Hello all,
I have some messages in my xsession-errors file for which I would kindly request some help in order to sort them out:
** (wrapper-2.0:584): WARNING **: 10:38:39.615: Binding 'XF86AudioLowerVolume' failed!
(wrapper-2.0:584): pulseaudio-plugin-WARNING **: 10:38:39.615: Could not have grabbed volume control keys. Is another volume control application (xfce4-volumed) running?
(wrapper-2.0:584): libnotify-WARNING **: 10:38:39.627: Failed to connect to proxy
** (xfce4-clipman:610): WARNING **: 10:38:40.602: Unable to register GApplication: For the interface org.gtk.Application on /org/xfce/clipman already an object was exported
(xfce4-clipman:610): GLib-GIO-CRITICAL **: 10:38:40.603: g_application_get_is_remote: assertion 'application->priv->is_registered' failed
(xfce4-clipman:610): GLib-WARNING **: 10:38:40.603: g_set_application_name() called multiple times
(wrapper-2.0:579): Gtk-WARNING **: 10:38:40.620: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner GtkToggleButton)
** (xfce4-power-manager:615): WARNING **: 10:38:40.630: Failed to get name owner: GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Could not get owner of name 'org.freedesktop.PowerManagement': no such name
** (xfce4-power-manager:615): WARNING **: 10:38:40.631: Failed to get name owner: GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Could not get owner of name 'org.xfce.PowerManager': no such name
** (xfce4-screensaver:619): WARNING **: 10:38:40.707: Screensaver already running in this session
(wrapper-2.0:584): Gtk-WARNING **: 10:38:40.751: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner PulseaudioButton)
(wrapper-2.0:582): Gtk-WARNING **: 10:38:40.806: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner GtkButton)
(pamac-tray:622): Gdk-CRITICAL **: 10:38:40.971: gdk_window_thaw_toplevel_updates: assertion 'window->update_and_descendants_freeze_count > 0' failed
(xfce4-power-manager:615): GLib-GObject-WARNING **: 10:38:41.121: ../glib/gobject/gsignal.c:2614: signal 'Changed' is invalid for instance '0x55a15c45eac0' of type 'GDBusProxy'
(xfce4-power-manager:615): xfce4-power-manager-WARNING **: 10:38:41.135: could not map keysym 1008ffa8 to keycode
(xfce4-power-manager:615): xfce4-power-manager-WARNING **: 10:38:41.145: Failed to get keyboard max brightness level : GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface »org.freedesktop.UPower.KbdBacklight« of object in path /org/freedesktop/UPower/KbdBacklight
(xfce4-power-manager:615): xfce4-power-manager-WARNING **: 10:38:41.193: ../panel-plugins/power-manager-plugin/power-manager-button.c:858: invalid property id 2 for "show-panel-label" of type 'GParamInt' in 'PowerManagerButton'
(xfce4-power-manager:615): xfce4-power-manager-WARNING **: 10:38:41.193: ../panel-plugins/power-manager-plugin/power-manager-button.c:858: invalid property id 3 for "presentation-mode" of type 'GParamBoolean' in 'PowerManagerButton'
(xfce4-power-manager:615): xfce4-power-manager-WARNING **: 10:38:41.193: ../panel-plugins/power-manager-plugin/power-manager-button.c:858: invalid property id 4 for "show-presentation-indicator" of type 'GParamBoolean' in 'PowerManagerButton'
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
(xfce4-panel:568): Gtk-WARNING **: 12:45:22.510: Content added to the action area of a dialog using header bars
(xfce4-panel:568): Gtk-WARNING **: 12:45:22.511: Content added to the action area of a dialog using header bars
(xfce4-panel:568): Gtk-WARNING **: 12:45:22.990: Failed to measure available space: The specified place is not supported
Unless your X-session is completely broken - errors printed to xsession-errors are usually informational regardless of the text printed and can be caused by a multitude combinations - races between applications etc.
Ensure your system is up-to-date - always the first step in trouble shooting
sudo pacman -Syu
Are you by any chance using gtk3-classic/mushrooms?
System is up to date - I checked several times yesterday and today as well.
Not to my knowledge.
I am only a bit concerned about those CRITICAL messages and hence, thought it would make sense to try to sort the errors out.
Understandable - but it is an application that is throwing the error - and you cannot fix application calls to gtk - unless you are a sharp coder and can fix gtk errors?
If you are very concerned - check with the application(s) in question and raise the question upstream to the applications developers.
