This chapter follows Terminals and shells in Linux.
A graphical Debian session is layers of software on the same kernel. Applications draw through GTK or Qt; a Wayland compositor or X11 server owns the screen; DRM/KMS in the kernel drives the GPU. Choosing GNOME, KDE, or Xfce at install time picks a bundle of those pieces—not a different kernel.
Kernel display basics
DRM (Direct Rendering Manager) and KMS (Kernel Mode Setting) let the kernel set modes and buffer flips. Userspace talks through /dev/dri/; glxinfo or eglinfo (when installed) show driver capabilities.
Firmware and drivers from non-free-firmware and vendor packages still matter—see Hardware and devices in Linux.
X11 versus Wayland
X11 (Xorg) is the decades-old network-capable display server: clients send drawing requests; a compositor/window manager decorates windows. Wayland flips the model: clients submit buffers; the compositor is the display server with tighter security (no global screen scraping by default).
| Aspect | X11 | Wayland |
|---|---|---|
| Legacy apps | Broad | XWayland bridge for many X clients |
| Remote desktop | SSH X forwarding tradition | RDP/VNC/portal patterns |
| Debian default (recent GNOME) | Fallback | Preferred session |
Debian installers offer desktop tasks; /etc/X11/default-display-manager points at gdm3, sddm, lightdm, etc.
flowchart TB apps[GTK Qt applications] toolkit[Toolkits] compositor[Wayland compositor or Xorg] drm[DRM KMS kernel driver] apps --> toolkit --> compositor --> drm
Compositors, window managers, and desktop environments
A window manager titles and focuses windows. A desktop environment (DE) bundles panel, settings, file manager, and session services:
- GNOME — Mutter compositor, gdm, tightly integrated apps.
- KDE Plasma — KWin, SDDM, Qt-heavy ecosystem.
- Xfce — Lightweight, GTK-based, good on older hardware.
i3 and Sway (Wayland tiling) are compositor-centric without full DE baggage.
Display managers and session login
Display managers (GDM, SDDM, LightDM) show greeter, start X or Wayland session, and launch /etc/X11/Xsession or compositor-specific session files. loginctl tracks seats and sessions tying back to PAM and systemd.
Console TTY login and graphical login are parallel entry points to the same user accounts.
Toolkits and theming
GTK and Qt define widget look and portal integration (file pickers, dark mode). Flatpak apps may bundle their own runtime versions; Debian packages share system libraries via APT.
Wayland xdg-desktop-portal bridges sandboxed apps to desktop services (screenshots, inhibiting sleep).
Running Linux without bare metal—WSL, containers, VMs—is the closing chapter: Linux on Windows, WSL, containers, and VMs.
The next chapter is Linux on Windows, WSL, containers, and VMs.
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