptop from a external usb flash which have a ununtu img, because my laptop can not start

@Rock usb2.0 is udb type a connector?

my cm5-laptop can not start, I use Etcher to program ubuntu img to a USB flash,
but I do not kown how to start from the USB flash,
And if cm5-laptop start from the USB flash, how do I format the EMMC, is there some doc for starter?

@Rock you should download Etcher, then use the software to program the image

@george 谢谢，大概看了下文档，应该可以搞定。多谢：）