bug#73859: lightdm-service-type is almost unusable

[Dariqq]

Hi Guix,

This is to report some of the issues and workarounds when trying to 
setup lightdm-service-type.


1. Unable to choose a session (https://issues.guix.gnu.org/68055)

This appearently never worked: https://issues.guix.gnu.org/57168#0

This means one currently has to specify the default session with 
something like

(service lightdm-service-type
         (lightdm-configuration
          (seats
           (list
            (lightdm-seat-configuration
             (name "*")
             (user-session "xfce"))))))

2. gtkgreeter chooses the wrong default session

This is related to 1. If one already had set the default user session 
(i.e. from using default configuration => default.xsession) or one wants 
to use a different session, lightdm gtkgreeter still requests the old one.

After a lot of searching I found this 
https://github.com/Xubuntu/lightdm-gtk-greeter/issues/163 .

I.e. lightdm asks the accountsservice for the default-session rather 
than lightm which still has cashed the old/wrong one. Thus with no 
option to select a different session one is unable to login.

The workaorund here is to delete/modify /var/lib/AccountService/users to 
make sure accountsservice recreates/updates the configurration.


3. After the lightdms users .Xauthority file is created it has wrong 
permissions on subsequent boots.

this can be "fixed" by manually setting less restrictive permissions on 
/var/lib/lightdm/.Xauthority

This might be fixed by making the lightdm-activiation snippet actually 
useful: It currently searches for a file named "directory" to fix 
permissions rather than the content of the variable 'directory'.

(find-files "directory"  #:directories? #t) vs
(find-files directory  #:directories? #t)

here 
https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/lightdm.scm#n527

4. tigervnnc

default tigervnc is (file-append tigervnc-server "bin/Xvnc") rather than 
(file-append tigervnc-server "/bin/Xvnc")