Dear Maintainer, After upgrade to 1.33.0-1 system no longer allows opening sessions for other users, $ dm-tool switch-to-greeter Unable to switch to greeter: GDBus.Error:org.freedesktop.DBus.Error.Failed: Failed to switch to greeter Downgrading to previous 1.32.0-7+b1 makes this problem disappear. Thanks for caring of lightdm, hope this helps.
control: tag -1 unreproducible moreinfo Hey, it seems to work fine here. Out of curiosity, which DM are you running and are you running Wayland by any chance? Regards,
Hi Yves-Alexis, thanks for the very quick reply, $ cat /etc/X11/default-display-manager /usr/sbin/lightdm $ readlink /etc/alternatives/x-session-manager /etc/alternatives/x-terminal-emulator /etc/alternatives/x-window-manager /etc/alternatives/lightdm-greeter /usr/bin/startxfce4 /usr/bin/xfce4-terminal.wrapper /usr/bin/mutter /usr/share/xgreeters/lightdm-gtk-greeter.desktop I do not remember to have enabled Wayland explicitly, but it is installed, $ dpkg -l '*wayland*' +-- Desired=Unknown/Install/Remove/Purge/Hold |+- Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend ||+ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) ||| Name Version Architecture Description +++-========================================-==============-============-======================================================== un gir1.2-gdkwayland-4.0 <none> <none> (no description available) un gir1.2-gstglwayland-1.0 <none> <none> (no description available) un kwayland-data <none> <none> (no description available) ii kwayland-integration:amd64 6.5.4-2+b1 amd64 kwayland runtime integration plugins for Qt5/KF5 ii kwayland5-data 4:5.116.0-1 all Qt library wrapper for Wayland libraries - data files ii libkf5waylandclient5:amd64 4:5.116.0-1+b3 amd64 Qt library wrapper for Wayland libraries ii libqt5waylandclient5:amd64 5.15.19-2 amd64 QtWayland client library ii libqt5waylandcompositor5:amd64 5.15.19-2 amd64 QtWayland compositor library ii libqt6waylandclient6:amd64 6.10.2+dfsg-16 amd64 Qt 6 Wayland client module ii libqt6waylandcompositor6:amd64 6.10.2-5 amd64 Qt 6 Wayland Compositor library un libqt6waylandeglclienthwintegration6 <none> <none> (no description available) un libqt6waylandeglcompositorhwintegration6 <none> <none> (no description available) ii libva-wayland2:amd64 2.24.1-2 amd64 Video Acceleration (VA) API for Linux -- Wayland runtime ii libwayland-client0:amd64 1.26.0-1 amd64 wayland compositor infrastructure - client library ii libwayland-cursor0:amd64 1.26.0-1 amd64 wayland compositor infrastructure - cursor library ii libwayland-egl1:amd64 1.26.0-1 amd64 wayland compositor infrastructure - EGL library ii libwayland-server0:amd64 1.26.0-1 amd64 wayland compositor infrastructure - server library ii qt6-wayland:amd64 6.10.2-5 amd64 Qt 6 Wayland platform plugin un qt6-waylandcompositor-private-abi <none> <none> (no description available) un qtwayland-client-abi-5-15-19 <none> <none> (no description available) un qtwayland-compositor-abi-5-15-19 <none> <none> (no description available) ii qtwayland5:amd64 5.15.19-2 amd64 QtWayland platform plugin ii xwayland 2:24.1.13-1 amd64 X server for running X clients under Wayland Hope this helps, Regards,
Hi, Similar happens here but under Xorg. $ dm-tool switch-to-greeter Unable to switch to greeter: GDBus.Error:org.freedesktop.DBus.Error.Failed: Failed to switch to greeter As a consequence, locking the screen (ctrl-alt-del): 1.33.0-1: I am not able to re-enter Xorg again => loosing any unsaved work. 1.32.0-7+b1: Works as expected. Due to below, culprit is lightdm 1.33.0-1, not liblightdm-gobject-1-0:amd64. Fail: $ dpkg -l "*lightdm*" ┌── Desired=Unknown/Install/Remove/Purge/Hold │┌─ Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend ││┌ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) │││ Name Version Architecture Description ├┼┼─════════════════════════════─════════════─════════════─════════════════════════════════════════ hi liblightdm-gobject-1-0:amd64 1.32.0-7+b1 amd64 simple display manager (GObject library) ii lightdm 1.33.0-1 amd64 simple display manager un lightdm-greeter <none> <none> (no description