The SQL Server Audit object collects a single instance of server or database-level actions and groups of actions to monitor. The audit is at the SQL Server instance level. You can have multiple audits per SQL Server instance.

When you define an audit, you specify the location for the output of the results. This is the audit destination. The audit is created in a disabled state, and does not automatically audit any actions. After the audit is enabled, the audit destination receives data from the audit.

The Server Audit Specification object belongs to an audit. You can create one server audit specification per audit, because both are created at the SQL Server instance scope.

The server audit specification collects many server-level action groups raised by the Extended Events feature. You can include audit action groups in a server audit specification. Audit action groups are predefined groups of actions, which are atomic events occurring in the Database Engine. These actions are sent to the audit, which records them in the target.

Server-level audit action groups are described in the topic SQL Server Audit Action Groups and Actions.

The Database Audit Specification object also belongs to a SQL Server audit. You can create one database audit specification per SQL Server database per audit.

The database audit specification collects database-level audit actions raised by the Extended Events feature. You can add either audit action groups or audit events to a database audit specification. Audit events are the atomic actions that can be audited by the SQL Server engine. Audit action groups are predefined groups of actions. Both are at the SQL Server database scope. These actions are sent to the audit, which records them in the target. Do not include server-scoped objects, such as the system views, in a user database audit specification.

Database-level audit action groups and audit actions are described in the topic SQL Server Audit Action Groups and Actions.

The results of an audit are sent to a target, which can be a file, the Windows Security event log, or the Windows Application event log. (Writing to the Security log is not available on Windows XP.) Logs must be reviewed and archived periodically to make sure that the target has sufficient space to write additional records.

Writing to the Windows Security log requires the SQL Server service account to be added to the Generate security audits policy. By default, the Local System, Local Service, and Network Service are part of this policy. This setting can be configured by using the security policy snap-in (secpol.msc). Additionally, the Audit object access security policy must be enabled for both Success and Failure. This setting can be configured by using the security policy snap-in (secpol.msc). In Windows Vista or Windows Server 2008, you can set the more granular application generated policy from the command line by using the audit policy program (AuditPol.exe). For more information about the steps to enable writing to the Windows Security log, see How to: Write Server Audit Events to the Security Log. For more information about the Auditpol.exe program, see Knowledge Base article 921469, How to use Group Policy to configure detailed security auditing. The Windows event logs are global to the Windows operating system. For more information about the Windows event logs, see Event Viewer Overview. If you need more precise permissions on the audit, use the binary file target.

When you are saving audit information to a file, to help prevent tampering, you can restrict access to the file location in the following ways:

• The SQL Server Service Account must have both Read and Write permission.
  
• Audit Administrators typically require Read and Write permission. This assumes that the Audit Administrators are Windows accounts for administration of audit files, such as: copying them to different shares, backing them up, and so on.
  
• Audit Readers that are authorized to read audit files must have Read permission.
  

Even when theDatabase Engine is writing to a file, other Windows users can read the audit file if they have permission. The Database Engine does not take an exclusive lock that prevents read operations.

Because the Database Engine can access the file, SQL Server logins that have CONTROL SERVER permission can use the Database Engine to access the audit files. To record any user that is reading the audit file, define an audit on master.sys.fn_get_audit_file. This records the logins with CONTROL SERVER permission that have accessed the audit file through SQL Server.

If an Audit Administrator copies the file to a different location (for archive purposes, and so on), the ACLs on the new location should be reduced to the following permissions:

• Audit Administrator – Read / Write
  
• Audit Reader – Read
  

We recommend that you generate audit reports from a separate instance of SQL Server, such as an instance of SQL Server Express, to which only Audit Administrators or Audit Readers have access. By using a separate instance of the Database Engine for reporting, you can help prevent unauthorized users from obtaining access to the audit record.

You can offer additional protection against unauthorized access by encrypting the folder in which the audit file is stored by using Windows BitLocker Drive Encryption or Windows Encrypting File System.

For more information about the audit records that are written to the target, see SQL Server Audit Records.

Attaching a database that has an audit specification and specifies a GUID that does not exist on the server will cause an orphaned audit specification. Because an audit with a matching GUID does not exist on the server instance, no audit events will be recorded. To correct this situation, use the ALTER DATABASE AUDIT SPECIFICATION command to connect the orphaned audit specification to an existing server audit. Or, use the CREATE SERVER AUDIT command to create a new server audit with the specified GUID.

You can attach a database that has an audit specification defined on it to another edition of SQL Server that does not support SQL Server Audit, such as SQL Server Express but it will not record audit events.

A database that has a database audit specification defined and that uses database mirroring will include the database audit specification. To work correctly on the mirrored SQL instance, the following items must be configured:

• The mirror server must have an audit with the same GUID to enable the database audit specification to write audit records. This can be configured by using the command CREATE AUDIT WITH GUID= <GUID from source Server Audit>.
  
• For binary file targets, the mirror server service account must have appropriate permissions to the location where the audit trail is being written.
  
• For Windows event log targets, the security policy on the computer where the mirror server is located must allow for service account access to the security or application event log.