這個問題是由於時間問題引起的！
查看cacti的日誌就可以看出來：
Log File [Total Lines: 14 - All Items Shown]
05/18/2012 09:50:49 AM - AUTH LOGIN: User 'admin' Authenticated
05/18/2012 09:50:16 AM - MANAGE: Poller[0] Checking Manage
05/18/2012 09:50:06 AM - SYSTEM SYSLOG STATS:Time:0.28 Deletes:0 Incoming:0 Removes:0 XFers:39 Alerts:0 Alarms:0 Reports:0
05/18/2012 09:50:06 AM - SYSTEM THOLD STATS: Time:0.0172 Tholds:0 DownHosts:0
05/18/2012 09:50:06 AM - SYSTEM STATS: Time:-28796.2396 Method:spine Processes:1 Threads:1 Hosts:2 HostsPerProcess:2 DataSources:15 RRDsProcessed:15
05/18/2012 05:45:16 PM - MANAGE: Poller[0] Checking Manage
05/18/2012 05:45:10 PM - RECACHE STATS: RecacheTime:4.3342 HostsRecached:1
05/18/2012 05:45:06 PM - SYSTEM SYSLOG STATS:Time:0.55 Deletes:0 Incoming:0 Removes:0 XFers:30 Alerts:0 Alarms:0 Reports:0
05/18/2012 05:45:06 PM - PCOMMAND: Poller[0] Host[1] WARNING: Recache Event Detected for Host
05/18/2012 05:45:05 PM - SYSTEM THOLD STATS: Time:0.0343 Tholds:0 DownHosts:0
05/18/2012 05:45:05 PM - SYSTEM STATS: Time:2.6126 Method:spine Processes:1 Threads:1 Hosts:2 HostsPerProcess:2 DataSources:15 RRDsProcessed:15
05/18/2012 05:45:02 PM - POLLER: Poller[0] WARNING: Cron is out of sync with the Poller Interval! The Poller Interval is '300' seconds, with a maximum of a '300' second Cron, but 1296601 seconds have passed since the last poll!
05/03/2012 05:35:16 PM - MANAGE: Poller[0] Checking Manage
05/03/2012 05:35:10 PM - WEBUI: Cacti Log Cleared from Web Management Interface
可以看出剛開始時間是下午5：45，最後又變成早上9：50，時間是先超前最後又變成正確的了（這是由於系統每過10分鐘會和時間服務器同步一次時間）。
這樣會導致數據庫記錄poller的執行時間出問題：
mysql> select * from poller_time
-> ;
+----+------+-----------+---------------------+---------------------+
| id | pid | poller_id | start_time | end_time |
+----+------+-----------+---------------------+---------------------+
| 1 | 2231 | 0 | 2012-05-18 17:50:03 | 2012-05-18 09:50:05 |
+----+------+-----------+---------------------+---------------------+
1 row in set (0.00 sec)
mysql>
可以看出poller的執行結束時間end_time比開始時間start_time更早，這樣會導致poller進程停止工作，直到系統時間超過了start_time，poller進程纔回開始工作，圖像才能出來！這裏要特別說明下：不能簡單地修改數據庫poller_time表裏的時間，因爲數據庫裏面還有好多表也記錄了採集各種數據的時間。
所以解決辦法有兩個：
1 等系統時間超過start_time（過了下午5點50），一切恢復正常（如果你有耐心 ）。
2 如果現在系統的時間不正確先把系統時間修改正確，然後刪除/var/www/html/rra/下面的所有文件，最後強制執行poller程序重新生成/var/www/html/rra/下面的所有文件。操作過程如下：
[root@Yunweiw ~]# rm -rf /var/www/html/rra/*
[root@Yunweiw ~]# /usr/bin/php /var/www/html/poller.php --force
Manage : initializing...
Checking Manage... TCP :
Data Source : 9 is : 1
Checking Manage... TCP :
Data Source : 8 is : 1
OK u:0.00 s:0.01 r:1.87
OK u:0.00 s:0.01 r:1.87
OK u:0.00 s:0.02 r:1.88
OK u:0.00 s:0.02 r:1.88
OK u:0.00 s:0.02 r:1.90
OK u:0.00 s:0.02 r:1.90
OK u:0.00 s:0.02 r:1.91
OK u:0.00 s:0.02 r:1.91
OK u:0.00 s:0.02 r:1.92
OK u:0.00 s:0.02 r:1.92
OK u:0.00 s:0.02 r:1.93
OK u:0.00 s:0.02 r:1.93
OK u:0.00 s:0.02 r:1.95
OK u:0.00 s:0.02 r:1.95
OK u:0.00 s:0.02 r:1.96
OK u:0.00 s:0.02 r:1.96
OK u:0.00 s:0.02 r:1.97
OK u:0.00 s:0.02 r:1.97
OK u:0.00 s:0.02 r:1.98
OK u:0.00 s:0.02 r:1.98
OK u:0.00 s:0.02 r:1.99
OK u:0.00 s:0.02 r:1.99
OK u:0.00 s:0.03 r:2.00
OK u:0.00 s:0.03 r:2.01
OK u:0.00 s:0.03 r:2.02
OK u:0.00 s:0.03 r:2.02
OK u:0.00 s:0.03 r:2.03
OK u:0.00 s:0.03 r:2.03
OK u:0.00 s:0.03 r:2.05
OK u:0.00 s:0.03 r:2.05
05/18/2012 11:38:00 AM - SYSTEM STATS: Time:2.2115 Method:spine Processes:1 Threads:1 Hosts:2 HostsPerProcess:2 DataSources:15 RRDsProcessed:15
[root@Yunweiw ~]#
注意一定要先刪除/var/www/html/rra/下的所有文件在執行/usr/bin/php /var/www/html/poller.php --force，不然有些rra會報時間錯誤！
刷新下界面就好了