debianito-post-install/docs/desktops_display.md

# Option 13: Desktop & Display

### 1. What does this component do?

This component manages both desktop environments and display managers. Desktop Environment installs **GNOME, KDE Plasma, XFCE, or LXDE**; Display Manager handles LightDM, GDM3, SDDM, and greetd (login screens). It handles autologin setup, user list visibility toggles, and a specific Wayland override for NVIDIA GPUs. Desktop Environment management supports **XFCE** (full / minimal / Wayland `labwc` on Trixie / custom), **LXDE** (full / core), **GNOME** (full / core) and **KDE Plasma** (full / minimal), with polkit rules for suspend/backlight where applicable.

**Modular layout:** the menu, the shared helpers (`_existing_display_manager`, `_offer_pipewire_after_desktop`) and the display-manager configuration routines live in `modules/desktop_display.sh`; every desktop installer lives in its own module under `modules/desktops/` (`desktop_xfce.sh`, `desktop_lxde.sh`, `desktop_gnome.sh`, `desktop_kde.sh`), lazily loaded on demand via `_load_module`.

### 2. Logical Flow of Execution

The execution logic is divided into five functional blocks:

**Block 1: Desktop Environment Selection & Installation**

- The main menu (`manage_desktop_display` in `desktop_display.sh`) offers two primary options: `1  Desktop Environment` and `2  Display Manager` (plus `3  Back to main menu`).
- **Desktop Environment** opens `desktop_environment_menu` with four environments:
  1. **XFCE**: full / minimal / Wayland (`labwc`, Debian 13 only) / custom package checklist.
  2. **LXDE**: full / core.
  3. **GNOME**: full (`gnome`) / core (`gnome-core`), with GDM3.
  4. **KDE Plasma**: full (`kde-standard`) / minimal (`kde-plasma-desktop`), with SDDM.
- Each environment lives in its own module under `modules/desktops/` and is lazy-loaded from the menu dispatch with `_load_module xfce|lxde|gnome|kde` (dependencies: `desktop_display` + `audio`).
- **Display Manager** opens `display_manager_menu`: LightDM, GDM3, SDDM, and greetd (12/13 only).
- **Available Managers:**
  - LightDM (available on all Debian versions).
  - GDM3 (available on all Debian versions).
  - SDDM (available on all Debian versions).
  - greetd (available only on Debian 12 and 13).
- Each selected manager opens its own dedicated configuration submenu.

**Block 2: LightDM Configuration**

- A checklist menu presents three options:
  1. Install LightDM + GTK Greeter (auto-selects the display manager via debconf-set-selections).
  2. Enable user list at login screen (writes `greeter-hide-users=false` to a configuration file in `.conf.d`).
  3. Enable autologin for current user (uncomments `autologin-user` and sets timeout to 0 in the main config).
- **Idempotency:** The script checks if `lightdm` and `lightdm-gtk-greeter-settings` are already installed before attempting installation, skipping redundant steps.

**Block 3: GDM3 Configuration**

- A checklist menu presents up to four options:
  1. Install/Reinstall gdm3 (auto-selects via debconf).
  2. Toggle user list visibility (toggles `disable-user-list` in greeter.dconf-defaults).
  3. Configure autologin (prompts for a username via whiptail inputbox to set in daemon.conf).
  4. Force Enable Wayland on NVIDIA (Bookworm/Trixie + NVIDIA only).
     - **Mechanism:** Creates or removes a symlink: `/etc/udev/rules.d/61-gdm.rules` → `/dev/null`.
     - **Purpose:** This disables the udev rule that blocks GDM from using Wayland on NVIDIA GPUs.
     - **Risk Warning:** Displays a warning that this may break graphics or cause instability.
     - **Toggle Behavior:** If the symlink exists, removing it reverts to default behavior; if not present, creating it enables the override.

**Block 4: SDDM Configuration**

- A submenu offers two options:
  1. Install SDDM (auto-selects via debconf).
  2. Enable Autologin:
     - **Session Detection:** Auto-detects the installed session by checking `.desktop` files in priority order: `plasmawayland` → `lxqt-wayland` → `plasma` → `lxqt`.
     - **Configuration:** Writes autologin settings to `/etc/sddm.conf.d/autologin.conf`.
     - **Fallback:** If no session is found, it enables autologin but warns that SDDM will use the default session.

**Block 5: greetd Configuration**

- greetd is a minimal, modern display manager designed for Wayland environments.
- Submenu options vary by Debian version:
  - **All Versions:** Install base `greetd`, Install `greetd` + `tuigreet` (recommended TUI greeter).
  - **Debian 13 only:** Additional options to install `gtk-greet`, `nwg-hello`, or `wlgreet`.
- **Backports Handling:** On Bookworm, `tuigreet` is installed from backports if not enabled.
- **Important Warning:** greetd is installed but NOT configured by the script. The user must manually create `/etc/greetd/config.toml` to be able to log in. The script displays a warning with references to man pages for configuration details.

