mv ~/.cache/xfce4 ~/.cache/xfce4_orig
 mv ~/.config/xfce4 ~/.config/xfce4_orig

result.width = (crtc_info->width == 0 ? 1024 : crtc_info->width);
result.height = (crtc_info->height == 0 ? 768 : crtc_info->height);

result.width  = (crtc_info->width  > 0 ? crtc_info->width  : fallback.width  > 0 ? fallback.width  : 1024);
result.height = (crtc_info->height > 0 ? crtc_info->height : fallback.height > 0 ? fallback.height :  768);

+ Test the slim currently installed
 + devuan_excalibur_6.0.0_amd64_netinstall.iso
   * Software selection
     - Devuan desktop environment
     - Xfce
     - ssh server
     - standard system utilities

 * Test slim, installed version
   * Details
     - Version: 1.4.1-1devuan1

   ! slim - auto_login (yes) - untitled window?
     ! Ans: Reproduced: Untitled window appears

   ! slim - auto_login (yes) + default_user (bad name). What will the error handling do?
     ! Ans: No login screen.
       - slim appears to have crashed: "ps -ef | grep slim" doesn't show slim running.
       - This is a NEW crash.

       * Test on daedalus slim: 1.4.0-0devuan2
         ! Ans: Yes, daedalus slim ALSO crashes.

   + slim - auto_login (yes) + default_user (no name). What will the error handling do?
     + Login screen is displayed normally.

   ! Monitorless slim crash
     ! Ans: Reproduced: No login screen.
       - slim appears to have crashed: "ps -ef | grep slim" doesn't show slim running.

N: Repository 'http://deb.devuan.org/merged excalibur InRelease' changed its 'Suite' value from 'testing' to 'stable'
N: Repository 'http://deb.devuan.org/merged excalibur-security InRelease' changed its 'Suite' value from 'testing-security' to 'stable-security'
N: Repository 'http://deb.devuan.org/merged excalibur-updates InRelease' changed its 'Suite' value from 'testing-updates' to 'stable-updates'

#!/usr/bin/perl -W

use strict  ;
use warnings;
use Cwd     ;
use constant false => 0;
use constant true  => 1;

#In Xfce 4.16, the code switched to use rDNS (reverse DNS) icon file names. Example: The file name that Xfce expects
#for showing the desktop was changed from "user-desktop.png" to "org.xfce.panel.showdesktop.png". See:
#  https://wiki.xfce.org/releng/4.16/icons_rdns_naming_for_icons
#
#In Devuan Excalibur, most of the icon themes have NOT been updated to include the rDNS files, so the theme's icons
#are not loaded.
#
#This script will take in an icon directory and add symbolic links using Xfce's new rDNS file names to the old file names
#currently in the icon theme. The symlinks are created only if the symlink doesn't exist AND if the old file name
#exists.

######## VARIABLES ########

my $gstrIconDir = "";   #The user specified directory to an icon theme. The directory must contain the file icon-theme.cache.

#A hash of Xfce's new rDNS (reverse DNS) icon file names to the old file names.
#The table came from 2 sources:
#  - Xfce's official list from 4.16.
#    https://wiki.xfce.org/releng/4.16/icons_rdns_naming_for_icons
#  - A user's script, which contains a few more entries than the original table.
#    https://gist.github.com/bluesabre/582d886a02c793285f4e3081df9b2a3c
#  * Notes
#    - In Xfce's list, the new "xfsm-hibernate" maps to two old files: "system-hibernate", "system-suspend-hibernate".
#      In the user's script, that's mapped to only "system-suspend-hibernate".
#      - I decided to support both, with "system-hibernate" as the first choice, since that more closely matches the new name.
#    - In Xfce's list, the old "preferences-desktop-default-applications" is mapped to the new
#      "org.xfce.settings.preferred-application". But in the user's script, it's mapped to "org.xfce.settings.default-applications".
#      - I decided to map it to "preferences-desktop-default-applications", because I see it in the Xfce changelog for 4.18.
#
#For new icons that refer to multiple old file names, I used a | to separate the old file names.
my %hashXfceNewtoOldFileNames =
(
    "org.xfce.about"       => "help-about"         ,
    "org.xfce.appfinder"   => "edit-find"          ,
    "org.xfce.catfish"     => "catfish"            ,
    "org.xfce.Dictionary"  => "xfce4-dict"         ,
    "org.xfce.filemanager" => "system-file-manager",

