This page describes the plan to fix Active Directory at UCC, potentially used in place of the previous AD from 2019 onwards.

Note that this document and the system it describes are in an early development stage.

> In a virtually perfect world, our servers will be named after what they do and not after species of fish.

For testing, a subdomain for the "Virtual" AD will be configured as ad.v.ucc.asn.au with NETBIOS domain name VUCC, on a separate virtual network using a virtualised Proxmox VE instance (yes, running VMs inside of VMs). The primary DNS server for domain is vucc0.v.ucc.asn.au, which is also the (virtual) Proxmox VE host. The "primary" DC for domain will also be dc0.v.ucc.asn.au, and a second DC will be dc1.v.ucc.asn.au. Note that whilst RODCs can be configured using Samba, replication makes things just so much cooler (and more prone to inexplicable breakage) so we might be stuck with that for the time being.

v.ucc.asn.au is delegated using separate zones in Mooneye's /etc/bind/named.conf.local.

• zone "v.ucc.asn.au" {
          type forward;
          forward only;
          forwarders {
                  130.95.13.35; // vucc0 (proxmox VM on maltair, running dnsmasq)
          };
  };

dnsmasq on the (virtualised) Proxmox VM host vucc0.ucc.asn.au then delegates the ad.v.ucc.asn.au domain to the domain controller(s).

Setup Process

Domain Controllers

Clean Installation of samba & dependencies

The domain controller dc0.v.ucc.asn.au is based off a clone of samurai, cleaned up and configured using the steps below.

A fresh domain controller can probably be set up using the same steps; Note: These instructions are valid for Samba 4.7 and 4.8.5, older versions of Samba may be missing important configuration options and newer ones may behave slightly differently.

• Configure name resolution

  • Edit /etc/hosts

    127.0.0.1       localhost
    192.168.9.2     dc0.v.ucc.asn.au        dc0
    192.168.9.3     dc1.v.ucc.asn.au        dc1

  • Edit /etc/resolv.conf

    search ad.v.ucc.asn.au
    search v.ucc.asn.au
    search ucc.asn.au
    # This is configured to forward ad.* queries back to us and also deals with other DNS magic, so use it instead of ourselves as primary nameserver
    nameserver 192.168.9.35

• Purge existing configs and packages:

  apt-get purge samba* libpam-sss libnss-sss libgpgme11 krb5-* sssd-* libsss-* winbind
  rm -rvf /etc/samba /etc/krb5.conf /etc/krb5.keytab /var/run/samba/ /var/lib/samba/ /var/cache/samba/ /var/lib/sss

• Configure the apt repositories and preferences

  • Edit /etc/apt/preferences.d/80-ucc-samba, add the following:

    Package: *
    Pin: release a=stable
    Pin-Priority: 900
    
    Package: *
    Pin: release a=stable-backports
    Pin-Priority: 800
    
    Package: *
    Pin: release a=testing
    Pin-Priority: 99
    
    Package: *
    Pin: release a=unstable
    Pin-Priority: 98

  • Edit /etc/apt/sources.list.d/debian-unstable.list:

    # Testing repository - main, contrib and non-free branches
    deb http://mirror.waia.asn.au/debian testing main non-free contrib
    deb-src http://mirror.waia.asn.au/debian testing main non-free contrib
    
    # Testing security updates repository
    deb http://security.debian.org/ testing/updates main contrib non-free
    deb-src http://security.debian.org/ testing/updates main contrib non-free
    
    # Unstable repo main, contrib and non-free branches, no security updates here
    deb http://mirror.waia.asn.au/debian unstable main non-free contrib
    deb-src http://mirror.waia.asn.au/debian unstable main non-free contrib

• Install packages:

  apt-get update && apt-get -y upgrade
  apt-get -t testing install samba sssd-ad sssd-tools sssd-krb5 krb5-user libpam-krb5 libpam-sss libnss-sss libgpgme11 smbclient winbind
  apt-get install net-tools vim less molly-guard chrony rsync csync2 nfs-common finger sudo zsh git dnsutils mlocate

The rest of these instructions are based off the official Samba AD setup guide.

• Disable the systemd units for the non-DC setup & default configuration:

  systemctl stop smbd
  systemctl stop nmbd
  systemctl stop winbind
  systemctl disable smbd
  systemctl disable nmbd
  systemctl disable winbind

• Remove all Samba database and config files, such as *.tdb and *.ldb files, so we can start with a clean installation.

  rm -fv /etc/samba/smb.conf /etc/krb5.conf /etc/krb5.keytab
  find /var/run/samba/ /var/lib/samba/ /var/cache/samba/ | grep -e tdb -e ldb | xargs rm -fv

Provisioning a new AD Domain

Note: Don't do this unless you want to set up a fresh domain, in which case you will need to change all the settings below to appropriate values.

