sudo apt-get install xserver-xorg lxde xfonts-base (policykit-1) (xinit)

to install very basic xserver

log:

less /var/log/Xorg.0.log

list resolutions supported by fbdev:

cat /sys/class/graphics/fb0/modes

“no session for pid” comes only up if xserver is started via startx. after install make a reboot the lightdm-login-form comes up and after login no error-message appears.