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Rotate keytabs for SQL Server on Linux

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Applies to: SQL Server - Linux

Based on your organization's security best practices, you might be required to rotate the password regularly for the Windows Active Directory account provided as network.privilegedadaccount in mssql.conf, or any other account that owns the service principal names (SPN) for the SQL Server service. The supported method for changing the password for the account is documented in this article. The password change takes effect without the need to restart the SQL Server service on Linux.

The adutil tool is used to update the keytab. The adutil command must be run from a domain-joined machine. For more information about adutil and how to download the tool, see Introduction to adutil - Active Directory Utility.

It's critical to update the new password in the keytab with the next kvno number before updating it in Active Directory. Using the next kvno number prevents the SQL Server service from the need to be restarted after the password change. If you update the password in Active Directory first, and then change the keytab, you must restart the SQL Server service to ensure that Active Directory authentication works properly.

Scenario for rotating the keytab

Let's consider an example. Active Directory authentication is already enabled for SQL Server on Linux. In the mssql.conf file, you have set the network.privilegedadaccount to sqluser. The account sqluser@CONTOSO.COM is already created in Active Directory, and the keytab has also been created at the default location /var/opt/mssql/secrets/mssql.keytab. Now you want to change the password for the sqluser@CONTOSO.COM. Here are the steps that you need to follow:

  1. Install adutil on the domain joined machine.

  2. Obtain or renew the Kerberos TGT (ticket-granting ticket) using the kinit command. Use a privileged account for the kinit command. The account needs to have permission to connect to the domain and should be able to create accounts and SPNs in the domain. In this case, we're using the account privilegeduser@CONTOSO.COM that has permissions to create accounts and SPNs in our domain called CONTOSO.COM.

    kinit privilegeduser@CONTOSO.COM

  3. Once you've run kinit to obtain/renew the TGT, query the current kvno number of the network.privilegedadaccount. In this case, it's sqluser@CONTOSO.COM.

    kvno sqluser@CONTOSO.COM

You can choose to rotate the keytab with mssql-conf, or rotate the keytab manually using adutil.

Rotate the keytab with mssql-conf

You can install adutil and integrate it with mssql-conf, which means you can rotate the keytab using mssql-conf.

  1. Sign in as the root user and switch to the mssql user.

    su mssql

  2. Obtain or renew the Kerberos TGT (ticket-granting ticket) using the kinit command. Use a privileged account for the kinit command. The account needs to have permission to connect to the domain and should be able to create accounts and SPNs in the domain. In this case, we're using the account privilegeduser@CONTOSO.COM that has permissions to create accounts and SPNs in our domain called CONTOSO.COM.

    kinit privilegeduser@CONTOSO.COM

  3. Run the mssql-conf command, providing the SQL Server keytab and the network.privilegedadaccount details. In this example, the privilegedadaccount is sqluser.

    ./mssql-conf setup-ad-keytab /var/opt/mssql/secrets/mssql.keytab sqluser --use-next-kvno'

    When prompted for a password, enter a new password that you intend to use. The --use-next-kvno option allocates the current kvno + 1.

    Optional: You could also use --kvno option with the mssql-conf setup-ad-keytab command to provide a specific kvno. You must ensure that you get the current kvno for the user first, and then update the new kvno accordingly, which would be the current kvno + 1.

  4. You can list the keys of the keytab using the command:

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

    You'll notice that the keytab is updated with the next kvno for both the user and SPN entries.

  5. You can now change the password for the sqluser user. Here's an example.

    Important

    If you are prompted to restart SQL Server during this step, you can ignore it. Remember to change the password in Active Directory as well.

    bash-4.4$ kinit privilegedaccount@CONTOSO.COM
Password for privilegedaccount@CONTOSO.COM:

bash-4.4$ ./mssql-conf setup-ad-keytab /var/opt/mssql/secrets/mssql.keytab sqluser --use-next-kvno
sqluser@contoso.com's password:
Confirm sqluser@contoso.com's password:

SQL Server needs to be restarted in order to adopt the new AD configuration, please run 'systemctl restart mssql-server.service'.

bash-4.4$ klist -kte /var/opt/mssql/secrets/mssql.keytab
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)
   5 12/30/2021 20:06:34 sqluser@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   5 12/30/2021 20:06:34 MSSQLSvc/sql1.contoso.com:1433@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   5 12/30/2021 20:06:34 MSSQLSvc/sql1.contoso.com@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   5 12/30/2021 20:06:34 MSSQLSvc/sql1:1433@CONTOSO.COM (aes256-cts-hmac-sha1-96)
   5 12/30/2021 20:06:34 MSSQLSvc/sql1@CONTOSO.COM (aes256-cts-hmac-sha1-96)

Rotate the keytab manually with adutil

If you want to update the keytab manually using adutil, refer to the following steps.

Updating the keytab using adutil adds an entry into the current keytab. For example, if the kvno number from the previous command is 2, use the kvno number 3 when updating the keytab. Following are the adutil commands that you need to run.

  • Change the port number (-p), hostname (-H), path to keytab (-k), and kvno number to match your environment.
adutil keytab createauto -k /var/opt/mssql/secrets/mssql.keytab -p 1433 -H mssql.contoso.com --password '<newpassword>' -s MSSQLSvc --kvno 3

adutil keytab create -k /var/opt/mssql/secrets/mssql.keytab -p sqluser --password '<newpassword>' --kvno 3

-k: is the path to the current keytab that is being used by SQL Server and set using the option network.kerberoskeytabfile in the mssql.conf file.

-H: is the fully qualified domain name of the SQL Server host.

-p: is the port that SQL Server service is configured to listen on in the first command. In the second command, -p represents the network.privilegedadaccount that you're going to update the password for.

kvno: value needs to be the current kvno + 1. The current kvno value is obtained from step 3.

Once you run the above commands, you must provide your choice of encryption type for the keytab entries. Ensure you choose the right one for your environment.

Check the keytab entries

After updating the keytab, you should now see the entries in the keytab for the kvno 3 (new), and also kvno 2 (old) for the same account sqluser@CONTOSO.COM and SPNs. You can run the following klist command to check the entries in the keytab:

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

Change the account password in Active Directory

The last step is to update the password of the network.privilegedadaccount or the account that owns the SQL Server SPNs in Windows Active Directory. In the previous scenario, we have to update the password for sqluser@CONTOSO.COM in Active Directory. Change the password to the <newpassword> that you provided in the step 3 in the previous section. Active Directory authentication should continue to work, and without the need for the SQL Server service to restart.

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