Every time I log into Xubuntu's Xfce, using LightDM I can see the following log lines in /var/log/lightdm/seat0-greeter.log

The configuration was not changed significantly, except for lightdm-gtk-greeter-settings, in which I chose theme Adwaita-dark and icons elementary-xfce-dark.


** Message: 22:15:21.895: Starting lightdm-gtk-greeter 2.0.5 (Mar 20 2018, 09:53:31)
** Message: 22:15:21.896: [Configuration] Reading file: /usr/share/lightdm/lightdm-gtk-greeter.conf.d/01_ubuntu.conf
** Message: 22:15:21.896: [Configuration] Reading file: /usr/share/lightdm/lightdm-gtk-greeter.conf.d/30_xubuntu.conf
** Message: 22:15:21.896: [Configuration] Reading file: /etc/lightdm/lightdm-gtk-greeter.conf

** (lightdm-gtk-greeter:3030): WARNING **: 22:15:22.155: [PIDs] Failed to execute command: upstart

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:22.401: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.215: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.240: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.290: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.306: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.323: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.341: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.356: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.374: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.391: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.408: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.424: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.441: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.457: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.474: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.491: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.507: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.523: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.540: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.557: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.574: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.675: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.692: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.708: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.724: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.742: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.759: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.775: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.791: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.807: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.825: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.841: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:30.858: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:35.411: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)

(lightdm-gtk-greeter:3030): Gtk-WARNING **: 22:15:35.424: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar)
Gdk-Message: 22:15:35.639: lightdm-gtk-greeter: Fatal IO error 11 (Resource temporarily unavailable) on X server :1.