Disadvantage of VNC ServerVNC Server will just replicate the session which is already active on the server to be accessed remotely. But if say , you've logged out of the server , then you cannot use VNC server to start a new session. For that you can use any XDMCP clients like XManager or XMing. I will demonstrate here how to use XMing in Windows Vista to start a new remote sessions with Ubuntu Server.
Settings to be done in Ubuntu Server:You must enable XDMCP server on Ubuntu. For that go to /etc/gdm folder and edit custom.conf file present there. If not present, Create a new custom.conf file. In this add as follows:
[daemon] RemoteGreeter=/usr/lib/gdm/gdmlogin [xdmcp] Enable=true DisplaysPerHost=2Now restart your GDM using sudo service gdm restart or get a full restart of the server.