other: 0.959 graphic: 0.958 semantic: 0.950 permissions: 0.949 debug: 0.946 PID: 0.934 performance: 0.932 device: 0.930 vnc: 0.926 network: 0.922 socket: 0.919 boot: 0.910 KVM: 0.892 files: 0.890 KVM guest VM does not reattach a throughpassed USB printer from Host after switching printer off and on Host OS: Gentoo, all packages built 2014-10-01 qemu version 2.1.0-r1 Linux kernel 3.14.14 x86_64 Intel(R) Core(TM) i3-3220T CPU @ 2.80GHz GenuineIntel GNU/Linux Guest VM: Debian 7 (Wheezy) Linux 3.2.0 686 Start command: /usr/bin/qemu-system-i386 -enable-kvm -name wheezy -k de -serial null -parallel null -hda /var/kvm/wheezy.kvm-img -daemonize -net nic,macaddr=02:00:00:00:01:31 -net tap,ifname=tap3,script=no,downscript=no -m 512 -pidfile /var/run/kvm/wheezy.pid -usb -usbdevice tablet -runas myuser -vnc 127.0.0.1:3 -usbdevice host:04e8:3242 Problem: USB printer pass-through from KVM host to guest vm only works if I start the qemu kvm when the USB printer (vendor/product ID 04e8:3242) is switched on and therefore shown in lsusb on the host. Then it is available in the started VM. But when I switch the usb printer attached to the host off, it disappears in lsusb both on the host and the VM (as expected) but when I switch the USB printer on again, it is shown on the host and also on the QEMU Monitor (Crtl Alt Shift 2 -> info usbhost), but in the VM lsusb does not show it again- so USB pass-through / hot plugging does not work. It worked with a previous Version of qemu (1.0 or something). That is very annoying, because every time I want to print something, I need to shutdown the VM, start the printer, and then start the VM (which runs cups as printer server). But after printing, I do not want the printer to keep running, so I switch it off. This is a very annoying bug, and it is still not solved after six months, last versions tested with the bug: KVM host qemu version 2.2.1 KVM host Linux version 3.14.37 Please fix this. This is a very annoying bug, and it is still not solved after 2.7 years. Last versions tested and affected by this bug: KVM host qemu version 2.9.0 KVM host Linux version 4.9.6 x86_64 Please fix this. I guess switching the printer off and on again is like attaching a new USB device to your host (so it only shows up in the host, of course, and not in the guest). Have you already tried to do a new "device_add usb-host,..." in the QEMU monitor to attach it to the guest again while the VM is running? Thanks Thomas for Your suggestion. Unfortunately I cannot achieve the reconnection: KVM runs with following parameters: -usb -device usb-host,vendorid=0x04e8,productid=0x3242,id=drucker -monitor unix:qemu-monitor-socket,server,nowait With the Unix socket, I can now pipe commands to the qemu monitor. This info command works: echo 'info status' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) info status VM status: running What I have is this: - disconnect USB printer (Product Samsung ML-1510_700) - stop KVM - connect USB printer - start KVM echo 'info usb' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) info usb Device 0.1, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet Device 0.2, Port 2, Speed 12 Mb/s, Product QEMU USB Hub Device 0.3, Port 2.1, Speed 12 Mb/s, Product Samsung ML-1510_700, ID: drucker Printer works. - disconnect printer echo 'info usb' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) info usb Device 0.2, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet Device 0.3, Port 2, Speed 12 Mb/s, Product QEMU USB Hub Device 0.4, Port 2.1, Speed 12 Mb/s, Product Samsung ML-1510_700, ID: drucker USB Info still shows the printer, allthough it is disconnected. Remove device from KVM: echo 'device_del drucker' | socat - unix-connect:/qemu-monitor-socket Printer is removed from the device list: info usbdrucker' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) info usb Device 0.2, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet Device 0.3, Port 2, Speed 12 Mb/s, Product QEMU USB Hub -connect printer printer is not shown: echo 'info usb' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) info usb Device 0.2, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet Device 0.3, Port 2, Speed 12 Mb/s, Product QEMU USB Hub Add printer device: echo 'device_add usb-host,vendorid=0x04e8,productid=0x3242,id=drucker ' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) device_add usb-host,vendorid=0x04e8,productid=0x3242,id=drucker echo 'info usb' | socat - unix-connect:/qemu-monitor-socket QEMU 4.2.0 monitor - type 'help' for more information (qemu) info usb Device 0.2, Port 1, Speed 12 Mb/s, Product QEMU USB Tablet Device 0.3, Port 2, Speed 12 Mb/s, Product QEMU USB Hub Device 0.0, Port 2.2, Speed 1.5 Mb/s, Product USB Host Device, ID: drucker Device is shown, but not like when KVM is started with connected printer: Speed only 1.5 Mb/s, no vendor and product info. Printer does _not_ work. This is an automated cleanup. This bug report has been moved to QEMU's new bug tracker on gitlab.com and thus gets marked as 'expired' now. Please continue with the discussion here: https://gitlab.com/qemu-project/qemu/-/issues/110