Directory Services Restore Mode (DSRM) is a safe mode boot option for Windows Server domain controllers. DSRM allows an administrator to repair or recover to repair or restore an Active Directory database.
When Active Directory is installed, the install wizard prompts the administrator to choose a DSRM password. This password provides the administrator with a back door to the database in case something goes wrong later on, but it does not provide access to the domain or to any services. In the event a DSRM password is forgotten, it can be changed by using the command-line tool NTDSUtil.