Demoting a Samba AD DC

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Introduction

In certain situations, it is necessary that you permanently remove a domain controller (DC) from Active Directory (AD). While for a regular domain member,you only delete the machine account entry, you have to demote a DC, to remove it from AD.

If a DC is not demoted correctly, your AD can get unstable. For example:

  • replication failures can occur.
  • the remaining DCs can slow down due to time outs and failed replication attempts.
  • log ins on domain members can fail or take longer.



Demoting an Online Domain Controller

If the domain controller (DC) to remove is still working correctly:

  • Log in locally to the DC to demote.
In case that the DC owns one or more FSMO roles, transfer them to a different DC. See Transferring an FSMO Role.
  • Optionally, display the objectGUID of the DC. For example, for the DC2 host:
# ldbsearch -H /usr/local/samba/private/sam.ldb '(invocationId=*)' --cross-ncs objectguid | grep -A1 DC2
dn: CN=NTDS Settings,CN=DC2,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samdom,DC=example,DC=com
objectGUID: c14a774f-9732-4ec2-b9fa-2156c95c4e48
If you want to verify that all DNS entries were deleted ater you demoted the DC, you need to know the host name, IP address, and the objectGUID of the DC.
  • Demote the DC:
# samba-tool domain demote -Uadministrator
Using DC1.samdom.example.com as partner server for the demotion
Password for [SAMDOM\administrator]:
Deactivating inbound replication
Asking partner server DC1.samdom.example.com to synchronize from us
Changing userControl and container
Removing Sysvol reference: CN=DC2,CN=Enterprise,CN=Microsoft System Volumes,CN=System,CN=Configuration,DC=samdom,DC=example,DC=com
Removing Sysvol reference: CN=DC2,CN=samdom.example.com,CN=Microsoft System Volumes,CN=System,CN=Configuration,DC=samdom,DC=example,DC=com
Removing Sysvol reference: CN=DC2,CN=Domain System Volumes (SYSVOL share),CN=File Replication Service,CN=System,DC=samdom,DC=example,DC=com
Removing Sysvol reference: CN=DC2,CN=Topology,CN=Domain System Volume,CN=DFSR-GlobalSettings,CN=System,DC=samdom,DC=example,DC=com
Demote successful
  • Stop the samba service.
  • If this DC ran a DNS service for the Active Directory (AD) zones:
  • stop the DNS service, if you used the BIND9_DLZ DNS back end.
  • verify that domain members and DCs do no longer use this host to resolve the AD DNS zones.



Demoting an Offline Domain Controller

In certain situations, such as hardware failures, it is necessary to remove a domain controller (DC) from the domain, that is no longer accessible. In this case, demote the DC using a remaining working Samba DC.

To remotely demote an offline DC:

