今天檢查公司生產服務器的SQL Server數據庫，驚訝的發現有三個生產數據庫變為了single user mode。奇怪的是沒有任何人和程序執行過SQL語句將這三個數據庫設置為single user mode，是自動變的。后來在網上查了查原來發現，重啟windows server原來有可能導致SQL Server數據庫意外變為single user mode。原文如下：
問題：
Why did SQL Server go into single user mode?
I've had an application that's been running great for several months. Thankfully I use try/catch blocks in my database calls because this morning I get an email alert from my catch block that said:
Message: Login failed for user 'NT AUTHORITY\NETWORK SERVICE'. Reason: Server is in single user mode. Only one administrator can connect at this time. Source: .Net SqlClient Data Provider Data: System.Collections.ListDictionaryInternal
So I go and try to access the application, and yep, verified that it doesn't work.
I was able to remote desktop over to the server and log into SQL Server which suddenly "fixed" the issue, but I don't know why this happened. ("Fixed" as in now the application does it's normal CRUD operations.)
Does anyone know why this might have spontaneously happened?
Also, if I go to database -> properties -> options -> State, I verified that Restrict Access is in "MULTI_USER".
The app is powered by the mighty SQL Server 2005 express. Is that the problem?
回答：
Did you check your Windows Event Logs to see if anything happened to the server? Did it reboot after installing any updates?
Got a crazy system admin that didn't let me know that was going on. Just checked the event viewer and saw that's exactly what was going on. Thanks for helping me verify what was going on! – Anjisan Mar 31 '09 at 14:18
所以我們看到有些windows server的安全補丁安裝后，要求重啟服務器。這有可能導致SQL Server的某些數據庫變為single user mode。所以在重啟服務器前要小心，最好將所有SQL Server的數據庫offline之后再重啟服務器，這是最安全的做法。