Bug#969564: lightdm: could not acquire name on session bus by simultaneous login by XDMCP and keyboard

[Ryutaroh Matsumoto <ryutaroh@ict.e.titech.ac.jp>]

Package: lightdm
Version: 1.26.0-7
Severity: normal
Tags: upstream
Control: -1 forwarded https://bugs.launchpad.net/lightdm/+bug/1894356

Dear Maintainer,

1. Add the following lines to /etc/lightdm/lightdm.conf

[XDMCPServer]
enabled=true

and restart lightdm.

2. Login as a normal user from keyboard.

3. Login as the same user as 2 from XDMCP gives
"Could not acquire name on session bus"
and I cannot login from XDMCP.
Without Step 2, XDMCP login succeeds.

* The session is Mate.

The same symptom is reported at
https://github.com/neutrinolabs/xrdp/issues/1559#issuecomment-623977001
which recommends removal of "dbus-user-session" Debian package.

I worked around the above issue by putting
"unset DBUS_SESSION_BUS_ADDRESS"
in /etc/X11/Xsession.d/

I believe this is an upstream issue and reported at
https://bugs.launchpad.net/lightdm/+bug/1894356

I think that LightDM should not set DBUS_SESSION_BUS_ADDRESS
when it starts a session.

Best regards, Ryutaroh Matsumoto


-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.7.0-3-amd64 (SMP w/2 CPU threads)
Kernel taint flags: TAINT_FIRMWARE_WORKAROUND
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages lightdm depends on:
ii  adduser                                3.118
ii  dbus                                   1.12.20-1
ii  debconf [debconf-2.0]                  1.5.74
ii  libaudit1                              1:2.8.5-3+b1
ii  libc6                                  2.31-3
ii  libgcrypt20                            1.8.6-2
ii  libglib2.0-0                           2.64.4-1
ii  libpam-systemd [logind]                246.4-1
ii  libpam0g                               1.3.1-5
ii  libxcb1                                1.14-2
ii  libxdmcp6                              1:1.1.2-3
ii  lightdm-gtk-greeter [lightdm-greeter]  2.0.8-1
ii  lsb-base                               11.1.0

Versions of packages lightdm recommends:
pn  xserver-xorg  <none>

Versions of packages lightdm suggests:
ii  accountsservice  0.6.55-3
ii  upower           0.99.11-2
pn  xserver-xephyr   <none>

-- Configuration Files:
/etc/lightdm/lightdm.conf changed:
[LightDM]
start-default-seat=true
remote-sessions-directory=/usr/share/lightdm/sessions:/usr/share/xsessions:/usr/share/wayland-sessions
[Seat:*]
[XDMCPServer]
enabled=true
[VNCServer]


-- debconf information:
* shared/default-x-display-manager: lightdm
  lightdm/daemon_name: /usr/sbin/lightdm