available) ii lightdm-gtk-greeter 2.0.9-1 amd64 simple display manager (GTK+ greeter) Fail: $ dpkg -l "*lightdm*" ┌── Desired=Unknown/Install/Remove/Purge/Hold │┌─ Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend ││┌ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) │││ Name Version Architecture Description ├┼┼─════════════════════════════─════════════─════════════─════════════════════════════════════════ ii liblightdm-gobject-1-0:amd64 1.33.0-1 amd64 simple display manager (GObject library) ii lightdm 1.33.0-1 amd64 simple display manager un lightdm-greeter <none> <none> (no description available) ii lightdm-gtk-greeter 2.0.9-1 amd64 simple display manager (GTK+ greeter) Work: $ dpkg -l "*lightdm*" ┌── Desired=Unknown/Install/Remove/Purge/Hold │┌─ Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend ││┌ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) │││ Name Version Architecture Description ├┼┼─════════════════════════════─════════════─════════════─════════════════════════════════════> hi liblightdm-gobject-1-0:amd64 1.32.0-7+b1 amd64 simple display manager (GObject libr> hi lightdm 1.32.0-7+b1 amd64 simple display manager un lightdm-greeter <none> <none> (no description available) ii lightdm-gtk-greeter 2.0.9-1 amd64 simple display manager (GTK+ greeter) Kind regards, Franck
You'll have to investigate a bit more, checks logs etc. because as I said I can't reproduce here... Does this mean you're using light-locker? Please migrate to xfce4-screensaver, it's been a while since we transitioned to it. It seems there might be incompatibilities between lightdm 1.33 and light-locker, which is unmaintained so they're unlikely to be fixed. Then check against the switch-to-greeter command? Regards,
Hi, no trace of failure in syslog, last greeter related commands were 2026-08-11T11:49:02.375505+02:00 mybox dbus-daemon[36703]: [session uid=115 pid=36703 pidfd=6] Activating via systemd: service name='org.a11y.Bus' unit='at-spi-dbus-bus.service' requested by ':1.3' (uid=115 pid=36710 comm="/usr/sbin/lightdm-gtk-greeter" label="unconfined") 2026-08-11T11:49:02.442930+02:00 mybox dbus-daemon[36703]: [session uid=115 pid=36703 pidfd=6] Activating via systemd: service name='org.gtk.vfs.Daemon' unit='gvfs-daemon.service' requested by ':1.9' (uid=115 pid=36710 comm="/usr/sbin/lightdm-gtk-greeter" label="unconfined") 2026-08-11T11:49:02.973286+02:00 mybox dbus-daemon[36703]: [session uid=115 pid=36703 pidfd=6] Activating via systemd: service name='org.gtk.vfs.Metadata' unit='gvfs-metadata.service' requested by ':1.9' (uid=115 pid=36710 comm="/usr/sbin/lightdm-gtk-greeter" label="unconfined") 2026-08-11T11:49:03.096065+02:00 mybox at-spi-bus-launcher[36736]: dbus-daemon[36736]: Activating service name='org.a11y.atspi.Registry' requested by ':1.1' (uid=115 pid=36710 comm="/usr/sbin/lightdm-gtk-greeter" label="unconfined") No apparently related errors in .xsession-errors. Just some bluez errors and this apparently unrelated messages (polkit-mate-authentication-agent-1:12748): GLib-CRITICAL **: 17:08:12.822: g_variant_new_string: assertion 'string != NULL' failed (polkit-mate-authentication-agent-1:12748): polkit-mate-1-WARNING **: 17:08:12.823: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files I am attaching the result of running "dm-tool switch-to-greeter" under strace and ltrace, apparently no relevant info (at least for me). Using xscreensaver here. I can lock and unlock screen properly with it (also while this switch problem is happening). Anyway, if this can cause data loss with light-locker, should not this bug's severity be raised? Also, note that I need to restart lightdm.service (or reboot) after upgrade for problem to start appearing (and similar after downgrade for problem to disappear). Regards,
On Tue, 2026-08-11 at 17:56 +0200, Agustin Martin wrote: Hey Agustin, thanks for the feedback. xscreensaver as locker so, for what exactly are you using dm-tool switch-to- greeter? You mention it in the context of locking the screen, but that's not really how xscreensaver does it, so I'm confused, could you elaborate? light-locker will be removed from Debian as soon as possible. Did you do a full reboot at some point after upgrading or are you still on the same boot? Can you try to do the 1.33 upgrade, reboot and see if that still happens? Regards,
