Xsession

Xsession is a startup script used by the X Window System to launch a user’s graphical session after the X server starts. It is typically invoked by a display manager (such as GDM, LightDM, or SDDM) or by the startx command when starting a session. The script acts as a framework for environment setup and for launching the actual window manager or desktop environment that the user will use.

Location and structure: The canonical system-level script is often called Xsession and is found as /usr/bin/Xsession or /etc/X11/Xsession, with supporting fragments in /etc/X11/Xsession.d or a collection of desktop entries in /usr/share/xsessions. Xsession performs initial configuration, loads resources, and sets environment variables. It then delegates to the user’s session command. The user may influence what starts by providing a session description in a file such as ~/.Xsession or ~/.xinitrc. If these are not present, the display manager or Xsession will fall back to a default session described by a desktop entry from /usr/share/xsessions, which typically launches a desktop environment (for example GNOME, KDE, XFCE) or a lightweight window manager (such as twm).

Behavior and customization: During startup, Xsession often sources a series of helper scripts in /etc/X11/Xsession.d to apply system-wide settings and autostart applications. When the session process completes, the session terminates and the X server may shut down. Users can customize their session by creating an executable ~/.Xsession or ~/.xinitrc that starts the desired window manager or desktop environment. The exact behavior can vary by platform and display manager, but the general role of Xsession is to select and initiate the user’s graphical session within the X Window System.