由于restore msdb的时候需要把原有的msdb的Restrict Access设置为SINGLE_USER。

今天在公司把msdb设置为SINGLE_USER后，发现不能查看服务器上的任何数据库。提示如下信息：s

把Restrict Access修改为MULTI_USER的时候也提示报错：

alter database msdb set MULTI_USER  

Msg 5064, Level 16, State 1, Line 1
Changes to the state or options of database ''msdb'' cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.
Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.

根据提示信息运行如下命令查看MSDB上有哪些连接：

 Select * from sys.databases Where name='msdb' Select * from sys.dm_exec_connections Where session_id=55 select * from sys.sysprocesses WHERE dbid = 4 select * from sys.dm_tran_locks where resource_database_id=4

 如上图，发现有55号进程是连接到msdb的，于是把该进程Kill掉，然后再设置为MULTI_USER OK。可以显示数据库。

kill 55