Initial commit: MAAS-deployable Samba Active Directory domain controller
Builds a Debian image that MAAS deploys to bare metal as an Active Directory
domain controller, with first-boot automation that either creates a domain or
joins an existing one without anyone logging in. To a Windows client the result
is an AD domain: same Kerberos, same LDAP, same Group Policy, same domain join.
The request was for "primary and backup domain controllers", which is NT 4
terminology. Active Directory has no such split — every DC holds a writable copy
and any of them can service a logon. What lives on one DC at a time are the five
FSMO roles, one confusingly named "PDC Emulator". The image therefore offers
provision (create the domain) and join (add another equal DC), which is the
distinction that actually exists.
Contents:
* customize-samba-ad.sh, run inside the packer-maas build VM: installs samba,
winbind, Kerberos, chrony and rsync, swaps the cloud kernel for the generic
one, and deletes every trace of a domain so one image can produce many DCs
* adc-maas-init, a first-boot state machine covering /etc/hosts, node-unique
identifiers, time, the resolver, provisioning or joining, the service
switchover and a self-test that proves Kerberos issues a ticket
* adc-sysvol-sync, a systemd timer implementing the SYSVOL workaround
* a MAAS curtin preseed, cloud-init examples, and the release pipeline
Two findings shaped the design.
Debian builds Samba against its bundled Heimdal rather than system MIT Kerberos
— samba-ad-dc does not depend on krb5-kdc — so the AD DC role is in Samba's
supported configuration, not the experimental MIT one. The build asserts this
and fails if it ever changes.
Samba implements neither DFS-R nor FRS, so SYSVOL — where Group Policy lives —
does not replicate between DCs. Left alone, a policy created on one DC never
reaches the others and clients behave differently depending on which DC answered
them, with nothing reporting an error. adc-sysvol-sync applies the Samba wiki's
rsync workaround: sync idmap.ldb once so SID-to-uid mappings agree, rsync the
tree, then samba-tool ntacl sysvolreset because rsync carries POSIX bits while
the Windows ACLs live in AD. Without an SSH key to the source DC it exits with
an explanation rather than letting Group Policy diverge quietly.
Also carried over from maas-proxmox, where they were verified on real hardware:
the curtin-hooks that skip the kernel install and pin interface names by MAC,
Type=simple on the first-boot unit to avoid the systemd ordering cycle, and
shipping networking.service disabled so MAAS owns the network on first boot.
Specific to this image, the Debian cloud kernel is replaced with the generic one
— a bare-metal node booted with the cloud kernel can come up with no disk.
Nothing here has been built or deployed. The README says so at the top and in a
Verified status section that separates what was checked from what was not.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
247
scripts/customize-samba-ad.sh.in
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247
scripts/customize-samba-ad.sh.in
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#!/bin/bash
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# Copyright (C) 2026 Ilker Manap
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# SPDX-License-Identifier: AGPL-3.0-or-later
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#
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# customize-samba-ad.sh - runs inside the packer-maas build VM.
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#
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# Installs everything a Samba Active Directory domain controller needs on top of
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# the Debian cloud image, then removes every trace of domain state so the image
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# is generic. The domain itself is created or joined on first boot by
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# adc-maas-init, driven by the cloud-init user-data MAAS supplies.
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#
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# This file is a template; the Makefile fills in the @@...@@ placeholders and
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# appends the overlay archive, base64 encoded, after the marker at the end.
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#
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# Packer runs this with expect_disconnect = true.
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set -euo pipefail
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DEBIAN_SUITE="@@DEBIAN_SERIES@@"
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AD_EXTRA_PACKAGES="@@AD_EXTRA_PACKAGES@@"
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PACKER_MAAS_REF="@@PM_REF@@"
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export DEBIAN_FRONTEND=noninteractive
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APT="apt-get -y -o Dpkg::Options::=--force-confold -o Dpkg::Options::=--force-confdef"
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use_eatmydata() {
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command -v eatmydata >/dev/null 2>&1 || return 0
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APT="eatmydata ${APT}"
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log "eatmydata enabled (dpkg fsync calls disabled)"
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}
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log() { echo "==> [ad-image] $*"; }
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# ---------------------------------------------------------------------------
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# 1. Unpack the overlay embedded at the end of this script
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# ---------------------------------------------------------------------------
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log "unpacking the overlay"
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sed -n '/^__ADC_MAAS_OVERLAY__$/,$p' "$0" | tail -n +2 | base64 -d \
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| tar xzf - -C / --no-same-owner --no-same-permissions
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chown -R root:root /usr/local/sbin/adc-maas-init /usr/local/sbin/adc-sysvol-sync \
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/etc/adc-maas /etc/systemd/system/adc-maas-init.service \
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/etc/systemd/system/adc-sysvol-sync.service \
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/etc/systemd/system/adc-sysvol-sync.timer /curtin
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chmod 0755 /usr/local/sbin/adc-maas-init /usr/local/sbin/adc-sysvol-sync
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chmod 0755 /curtin /curtin/curtin-hooks
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chmod 0644 /etc/adc-maas/adc-maas.conf
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mkdir -p /etc/adc-maas/conf.d /var/lib/adc-maas
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# ---------------------------------------------------------------------------
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# 2. The build hostname has to resolve while packages configure themselves
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# ---------------------------------------------------------------------------
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BUILD_HOST="$(hostname -s)"
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BUILD_IP="$(ip -4 -o route get 1.1.1.1 2>/dev/null | awk '{for(i=1;i<=NF;i++) if($i=="src") print $(i+1)}' | head -1)"
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: "${BUILD_IP:=127.0.1.1}"
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log "build hostname=${BUILD_HOST} ip=${BUILD_IP}"
