1/- env | grep SESSION 

XDG_SESSION_ID=2
DESKTOP_SESSION=xfce
XDG_SESSION_TYPE=x11
XDG_SESSION_DESKTOP=xfce
GDMSESSION=xfce
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0
SESSION_MANAGER=local/mamachine:@/tmp/.ICE-unix/620,unix/mamachine:/tmp/.ICE-unix/620


2/- cat .xsession-errors

Xsession: X session started for moimeme at mercredi 29 mai 2019, 16:31:43 (UTC+0200)
dbus-update-activation-environment: setting DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
dbus-update-activation-environment: setting DISPLAY=:0
dbus-update-activation-environment: setting XAUTHORITY=/home/moimeme/.Xauthority
localuser:moimeme being added to access control list
dbus-update-activation-environment: setting GTK_MODULES=gail:atk-bridge
dbus-update-activation-environment: setting QT_ACCESSIBILITY=1
dbus-update-activation-environment: setting QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1
OpenGL version: 3.
dbus-update-activation-environment: setting USER=moimeme
dbus-update-activation-environment: setting XDG_SESSION_TYPE=x11
dbus-update-activation-environment: setting HOME=/home/moimeme
dbus-update-activation-environment: setting QT4_IM_MODULE=xim
dbus-update-activation-environment: setting DESKTOP_SESSION=xfce
dbus-update-activation-environment: setting XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0
dbus-update-activation-environment: setting GTK_MODULES=gail:atk-bridge
dbus-update-activation-environment: setting QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1
dbus-update-activation-environment: setting DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
dbus-update-activation-environment: setting IM_CONFIG_PHASE=1
dbus-update-activation-environment: setting LOGNAME=moimeme
dbus-update-activation-environment: setting GTK_IM_MODULE=xim
dbus-update-activation-environment: setting PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
dbus-update-activation-environment: setting GDM_LANG=fr_FR.utf8
dbus-update-activation-environment: setting XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0
dbus-update-activation-environment: setting XDG_RUNTIME_DIR=/run/user/1000
dbus-update-activation-environment: setting DISPLAY=:0
dbus-update-activation-environment: setting LANG=fr_FR.UTF-8
dbus-update-activation-environment: setting XDG_CURRENT_DESKTOP=XFCE
dbus-update-activation-environment: setting XDG_SESSION_DESKTOP=xfce
dbus-update-activation-environment: setting XAUTHORITY=/home/moimeme/.Xauthority
dbus-update-activation-environment: setting XMODIFIERS=@im=ibus
dbus-update-activation-environment: setting XDG_GREETER_DATA_DIR=/var/lib/lightdm/data/moimeme
dbus-update-activation-environment: setting SHELL=/bin/bash
dbus-update-activation-environment: setting GDMSESSION=xfce
dbus-update-activation-environment: setting QT_ACCESSIBILITY=1
dbus-update-activation-environment: setting GPG_AGENT_INFO=/run/user/1000/gnupg/S.gpg-agent:0:1
dbus-update-activation-environment: setting QT_IM_MODULE=ibus
dbus-update-activation-environment: setting PWD=/home/moimeme
dbus-update-activation-environment: setting XDG_DATA_DIRS=/usr/share/xfce4:/usr/local/share/:/usr/share/
dbus-update-activation-environment: setting CLUTTER_IM_MODULE=xim
/usr/bin/startxfce4: X server already running on display :0

** (xfce4-session:620): CRITICAL **: polkit_unix_process_set_property: assertion 'val != -1' failed
xfce4-session-Message: SSH authentication agent is already running
gpg-agent[659]: WARNING: "--write-env-file" is an obsolete option - it has no effect
gpg-agent: a gpg-agent is already running - not starting a new one

(xfce4-session:620): xfce4-session-WARNING **: gpg-agent returned no PID in the variables

(wrapper-2.0:708): Gtk-WARNING **: gtk_widget_size_allocate(): attempt to allocate widget with width -3 and height 26