Franck mentioned that using light-locker failed in a way he associates to this problem. I just added that this does not happen with xscreensaver. I use dm-tool switch-to-greeter to open and have some simultaneous sessions for different users (I usually use it through menu options, not explicitely. Only put it explicitely to show this problem). Even with a package about to be dropped, data loss is not a good thing. Sure, I first noticed the problem after a full reboot with 1.33 installed. Later noticed that restarting ligthdm service also shows it. Done some reboots later in both directions after changes. Regards,
Hi Yves-Alexis, Yes good hunch, I had: $ dpkg -l xfce4-screensaver light-locker (header) ii light-locker 1.8.0-3+b1 amd64 simple screen locker for lightDM display manager un xfce4-screensaver <none> <none> (no description available) $ aptitude install xfce4-screensaver $ aptitude purge light-locker updating to 1.33.0-1: $ dpkg -l "*lightdm*" (header) ii liblightdm-gobject-1-0:amd64 1.33.0-1 amd64 simple display manager (GObject libr> ii lightdm 1.33.0-1 amd64 simple display manager un lightdm-greeter <none> <none> (no description available) ii lightdm-gtk-greeter 2.0.9-1 amd64 simple display manager (GTK+ greeter) Rebooting. As a consequence, after locking the screen (ctrl-alt-del), I can now unlock & re-enter Xorg again. Thank you. However no change for: $ dm-tool switch-to-greeter Unable to switch to greeter: GDBus.Error:org.freedesktop.DBus.Error.Failed: Failed to switch to greeter Same error occurs if I use xfce gui 'Switch User' So Agustin uses Wayland, I use Xorg, but same error. [ Some (useless?) info ] # lightdm --show-config [Seat:*] A greeter-session=lightdm-greeter B greeter-hide-users=false A session-wrapper=/etc/X11/Xsession Sources: A /usr/share/lightdm/lightdm.conf.d/01_debian.conf B /etc/lightdm/lightdm.conf.d/10_fr_changes_lightdm.conf C /etc/lightdm/lightdm.conf Kind regards, Franck
Ah ok. That makes sense. Ok, but still that doesn't really explain what happens and what goes wrong (and why it only happens on your installations). Regards,
Thanks. Still confused though.
Can you check the output of various other dm-tool commands, for example:
dm-tool list-seats
Seat0
CanSwitch=true
HasGuestAccount=false
Session1
UserName='corsac'
Does that work for you?
There are multiple commits between 1.32 and 1.33 related to seats:
git log 1.32.0..1.33.0 --format=oneline --grep seat --grep Seat . ':!debian'
f5bafc8a819d3c50d8977ebf833fae6bf0164fb4 Fix CI (#430)
38ad694c40fc30ffe26e06ba0eefdba571d27838 Allow Wayland sessions to start on seat0 on kernels with no VTs
e520b32f9c4ab67b704874341f95925980349eab Disable user switching if logind says it isn't supported
c84feb03279e7b1993e5307d4542e02bd5475629 Move supports_multi_session initialization to init
967f16c230ae270324b7553dff0ab9395adc47e6 Consolidate Seat.setup and Seat.start for readability
454756fc119705620415528d70ac3c8f6d9c77db Try activating an existing greeter before checking for switch support
7c0f546992c73aed50d741deb594ad5e74f078e0 Improve debug logging when seat_switch_to_greeter fails
8493ec0a100c2bfcc399bfe5ccd2132eef78cd80 Use systemd-logind to discover active session on non-seat0 seats
abf43606f09cb4e340597b407d2fe3b1cb64d5eb tests: New FENCE script command to ensure event order
dcd37d9548049a9764a4286dd238f6731826e8ee Initialize WaylandSessionPrivate.vt to -1
75bf8fb062e3f409d6252449dae631440aa95b72 x-server: Avoid reusing the local X server if the hostname has changed
One another thing that comes to mind: do you use systemd/logind? What's the
output of loginctl?
Regards,
Hi Yves-Alexis,
Thanks for your follow-up.
[ dm tools & loginct ]
< with lightdm & liblightdm-gobject-1-0 1.33.0-1 >
$ dm-tool list-seats
Seat0
CanSwitch=false
HasGuestAccount=false
Session0
UserName='f'
=> "CanSwitch=false" I did not configure that => seems default. Unsure if it means switching users or not.
