display-autoresize

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1. Description

Script to autoresize display in SPICE session. Tested on Arch Linux with:

• X11: i3 windows manager;
• Wayland: sddm login manager, sway wayland compositor.

Preview:

2. Requirements

2.1. Guest

1. Install required packages:

   • Arch-based:

     sudo pacman --sync --refresh --needed bash xorg-xrandr screen jq spice-vdagent xf86-video-qxl

     • bash - for script execution;
     • xorg-xrandr - for xrandr command to get and modify display outputs;
     • screen - to run script for sway in background;
     • jq - to parse swaymsg output;
     • spice-vdagent and xf86-video-qxl - SPICE guest tools.

2. Install drm_info:

   • Arch-based:

     yay --sync --refresh --needed --sudoloop drm_info

3. Download script display-autoresize from this repository and make it executable:

   sudo wget -O /usr/local/bin/display-autoresize https://raw.githubusercontent.com/Nikolai2038/display-autoresize/refs/heads/main/display-autoresize && \
   sudo chmod +x /usr/local/bin/display-autoresize

   • You can put script not in /usr/local/bin/display-autoresize, but make sure to change path to it in udev rule too (see below).

4. Create udev rule:

   echo 'ACTION=="change", KERNEL=="card[0-9]*", SUBSYSTEM=="drm", RUN+="/usr/local/bin/display-autoresize"' | sudo tee /etc/udev/rules.d/50-display-autoresize.rules && \
   sudo udevadm control --reload-rules

5. Make sure spice-vdagentd is loaded and running fine.

2.1.1. [UNSTABLE] Login Manager (SDDM)

Additionally, if you want this script to work for login manager you are using (SDDM for example) - make sure to start login manager from unprivileged user. As I tested with SDDM, if it is running from root, udev events does not occur so script to autoresize is not called. To start SDDM as unprivileged user:

sudo mkdir --parents /etc/sddm.conf.d && \
echo '[General]
DisplayServer=x11-user' | sudo tee /etc/sddm.conf.d/set_compositor.conf && \
echo 'allowed_users = anybody
needs_root_rights = no' | sudo tee --append /etc/X11/Xwrapper.config && \
sudo systemctl restart sddm.service

For more info, check:

man sddm.conf
man Xorg.wrap

Update 2025-01-13:

• I tried x11-user and wayland for DisplayServer setting for some time, and found out, that they are a lot more unstable, than the default x11 setting. Specifically, x11-user will cause user session (after you logged in) to crash after some time. As for wayland - it has freeze problems when connected via aSPICE Android app. I don't test all this properly, but will stick to default x11 for now.

2.2. Host

Just make sure that auto-resize is enabled when you are connecting via virt-viewer/spicy.

3. Debugging

• Watch udev events on resize with udevadm monitor;
• Watch dmesg -w (may not be super useful);
• Watch logs with tail -f /var/log/display-autoresize.log.

4. Credits

• "Forked" from gist but with XAUTHORITY and Sway (Wayland) support;
• Credit for finding sessions as root;
• Credit for resizing via udev;
• Credit for drm_info solution to get current window resolution in Wayland.

5. Contribution

You can help me with:

• Testing in other distributions (Debian, Fedora, etc.) and update instructions for them;
• Testing on other Window Managers and Wayland compositors;
• Maybe optimizing code and finding more elegant and fast solutions for parsing;
• Translate README.md to other languages.

Feel free to contribute via pull requests or issues!