how can I fix the Desktop Manager issue?

[Insun Chow]

Hi guys

 

I got a problem when I running armbian ubuntu 16.04 on my s905 board

its running well from hdmi monitor console

 

after login, I can use startx to start the desktop everioument

 

 

but when I installed a xdm/gdm ,the problem comes

 

 

why running startx after login  different from automatic start??