About Android fastboot

I am trying to build an Android environment by referring to the contents of this URL.
elinux.org/.../Android_P

In "Flashing images using fastboot", I ran the "fastboot" command on u-boot.
Next, I ran the "sudo ./fastboot oem format" command on the host PC (ubuntu on VirtualBox).
However, nothing seems to be done.

Could you please tell me the solution?

Thanks.