OS user. Creates a server instance and is the only user who has the right to run operating system commands on a server instance by using the dsadm command. DSCC might request the OS user password in some cases. This user must have a password and must be able to create directory server instances.
Directory Administrator. Administers a Directory Server. This user has the same rights as the Directory Manager but are subject to access controls, password policies, and authentication requirements. You can create as many Directory Administrators as you need.
Directory Service Manager. Manages server configuration and data on multiple machines through DSCC. This user has the same rights as the Directory Manager for each of the servers registered in DSCC and is a member of the Directory Administrators Group.