我的xmanager版本是6，centos系統版本是5.11，桌面是gnome，版本是2.16.0，我用xmanager連接centos的時候老是出錯，如下圖所示：
查xmanager日誌，看到如下錯誤信息：
Xdmcp: received an ACCEPT message.
Xdmcp: sent a MANAGE message.
Xdmcp: Timed out, state 8. Retransmissions: 0
Xdmcp: sent a MANAGE message.
Xdmcp: Timed out, state 8. Retransmissions: 1
Xdmcp: sent a MANAGE message.
Xdmcp: Timed out, state 8. Retransmissions: 2
Xdmcp: sent a MANAGE message.
Xdmcp: Timed out, state 8. Retransmissions: 3
MessageBox: Xmanager: XDMCP連接, XDMCP連接失敗。是否要重試?
XDM go to sleep: too many retransmissions
在網上狂找解決方法，功夫不負有心人，最終在這個帖子裏找到解決方法：
RESOLUTION
This problem is usually caused by one of the following reasons:
1，Firewall settings on PC, physical firewall, gateway or router.
2，Incorrect entry in the DNS.
3，Improper operation of display manager such as gdm, kdm or xdm.
Depending on the reason, try the following solutions:
1，Follow the instruction on the Xmanager FAQ and configure your firewall.
How can I configure firewall settings in Windows?
2，Add your PC IP address in /etc/hosts as following:
172.16.2.120 PC_NAME
3，Restart the display manager process. You can also try restarting the remote server.
我出錯的原因是第二條，解決方法很簡單，在/etc/hosts加上pc機（運行xmanager）的地址就行了，PC_NAME名字任意。
我分析具體的原因可能是我的centos5.11系統XDMCP連接只認/etc/hosts文件裏指定的主機，不在裏面的主機無權建立連接，所以在我加入PC IP地址前，XDMCP連接失敗。
上一張連接成功的圖：
最後提醒一下，把PC IP地址加入/etc/hosts文件，要過一分鐘或兩分鐘，才能生效。