Proxmox VM boot from USB image

To boot from USB image in VM, such as USB image of memtest86-usb.img, import the disk as hard disk using following command.

qm importdisk 100 memtest86-usb.img upool1

Then

Add Unused disk into VM using Proxmox VM UI interface.

Then

Change boot order to new hard disk first in VM Options.

References

Fusion reports error, and it can not connect to USB drive to boot.

Fusion does not support USB adapters for connecting displays to your virtual machines.

Note: I haven't tried to change UEFI mode to BIOS mode, maybe this is the cause.