Reset the Directory Services Restore Mode (DSRM) Password
The DSRM password is the local-Administrator credential a domain controller uses when AD is offline - the only account that works during authoritative restores, ntds.dit corruption recovery, or last-DC rebuilds. Forgetting it means none of those recoveries work when you actually need them. This article walks the full reset + verify cycle on a real DC: rotate the password with ntdsutil (set dsrm password / reset password on server null - takes one minute, no reboot, no downtime), then prove the new credential works by rebooting into DSRM via F8 or 'bcdedit /set safeboot dsrepair', signing in as .\\administrator with the new password, observing the directory is offline (NTDS / Intersite Messaging / DFSR / KDC stopped, dsa.msc red-crossed), then rebooting back to normal with 'bcdedit /deletevalue safeboot'. Includes the multi-DC rotation pattern, the local-admin-vs-DSRM-vs-domain-admin distinction, and why storing the DSRM password in an AD-integrated vault is a circular dependency.