$ dm-tool lock
Unable to lock seat: GDBus.Error:org.freedesktop.DBus.Error.Failed: Failed to lock seat
$ dm-tool --session-bus switch-to-greeter
Unable to switch to greeter: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.DisplayManager was not provided by any .service files
$ loginctl
SESSION UID USER SEAT LEADER CLASS TTY IDLE SINCE
2 1000 f seat0 1915 user - no -
3 1000 f - 2128 manager - no -
2 sessions listed.
< with lightdm & liblightdm-gobject-1-0 1.32.0-7 >
$ dm-tool list-seats
Seat0
CanSwitch=true
HasGuestAccount=false
Session0
UserName='f'
=> Now "CanSwitch=true". I did not change any config file between 1.33 & 1.32, just reinstalled 1.32 & rebooted.
$ dm-tool lock
lock the screen as expected (and I can return later to Xorg)
$ dm-tool --session-bus switch-to-greeter
Unable to switch to greeter: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.DisplayManager was not provided by any .service files
=> same as with 1.33
$ loginctl
SESSION UID USER SEAT LEADER CLASS TTY IDLE SINCE
2 1000 f seat0 1919 user - no -
3 1000 f - 2116 manager - no -
2 sessions listed.
=> same as with 1.33
< difference >
1.33 : CanSwitch=false
1.32 : CanSwitch=true
only due to package, not to any user config file change
cd /etc/lightdm
1.32:
# grep -ri switch
lightdm.conf:# allow-user-switching = True if allowed to switch users
lightdm.conf:#allow-user-switching=true
1.33:
# grep -ri switch
lightdm.conf:# allow-user-switching = True if allowed to switch users
lightdm.conf:#allow-user-switching=true
=> same as 1.32.
[ no help: 1.33 with allow-user-switching=true ]
vi /etc/lightdm/lightdm.conf.d/10_fr_changes_lightdm.conf
/etc/lightdm/lightdm.conf
before:
[Seat:*]
greeter-hide-users=false
now putting:
[Seat:*]
greeter-hide-users=false
allow-user-switching=true
reboot
$ dm-tool list-seats
Seat0
CanSwitch=false
HasGuestAccount=false
Session0
UserName='f'
=> still "CanSwitch=false" !
but 1.32 & you with 1.33 have "CanSwitch=true"...why ?
$ dm-tool switch-to-greeter
Unable to switch to greeter: GDBus.Error:org.freedesktop.DBus.Error.Failed: Failed to switch to greeter
# lightdm --show-config
[Seat:*]
A greeter-session=lightdm-greeter
B greeter-hide-users=false
A session-wrapper=/etc/X11/Xsession
B allow-user-switching=true
Sources:
A /usr/share/lightdm/lightdm.conf.d/01_debian.conf
B /etc/lightdm/lightdm.conf.d/10_fr_changes_lightdm.conf
C /etc/lightdm/lightdm.conf
[ checking logs before/after dm-tool switch-to-greeter ]
with 1.32:
# cp /var/log/lightdm/lightdm.log /tmp/lightdm.log-with_1.32.0-7-before_switch.txt
$ dm-tool switch-to-greeter
# cp /var/log/lightdm/lightdm.log /tmp/lightdm.log-with_1.32.0-7-after_switch.txt
install 1.33, reboot:
# cp /var/log/lightdm/lightdm.log /tmp/lightdm.log-with_1.33.0-1-before_switch.txt
$ dm-tool switch-to-greeter
# cp /var/log/lightdm/lightdm.log /tmp/lightdm.log-with_1.33.0-1-after_switch.txt
=> 1.33 says "[+53.94s] DEBUG: Seat seat0: Unable to switch to greeter because the seat already has a session and does not support session switching"
[ systemd ]
I use systemd
$ dpkg -l "systemd*"
┌── Desired=Unknown/Install/Remove/Purge/Hold
│┌─ Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
││┌ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
│││ Name Version Architecture Description
├┼┼─═══════════════════════════─════════════─════════════─═════════════════════════════════════>
ii systemd 261.2-1 amd64 system and service manager
un systemd-boot <none> <none> (no description available)
un systemd-container <none> <none> (no description available)
un systemd-cron <none> <none> (no description available)
ii systemd-cryptsetup 261.2-1 amd64 Provides cryptsetup, integritysetup a>
un systemd-homed <none> <none> (no description available)
un systemd-imds <none> <none> (no description available)
un systemd-repart <none> <none> (no description available)
un systemd-report <none> <none> (no description available)
un systemd-resolved <none> <none> (no description available)
un systemd-shim <none> <none> (no description available)
un systemd-standalone-sysusers <none> <none> (no description available)
un systemd-standalone-tmpfiles <none> <none> (no description available)
un systemd-sysusers <none> <none> (no description available)