At least, it looks like I got rid of the clipman error following a recommendation from the net to not start xfce4-clipman directly in the Autostart but rather use xfce4-clipman-plugin in the Panel.
Now, my .xsession-errors looks a bit different:
xrdb: "Xft.hinting" on line 8 overrides entry on line 5
xrdb: "Xft.hintstyle" on line 11 overrides entry on line 6
/usr/bin/iceauth: creating new authority file /run/user/1000/ICEauthority
gpg-agent: A gpg-agent is already running - not starting a new one
** (wrapper-2.0:578): WARNING **: 15:19:59.401: Binding 'XF86AudioLowerVolume' failed!
(wrapper-2.0:578): pulseaudio-plugin-WARNING **: 15:19:59.401: Could not have grabbed volume control keys. Is another volume control application (xfce4-volumed) running?
(wrapper-2.0:578): libnotify-WARNING **: 15:19:59.406: Failed to connect to proxy
(wrapper-2.0:573): Gtk-WARNING **: 15:20:00.080: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner GtkToggleButton)
(wrapper-2.0:576): Gtk-WARNING **: 15:20:00.142: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner GtkButton)
(wrapper-2.0:575): Gtk-WARNING **: 15:20:00.154: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner GtkToggleButton)
(wrapper-2.0:578): Gtk-WARNING **: 15:20:00.165: Negative content width -1 (allocation 1, extents 1x1) while allocating gadget (node button, owner PulseaudioButton)
** (xfce4-power-manager:631): WARNING **: 15:20:00.438: Failed to get name owner: GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Could not get owner of name 'org.freedesktop.PowerManagement': no such name
** (xfce4-power-manager:631): WARNING **: 15:20:00.438: Failed to get name owner: GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Could not get owner of name 'org.xfce.PowerManager': no such name
(xfce4-power-manager:631): libnotify-WARNING **: 15:20:00.477: Failed to connect to proxy
** (xfce4-screensaver:640): WARNING **: 15:20:00.690: Screensaver is already running in this session
(xfce4-power-manager:631): GLib-GObject-WARNING **: 15:20:00.971: ../glib/gobject/gsignal.c:2614: signal 'Changed' is invalid for instance '0x56395c403a80' of type 'GDBusProxy'
(xfce4-power-manager:631): xfce4-power-manager-WARNING **: 15:20:00.990: could not map keysym 1008ffa8 to keycode
(xfce4-power-manager:631): xfce4-power-manager-WARNING **: 15:20:01.002: Failed to get keyboard max brightness level : GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface »org.freedesktop.UPower.KbdBacklight« of object in path /org/freedesktop/UPower/KbdBacklight
(xfce4-power-manager:631): xfce4-power-manager-WARNING **: 15:20:01.056: ../panel-plugins/power-manager-plugin/power-manager-button.c:858: invalid property id 2 for "show-panel-label" of type 'GParamInt' in 'PowerManagerButton'
(xfce4-power-manager:631): xfce4-power-manager-WARNING **: 15:20:01.056: ../panel-plugins/power-manager-plugin/power-manager-button.c:858: invalid property id 3 for "presentation-mode" of type 'GParamBoolean' in 'PowerManagerButton'
(xfce4-power-manager:631): xfce4-power-manager-WARNING **: 15:20:01.056: ../panel-plugins/power-manager-plugin/power-manager-button.c:858: invalid property id 4 for "show-presentation-indicator" of type 'GParamBoolean' in 'PowerManagerButton'
(xfce4-panel:562): xfce4-panel-CRITICAL **: 15:20:13.688: panel-window.c:2380 (panel_window_active_window_geometry_changed): expression 'WNCK_IS_WINDOW (active_window)' failed.
** Message: 15:20:30.227: updates_checker.vala:71: check updates
** Message: 15:20:31.014: updates_checker.vala:101: 0 updates found
For the xfce4-power-manager related entries, I found an explanation, together with a solution at FS#69091 : [xfce4-power-manager] .xsession-errors.
In a nutshell, amend the Exec line in /etc/xdg/autostart/xfce4-power-manager.desktop to read like
Exec=xfce4-power-manager --daemon
Adding --daemon worked for me too. By that, I mean I no longer get the “Failed to get name owner” messages, plus a number of other messages like “No output have backlight property”.
I added the Exec line to the local file, $HOME/.config/autostart/xfce4-power-manager.desktop rather than /etc/. Works either way 
Thanks for asking this question and providing an update. It was very helpful.