Sometime before, I was giving training on basics of SQL Server. One of attendee is having doubt & want to confirm that SQL Server really Reserve 1 user connection for DAC (Dedicated Administrator Connection).

So I decide to show a demo for the same. I have changed the no. of User Connections to 1 & then try to login. So below is the PROOF.

Steps Performed for Demo

1. User Connections Current settings

2. User Connections New settings. You need to restart SQL Services after this.

3. I Try to Login to SQL Server by SSMS & got Error. But Why ?

4. I Try to Login to SQL Server by SQLCMD & got Error. But Why ?

5. Reason of getting error at step 3 & 4 is DAC (Dedicated Administrator Connection). SQL Server reserve one user connection for DAC.

6. Rollback the changes using DAC & come back to previous settings. You need to restart SQL Services after this.

7. User Connections After Rollback

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Reference : Rohit Garg (http://mssqlfun.com/)