Troubleshooting

Start with the symptom below. Avoid changing polling, synchronization or renderer options until the basic server, shared-memory and version checks pass.

The Looking Glass monitor is missing in Windows

  1. Confirm that the guest runs Windows 10 version 1803 or newer, or Windows 11.

  2. Confirm that the IDD installer completed and restart Windows if requested.

  3. Open the IDD helper and its log directory. See IDD status and logs.

  4. In looking-glass-idd.txt, confirm that IVSHMEM opened with the expected size and that at least one configured display mode fits.

  5. Increase IVSHMEM if every suitable mode was filtered. Restart the VM after changing its size.

  6. Ensure the legacy Host service is disabled. Only one Looking Glass Server implementation should use the Looking Glass IVSHMEM device.

A missing passed-through GPU does not by itself prevent the IDD display from appearing. The IDD can start in software mode, although that mode is slower and SDR-only.

The client remains on the waiting screen

  • Confirm that the Windows Looking Glass monitor is active and producing a desktop.

  • Check that the client selected the same KVMFR device or shared-memory file as the VM.

  • Confirm that the Linux user has read and write access to that device.

  • Use matching client and IDD releases. A KVMFR or LGMP protocol mismatch is a hard incompatibility.

  • If /dev/kvmfr0 is a regular file instead of a character device, stop the VM, remove that accidental file and load KVMFR before starting the VM again.

The image is slow or stutters

Open the timing graphs with ScrLk + T and follow Measure performance and latency. Also check:

  • the IDD helper reports GPU acceleration rather than software processing;

  • lgmp:allowDMA=yes is using a direct import when the host driver supports it;

  • enough CPU cores remain available to Linux;

  • the guest resolution and refresh do not exceed available memory bandwidth;

  • the compositor is not adding an unexpected frame queue; and

  • the fastest active client or OBS source is requesting the intended cadence.

Do not set the guest to an extreme refresh rate merely to raise UPS. The IDD can acquire newer frames and skip superseded ones before transport, but the guest still pays the cost of rendering them.

Keyboard or mouse input does not work

  • Press ScrLk + I to ensure guest input is enabled.

  • Check looking-glass-input.txt and the client’s selected input provider.

  • Only one LGMP client owns direct input. Close another controlling client if necessary.

  • If SPICE video fallback is active, keep spice:input=yes. The client uses the VM’s default PS/2 keyboard and mouse and intentionally switches input with the video source.

  • If input:captureOnly=yes, press ScrLk to enter capture mode.

See Keyboard and mouse input for normal, automatic keyboard and capture modes.

The clipboard is not working

  • Is clipboard synchronization enabled?

  • Did you install the Spice Guest Tools?

    • The SPICE Guest Tools driver must be installed inside the Windows guest to synchronize the clipboard. The download is labeled “spice-guest-tools”.

      Warning

      Do NOT install the QEMU Guest Tools driver. These are not the same.

    • Is it installed twice?

      • The Spice VDAgent is available in both Spice Guest Tools, and standalone as a separate installer. Check your installed programs and uninstall the VDAgent if it’s installed separately.

Keyboard shortcuts are not captured on GNOME Wayland

Capture mode may fail to capture compositor shortcuts like ALT+Tab or ALT+Middle Mouse - they go to GNOME instead of the guest VM.

When Looking Glass first requests to inhibit shortcuts, GNOME shows a dialog asking for permission. If you clicked “Deny” (or dismissed the dialog), GNOME permanently blocks the application and never shows the dialog again.

Use the flatpak command to view or grant the permission, this works even if LookingGlass is not a Flatpak application, as GNOME stores these permissions in Flatpak’s database:

flatpak permission-set gnome shortcuts-inhibitor looking-glass-client.desktop GRANTED

To verify the permission was set:

flatpak permissions gnome shortcuts-inhibitor

USB audio does not appear or play

  • Confirm that the client was built with libusbredirparser-0.5 version 0.7.1 or newer.

  • Add an unused SPICE USB Redirector device to the VM.

  • Keep spice:enable=yes, spice:audio=yes and spice:usbAudio=yes.

  • In Windows Sound settings, select the Looking Glass USB Audio speakers as the output device.

  • Check the client startup log. If USB audio creation failed before connection, Looking Glass falls back to classic SPICE audio and reports why.

The microphone is unavailable

The current PipeWire backend supports recording; the PulseAudio backend does not. Ensure the client selected PipeWire, then check audio:micDefault and the microphone indicator. Press ScrLk + C to change the default permission and ScrLk + E to toggle recording.