Bug#772932: cannot login, only gdm background shown, without any user prompt/chooser

[Stefano Zacchiroli]

Package: gdm3
Version: 3.14.1-3
Severity: serious

After my route upgrade of yesterday on testing, I can no longer login into an X
session using GDM. Upon (re)start, GDM seems to start properly, but only shows
its background, without any way of choosing the login user (neither via the
user list, nor via the login prompt).

As I've had gnome-shell induced GDM issues in the past, I've tried to upgrade
my gnome-shell* packages to the versions currently in unstable, to no avail.[

I've tried to look up relevant log information but: 1) /var/log/gdm3 only
contains files that are 5+ months old (is that dir no longer used by GDM for
logging?) and 2) /var/log/syslog doesn't seem to contain anything
interesting. If you have tips on how I can provide you with interesting
debugging informations, please let me know.

Also, knowing how to get a X session for my user would be nice, as plain old
"startx" doesn't seem to work either.

TIA,
Cheers.

-- System Information:
Debian Release: 8.0
  APT prefers testing
  APT policy: (500, 'testing'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.16.0-4-amd64 (SMP w/4 CPU cores)
Locale: LANG=it_IT.UTF-8, LC_CTYPE=it_IT.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages gdm3 depends on:
ii  accountsservice                              0.6.37-3+b1
ii  adduser                                      3.113+nmu3
ii  awesome [x-window-manager]                   3.4.15-1+b1
ii  dconf-cli                                    0.22.0-1
ii  dconf-gsettings-backend                      0.22.0-1
ii  debconf [debconf-2.0]                        1.5.54
ii  gir1.2-gdm3                                  3.14.1-3
ii  gnome-session [x-session-manager]            3.14.0-2
ii  gnome-session-bin                            3.14.0-2
ii  gnome-session-flashback [x-session-manager]  3.8.1-7
ii  gnome-settings-daemon                        3.14.2-2
ii  gnome-shell                                  3.14.2-2
ii  gnome-terminal [x-terminal-emulator]         3.14.1-1
ii  gsettings-desktop-schemas                    3.14.1-1
ii  libaccountsservice0                          0.6.37-3+b1
ii  libaudit1                                    1:2.4-1+b1
ii  libc6                                        2.19-13
ii  libcanberra-gtk3-0                           0.30-2.1
ii  libcanberra0                                 0.30-2.1
ii  libgdk-pixbuf2.0-0                           2.31.1-2+b1
ii  libgdm1                                      3.14.1-3
ii  libglib2.0-0                                 2.42.1-1
ii  libglib2.0-bin                               2.42.1-1
ii  libgtk-3-0                                   3.14.5-1
ii  libpam-modules                               1.1.8-3.1
ii  libpam-runtime                               1.1.8-3.1
ii  libpam-systemd                               215-7
ii  libpam0g                                     1.1.8-3.1
ii  librsvg2-common                              2.40.5-1
ii  libselinux1                                  2.3-2
ii  libsystemd0                                  215-7
ii  libwrap0                                     7.6.q-25
ii  libx11-6                                     2:1.6.2-3
ii  libxau6                                      1:1.0.8-1
ii  libxdmcp6                                    1:1.1.1-1+b1
ii  libxrandr2                                   2:1.4.2-1+b1
ii  lsb-base                                     4.1+Debian13+nmu1
ii  metacity [x-window-manager]                  1:3.14.3-1
ii  mutter [x-window-manager]                    3.14.2-1
ii  policykit-1                                  0.105-8
ii  ucf                                          3.0030
ii  x11-common                                   1:7.7+7
ii  x11-xserver-utils                            7.7+3+b1
ii  xterm [x-terminal-emulator]                  312-1

Versions of packages gdm3 recommends:
ii  at-spi2-core               2.14.0-1
ii  desktop-base               7.0.3
ii  gnome-icon-theme           3.12.0-1
ii  gnome-icon-theme-symbolic  3.12.0-1
ii  x11-xkb-utils              7.7+1
ii  xserver-xephyr             2:1.16.1.901-1
ii  xserver-xorg               1:7.7+7
ii  zenity                     3.14.0-1

Versions of packages gdm3 suggests:
ii  gnome-orca            3.14.0-2
ii  libpam-gnome-keyring  3.14.0-1+b1

-- debconf information:
* shared/default-x-display-manager: gdm3
  gdm3/daemon_name: /usr/sbin/gdm3