Start SQL Server in single user mode with parameter -m doesn't work well

Question

C:\Windows\system32>net start mssqlserver /m "Microsoft SQL Server Management St
udio - Query"
The SQL Server (MSSQLSERVER) service is starting.
The SQL Server (MSSQLSERVER) service was started successfully.
C:\Windows\system32>sqlcmd -S . -e
1> go
1> select @@servername;
2> go
select @@servername;
myserver
(1 rows affected)
1>
As you can see, I'm still able to connect with sqlcmd prompt to SQL Server. According production doc of SQL Server 2014, it should not be conncting by sqlcmd. it shall only be connected by SSMS.
below the original doc on msdn:
Start SQL Server in Single-User Mode
Provide Feedback
Under certain circumstances, you may have to start an instance of SQL Server
in single-user mode by 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.
Starting SQL Server in single-user mode enables any member of the computer's
local Administrators group to connect to the instance of SQL Server as a member
of the sysadmin fixed server role. For more information, see Connect to
SQL Server When System Administrators Are Locked
Out.
When you start an instance of SQL Server in single-user mode, note the
following:
Only one user can connect to the server.
The CHECKPOINT process is not executed. By default, it is executed
automatically at startup.
Note
Stop the SQL Server Agent service before connecting to an instance of SQL
Server in single-user mode; otherwise, the SQL Server Agent service uses the
connection, thereby blocking it.
When you start an instance of SQL Server in single-user mode, SQL Server
Management Studio can connect to SQL Server. Object Explorer in Management
Studio might fail because it requires more than one connection for some
operations. To manage SQL Server in single-user mode, execute Transact-SQL
statements by connecting only through the Query Editor in Management Studio, or
use the
sqlcmd utility.
When you use the -m option with sqlcmd or
Management Studio, you can limit the connections to a specified client
application. For example, -m"sqlcmd" limits connections to a
single connection and that connection must identify itself as the
sqlcmd client program. Use this option when you are starting
SQL Server in single-user mode and an unknown client application is taking the
only available connection. To connect through the Query Editor in Management
Studio, use -m"Microsoft SQL Server Management Studio - Query".
Shawn

Answer 1

Hi Shawn Xiao,
For starting SQL Server instance in single user mode, we can add –m; parameter in SQL Server Configuration Manager, also we can run CMD with ‘Run as administrator’ and input the following statement.
NET START MSSQLSERVER /m
I do a test in SQL Server 2014 Express version, after starting SQL with Single User Mode, SQL Server will only accept one connection. If you connect to SQL Server with a user account, the following error will occur.
Login failed for user ‘domain\username’. Reason: Server is in single user mode. Only one administrator can connect at this time.
However, in your situation, you can connect to SQL Server and run T-SQL statement successfully, it can be due to connection with the administrator account in your sqlcmd.
For more information, you can review the following article.
http://zarez.net/?p=117
Regards,
Sofiya Li
Sofiya Li
TechNet Community Support