005/006: mount /dev/sdb at /var/lib/postgresql + install PostgreSQL 17 on it

migrations/006-install-postgres.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# 006-install-postgres - Install PostgreSQL (Debian 13 -> PG 17).
+# Must run after 005: with /var/lib/postgresql already being the dedicated
+# disk, the Debian installer creates the cluster directly on it - no
+# data_directory changes needed.
+# up:   apt install postgresql + contrib, cluster started/enabled
+# down: stop + purge packages and /etc/postgresql; data on disk is kept
+set -euo pipefail
+
+export DEBIAN_FRONTEND=noninteractive
+PGROOT=/var/lib/postgresql
+
+case "${1:-}" in
+  up)
+    if command -v pg_lsclusters >/dev/null 2>&1 && pg_lsclusters --no-header | grep -q .; then
+      echo "    postgres cluster already present - skipping"
+      exit 0
+    fi
+    apt-get update -qq
+    apt-get install -y postgresql postgresql-contrib >/dev/null
+    chown postgres:postgres "$PGROOT"
+    systemctl enable --now postgresql >/dev/null
+    pg_isready -q
+    pg_lsclusters --no-header | while read -r _ _ _ _ _ datadir _; do
+      if findmnt -rn "$datadir" >/dev/null; then
+        echo "    cluster data on dedicated disk: $datadir"
+      else
+        echo "    WARNING: $datadir is NOT on the dedicated disk" >&2
+      fi
+    done
+    pg_lsclusters --no-header
+    ;;
+  down)
+    { pg_lsclusters --no-header 2>/dev/null || true; } | while read -r ver name _; do
+      pg_ctlcluster "$ver" "$name" stop 2>/dev/null || true
+    done
+    apt-get purge -y 'postgresql*' >/dev/null
+    apt-get autoremove --purge -y >/dev/null
+    rm -rf /etc/postgresql
+    echo "    postgres stopped + packages purged (data kept under $PGROOT)"
+    ;;
+esac