ii systemd-sysv 261.2-1 amd64 system and service manager - SysV com>
ii systemd-timesyncd 261.2-1 amd64 minimalistic service to synchronize l>
un systemd-tmpfiles <none> <none> (no description available)
ii systemd-tpm 261.2-1 amd64 Provides tpm2 utilities and units
ii systemd-userdbd 261.2-1 amd64 dynamic user/group manager
Kind regards,
Franck
Sorry if you are receiving this message repeated. Seems I am having some problems with the BTS and my last mails and I am not sure they reached you. Results below are similar to Franck's and come from a different box running up-to-date testing, where only lightdm was upgraded to sid 1.33.0-1 version. Problem is reproduced here too. Regards,---------- Forwarded message --------- On Wed, Aug 12, 2026 at 11:05:33AM +0200, Yves-Alexis Perez wrote:kb ... Seat0 CanSwitch=false HasGuestAccount=false Session0 UserName='myuser' SESSION UID USER SEAT LEADER CLASS TTY IDLE SINCE 2 1007 myuser seat0 1800 user - no - 3 1007 myuser - 1849 manager - no - 2 sessions listed. Hope this helps,
Ah, so I guess we have somewhere to look at. It's likely why dm-tool switch- to-greeter doesn't work. Can you check the result under 1.32 but I assume it'll show =true and we need to investigate why. Regards,
Thanks for the information and yes it's likely the reason. But as far as I can tell "CanSwitch" is just the symptom, dm-tool/lightdm gets that information from the environment (I think it's more like "is the user permitted to do that". I can't really investigate right now but it's likely because of the current environment (might be other logged in users or things like that) plus something which changed in 1.33 (likely in the various commits I pointed to). Unfortunately I won't have time to dig further in the next couple of weeks. Regards,
Hi Yves-Alexis, Lightdm 1.33.1 got released upstream. https://github.com/ubuntu/lightdm/releases/tag/1.33.1 Changelog includes "Assume that the seat CanMultiSession by default by @n3rdopolis in #454" https://github.com/ubuntu/lightdm/pull/454 #454 starts with "logind having dropped listing the CanMultiSession property in 2024 now makes lightdm assume it is always false. This is incorrect as the reason why logind now hides this property, is because it is actually unconditionally true." and ends with "made CanMultisession not get reported by ListProperties since it is always yes, which seems like that broke lightdm's enumeration of the properties, and it was not getting set to true at all." Once you are back, it might be worth to package it to see if it also solves our issue. Regards, Franck
Long ago I added a button on a Xfce panel which invokes the 'dm-tool switch-to-user' functionality. It has worked fine until the latest Debian version (1.33.0-1) appeared. When I noticed that it no longer worked, I was going to file a bug report... but I notice this bug (#1144037) had already been filed. After that, I was going to attempt to bisect (as per the comments of Yves-Alexis in msg #57), but then saw the comment by Franck (in msg #82) that upstream had a new version. I used git to clone lightdm from upstream, and also to clone the Debian repo on salsa, and then combined the 'debian' directory from the latest Debian release with the new upstream version (adding a new entry to the changelog appropriate for my local package) and built DEBs for the new upstream version. I am happy to report that all works well now: my user-switch button works again, and (so far) everything else is working fine as well! Hope that helps! Dave W.
El dom, 16 ago 2026 a las 22:19, <franckr01@online.de> escribió: Hi, Yves-Alexis, When preparing fixed package, please consider setting lightdm Homepage field in debian/control to https://github.com/ubuntu/lightdm to also fix #1110922 [lightdm: homepage field invalid]. Thanks for caring of this.
I saw that version 1.33.1-1 was available from the servers today. I installed it, and can verify that the Xfce button for switching to another user works fine again. Thank you for the new package, Yves-Alexis! Dave W.
Version: 1.33.1-1 Thanks for uploading this upstream bugfix version. I confirm that it fixes my problem, so I am closing this bug report. Please look at #1110922 [lightdm: homepage field invalid] for next upload. Regards,