tested on : Linux debian 3.2.0-4-486 #1 Debian 3.2.60-1+deb7u3 i686 GNU/Linux

0.

ls -lah /usr/share/xsessions
total 28K
drwxr-xr-x 2 root root 4.0K Oct 13 18:34 .
drwxr-xr-x 156 root root 4.0K Oct 13 18:35 ..
-rw-r--r-- 1 root root 86 Aug 6 2011 lightdm-xsession.desktop
-rw-r--r-- 1 root root 458 May 18 2012 LXDE.desktop
-rw-r--r-- 1 root root 300 Mar 27 2013 openbox.desktop
-rw-r--r-- 1 root root 218 Mar 27 2013 openbox-gnome.desktop
-rw-r--r-- 1 root root 205 Mar 27 2013 openbox-kde.desktop

1.
vim /etc/lightdm/lightdm.conf

[SeatDefaults]
#xserver-command=X
#xserver-layout=
#xserver-config=
xserver-allow-tcp=false
#xdmcp-manager=
#xdmcp-port=177
#xdmcp-key=
greeter-session=lightdm-greeter
greeter-hide-users=true
#greeter-allow-guest=true
#greeter-show-manual-login=false
#login with LXDE as default (default xSession)
user-session=LXDE
#allow-guest=true
#guest-session=UNIMPLEMENTED
session-wrapper=/etc/X11/Xsession
#display-setup-script=
#greeter-setup-script=
#session-setup-script=
#session-cleanup-script=
#autologin-guest=false
###################### > CHANGE THIS LINE TO THE USER THAT SHOULD AUTO LOGIN
autologin-user=root

root@clonezilla:~# find / -name org.freedesktop.udisks.policy
/usr/share/polkit-1/actions/org.freedesktop.udisks.policy

2.search for: org.freedesktop.udisks.filesystem-mount-system-internal

vim /usr/share/polkit-1/actions/org.freedesktop.udisks.policy

  <action id="org.freedesktop.udisks.filesystem-mount-system-internal">
    <description>Mount a system-internal device</description>
    <description xml:lang="da">Montér en intern enhed</description>
    <description xml:lang="de">Eingebautes Gerät einhängen</description>
    <description xml:lang="pt_BR">Montar um dispositivo interno</description>
    <message>Authentication is required to mount the device</message>
    <message xml:lang="da">Autorisering er påkrævet for at montere et fil system</message>
    <message xml:lang="de">Zugriffsrechte werden benötigt um das Gerät einzuhängen</message>
    <message xml:lang="pt_BR">Autenticação é requerida para montar o dispositivo</message>
    <defaults>
      <allow_any>no</allow_any>

###################### > CHANGE THIS LINE TO YES
      <allow_inactive>yes</allow_inactive>

      <allow_active>auth_admin_keep</allow_active>
    </defaults>
  </action>

you don't need to do this:

I had a virtually identical challenge with wheezy stable,

I switched from LXDE to a plain openbox WM and had to select it manually for each login.

To change the default you need to change the symlink at

/etc/alternatives/x-session-manager

to point at the appropriate session starter (so I needed to point it at /usr/bin/openbox-session).

The easiest way to accomplish this (the way I actually did it) is to use update-alternatives:

update-alternatives --config x-session-manager

There are 3 choices for the alternative x-session-manager (providing /usr/bin/x-session-manager).

Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/bin/startlxde 50 auto mode
1 /usr/bin/lxsession 49 manual mode
2 /usr/bin/openbox-session 40 manual mode
3 /usr/bin/startlxde 50 manual mode

Press enter to keep the current choice[*], or type selection number:

source: http://l3net.wordpress.com/2014/03/03/lightweight-debian-lxde-desktop-from-scratch-part-2/

source: http://www.linuxquestions.org/questions/linux-newbie-8/lightdm-cannot-figure-out-how-to-change-default-xsession-debian-wheezy-943468/

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