Under certain circumstances, you may need to start an instance of Microsoft® SQL Server™ in single-user mode using the startup option -m. For example, you may want to change server configuration options or recover a damaged master database or other system database. Both actions require starting an instance of SQL Server in single-user mode.
When you start an instance of SQL Server in single-user mode:
Only one user can connect to the server.
The CHECKPOINT process is not executed. By default, it is executed automatically at startup.
The sp_configure system stored procedure allow updates option is enabled. By default, the allow updates option is disabled.
To start SQL Server in single-user mode
From a command prompt, enter:
sqlservr.exe -c -m