• Provision the new domain:

  samba-tool domain provision --use-rfc2307 --realm=ad.v.ucc.asn.au --domain=VUCC --server-role=dc --dns-backend=SAMBA_INTERNAL --adminpass=$PASSWORD

• Copy /var/lib/samba/private/krb5.conf to /etc/krb5.conf:

  cp /var/lib/samba/private/krb5.conf /etc/krb5.conf

  • Make sure /etc/krb5.conf looks something like this, add lines where necessary.

    [libdefaults]
            default_realm = AD.V.UCC.ASN.AU
            dns_lookup_realm = false
            dns_lookup_kdc = true
            rdns = false
            forwardable = yes

• Export the domain's keytab

  samba-tool domain exportkeytab /etc/krb5.keytab

• Edit /etc/nsswitch.conf

  # /etc/nsswitch.conf
  # See http://wiki.ucc.asn.au/ActiveDirectoryNew
  
  passwd:         files sss
  group:          files sss
  shadow:         files
  gshadow:        files
  
  hosts:          files dns
  networks:       files
  
  protocols:      db files
  services:       db files sss
  ethers:         db files
  rpc:            db files
  
  netgroup:       nis sss
  sudoers:        files

• and /etc/sssd/sssd.conf

  [sssd]
  config_file_version = 2
  domains = ad.v.ucc.asn.au
  services = nss, pam, pac
  
  [domain/AD.V.UCC.ASN.AU]
  enumerate = true
  id_provider = ad
  auth_provider = ad
  chpass_provider = ad
  access_provider = ad
  ldap_id_mapping = false

• fix sssd.conf permissions

  chmod 600 /etc/sssd/sssd.conf

• enable sssd auth in pam via pam-auth-update

• Start the samba service:

  systemctl unmask samba-ad-dc
  systemctl enable samba-ad-dc
  systemctl restart samba-ad-dc
  systemctl enable sssd
  systemctl restart sssd

• DO NOT use winbind on a domain controller, it sucks for multiple reasons.

Joining a new DC to an existing AD domain

• Copy /etc/sssd/sssd.conf, /etc/krb5.conf, /etc/nsswitch.conf from an existing domain controller.

• verify kerberos with: kinit <username>

• join the domain with: samba-tool domain join ad.v.ucc.asn.au DC -U"VUCC\Administrator" --dns-backend=SAMBA_INTERNAL --option='idmap_ldb:use rfc2307 = yes'

  • You may see an error saying something about DNS not being configured, you can probably ignore it.

• replicate the SYSVOL directory to the new DC, then fix the permissions with: samba-tool ntacl sysvolreset

• start the samba service, the service may have a different name depending on the samba version used.

• samba-tool domain exportkeytab /etc/krb5.keytab
  chmod 600 /etc/sssd/sssd.conf
  systemctl unmask samba-ad-dc
  systemctl enable samba-ad-dc
  systemctl restart samba-ad-dc
  systemctl enable sssd
  systemctl restart sssd

• enable sssd auth in pam via pam-auth-update

Sysvol replication

Samba doesn't support sysvol replication and probably never will, but they have some (old) suggested workarounds. At the most basic level, the directory /var/lib/samba/sysvol must be synchronised between DCs to keep things working smoothly. Unfortunately the filesystem needs to support xattr and POSIX ACLs so using a simple NFS share isn't possible, and rsync is painful when it comes to two-way synchronisation.

Fortunately csync2 does exactly what we want (minus ACLs/xattr, but those can be fixed using samba-tool ntacl sysvolreset). Here's how you can set it up.

• put the following into /etc/csync2.cfg (and update with the correct domain controller hostnames): see the documentation

  #### csync2 configuration
  # disable 
  nossl dc[01] dc[01];
  group vucc-domain-controllers
  {
          host dc0 dc1;
          key /etc/csync2.key-vucc;
          include /var/lib/samba/sysvol;
  
          # restart samba-ad-dc if changes to the configuration file /etc/samba/smb.conf are synced
          action
          {
                  pattern /etc/samba/smb.conf;
                  exec "/bin/systemctl samba-ad-dc reload";
                  do-local;
          }
  
          # fix xattrs on files when they are updated
          action
          {
                  pattern /var/lib/samba/sysvol;
                  exec "/usr/bin/samba-tool ntacl sysvolreset";
                  do-local;
          }
  
          # Store backups (with logical names) somewhere reasonable
          backup-directory /var/lib/samba/sysvol-backups;
          backup-generations 3;
  
