Proxmox SPICE Mouse Acceleration Bug: Fix the Jumpy Cursor

The Proxmox SPICE mouse acceleration bug makes the cursor jump around like it’s had too much coffee. The fix is usually one of three things: enable the guest agent, switch to tablet mode, or adjust the client settings. Here’s the step-by-step to isolate the real cause.

Check the Guest Agent First

The SPICE guest agent handles pointer positioning. If it’s not installed or not running, the mouse falls back to relative positioning, which causes acceleration issues. Install it in the VM:

apt install spice-vdagent

For Windows VMs, grab the spice-guest-tools ISO from the Proxmox wiki and install it. Then make sure the agent is running:

systemctl status spice-vdagent

If it’s not active, start it and enable it on boot. The agent also needs the VM configured to use it. In the Proxmox web UI, go to the VM’s Options, then QEMU Guest Agent, and set it to Yes. This tells Proxmox to expect the agent and use it for mouse input.

Tablet Mode vs. Mouse Mode

SPICE has two input modes: tablet and mouse. Tablet mode sends absolute coordinates, which eliminates acceleration. Mouse mode sends relative deltas, which the guest OS then accelerates. The default is usually tablet, but some configurations end up in mouse mode. To force tablet mode, edit the VM’s config file:

nano /etc/pve/qemu-server/100.conf

Look for the args line and add or modify it to include -device virtio-tablet-pci. If there’s no args line, add one:

args: -device virtio-tablet-pci

Then restart the VM. This is the most reliable fix for the jumpy cursor, because it bypasses the guest’s acceleration entirely.

Client-Side Settings

Sometimes the problem is in the SPICE client, not the VM. If you’re using virt-viewer or remote-viewer, check the mouse settings. In virt-viewer, go to View > Display and make sure “Resize guest with window” is checked. Also try disabling pointer acceleration in the client’s preferences if available. For the Proxmox web console (which uses noVNC), there’s no acceleration setting, but you can try switching to a different browser or enabling “Use tablet for pointer” in the console settings if present.

My Take

This bug is annoying because it’s inconsistent. Sometimes it’s the agent, sometimes it’s the tablet mode. The quickest test is to install the guest agent and enable it in Proxmox. If that doesn’t fix it, force tablet mode. Don’t bother with client-side tweaks unless you’ve ruled out the VM-side issues first. And if you’re still stuck, check out the Proxmox Windows 11 CPU flags post—sometimes weird input issues come from a mismatched CPU type.