feat: migrate from SDDM to greetd+tuigreet

- Add greetd role with tuigreet greeter (3 packages, 4.9MB) - Replace SDDM as display-manager.service with greetd - Add ADR 0003 documenting migration rationale - Rename hyprland task: "register session in SDDM" -> "register Wayland session desktop entry" - Add display_manager variables to vars/main.yml - Add greetd role to workstation.yml - Update setup.md timestamp
2026-05-20 12:51:25 +02:00
parent 1274b3e2cb
commit 9d06a71f71
8 changed files with 147 additions and 2 deletions
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+---
+description: >-
+  Replace SDDM (Qt-based graphical display manager) with greetd + tuigreet
+  for a minimal, Wayland-first login experience with zero heavy GUI dependencies.
+status: accepted
+date: 2026-05-20
+replaces: SDDM as display-manager.service
+---
+
+# 0003: SDDM to greetd Migration
+
+## Context
+
+The workstation uses Hyprland as the primary Wayland compositor. SDDM was
+pulled in as the display manager with significant Qt dependencies (~50+
+transitive packages). For a single-user dev workstation running Hyprland,
+this is unnecessary overhead — heavy, slow-booting, and over-engineered for
+the use case.
+
+SDDM provides: graphical login prompt, session selection, PAM authentication.
+All three can be achieved with far lighter tools.
+
+## Decision
+
+Migrate from SDDM to greetd + tuigreet.
+
+- **greetd**: minimal display manager daemon, designed for Wayland first-class.
+- **tuigreet**: TUI greeter with time display, user remembering, session
+  discovery from `/usr/share/wayland-sessions/` and `/usr/share/xsessions/`.
+
+### What changed
+
+| Before | After |
+|--------|-------|
+| sddm.service (display-manager) | greetd.service (display-manager) |
+| Qt5/Qt6 dependency chain | greetd + greetd-tuigreet (3 packages, 4.9MB) |
+| /etc/sddm.conf | /etc/greetd/config.toml |
+| Graphical login screen | Text-based TUI login screen |
+| Heavy PAM surface | Standard PAM chain (system-local-login) |
+
+### Ansible changes
+
+- Added `greetd` role: installs packages, configures config.toml from template,
+  enables greetd as display-manager.service
+- Hyprland task renamed: "register session in SDDM" -> "register Wayland session
+  desktop entry" (no functional change, just accurate naming)
+- vars/main.yml: added `display_manager_package`, `display_manager_greeter`,
+  `display_manager_config` variables
+
+### Configuration
+
+```toml
+[terminal]
+vt = 1
+[default_session]
+command = "tuigreet --time --remember --asterisks --cmd Hyprland"
+user = "greeter"
+```
+
+### Rationale
+
+1. **Wayland-native**: greetd handles Wayland sessions cleanly without X
+   compatibility layers
+2. **Minimal**: 3 packages vs Qt dependency chain; <5MB vs ~500MB
+3. **Maintained**: Rust codebase, clean TOML config, Arch repos (no AUR)
+4. **AI-agent friendly**: TOML config is trivially parseable/modifiable;
+   clean systemd service with structured journalctl output
+5. **Simplicity principle**: maximizes work not done
+
+## Consequences
+
+### Positive
+
+- Faster boot (no Qt/Xorg init)
+- Smaller attack surface
+- Less disk usage
+- No Qt dependencies to maintain
+- Clean systemd service management
+
+### Negative
+
+- No graphical login (only a limitation if multi-user GUI switching is needed)
+- SDDM themes not available (not a requirement for this workstation)
+- Tuigreet has fewer visual customization options
+
+### Migration path back
+
+```bash
+sudo systemctl disable greetd
+sudo systemctl enable sddm
+sudo ln -sf /usr/lib/systemd/system/sddm.service /etc/systemd/system/display-manager.service
+```
+
+Reversible with zero data loss — the hyprland.desktop session entry is
+unchanged and works with both DMs.