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Connect to SQL Server when system administrators are locked out

  • Artikkel

Applies to: SQL Server

This article describes how you can regain access to the SQL Server Database Engine as a system administrator if you're locked out. A system administrator can lose access to an instance of SQL Server due to one of the following reasons:

  • All logins that are members of the sysadmin fixed server role were removed by mistake.

  • All Windows Groups that are members of the sysadmin fixed server role were removed by mistake.

  • The logins that are members of the sysadmin fixed server role are for individuals who left the company or who aren't available.

  • The sa account is disabled or no one knows the password.

Resolution

In order to resolve your access issue, we recommend that you start the instance of SQL Server in single-user mode. This mode prevents other connections from occurring while you try to regain access. From here, you can connect to your instance of SQL Server and add your login to the sysadmin server role. Detailed steps for this solution are provided in the step-by-step-instructions section.

You can start an instance of SQL Server in single-user mode with either the -m or -f options from the command line. Any member of the computer's local Administrators group can then connect to the instance of SQL Server as a member of the sysadmin fixed server role.

When you start the instance in single-user mode, stop the SQL Server Agent service. Otherwise, SQL Server Agent might connect first, taking the only available connection to the server and blocking you from signing in.

It's also possible for an unknown client application to take the only available connection before you're able to sign in. In order to prevent this from happening, you can use the -m option followed by an application name to limit connections to a single connection from the specified application. For example, starting SQL Server with -mSQLCMD limits connections to a single connection that identifies itself as the sqlcmd client program. To connect through the Query Editor in Management Studio, use -m"Microsoft SQL Server Management Studio - Query".

Important

Don't use -m with an application name as a security feature. Client applications specify the application name through the connection string settings, so it can easily be spoofed with a false name.

The following table summarizes the different ways to start your instance in single-user mode in the command line.

Option Description When to use
-m Limits connections to a single connection There are no other users attempting to connect to the instance, or you aren't sure of the application name you're using to connect to the instance.
-mSQLCMD Limits connections to a single connection that must identify itself as the sqlcmd client program You plan to connect to the instance with sqlcmd, and you want to prevent other applications from taking the only available connection.
-m"Microsoft SQL Server Management Studio - Query" Limits connections to a single connection that must identify itself as the Microsoft SQL Server Management Studio - Query application. You plan to connect to the instance through the Query Editor in Management Studio and you want to prevent other applications from taking the only available connection.
-f Limits connections to a single connection and starts the instance in minimal configuration Some other configuration is preventing you from starting.

Step-by-step instructions

For step-by-step instructions about how to start SQL Server in single-user mode, see Start SQL Server in Single-User Mode.

Use PowerShell

Option 1: Run the steps directly in an executable notebook using Azure Data Studio

Note

Before attempting to open this notebook, check that Azure Data Studio is installed on your local machine. To install Azure Data Studio, see Learn how to install Azure Data Studio.

Open Notebook in Azure Data Studio

Option 2: Follow the step manually

  1. Open an elevated Windows PowerShell command prompt.

  2. Set up service name and SQL Server instance, and Windows login variables. Replace these values with values that match your environment.

    If you have a default instance, use MSSQLSERVER without an instance name.

    $service_name = "MSSQL`$instancename"
$sql_server_instance = "machine_name\instance"
$login_to_be_granted_access = "[CONTOSO\PatK]"

  3. Stop the SQL Server service so it can be restarted with single-user mode, using the following command:

    If you have a default instance, use MSSQLSERVER without an instance name.

    net stop $service_name

  4. Now start your SQL Server instance in a single user mode and only allow SQLCMD.exe to connect (/mSQLCMD):

    Note

    Be sure to use upper-case SQLCMD

    If you have a default instance, use MSSQLSERVER without an instance name.

    net start $service_name /f /mSQLCMD

  5. Using sqlcmd, execute a CREATE LOGIN command followed by ALTER SERVER ROLE command. This step assumes you logged into Windows with an account that is a member of the Local Administrators group. This step assumes you replaced the domain and login names with the credentials you want to give sysadmin membership.

    If you have a default instance, use the name of the server.

    sqlcmd.exe -E -S $sql_server_instance -Q "CREATE LOGIN $login_to_be_granted_access FROM WINDOWS; ALTER SERVER ROLE sysadmin ADD MEMBER $login_to_be_granted_access; "

    If you receive the following error, you must ensure no other sqlcmd is connected to SQL Server:

    Sqlcmd: Error: Microsoft ODBC Driver X for SQL Server : Login failed for user 'CONTOSO\BobD'. Reason: Server is in single user mode. Only one administrator can connect at this time.

  6. Mixed Mode (optional): If your SQL Server instance is running in mixed authentication mode, you can also:

    1. Grant the sysadmin role membership to a SQL Server login. Execute code such as the following to create a new SQL Server authentication login that is a member of the sysadmin fixed server role. Replace <strong_password> with a strong password of your choice.

      If you have a default instance, use the name of the server.