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cp -a /etc/hosts /etc/hosts.ad-image-backup
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sed -i "/[[:space:]]${BUILD_HOST}\([[:space:]]\|$\)/d" /etc/hosts
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echo "${BUILD_IP} ${BUILD_HOST}.local ${BUILD_HOST}" >> /etc/hosts
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hostname -f || echo "WARNING: hostname -f does not resolve" >&2
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# ---------------------------------------------------------------------------
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# 3. Keep the MAAS-compatible cloud-init packer-maas installed
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# ---------------------------------------------------------------------------
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log "holding the cloud-init package"
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apt-mark hold cloud-init || true
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apt-get update
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$APT install eatmydata || true
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use_eatmydata
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log "full-upgrade"
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$APT full-upgrade
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# ---------------------------------------------------------------------------
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# 4. Answer the questions the packages would otherwise ask
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# ---------------------------------------------------------------------------
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# samba-common would offer to take WINS settings from DHCP, which is wrong for
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# a DC. krb5-config wants a realm; the real one is not known until first boot,
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# and adc-maas-init replaces /etc/krb5.conf with Samba's own anyway.
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debconf-set-selections <<EOF
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samba-common samba-common/dhcp boolean false
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samba-common samba-common/do_debconf boolean false
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krb5-config krb5-config/default_realm string EXAMPLE.LAN
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krb5-config krb5-config/add_servers_realm string EXAMPLE.LAN
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krb5-config krb5-config/read_conf boolean true
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EOF
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# ---------------------------------------------------------------------------
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# 5. Defer initramfs regeneration until the end
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# ---------------------------------------------------------------------------
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log "diverting update-initramfs for the duration of the install"
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dpkg-divert --local --rename --add /usr/sbin/update-initramfs >/dev/null
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ln -sf /bin/true /usr/sbin/update-initramfs
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# ---------------------------------------------------------------------------
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# 6. The domain controller itself
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#
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# What an Active Directory domain actually consists of, all of it served by the
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# single samba daemon unless noted:
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#
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# LDAP the directory: users, groups, computers, policy links
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# Kerberos the KDC that issues the tickets clients authenticate with
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# DNS AD is unusable without it — clients find DCs through SRV records
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# SMB the SYSVOL and NETLOGON shares, where Group Policy lives
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# NTP chrony; Kerberos rejects a clock skew over five minutes
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# ---------------------------------------------------------------------------
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log "installing the Samba AD domain controller"
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$APT install \
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samba samba-ad-dc samba-ad-provision samba-dsdb-modules \
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winbind libnss-winbind libpam-winbind \
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smbclient ldb-tools \
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krb5-user \
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chrony \
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rsync
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if [ -n "${AD_EXTRA_PACKAGES}" ]; then
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log "installing extra packages: ${AD_EXTRA_PACKAGES}"
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# shellcheck disable=SC2086
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$APT install ${AD_EXTRA_PACKAGES}
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fi
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log "installed versions:"
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dpkg-query -W -f='${Package} ${Version}\n' samba samba-ad-dc winbind krb5-user chrony || true
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# Confirm this Samba can actually be a DC. Debian builds Samba against its
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# bundled Heimdal; a build against system MIT Kerberos would make the AD DC role
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# experimental, and samba-ad-dc would then pull in krb5-kdc.
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if dpkg-query -W -f='${Depends}' samba-ad-dc 2>/dev/null | grep -q 'krb5-kdc'; then
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echo "ERROR: this samba-ad-dc depends on the MIT KDC; the AD DC role is" >&2
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echo " experimental in that configuration and is not used here." >&2
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exit 1
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fi
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log "samba-ad-dc uses the bundled Heimdal KDC (the supported configuration)"
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# ---------------------------------------------------------------------------
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# 6b. Swap the cloud kernel for the generic one
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#
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# The Debian cloud image ships linux-image-cloud-amd64, which is built for
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# virtual machines and leaves out most physical-hardware drivers. This image is
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# deployed to bare metal by MAAS, so it needs the generic kernel or the node may
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# come up with no disk or no network. curtin does not install a kernel here
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# (see /curtin/curtin-hooks), so whatever is in the image is what boots.