    "org.xfce.genmon"       => "utilities-system-monitor",
    "org.xfce.gigolo"       => "gtk-network"             ,
    "org.xfce.mailreader"   => "emblem-mail"             ,
    "org.xfce.mousepad"     => "accessories-text-editor" ,
    "org.xfce.notification" => "xfce4-notifyd"           ,

    "org.xfce.panel"                  => "xfce4-panel"               ,
    "org.xfce.panel.actions"          => "system-log-out"            ,
    "org.xfce.panel.applicationsmenu" => "xfce4-panel-menu"          ,
    "org.xfce.panel.clock"            => "x-office-calendar"         ,
    "org.xfce.panel.directorymenu"    => "folder"                    ,
    "org.xfce.panel.launcher"         => "application-x-executable"  ,
    "org.xfce.panel.pager"            => "xfce4-workspaces"          ,
    "org.xfce.panel.separator"        => "list-remove-symbolic"      ,
    "org.xfce.panel.showdesktop"      => "user-desktop"              ,
    "org.xfce.panel.tasklist"         => "preferences-system-windows",
    "org.xfce.panel.windowmenu"       => "preferences-system-windows",

    "org.xfce.parole"        => "parole"                         ,
    "org.xfce.powermanager"  => "xfce4-power-manager-settings"   ,
    "org.xfce.ristretto"     => "ristretto"                      ,
    "org.xfce.ScreenSaver"   => "preferences-desktop-screensaver",
    "org.xfce.screenshooter" => "applets-screenshooter"          ,
    "org.xfce.session"       => "xfce4-session"                  ,

    "org.xfce.settings.accessibility"        => "preferences-desktop-accessibility"       ,
    "org.xfce.settings.appearance"           => "preferences-desktop-theme"               ,
    "org.xfce.settings.color"                => "xfce4-color-settings"                    ,
    "org.xfce.settings.default-applications" => "preferences-desktop-default-applications",
    "org.xfce.settings.display"              => "video-display"                           ,
    "org.xfce.settings.editor"               => "preferences-system"                      ,
    "org.xfce.settings.keyboard"             => "preferences-desktop-keyboard"            ,
    "org.xfce.settings.manager"              => "preferences-desktop"                     ,
    "org.xfce.settings.mouse"                => "preferences-desktop-peripherals"         ,

    "org.xfce.taskmanager"       => "utilities-system-monitor",
    "org.xfce.terminal-settings" => "utilities-terminal"      ,
    "org.xfce.terminal"          => "utilities-terminal"      ,
    "org.xfce.terminalemulator"  => "utilities-terminal"      ,
    "org.xfce.thunar"            => "Thunar"                  ,

    "org.xfce.volman"      => "drive-removable-media",
    "org.xfce.webbrowser"  => "web-browser"          ,
    "org.xfce.workspaces"  => "xfce4-workspaces"     ,
    "org.xfce.xfburn"      => "xfburn"               ,
    "org.xfce.xfdashboard" => "xfdashboard"          ,

    "org.xfce.xfdesktop"    => "preferences-desktop-wallpaper",
    "org.xfce.xfmpc"        => "multimedia-player"            ,
    "org.xfce.xfwm4-tweaks" => "wmtweaks"                     ,
    "org.xfce.xfwm4"        => "xfwm4"                        ,

    "xfsm-hibernate"   => "system-hibernate|system-suspend-hibernate",
    "xfsm-lock"        => "system-lock-screen",
    "xfsm-logout"      => "system-log-out"    ,
    "xfsm-reboot"      => "system-reboot"     ,
    "xfsm-shutdown"    => "system-shutdown"   ,
    "xfsm-suspend"     => "system-suspend"    ,
    "xfsm-switch-user" => "system-users"      ,
);

######## FUNCTIONS ########

#Perform cleanup before the script exits with the given exit code.
#
#$_[0] [in] - Optional - The exit code to exit the script with. Default = 0.
sub CleanupExit
{
    my $iExitCode = @_ >= 1 ? $_[0] : 0;

    #Insert extra cleanup here before the script exits.

