[HOWTO] Start X server manually instead of using a login manager

[Alex Kost]

Hello,

People often ask how they can use startx/xinit on GuixSD.  It is
possible, although it is not as easy as on other distros.  Hopefully,
this tutorial will answer some questions on the subject.

At first, a couple of points:

- We will run X server with user privileges, so if something goes wrong,
  look at the X log, which is placed at "~/.local/share/xorg/Xorg.N.log"
  by default.

- We will run "xinit", not "startx": the latter is just a wrapper that
  does some preparations and runs "xinit".  (startx is a usual shell
  script with a usual script's behavior: it does not like that Guix
  violates Filesystem Hierarchy Standard, so it successfully fails to
  start).

Now the steps you need to do to use "xinit":

1. Install xinit, X server and required modules to some guix profile,
   for example:

     guix package -i xinit xorg-server xf86-input-libinput xf86-video-fbdev 
xf86-video-nouveau

2. Make "~/.xinitrc" file.  If you don't know what its content should
   be, just put "exec xterm" there, or even better read:

     https://wiki.archlinux.org/index.php/Xinit

3. Running "xinit" requires specifying multiple arguments, so you will
   probably make an auxiliary script to run it.  This script will look
   like this:

--8<---------------cut here---------------start------------->8---
#!/bin/sh

DIR=$HOME/.guix-profile

$DIR/bin/xinit -- $DIR/bin/Xorg :0 vt1 -keeptty \
               -configdir $DIR/share/X11/xorg.conf.d \
               -modulepath $DIR/lib/xorg/modules
--8<---------------cut here---------------end--------------->8---

  Note that using the current terminal ("vt1" in this case) and
  "-keeptty" is required, otherwise X server refuses to start without
  root privileges.

  For testing purposes, you may change the above arguments to ":1 vt2",
  switch to vt2 (Ctrl-Alt-F2) and run this script.

4. Finally (if the above script works), you can remove login manager
   from your os services (if you use %desktop-services):

--8<---------------cut here---------------start------------->8---
(use-modules
 ;; ...
 (srfi srfi-1)                  ; for 'remove'
 (gnu services desktop)
 (gnu services xorg))

(operating-system
  ;; ...
  (services
   (remove (lambda (service)
             (eq? (service-kind service) slim-service-type))
           %desktop-services)))
--8<---------------cut here---------------end--------------->8---

-- 
Alex