A lightweight display manager, built for Linux multiseat setups. Discovers seats via logind, shows a greeter on each seat, handles user authentication, and hands off to an independent user session per seat.

The Linux kernel and low-level system stack have had solid multiseat support for years: udev handles device assignment, logind manages independent user sessions per seat, and Wayland compositors work with whatever devices logind gives them. The weak link has always been the display manager. Existing ones usually treat multiseat as an afterthought, with implementations that are brittle and difficult to get working reliably.

atrium is designed around multiseat from the start, focusing on correct seat discovery, VT handling, and isolated session management. The project targets a modern Linux stack using systemd/logind, PAM, and a Wayland graphical environment. The lack of historical baggage keeps atrium's code base lean and tractable.

A multiseat setup allows multiple users to work on a single computer at the same time. By connecting multiple monitors, keyboards, and mice, each user gets their own separate desktop and a fully isolated user session. Great for co-working or multiplayer gaming. Each seat requires its own GPU (integrated graphics, a discrete card, or a USB graphics adapter all work).

v0.2 - fully functional but still in early development.

atrium runs well as a daily-driver display manager. The core workflow (seat discovery, user authentication, session lifecycle management) is fully operational. That said, atrium has been tested on a limited range of hardware and distributions, so expect some rough edges.

Other systemd-based distros should work - the only distro-specific piece is the PAM stack. Adapt one of the provided PAM configs as needed.

• libsystemd - logind session management
• libudev - seat discovery
• libpam - user authentication
• gtk4 - greeter UI
• cage - Wayland compositor hosting the greeter
• meson, ninja - build system

On Debian/Ubuntu:

sudo apt install libsystemd-dev libudev-dev libpam0g-dev libgtk-4-dev cage meson ninja-build

On Arch/CachyOS:

sudo pacman -S systemd pam gtk4 cage meson ninja

On Fedora:

sudo dnf install systemd-devel pam-devel gtk4-devel cage gcc meson ninja-build

This step can usually be skipped - the defaults work for a standard single-seat or multiseat setup.

atrium's config is currently hardcoded in lib/defs.h (daemon) and greeter/defs.h (greeter). If needed, these files must be edited before build and install.

meson setup build -Ddist=<your-distro>   # arch, debian, fedora
ninja -C build
sudo ninja -C build install

The -Ddist option (required) selects the correct PAM stack for the target distribution. Possible values for dist are: arch (for Arch/CachyOS), debian (for Debian/Ubuntu), or fedora (for Fedora).

Multiseat setups: seat assignment must be configured with loginctl attach before starting atrium - without this step only a single seat exists (TODO: link multiseat setup guide).

Disable the current display manager, and enable atrium:

sudo systemctl disable gdm   # substitute your current display manager
sudo systemctl enable atrium

Then reboot. atrium will start on boot and launch a greeter on every seat.

To copy the source to a remote machine and build remotely:

./tools/deploy.sh

To test atrium from within a user session:

sudo systemd-run --scope build/atrium-dev

systemd-run --scope is needed to run atrium in a fresh scope, not in the scope of the existing session.

To install only the daemon or only the greeter, use

sudo meson install -C build --tags daemon
sudo meson install -C build --tags greeter