Special Operating System Users and Groups 
To protect database resources from unauthorized access with operating system commands, the database system uses special operating system users and groups. Only these operating system users and members of these operating system groups can access database resources using operating system commands.
Caution
During installation, the installation program assigns the correct permissions to all your database directories and database files. Do not change the permissions of any database directories or files later, because this might render your database software installation unusable.
Microsoft Windows
On Microsoft Windows, the database system uses the SDB Operators special operating system user group.
It is available as of SAP MaxDB version 7.7.
More information: Special Operating System User Group on Microsoft
Unix and Linux
On Unix and Linux, the database systems uses the special operating system user <sdb_user> and the special operating system groups <sdba_group> and support group.
They are available as of SAP MaxDB version 7.5.
More information: Special Operating System Users and Groups on Unix and Linux
More Information
SAP MaxDB Security Guide, Data Storage Security