      $strong_password = "<strong_password>"
sqlcmd.exe -E -S $sql_server_instance -Q "CREATE LOGIN TempLogin WITH PASSWORD = '$strong_password'; ALTER SERVER ROLE sysadmin ADD MEMBER TempLogin; "

    2. Also, if your SQL Server instance is running in mixed authentication mode and you want to reset the password of an enabled sa account. Change the password of the sa account with the following syntax. Be sure to replace <strong_password> with a strong password of your choice:

      If you have a default instance, use the name of the server.

      $strong_password = "<strong_password>"
sqlcmd.exe -E -S $sql_server_instance -Q "ALTER LOGIN sa WITH PASSWORD = $strong_password; "

  7. Stop and restart your SQL Server instance in multi-user mode

    If you have a default instance, use MSSQLSERVER without an instance name.

    net stop $service_name
net start $service_name

Use SQL Server Configuration Manager and Management Studio (SSMS)

These instructions assume:

  • SQL Server is running on Windows 8 or higher. Slight adjustments for earlier versions of SQL Server or Windows are provided where applicable.

  • SQL Server Management Studio is installed on the computer.

Perform these instructions while logged in to Windows as a member of the local administrators group.

  1. From the Windows Start menu, right-click the icon for SQL Server Configuration Manager and choose Run as administrator to pass your administrator credentials to Configuration Manager.

  2. In SQL Server Configuration Manager, in the left pane, select SQL Server Services. In the right-pane, find your instance of SQL Server. (The default instance of SQL Server includes (MSSQLSERVER) after the computer name. Named instances appear in upper case with the same name that they have in Registered Servers.) Right-click the instance of SQL Server, and then select Properties.

  3. On the Startup Parameters tab, in the Specify a startup parameter box, type -m and then select Add. (That's a dash then lower case letter m.)

    For some earlier versions of SQL Server, there's no Startup Parameters tab. In that case, on the Advanced tab, double-click Startup Parameters. The parameters open up in a small window. Be careful not to change any of the existing parameters. At the very end, add a new parameter ;-m and then select OK. (That's a semi-colon then a dash then lower case letter m.)

  4. Select OK, and after the message to restart, right-click your server name, and then select Restart.

  5. After SQL Server restarts, your server will be in single-user mode. Make sure that SQL Server Agent isn't running. If started, it takes your only connection.

  6. From the Windows Start menu, right-click the icon for Management Studio and select Run as administrator. This passes your administrator credentials to SSMS.

    For earlier versions of Windows, the Run as administrator option appears as a submenu.

    In some configurations, SSMS attempts to make several connections. Multiple connections fail because SQL Server is in single-user mode. Based on your scenario, perform one of the following actions.

    1. Connect with Object Explorer using Windows Authentication, which includes your Administrator credentials. Expand Security, expand Logins, and double-click your own login. On the Server Roles page, select sysadmin, and then select OK.

    2. Instead of connecting with Object Explorer, connect with a Query Window using Windows Authentication (which includes your Administrator credentials). (You can only connect this way if you didn't connect with Object Explorer.) Execute code such as the following to add a new Windows Authentication login that is a member of the sysadmin fixed server role. The following example adds a domain user named CONTOSO\PatK.

      CREATE LOGIN [CONTOSO\PatK] FROM WINDOWS;
ALTER SERVER ROLE sysadmin ADD MEMBER [CONTOSO\PatK];

    3. If your SQL Server is running in mixed authentication mode, connect with a Query Window using Windows Authentication (which includes your Administrator credentials). Execute code such as the following to create a new SQL Server authentication login that is a member of the sysadmin fixed server role.

      CREATE LOGIN TempLogin WITH PASSWORD = '<strong_password>';
ALTER SERVER ROLE sysadmin ADD MEMBER TempLogin;

      Warning

      Replace <strong_password> with a strong password.

    4. If your SQL Server is running in mixed authentication mode and you want to reset the password of the sa account, connect with a Query Window using Windows Authentication (which includes your Administrator credentials). Change the password of the sa account with the following syntax.

      ALTER LOGIN sa WITH PASSWORD = '<strong_password>';

      Warning

      Replace <strong_password> with a strong password.

  7. Close Management Studio.

  8. These next few steps change SQL Server back to multi-user mode. In SQL Server Configuration Manager, in the left pane, select SQL Server Services.

  9. In the right-pane, right-click the instance of SQL Server, and then select Properties.

  10. On the Startup Parameters tab, in the Existing parameters box, select -m and then select Remove.

    For some earlier versions of SQL Server, there's no Startup Parameters tab. In that case, on the Advanced tab, double-click Startup Parameters. The parameters open up in a small window. Remove the ;-m that you added earlier, and then select OK.

  11. Right-click your server name, and then select Restart. Make sure to start SQL Server Agent again if you stopped it before starting SQL Server in single-user mode.

Now you should be able to connect normally with one of the accounts that is now a member of the sysadmin fixed server role.

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