    exit($iExitCode);
}

#Args: none
#Return: 0
sub PrintHelp
{
    printf("Usage: The first arg must be a directory of an icon theme. The directory must contain\n");
    printf("the file \"icon-theme.cache\".\n");

    return 0;
}

#Parses @ARGV for the path to the icon theme.
#
#Args: none
#
#Return: 0 on success, 1 on failure.
sub ParseArgv
{
    if (scalar(@ARGV) < 1)
    {
        PrintHelp();
        return 1;
    }
    
    my $strIconDir = $ARGV[0];
    
    if (! -e "$strIconDir")
    {
        printf("!!! Error: Directory does not exist: %s\n", $strIconDir);
        return 1;
    }

    if (! -d "$strIconDir")
    {
        printf("!!! Error: Specified path is not a directory: %s\n", $strIconDir);
        return 1;
    }
    
    my $strIconCacheFile = "$strIconDir/icon-theme.cache";

    if (! -e "$strIconCacheFile")
    {
        printf("!!! Error: The file \"icon-theme.cache\" was not found in the directory: %s\n", $strIconDir);
        return 1;
    }

    if (! -f "$strIconCacheFile")
    {
        printf("!!! Error: The \"icon-theme.cache\" in the directory \"%s\" is not a plain file.\n", $strIconDir);
        return 1;
    }

    $gstrIconDir = $strIconDir;

    return 0;
}

#Check that the required cmds or apps are found on the path.
#
#Args: none
#
#Return: 0 on success, 1 on failure.
sub CheckRequiredCmds
{
    if (system("which gtk-update-icon-cache > /dev/null") != 0)
    {
        printf("!!! Error: The cmd \"gtk-update-icon-cache\" was not found. This is needed to update the theme's icon cache file.\n");
        return 1;
    }

    return 0;
}

#Helper function to read the directory entries into an array, ignoring the special directories "." and "..".
#
#Args:
#  $_[0] - String of the directory name to open.
#  $_[1] - A reference to an array to receive the directory entry strings.
#
#Return: 0 on success, 1 on failure.
sub ReadDirEntriesIgnoreSpDirs
{
    my $strDir             = $_[0];
    my $refarstrDirEntries = $_[1];
    
    my $hDIR;
    
    @$refarstrDirEntries = ();

    #Open the current directory and read all of the directory entries into an array.
    if (!opendir($hDIR, $strDir))
    {
        printf("!!! Could not open the directory to get the subdirectories: %s\n", $strDir);
        return 1;
    }
    my @arstrDirEntries = readdir($hDIR);
    closedir($hDIR);

    #Ignore the special directories "." and "..". grep keeps the elements where the block function returns true.
    #$_ refers to each element in the array.
    @$refarstrDirEntries = grep { $_ ne "." && $_ ne ".." } @arstrDirEntries;

    return 0;
}

#Create symbolic links of the new Xfce icon names to the old file name. The symlinks are created only if the symlink
#doesn't exist AND if the old file name exists.
#
#Args: none
#
#Return: 0 on success, 1 on failure.
sub CreateNewXfceIconNames
{
    my $iRet = 1, my $iNumCreated = 0;
    my $hICONDIR, my $hSIZEDIR, my $hCATEGORYDIR;

    my @arNewFileNameKeys = keys(%hashXfceNewtoOldFileNames);

    #Supported file extensions for the icon file names.
    my @arFileExt = ( ".png", ".svg" );

    #Read all of the icon theme directory's entries, which should contain size subdirectories and other files.
    my @arstrIconDirEntries;
    if (ReadDirEntriesIgnoreSpDirs($gstrIconDir, \@arstrIconDirEntries) != 0)
        { goto CLEANUPRETURN; }

    #Sort all of the arrays, so the printed output is more organized and easier for the user to see what symlinks
    #were created.
    @arNewFileNameKeys   = sort(@arNewFileNameKeys  );
    @arstrIconDirEntries = sort(@arstrIconDirEntries);

    foreach my $strIconDirEntry (@arstrIconDirEntries)
    {
        #Skip anything that's not a subdirectory.
        if (! -d "$gstrIconDir/$strIconDirEntry")
            { next; }

        #We're have a subdirectory name of the icon theme directory that represents the icon size.
        #Example: 16x16, 22x22, scalable, etc.
        my $strThisSizeDir = "$gstrIconDir/$strIconDirEntry";

        #Read all of the size directory's entries, which should contain category subdirectories.
        my @arstrSizeDirEntries;
        if (ReadDirEntriesIgnoreSpDirs($strThisSizeDir, \@arstrSizeDirEntries))
            { goto CLEANUPRETURN; }

