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Tutorial: Use adutil to configure Active Directory authentication with SQL Server on Linux

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Applies to: SQL Server - Linux

This tutorial explains how to configure Windows Active Directory authentication for SQL Server on Linux using adutil. For another method of configuring Active Directory authentication using ktpass, see Tutorial: Use Active Directory authentication with SQL Server on Linux.

This tutorial consists of the following tasks:

  • Install adutil
  • Join Linux machine to your Active Directory domain
  • Create an Active Directory user for SQL Server and set the Service Principal Name (SPN) using adutil
  • Create the SQL Server service keytab (key table) file
  • Configure SQL Server to use the keytab file
  • Create Active Directory-based SQL Server logins using Transact-SQL
  • Connect to SQL Server using Active Directory authentication

Prerequisites

Before configuring Active Directory authentication, you need:

  • A Windows Domain Controller running Active Directory Domain Services in your network.
  • The adutil tool installed on a domain-joined host machine.

Domain machine preparation

Make sure there's a forwarding host (A) entry added in Active Directory for the Linux host IP address. In this tutorial, the IP address of sql1 host machine is 10.0.0.10. We add the forwarding host entry in Active Directory in the following example. The entry ensures that when users connect to sql1.contoso.com, it reaches the right host.

Screenshot of add host record.

For this tutorial, we're using an environment in Azure with three virtual machines (VMs). One VM is a Windows Server computer named adVM.contoso.com, running as a Domain Controller (DC) with the domain name contoso.com. The second VM is a client machine running Windows 10 named winbox, which has SQL Server Management Studio (SSMS) installed. The third machine is an Ubuntu 18.04 LTS machine named sql1, which hosts SQL Server.

Join the Linux host machine to your Active Directory domain

To join sql1 to the Active Directory domain, see Join SQL Server on a Linux host to an Active Directory domain.

Install adutil

To install adutil, follow the steps explained in the article Introduction to adutil - Active Directory utility on the host machine that you added to the domain in the previous step.

Use adutil to create an Active Directory user for SQL Server and set the Service Principal Name (SPN)

  1. Obtain or renew the Kerberos TGT (ticket-granting ticket) using the kinit command. You must use a privileged account for the kinit command, and the host machine should already be part of the domain. The account needs permission to connect to the domain, and create accounts and SPNs in the domain.

    In this example script, a privileged user called privilegeduser@CONTOSO.COM is already created on the domain controller.

    kinit privilegeduser@CONTOSO.COM

  2. Using adutil, create the new user that will be the privileged Active Directory account by SQL Server.

    Passwords can be specified in three different ways. If you use more than one of these methods, they take precedence in the following order:

    • Using the password flag: --password <password>
    • In an environment variable: ADUTIL_ACCOUNT_PWD
    • Interactive input at a command line prompt

    The environment variable or interactive input methods are more secure than the password flag.

    adutil user create --name sqluser --distname CN=sqluser,CN=Users,DC=CONTOSO,DC=COM --password 'P@ssw0rd'

    You can specify the name of the account using the distinguished name (--distname) as shown previously, or you can use the Organizational Unit (OU) name. The OU name (--ou) takes precedence over distinguished name in case you specify both. You can run the following command for more details:

    adutil user create --help

  3. Register SPNs to the principal created previously. You must use the machine's fully qualified domain name (FQDN). In this tutorial, we're using SQL Server's default port, 1433. Your port number could be different.

    adutil spn addauto -n sqluser -s MSSQLSvc -H sql1.contoso.com -p 1433
    • addauto creates the SPNs automatically, as long as there are sufficient privileges for the kinit account.
    • -n: The name of the account to assign the SPNs.
    • -s: The service name to use for generating SPNs. In this case it's for the SQL Server service, which is why the service name is MSSQLSvc.
    • -H: The hostname to use for generating SPNs. If not specified, the local host's FQDN is used. In this case, the host name is sql1 and the FQDN is sql1.contoso.com.
    • -p: The port to use for generating SPNs. If not specified, SPNs are generated without a port. SQL connections only work in this case when the SQL Server is listening to the default port, 1433.

Create the SQL Server service keytab file using mssql-conf

You can install adutil and integrate it with mssql-conf, to create and configure the keytab using mssql-conf directly. This method is preferred for creating a SQL Server service keytab file. Otherwise, you can create the SQL Server service keytab file manually.

Prerequisites

  1. Make sure that the /var/opt/mssql/mssql.conf file is owned by mssql and not root. If this isn't the case, you must run the mssql-conf commands using sudo.

  2. On a domain controller, in the Active Directory settings for the network.privilegedadaccount account (in these examples, sqluser@CONTOSO.COM), enable the following options under the Account tab, in the Account options section:

    • This account supports Kerberos AES 128 bit encryption
    • This account supports Kerberos AES 256 bit encryption

Create the keytab file

Once you create the user and SPNs, you can create the keytab using the following steps.

  1. Switch to the mssql user:

    su mssql

  2. Sign in as the Active Directory user using the kinit command:

    kinit privilegeduser@CONTOSO.COM

  3. Create the keytab file:

    /opt/mssql/bin/mssql-conf setup-ad-keytab /var/opt/mssql/secrets/mssql.keytab sqluser

    When prompted to restart the SQL Server service to adopt the new Active Directory configuration, you can do in the next section.

