Bug#802215: gdm3: DISPLAY env variable not set correctly for PostLogin script

[Jurij Smakov]

Package: gdm3
Version: 3.18.0-2
Severity: important

For quite a few years I had an /etc/gdm3/PostLogin/Default script 
which was executing the following command to set up a custom keyboard 
layout:

setxkbmap -option 'grp:caps_toggle' 'us,ru(phonetic)'

After sid update last night this command fails with

Cannot open display ""

A rather unfortunate consequence of that is that the greeter just 
displays "Failed to execute PostLogin script" after the password is 
entered, failing user login and rendering the system unusable.

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.2.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.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                              0.6.40-3
ii  adduser                                      3.113+nmu3
ii  awesome [x-window-manager]                   3.5.6-1
ii  dconf-cli                                    0.24.0-2
ii  dconf-gsettings-backend                      0.24.0-2
ii  debconf [debconf-2.0]                        1.5.57
ii  gir1.2-gdm3                                  3.18.0-2
ii  gnome-session [x-session-manager]            3.18.0-1
ii  gnome-session-bin                            3.18.0-1+b1
ii  gnome-session-flashback [x-session-manager]  3.18.1-1
ii  gnome-settings-daemon                        3.18.1-1+b1
ii  gnome-shell                                  3.18.0-1
ii  gnome-terminal [x-terminal-emulator]         3.18.1-1
ii  gsettings-desktop-schemas                    3.18.0-1
ii  i3-wm [x-window-manager]                     4.11-1
ii  libaccountsservice0                          0.6.40-3
ii  libaudit1                                    1:2.4.4-4
ii  libc6                                        2.19-22
ii  libcanberra-gtk3-0                           0.30-2.1
ii  libcanberra0                                 0.30-2.1
ii  libgdk-pixbuf2.0-0                           2.32.1-1
ii  libgdm1                                      3.18.0-2
ii  libglib2.0-0                                 2.46.1-1
ii  libglib2.0-bin                               2.46.1-1
ii  libgtk-3-0                                   3.18.2-1
ii  libpam-modules                               1.1.8-3.1
ii  libpam-runtime                               1.1.8-3.1
ii  libpam-systemd                               227-2
ii  libpam0g                                     1.1.8-3.1
ii  librsvg2-common                              2.40.11-1
ii  libselinux1                                  2.3-2+b1
ii  libsystemd0                                  227-2
ii  libwrap0                                     7.6.q-25
ii  libx11-6                                     2:1.6.3-1
ii  libxau6                                      1:1.0.8-1
ii  libxdmcp6                                    1:1.1.2-1
ii  lsb-base                                     9.20150917
ii  metacity [x-window-manager]                  1:3.18.1-1
ii  mutter [x-window-manager]                    3.18.0-1+b1
ii  notion [x-window-manager]                    3+2014010901-1
ii  policykit-1                                  0.105-12
ii  ucf                                          3.0030
ii  x11-common                                   1:7.7+12
ii  x11-xserver-utils                            7.7+5
ii  xterm [x-terminal-emulator]                  320-1

Versions of packages gdm3 recommends:
ii  at-spi2-core               2.18.0-1
ii  desktop-base               8.0.2
ii  gnome-icon-theme           3.12.0-1
ii  gnome-icon-theme-symbolic  3.12.0-1
ii  x11-xkb-utils              7.7+2
ii  xserver-xephyr             2:1.17.2-3
ii  xserver-xorg               1:7.7+12
ii  zenity                     3.18.0-1

Versions of packages gdm3 suggests:
pn  gnome-orca            <none>
ii  libpam-gnome-keyring  3.18.0-4

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

-- debsums errors found:
debsums: missing file /usr/share/gdm/greeter/autostart/orca-autostart.desktop (from gdm3 package)