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# ---------------------------------------------------------------------------
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DEB_ARCH="$(dpkg --print-architecture)"
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log "installing the generic kernel (linux-image-${DEB_ARCH})"
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$APT install "linux-image-${DEB_ARCH}"
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CLOUD_KERNELS="$(dpkg-query -W -f='${Package}\n' 'linux-image-*cloud*' 2>/dev/null | grep -E '^linux-image' || true)"
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if [ -n "${CLOUD_KERNELS}" ]; then
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log "removing the cloud-only kernel: ${CLOUD_KERNELS}"
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# shellcheck disable=SC2086
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$APT purge ${CLOUD_KERNELS} || true
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fi
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$APT autoremove --purge || true
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log "restoring update-initramfs and running it once"
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rm -f /usr/sbin/update-initramfs
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dpkg-divert --local --rename --remove /usr/sbin/update-initramfs >/dev/null
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update-initramfs -u -k all
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update-grub
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# ---------------------------------------------------------------------------
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# 7. Remove every trace of a domain
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#
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# Installing the packages leaves a default smb.conf and can leave TDB state. If
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# any of it shipped in the image, every machine deployed from it would start
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# from the same half-configured directory, and `samba-tool domain provision`
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# would refuse to run at all.
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# ---------------------------------------------------------------------------
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log "clearing domain state so the image is generic"
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systemctl stop samba-ad-dc smbd nmbd winbind 2>/dev/null || true
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rm -f /etc/samba/smb.conf
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rm -rf /var/lib/samba/private/* /var/lib/samba/sysvol/*
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find /var/lib/samba -maxdepth 1 -name '*.tdb' -delete 2>/dev/null || true
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find /var/cache/samba -type f -delete 2>/dev/null || true
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rm -f /etc/krb5.keytab
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# The standalone file-server daemons conflict with the AD DC daemon. Mask them
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# now; adc-maas-init unmasks and starts samba-ad-dc once a domain exists.
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systemctl disable smbd nmbd winbind 2>/dev/null || true
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systemctl mask smbd nmbd winbind 2>/dev/null || true
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systemctl disable samba-ad-dc 2>/dev/null || true
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# Node-unique, must not be shared between machines built from this image.
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rm -f /etc/iscsi/initiatorname.iscsi
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rm -f /root/.ssh/known_hosts /etc/ssh/ssh_known_hosts
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# ---------------------------------------------------------------------------
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# 8. Leave the network to MAAS on the first boot
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#
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# ifupdown/ifupdown2 writes the build VM's interface name into
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# /etc/network/interfaces. On a deployed node MAAS configures the network
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# through netplan and systemd-networkd; if ifupdown also starts, it takes the
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# real interface down using that stale definition and the node loses its network
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# before any of our automation runs.
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# ---------------------------------------------------------------------------
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log "disabling networking.service (MAAS owns the network on first boot)"
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cat > /etc/network/interfaces <<'EOF'
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# Left deliberately minimal. The network on a deployed node is configured by
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# MAAS through netplan and systemd-networkd.
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auto lo
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iface lo inet loopback
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source /etc/network/interfaces.d/*
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EOF
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rm -f /etc/network/interfaces.d/* /etc/network/interfaces.new 2>/dev/null || true
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systemctl disable networking.service 2>/dev/null || true
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# ---------------------------------------------------------------------------
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# 9. First-boot service, persistent logs, image metadata
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# ---------------------------------------------------------------------------
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log "enabling adc-maas-init.service"
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systemctl daemon-reload
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systemctl enable adc-maas-init.service
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# The first boot can reboot once, and a volatile journal loses everything that
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# happened before it — including why a stage failed.
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log "enabling a persistent journal"
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mkdir -p /var/log/journal
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systemd-tmpfiles --create --prefix /var/log/journal 2>/dev/null || true
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log "writing /etc/adc-maas/image-info"
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{
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echo "build_date=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
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echo "debian_suite=${DEBIAN_SUITE}"
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echo "packer_maas_ref=${PACKER_MAAS_REF}"
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dpkg-query -W -f='${Package}=${Version}\n' samba samba-ad-dc winbind krb5-user 2>/dev/null
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echo "kernel=$(ls -1 /boot/vmlinuz-* 2>/dev/null | sed 's|.*/vmlinuz-||' | head -1)"
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} > /etc/adc-maas/image-info
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cat /etc/adc-maas/image-info
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# ---------------------------------------------------------------------------
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# 10. Clean up
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# ---------------------------------------------------------------------------
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log "cleaning up"
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mv /etc/hosts.ad-image-backup /etc/hosts
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$APT clean
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rm -rf /var/lib/apt/lists/*
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find /var/log/journal -mindepth 1 -delete 2>/dev/null || true
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rm -rf /var/log/*.gz /var/log/*.1
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: > /var/log/wtmp || true
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: > /var/log/btmp || true
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cloud-init clean --logs || true
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log "image ready: Samba AD DC on Debian ${DEBIAN_SUITE}"
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exit 0
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# Everything after this marker is the base64 overlay archive the Makefile appends.
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