XDMCP fatal error: Session declined Maximum number of open sessions from...

最近搞XDMCP方式远程登录ubuntu，然后经常出这个问题：
XDMCP fatal error: Session declined Maximum number of open sessions from your host..
导致不能登录，在不懈努力下终于在X－win32的官网找到了原因及解决方案：
This is usually caused by a router using NAT. The problem is the host thinks the router is a Xserver trying to connect and because several users might be connecting to the host through the router, the host stops allowing the router to open new sessions. The fix for this is to increase the Displays per host on your Linux or UNIX host.

Under Linux, this setting is in the /etc/gdm/gdm.schemas file and the /etc/kde/kdm/kdmrc file. Here’s the part of the file(s) you need to look at:

    <schema>
      <key>xdmcp/DisplaysPerHost</key>
      <signature>i</signature>
      <default>1</default>
    </schema>

Increasing DisplaysPerHost will allow more users to connect before this error happens.

/etc/gdm/gdm.schemas configures more host connections for Gnome.
/etc/kde/kdm/kdmrc file configures more host connections for KDE.

If there are too many sessions, rebooting the host will fix this problem as well. However, the problem will return once the Displays per host is exceeded again.