There are certain situation when user wants to start SQL Server Engine in “single user” mode from the start up.
To start SQL Server in single user mode is very simple procedure as displayed below.
Go to SQL Server Configuration Manager and click on SQL Server 2005 Services. Click on desired SQL Server instance and right click go to properties. On the Advance table enter param ‘-m;‘ before existing params in Startup Parameters box.
Make sure that you entered semi-comma after -m. Once that is completed, restart SQL Server services to take this in effect. Once this is done, now you will be only able to connect SQL Server using sqlcmd.
Make sure to remove newly added params after required work is completed to restart it in multi user mode.
Reference : Pinal Dave (https://blog.sqlauthority.com)