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I have a realtek wireless dongle that I want to pass to a qemu virtual machine. When I start the VM, the usb device shows up on both the host and in the guest as expected (shows up in lsusb, under /sys/bus/usb). However the device immediately disappears as soon as I try to bring up its associated network interface.

The odd thing is that the device not only disappears from inside the guest but also from the host. Host device entries under /sys disappear, and normal resuscitation - e.g rebinding via /sys/bus/usb/drivers/usb/[un]bind - fail short of physically disconnecting and reconnecting the device.

The only thing that gets logged when this happens is:

... kernel: usb 2-1.7: USB disconnect, device number 77

What might be causing this and how can I fix it?

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  • Interesting, i just upgraded my qemu server (debian 9 to 10) yesterday and began seeing this same behavior, except with mice and keyboard and ONLY when a 2nd vm is started (even though each vm has dedicated keyboards and mice) Looking forward to seeing the answers! Commented Aug 5, 2020 at 17:57

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Does the guest have the necessary drivers and device firmware installed?

Some realtek wireless dongles require firmware to reinitialize and use. When you attempt to use these devices without the necessary firmware, the device softlocks itself until device power is cycled (i.e. by removing and reinserting the dongle).

For Debian and realtek specifically, you'll want to ensure that contrib and non-free are enabled in your apt sources, then install the necessary firmware:

apt install firmware-realtek
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