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.