Published on

September 25, 2009

Enabling the Dedicated Administrator Connection (DAC) in SQL Server Express

Have you ever encountered difficulties connecting to the Dedicated Administrator Connection (DAC) in SQL Server Express? If so, you’re not alone. SQL Server Express does not enable the DAC by default, which can cause confusion and frustration for users trying to access this powerful feature.

The DAC is a special connection that allows administrators to troubleshoot and diagnose issues with SQL Server instances. It provides direct access to the server, bypassing the normal connection process and allowing for more efficient troubleshooting.

The reason why the DAC is not enabled in SQL Server Express is due to the design mindset behind the Express edition. Express is intended to be lightweight and resource-efficient, and as a result, certain features, such as the DAC, are disabled by default to conserve resources.

However, there is a way to enable the DAC in SQL Server Express. By using a startup trace flag, specifically trace flag 7806, you can activate the DAC and gain access to its functionality.

To enable the DAC, follow these steps:

  1. Open SQL Server Configuration Manager.
  2. Click on “SQL Server Services” and locate your SQL Server Express instance.
  3. Right-click on the instance and choose “Properties”.
  4. In the “Advanced” tab, you’ll find the “Startup Parameters”.
  5. Add “-T7806” to the Startup Parameters, separating each parameter with a semi-colon (;).
  6. Click “OK” to save the changes.

Keep in mind that the changes won’t take effect until the next restart of the SQL Server Express instance. Once the instance has been restarted, you can verify that the DAC is enabled by checking the SQL Server Error Log.

In the Error Log, you should see a message indicating that the trace flag 7806 has been recognized, confirming that the DAC is now enabled. Additionally, you’ll notice a message stating that the DAC has been established and a port has been assigned.

By default, the DAC listens on TCP port 1434. However, if your SQL Server Express instance is a named instance or if TCP port 1434 is already in use, the DAC may use a different port. It’s important to take note of the assigned port, as you’ll need it to establish a connection to the DAC.

To connect to the DAC, you can use SQLCMD with the “-A” flag, which tells SQLCMD to attempt a DAC connection. Alternatively, if you’re using SQL Server Management Studio, you can specify “ADMIN:” before the server\instance name.

Once connected to the DAC, you can verify the connection by executing a query against a system base table. For example, you can run the following query:

SELECT class, id, grantee, type, state
FROM sys.sysprivs;

If the query returns a result set, congratulations! You’re connected via the DAC and can now take advantage of its functionality to troubleshoot and diagnose issues with your SQL Server Express instance.

Enabling the DAC in SQL Server Express can greatly enhance your ability to manage and maintain your database. By following the steps outlined above, you can unlock the power of the DAC and streamline your troubleshooting process.

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