NixOS: Ordering of X Startup Scripts

ordering_of_x_startup_scripts.md

Ordering of X Startup Scripts

This is specific to NixOS.

There are 2 cases, the text mode case, and the graphical mode case. This is the graphical mode case:

1. Bootup (systemd services)
2. Runs systemctl start display-manager either automatically or via terminal.
3. Launch Display Manager (Runs Display Manager Initialisation)
4. Launch X for the Display Manager (this doesn't run xserverrc nor xinitrc)
5. Login Occurs
6. PAM executes relevant routines. (Which could involve pam_env.so loading ~/.pam_environment.)
7. Runs Session Script (Starts DBUS, Starts GPGAgent, Starts PulseAudio, Sets up X logging, Loads ~/.Xresources and ~/.Xdefaults and ~/.xprofile, Optionally exec with ~/.xsession replacing the current session.)
8. Launch Window Manager/Desktop Environment (Runs XDG Autostart Scripts)

In the case of a text mode it's just (however on NixOS, this doesn't seem possible):

1. Bootup (systemd services).
2. Login into text console.
3. PAM executes relevant routines. (Which could involve pam_env.so loading ~/.pam_environment.)
4. Login shell executes startup routines.
5. Runs startx via the terminal.
6. Launches X by running xinit and runs ~/.xserverrc and ~/.xinitrc (if these files don't exist there are default packaged xserverrc and xinitrc and their locations are dependent on the distribution).
7. Launches Window/DesktopManager (Runs Autostart Scripts)

Here are the references:

• Systemd Services: https://www.freedesktop.org/software/systemd/man/systemd.service.html
• Display Manager Initialisation (usually called XSetup): http://unix.stackexchange.com/q/42611/56970 (for SDDM: see https://github.com/sddm/sddm/tree/master/data/scripts)
• The xinitrc and xserverrc: https://wiki.archlinux.org/index.php/Xinit
• Session Script: https://github.com/NixOS/nixpkgs/blob/01c197df689a9794885a80d965311696377e0efb/nixos/modules/services/x11/display-managers/default.nix#L30-L148
• Autostart Scripts: https://specifications.freedesktop.org/autostart-spec/autostart-spec-latest.html#startup and https://wiki.archlinux.org/index.php/autostarting#Graphical

For XMonad, its autostart scripts is just whatever is coded into ~/.xmonad/xmonad.hs.