lightdm-gtk-greeter SIGSEGV when invoked by Xvnc -inetd -query

[Bela Lubkin]

To reproduce:

1. Install Xubuntu 16.04 LTS, update fully

2. Install packages xinetd, vnc4server

3. Append to /etc/services:

vnc 5900/tcp # VNC Virtual Network Computing

4. Append to /etc/lightdm/lightdm.conf:

[XDMCPServer]
enabled=true

5. Create /etc/xinetd.d/vnc:

service vnc
{
        disable = no
        socket_type = stream
        protocol = tcp
        group = tty
        wait = no
        user = nobody
        server = /usr/bin/Xvnc
        server_args = -inetd -query localhost -once -securitytypes=none -geometry 1024x768
}
# NOTE: might need to add an arg like ":1" to get out of way of local X server
# my case is special as I am trying to run headless, nobody is logged in on console

6. Signal xinetd and lightdm to reconfigure:

$ sudo killall -1 xinetd
$ sudo service lightdm restart # or however your init system works

7. Don't know if significant (I am 400 miles away from test host and can't test):
do NOT have anyone logged in on the test host console. In fact, to most closely
reproduce my case, shut down the test host, power it off, disconnect all monitors
and keyboards, then power it on and access from the net.

8. From another system, connect to the test host:

$ gvncviewer testhost:0 # Your favorite VNC viewer & test host name...

9. VNC connects briefly, displays grey hashed background, disconnects. Syslog on
test host says:

Mar 29 15:07:40 osmium lightdm[13828]: (lightdm:13828): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Mar 29 15:07:40 osmium systemd[1]: Started Session c11 of user lightdm.
Mar 29 15:07:40 osmium lightdm[13828]: ** (lightdm:13828): WARNING **: Error activating login1 session: GDBus.Error:org.freedesktop.DBus.Error.NotSupported: Operation not supported
Mar 29 15:07:40 osmium kernel: [14985.100699] lightdm-gtk-gre[13972]: segfault at 0 ip 00007f3f23bd09bf sp 00007ffc64b32058 error 4 in libc-2.23.so[7f3f23b3b000+1bf000]
Mar 29 15:07:41 osmium lightdm[13828]: /etc/modprobe.d is not a file
Mar 29 15:07:41 osmium lightdm[13828]: message repeated 4 times: [ /etc/modprobe.d is not a file]
Mar 29 15:07:41 osmium lightdm[13828]: update-alternatives: error: no alternatives for x86_64-linux-gnu_gfxcore_conf

and core-like-thing ends up in /var/crash/...

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xorg 1:7.7+13ubuntu3
ProcVersionSignature: Ubuntu 4.4.0-70.91-generic 4.4.49
Uname: Linux 4.4.0-70-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Mar 29 14:52:52 2017
InstallationDate: Installed on 2017-03-28 (1 days ago)
InstallationMedia: Xubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
ProcEnviron:
 TERM=xterm
 SHELL=/bin/bash
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 XDG_RUNTIME_DIR=<set>
SourcePackage: xorg
Symptom: display
Title: Xorg crash
UpgradeStatus: No upgrade log present (probably fresh install)

[Bela Lubkin (filbo)]

Similar failure occurs with kylin-greeter.

Similar-seeming failure occurs with lightdm-webkit-greeter (at least a segfault shows up in syslog) -- with the CRUCIAL difference that, despite segfault, it actually allows me to login and do stuff over the session!

syslog is also full of crashes of:

panel-5-indicator (and Xfce keeps asking me if I want to keep trying it, or remove it from my config -- NEITHER, if it won't work in this situation then stop trying to run it but leave it in the config for when I'm on a local display...!)

/usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1
/usr/lib/update-notifier/system-crash-notification
/usr/lib/x86_64-linux-gnu/xfce4/panel/wrapper-2.0 (equals panel-5-indicator)
/usr/share/apport/apport-gtk

[Sean Davis (bluesabre)]

Is this still an issue in a supported release?

[Launchpad Janitor (janitor)]

[Expired for lightdm-gtk-greeter (Ubuntu) because there has been no activity for 60 days.]