          # automatically resolve conflicts by overwriting older files with newer ones
          auto younger;
  }

• edit the crontab on one node:

  dc0# crontab -e
  # sync every minute
  * * * * * /usr/sbin/csync2 -x

• csync2 is run as an inetd service, so you can check that the following line is present in /etc/inetd.conf on all servers in the cluster

  csync2          stream  tcp     nowait  root    /usr/sbin/csync2        csync2 -i -l

• generate a csync2 pre-shared key (PSK) and copy it and /etc/csync2.cfg to all the DCs in the cluster:

  csync2 -k /etc/csync2.key-vucc
  scp /etc/csync2.key-vucc /etc/csync2.cfg dc1:/etc dc2:/etc dc3:/etc ...

• make sure the directory /var/lib/samba/sysvol-backups exists on all nodes of the cluster

• Done! It should work now.

To manually replicate the sysvol directories between DCs:

dc0# scp -ar /var/lib/samba/sysvol dc1:/var/lib/samba/sysvol
dc1# samba-tool ntacl sysvolreset

Windows systems

Just join them to the domain. It Just Works (TM) - thanks Microsoft / Red Hat / IBM?!!

Linux systems

AD wasn't designed for Linux, and since most of our machines run Linux we have made things difficult for ourselves.

This is copied from ActiveDirectory and has not been tested yet, feel free to fix that.

Automatically using realmd

Thanks to realmd, joining machines to the domain is extremely simple.

• Install packages: apt install realmd

• Test to make sure you can connect to the domain: realm discover ad.ucc.gu.uwa.edu.au

• Join to the domain using realm join -v -U <user> ad.ucc.gu.uwa.edu.au

  • realmd defaults to using sssd, which is fine
  • It installs any necessary packages.
  • IT JUST WORKS!!

    • Except for one thing: comment the line use_fully_qualified_names = True in /etc/sssd/sssd.conf (prefix with a #)

    • Then it works!
• Done.

Manual Method

Based on the instructions from https://wiki.samba.org/index.php/Setting_up_Samba_as_a_Domain_Member and https://wiki.samba.org/index.php/Authenticating_Domain_Users_Using_PAM Before configuring the domain ensure the following:

• Install the required packages: apt install samba winbind krb5-user libpam-krb5 libpam-winbind libnss-winbind

• Ensure the system is configured according to the SOE.

• edit /etc/krb5.conf to point to the new domain:

•    [libdefaults]
          default_realm = ad.ucc.gu.uwa.edu.au
          dns_lookup_realm = false
          dns_lookup_kdc = true

• Make the following /etc/samba/smb.conf:

• [global]
  # Configure the domain infomation
          security = ads
          realm = ad.ucc.gu.uwa.edu.au
          workgroup = UCCDOMAYNE
  
  # use winbind to map users and groups
          winbind enum users = yes
          winbind enum groups = yes
          winbind use default domain = yes
          kerberos method = secrets and keytab
  
  #Config gid/sid mapping based on AD attributes
          winbind nss info = rfc2307
  
          idmap config * : backend = tdb
          idmap config * : range = 13000-17999
          
          #idmap config for UCCDOMAYNE
          idmap config UCCDOMAYNE:backend = ad
          idmap config UCCDOMAYNE:schema_mode = rfc2307
          idmap config UCCDOMAYNE:range = 1-999999
          idmap config UCCDOMAYNE:unix_nss_info = yes
          idmap config UCCDOMAYNE:unix_primary_group = yes

• Join the machine to the domain with: net ads join -U <username>.

• configure pam using pam-auth-update and enable Winbind NT/AD authentication.

• configure nsswitch.conf

• # /etc/nsswitch.conf
  #
  # Example configuration of GNU Name Service Switch functionality.
  # If you have the `glibc-doc-reference' and `info' packages installed, try:
  # `info libc "Name Service Switch"' for information about this file.
  
  passwd:         compat winbind
  group:          compat winbind
  shadow:         files
  gshadow:        files
  
  hosts:          files mdns4_minimal [NOTFOUND=return] dns
  networks:       files
  
  protocols:      db files
  services:       db files 
  ethers:         db files
  rpc:            db files
  
  netgroup:       nis 

• start the services:

• winbindd
  nmbd
  smbd

• Make sure the computer can fetch the domain users and groups with:

• wbinfo -g` and `wbinfo -u`

Diagnostics

Sometimes group memberships don't seem to be updated, this can often be fixed by clearing the cache:

• sss_cache -E if using sssd

• net cache flush if using winbind

• Or if the above fails to have an effect, try rejoining to the domain using the instructions below.