### 3. Automations

The component automates several steps:

- **debconf-set-selections:** Pre-selects the display manager as default before `apt install`, preventing the interactive "Configuring shared/default-x-display-manager" dialog that would otherwise pause the script execution.
- **Session Auto-Detection (SDDM):** Checks `.desktop` files in priority order (Wayland first, then X11) to set the correct session type for autologin configuration.
- **Wayland Toggle:** Creates or removes a udev rule symlink to `/dev/null`. This is a known workaround that disables the GDM rule blocking NVIDIA Wayland support.
- **greetd Backports:** On Bookworm, `tuigreet` is installed from backports (newer version) if not already enabled in the system.
- **Manual Config Warning:** The script explicitly informs users that greetd requires manual configuration and points to man pages for further details.
- **User Detection:** Uses `SUDO_USER` (the real user who ran sudo) instead of `$USER` (which is root during script execution). This ensures the correct user is set for automatic login across all display managers.
- **Pre-apply Summary:** every desktop installer shows a confirmation list of the packages (`_confirm_install_list`) before any debconf or apt transaction starts; declining aborts safely.
- **Existing DM Preservation:** the GNOME and KDE installers detect the current default display manager (`_existing_display_manager` reads `/etc/X11/default-display-manager`, falling back to an enabled DM systemd unit), preseed that manager instead of the new one, and skip `systemctl enable` so an already-configured login screen is never overwritten.
- **PipeWire Offer:** after any desktop install (XFCE, LXDE, GNOME, KDE), `_offer_pipewire_after_desktop` checks for `pipewire-audio` (`pipewire` on Bullseye) and, when missing, asks once before running `_install_pipewire_standard`. Declining is a choice, not an error: the helper always returns 0.
- **Stale-lists Guard:** `_ensure_apt_updated` runs before the GNOME/KDE `apt install` transactions, refreshing the package lists at most once per session.

### 4. Packages and Resources Managed

**Display Manager Packages:**

| DM | Packages | Debian Versions |
| --- | --- | --- |
| LightDM | lightdm, lightdm-gtk-greeter, lightdm-gtk-greeter-settings | All |
| GDM3 | gdm3 | All |
| SDDM | sddm | All |
| greetd (base) | greetd | 12, 13 |
| greetd + tuigreet | greetd, tuigreet | 12 (backports), 13 |
| greetd + gtk-greet | greetd, gtk-greet | 13 only |
| greetd + nwg-hello | greetd, nwg-hello | 13 only |
| greetd + wlgreet | greetd, wlgreet | 13 only |

**Desktop Environment Packages:**

| Environment | Variant | Packages | Display Manager |
| --- | --- | --- | --- |
| XFCE | Full | xfce4, xfce4-goodies, xfce4-power-manager | not managed by the installer |
| XFCE | Minimal | xfce4 | not managed by the installer |
| XFCE | Wayland (13 only) | xfce4, labwc | not managed by the installer |
| XFCE | Custom | user-selected checklist | not managed by the installer |
| LXDE | Full / Core | lxde / lxde-core | lightdm (always) |
| GNOME | Full / Core | gnome / gnome-core | gdm3 (installed; existing DM kept as default) |
| KDE Plasma | Full / Minimal | kde-standard / kde-plasma-desktop | sddm (installed; existing DM kept as default) |

**Configuration Files Modified:**

| DM | File Path | Configuration Purpose |
| --- | --- | --- |
| LightDM | /etc/lightdm/lightdm.conf.d/50-debianito-userlist.conf | User list visibility toggle |
| LightDM | /etc/lightdm/lightdm.conf | Autologin user + timeout settings |
| GDM3 | /etc/gdm3/greeter.dconf-defaults | User list toggle (disable-user-list) |
| GDM3 | /etc/gdm3/daemon.conf | Autologin user and enable flag |
| GDM3 | /etc/udev/rules.d/61-gdm.rules | Wayland override (symlink to /dev/null) |
| SDDM | /etc/sddm.conf.d/autologin.conf | Autologin user + session type |

**Session Detection Priority (SDDM Autologin):**

| Priority | Session File | Session Type |
| --- | --- | --- |
| 1 | /usr/share/wayland-sessions/plasmawayland.desktop | KDE Wayland |
| 2 | /usr/share/wayland-sessions/lxqt-wayland.desktop | LXQt Wayland |
| 3 | /usr/share/xsessions/plasma.desktop | KDE X11 |
| 4 | /usr/share/xsessions/lxqt.desktop | LXQt X11 |

> ⚠️ **Warning: Wayland on NVIDIA:** The "Force Enable Wayland on NVIDIA" option creates a symlink that disables the GDM udev rule. This is a known workaround but MAY cause graphics instability or breakage. To revert, remove `/etc/udev/rules.d/61-gdm.rules`.

> ⚠️ **Warning: greetd:** Unlike other display managers, greetd is installed but NOT configured by this script. You MUST manually create `/etc/greetd/config.toml` before you can log in. See `man greetd` and `man 5 greetd-sessions` for configuration details.

> ⚠️ **Warning: Autologin:** All autologin configurations use `SUDO_USER` (the user who ran sudo) instead of `$USER` (which is root during script execution). This ensures the correct user is set for automatic login.

> 💡 **Technical Note:** `debconf-set-selections` pre-selects the display manager before apt install, preventing the interactive "Configuring shared/default-x-display-manager" dialog that would otherwise pause the script.