Starting user software in X

There are currently many ways of starting software when a user session starts.

This is an attempt to collect a list of pointers to piece the big picture together. It's partial and some parts might be imprecise or incorrect, but it's a start, and I'm happy to keep it updated if I receive corrections.

x11-common

man xsession

  • Started by the display manager for example, /usr/share/lightdm/lightdm.conf.d/01_debian.conf or /etc/gdm3/Xsession
  • Debian specific
  • Runs scripts in /etc/X11/Xsession.d/
  • /etc/X11/Xsession.d/40x11-common_xsessionrc sources ~/.xsessionrc which can do little more than set env vars, because it is run at the beginning of X session startup
  • At the end, it starts the session manager (gnome-session, xfce4-session, and so on)

systemd --user

  • https://wiki.archlinux.org/index.php/Systemd/User
  • Started by pam_systemd, so it might not have a DISPLAY variable set in the environment yet
  • Manages units in:
    • /usr/lib/systemd/user/ where units provided by installed packages belong.
    • ~/.local/share/systemd/user/ where units of packages that have been installed in the home directory belong.
    • /etc/systemd/user/ where system-wide user units are placed by the system administrator.
    • ~/.config/systemd/user/ where the users put their own units.
  • A trick to start a systemd user unit when the X session has been set up and the DISPLAY variable is available, is to call systemctl start from a .desktop autostart file.

dbus activation

X session manager

xdg autostart

Other startup notes

~/.Xauthority

To connect to an X server, a client needs to send a token from ~/.Xauthority, which proves that they can read the user's provate data.

~/.Xauthority contains a token generated by display manager and communicated to X at startup.

To view its contents, use xauth -i -f ~/.Xauthority list