You can enable the remote login as following steps.
1. vi /etc/X11/xdm/Xaccess
Remove the below comment symbol of following line.
#any host can get a login windows
2. vi /etc/X11/xdm-config
comment out this line using the exclamation mark as following.
!DisplayManager.requestPort: 0
3. vi /etc/sysconfig/displaymanager
Change the first parameter to yes and the second parameter to yes in need.
DISPLAYMANAGER_REMOTE_ACCESS="yes"
DISPLAYMANAGER_ROOT_LOGIN_REMOTE="yes"
4. restart the xdm daemon
/usr/sbin/rcxdm restart