        @arstrSizeDirEntries = sort(@arstrSizeDirEntries);

        foreach my $strSizeDirEntry (@arstrSizeDirEntries)
        {
            #Skip anything that's not a subdirectory.
            if (! -d "$strThisSizeDir/$strSizeDirEntry")
                { next; }

            #We're have a subdirectory name of the size directory that represents the category.
            #Example: actions, apps, places, etc.
            my $strThisCategoryDir = "$strThisSizeDir/$strSizeDirEntry";

            #Read all of the category directory's entries, which should contain the theme icon files.
            my @arstrCategoryDirEntries;
            if (ReadDirEntriesIgnoreSpDirs($strThisCategoryDir, \@arstrCategoryDirEntries))
                { goto CLEANUPRETURN; }

            #Inside the category directory, we should have .png or .svg files that are the old icon files.
            #They may also include new icon files if this icon theme has already been updated with the new
            #Xfce rDNS file names. Also, some of these entries might be symbolic links to other files.
            
            #Check each new file to old file mapping. If the old file is here, and the new file is NOT here,
            #create a symbolic link. Check for both .png and .svg file extensions.
            foreach my $strThisNewFileName (@arNewFileNameKeys)
            {
                #Since a new file may contain multiple old files, we separate the old file string by the | to get
                #each old file name. We'll use the first matching old file.
                #Example: "xfsm-hibernate" => "system-hibernate|system-suspend-hibernate"
                my @arstrOldFileNames = split(/\|/, $hashXfceNewtoOldFileNames{$strThisNewFileName});
                
                #Check each of the supported file extensions. Example: .png, .svg.
                foreach my $strThisFileExt (@arFileExt)
                {
                    foreach my $strThisOldFileName (@arstrOldFileNames)
                    {
                        my $strThisOldFileNameExt = $strThisOldFileName . $strThisFileExt;
                        my $strThisNewFileNameExt = $strThisNewFileName . $strThisFileExt;
    
                        if (-e "$strThisCategoryDir/$strThisNewFileNameExt")
                            { next; }  #This new icon file has already been created.
                        
                        #This new icon file hasn't been created. Check if the old icon file exists in this category directory.
                        #$_ refers to each element in the array.
                        my @grepRet = grep { $_ eq $strThisOldFileNameExt } @arstrCategoryDirEntries;
                        if (scalar(@grepRet) == 0)
                            { next; }  #The old icon file wasn't found in this directory. Can't make a symlink.

                        #Construct the command to create the new file symbolic link to the old file. Reminder
                        #that the new symlink is supposed to be in the same directory as the old file. But we're not
                        #inside this category directory. So the symlink command will contain just the old file name
                        #as the "target", and the "link name" will be a path to where the symlink will be created.
                        #Example:
                        #  ln -sv "user-desktop.png" "Tango/32x32/places/org.xfce.panel.showdesktop.png"
                        #
                        #  -s : create symbolic link
                        #  -v : print name of each linked file
                        my $strCmd = sprintf("ln -sv \"%s\" \"%s/%s\"", $strThisOldFileNameExt, $strThisCategoryDir, $strThisNewFileNameExt);
                        if (system($strCmd) != 0)
                            { goto CLEANUPRETURN; }
                        
                        #We've created a new icon file name symlink to one of the old files. Skip any other old file names.
                        $iNumCreated++;
                        last;
                    }
                }
                #we're done with this new icon file name.
            }
            #We're done with this category subdirectory.
        }
        #We're done with this size subdirectory.
    }

    if ($iNumCreated > 0)
    {
        printf("\n");
        printf("* Updating the theme's \"icon-theme.cache\" so it knows about the new files.\n");
        my $strCmd = sprintf("gtk-update-icon-cache \"%s\"", $gstrIconDir);
        if (system($strCmd) != 0)
            { goto CLEANUPRETURN; }
    }
    else
    {
        printf("* No new files were created. Skipping updating the theme's \"icon-theme.cache\".\n");
    }
    
    #We've successfully updated the icon theme directory.
    $iRet = 0;
    
CLEANUPRETURN:

    return $iRet;
}

######## BEGIN SCRIPT ########

ParseArgv             () == 0 || CleanupExit(1);
CheckRequiredCmds     () == 0 || CleanupExit(1);
CreateNewXfceIconNames() == 0 || CleanupExit(1);

CleanupExit 0;

######## END SCRIPT ########

Adjusted how/when the pseudo-root window is created and removed, in
preparation for handling multiple monitors in SLiM