  • Log in to a working Samba DC in the Active Directory (AD) forest.
  • Verify that Samba 4.4 or later is installed:
# samba --version
You cannot demote an offline remote DC from a DC that runs Samba 4.4 or earlier. Update to Samba 4.4.0 or later before you continue. For details, see Updating Samba.
  • In case that the DC to demote owns one or more FSMO roles, seize them to the local DC. See Seizing an FSMO Role.
  • Verify that the DC to demote is turned off.
  • Optionally, display the objectGUID of the DC. For example, for the DC2 host:
# ldbsearch -H /usr/local/samba/private/sam.ldb '(invocationId=*)' --cross-ncs objectguid | grep -A1 DC2
dn: CN=NTDS Settings,CN=DC2,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samdom,DC=example,DC=com
objectGUID: c14a774f-9732-4ec2-b9fa-2156c95c4e48
If you want to verify that all DNS entries were deleted ater you demoted the DC, you need to know the host name, IP address, and the objectGUID of the DC.
  • Demote the remote DC. For example, to demote DC2:
# samba-tool domain demote --remove-other-dead-server=DC2
Removing nTDSConnection: CN=04baf417-eb41-4f31-a5f1-c739f0e92b1b,CN=NTDS Settings,CN=DC1,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samdom,DC=example,DC=com
Removing nTDSDSA: CN=NTDS Settings,CN=DC2,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samdom,DC=example,DC=com (and any children)
Removing RID Set: CN=RID Set,CN=DC2,OU=Domain Controllers,DC=samdom,DC=example,DC=com
Removing computer account: CN=DC2,OU=Domain Controllers,DC=samdom,DC=example,DC=com (and any child objects)
Removing Samba-specific DNS service account: CN=dns-DC2,CN=Users,DC=samdom,DC=example,DC=com
updating samdom.example.com keeping 3 values, removing 1 values
updating DC=_kerberos._tcp.Default-First-Site-Name._sites,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp.Default-First-Site-Name._sites,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_gc._tcp.Default-First-Site-Name._sites,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_kerberos._tcp,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_kerberos._udp,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_kpasswd._tcp,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_kpasswd._udp,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_gc._tcp,DC=samdom.example.com,CN=MicrosoftDNS,DC=DomainDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp.4d5258b9-0cd7-4d78-bdd7-99ebe6b19751.domains,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_kerberos._tcp.Default-First-Site-Name._sites.dc,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp.Default-First-Site-Name._sites.dc,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp.Default-First-Site-Name._sites.gc,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=c14a774f-9732-4ec2-b9fa-2156c95c4e48,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 0 values, removing 1 values
updating DC=_kerberos._tcp.dc,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp.dc,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
updating DC=_ldap._tcp.gc,DC=_msdcs.samdom.example.com,CN=MicrosoftDNS,DC=ForestDnsZones,DC=samdom,DC=example,DC=com keeping 1 values, removing 1 values
Removing Sysvol reference: CN=DC2,CN=Enterprise,CN=Microsoft System Volumes,CN=System,CN=Configuration,DC=samdom,DC=example,DC=com
Removing Sysvol reference: CN=DC2,CN=samdom.example.com,CN=Microsoft System Volumes,CN=System,CN=Configuration,DC=samdom,DC=example,DC=com
Removing Sysvol reference: CN=DC2,CN=Domain System Volumes (SYSVOL share),CN=File Replication Service,CN=System,DC=samdom,DC=example,DC=com
Removing Sysvol reference: CN=DC2,CN=Topology,CN=Domain System Volume,CN=DFSR-GlobalSettings,CN=System,DC=samdom,DC=example,DC=com
  • In case that the demoted DC ran a DNS service for the Active Directory (AD) zones, verify that domain members and DCs do no longer use this host to resolve the AD DNS zones.

Verifying the Demotion

To manually verify that the domain controller (DC) was successfully demoted:

  • Log in to a Windows domain member using an account that is member of the Domain Admins group, such as the AD domain Administrator account.
  • Install the Remote Server Administration Tools (RSAT). For details, see Installing RSAT.
  • Open the Active Directory Users and Computers application.
  • Navigate to the Domain Controllers entry and verify that the demoted DC was removed. For example:
ADUC Domain Controllers.png
  • If the entry is still listed, you can manually remove it:
  • Right-click to the DC entry and select Delete
  • Click Yes to confirm.
  • Select Delete this Domain Controller anyway. It is permanently offline and can no longer be removed using the removal wizard. and click OK.
  • If the DC is a global catalog server, click Yes to confirm.
  • Open the Active Directory Sites and Services application and verify that the demoted DC is no longer listed in any Active Directory (AD) site entry. For example:
ADSS Domain Controllers.png
  • If the entry is still listed, you can manually remove it:
  • Right-click to the DC entry and select Delete
  • Click Yes to confirm.
  • Open the DNS application and verify that the DC's host name, IP address, and objectGUID is no longer used in any DNS entry in any AD DNS zone. For example:
DNS Domain Controllers.png
  • If entries are still listed, you can manually remove them:
  • Right-click to the entry and select Delete
  • Click Yes to confirm.