~/.xinitrc

If the script starts programs (such a xscreensaver or xsetroot) it is important to start them in the background (with &) so that the script doesn't wait until they're finished.

However, the last program that is started by .xinitrc is usually a window manager or a terminal emulator (such as xterm) is started in the foreground so that the script doesn't exit.

When .xinitrc exits, it indicates to xinit that the user is done with the X session and that in turn xinit should exit as well.

The system-wide xinitrc script is /etc/X11/xinit/xinitrc.