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

Attach a raw image as a USB disk to the VM