How do I boot from a liveusb using qemu-kvm?

qemu-kvm has disappeared. use the hint in start qemu by giving it a path to a linux root instead. this means

qemu-system-x86_64 -usb -usbdevice disk:/dev/sdb

where /dev/sdb is your raw device (not partition) of the usb stick that you want to boot.

(however, as of 12/2014, it's been flaky for me. booting ubuntu-gnome 14.10 results eventually in a kernel panic on a stick verified to boot just fine on the metal.)

/iaw

qemu-kvm -hdb <device>, where <device> is the USB stick (e.g. /dev/sdb), should do it (tested with Ubuntu 12.04 on an USB stick and it works).

You will need write permission to the device (i.e. be root or change its permissions).

I don't know why exactly, but Renan's answer didn't quite work for me. KVM said to me it couldn't find a bootable drive (despite the usb partition being marked as such).

However I've found another solution. Get the USB device VendorID:ProductID with lsusb. Example:

$ lsusb
...
Bus 002 Device 007: ID 0781:5406 SanDisk Corp. Cruzer Micro U3

Pass that to KVM, and ask for the boot menu:

sudo  kvm -m 512 -smp 1 -drive file=/path/to/hardisk/file.img -usb \ 
-usbdevice host:0781:5406 -boot menu=on

Press F12 for the menu, choose the usb device, it works. There's probably a way to command the usb boot without needing to call the boot menu, but I didn't find any in man kvm.