  4. Confirm the keytab is created with the right entries:

    klist -kte /var/opt/mssql/secrets/mssql.keytab

    You should see output similar to this example:

    keytab name: FILE:/var/opt/mssql/secrets/mssql.keytab
KVNO Timestamp           Principal
---- ------------------- ------------------------------------------------------
   4 12/30/2021 14:02:08 sqluser@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   4 12/30/2021 14:02:08 MSSQLSvc/sql1.contoso.com:1433@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   4 12/30/2021 14:02:08 MSSQLSvc/sql1.contoso.com@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   4 12/30/2021 14:02:08 MSSQLSvc/sql1:1433@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   4 12/30/2021 14:02:08 MSSQLSvc/sql1@CONTOSO.COM (aes256-cts-hmac-sha1-96)

    If the /var/opt/mssql/mssql.conf file isn't owned by mssql, you must configure mssql-conf to set the network.kerberoskeytabfile and network.privilegedadaccount values according to the previous steps. Type the password when prompted.

    /opt/mssql/bin/mssql-conf set network.kerberoskeytabfile /var/opt/mssql/secrets/mssql.keytab
/opt/mssql/bin/mssql-conf set network.privilegedadaccount sqluser

  5. Validate your configuration to ensure that Active Directory authentication works without any issues.

    /opt/mssql/bin/mssql-conf validate-ad-config /var/opt/mssql/secrets/mssql.keytab

    You should see output similar to the following example:

    Detected Configuration:
Default Realm: CONTOSO.COM
Keytab: /var/opt/mssql/secrets/mssql.keytab
Reverse DNS Result: sql1.contoso.com
SQL Server Port: 1433
Detected SPNs (SPN, KVNO):
(MSSQLSvc/sql1.CONTOSO.COM:1433, 4)
(MSSQLSvc/sql1.CONTOSO.COM, 4)
(MSSQLSvc/sql1:1433, 4)
(MSSQLSvc/sql1, 4)
Privileged Account (Name, KVNO):
(sqluser, 4)

Create the SQL Server service keytab file manually

If you installed adutil and integrated it with mssql-conf, you can skip ahead to Create the SQL Server service keytab file using mssql-conf.

  1. Create the keytab file that contains entries for each of the four SPNs created previously, and one for the user.

    adutil keytab createauto -k /var/opt/mssql/secrets/mssql.keytab -p 1433 -H sql1.contoso.com --password 'P@ssw0rd' -s MSSQLSvc

    The possible command line options are:

    • -k: The path where the mssql.keytab file is created. In the previous example, the directory /var/opt/mssql/secrets/ should already exist on the host.
    • -p: The port to use for generating SPNs. If not specified, SPNs are generated without a port.
    • -H: The hostname to use for generating SPNs. If not specified, the local host's FQDN is used. In this case, the host name is sql1 and the FQDN is sql1.contoso.com.
    • -s: The service name to use for generating SPNs. For this example, the SQL Server service name is MSSQLSvc.
    • --password: The password of the privileged Active Directory user account that was created earlier.
    • -e or --enctype: Encryption types for the keytab entry. Use a comma-separated list of values. If not specified, an interactive prompt is presented.

    You can choose more than one encryption type, as long as your host and domain support the encryption type. In this example, you might choose aes256-cts-hmac-sha1-96 and aes128-cts-hmac-sha1-96. However, you should avoid arcfour-hmac in a production environment because it has weak encryption.

    If you'd like to choose the encryption type without prompting, you can specify your choice of encryption type using the -e argument in the previous command. For more help on the adutil keytab options, run this command:

    adutil keytab createauto --help

  2. Add an entry in the keytab for the principal name and password that SQL Server uses to connect to Active Directory:

    adutil keytab create -k /var/opt/mssql/secrets/mssql.keytab -p sqluser --password 'P@ssw0rd'
    • -k: Path where you would like to create the mssql.keytab file.
    • -p: Principal to add to the keytab.

    The adutil keytab [ create | autocreate ] doesn't overwrite the previous files; it just appends to the file if already present.

  3. Make sure the created keytab is owned by the mssql user, and that only the mssql user has read/write access to the file. You can run the chown and chmod commands as follows:

    chown mssql /var/opt/mssql/secrets/mssql.keytab
chmod 440 /var/opt/mssql/secrets/mssql.keytab

Configure SQL Server to use the keytab

Run the below commands to configure SQL Server to use the keytab created in the previous step, and set the privileged Active Directory account as the user created previously. In our example, the user name is sqluser.

/opt/mssql/bin/mssql-conf set network.kerberoskeytabfile /var/opt/mssql/secrets/mssql.keytab
/opt/mssql/bin/mssql-conf set network.privilegedadaccount sqluser

Restart SQL Server

Run the following command to restart the SQL Server service:

sudo systemctl restart mssql-server

Create Active Directory-based SQL Server logins in Transact-SQL

Connect to the SQL Server and run the following commands to create the login, and confirm that it exists.

CREATE LOGIN [contoso\privilegeduser] FROM WINDOWS;
SELECT name FROM sys.server_principals;

Connect to SQL Server using Active Directory authentication

To connect using SSMS or Azure Data Studio, log into the SQL Server with your Windows credentials.

You can also use a tool like sqlcmd to connect to the SQL Server using Windows Authentication.

sqlcmd -E -S 'sql1.contoso.com'

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