diff --git a/CHANGELOG.md b/CHANGELOG.md
index 56d2198..4807e8b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Fixed
+- Installer VM compatibility: legacy BIOS VM boots now install with GRUB, UEFI VM installs avoid depending on NVRAM boot-entry writes, VM users get clearer disk/resource guidance, and the internet check falls back to HTTPS when ICMP is blocked.
 - **Manual Backup now matches the system role**: on the Desktop Only role the Hub's
   "What gets backed up" list no longer shows Node / Server + Desktop items
   (nix-bitcoin secrets, `/var/lib` system service data, and the database/blockchain
diff --git a/README.md b/README.md
index 2852ad3..87efb87 100644
--- a/README.md
+++ b/README.md
@@ -397,6 +397,26 @@ installer. Do not format the drive.
 If the normal operating system starts instead, restart and try the boot-menu
 key again.
 
+### Installing in a virtual machine (optional)
+
+Sovran_SystemsOS can be tested in VirtualBox, VMware, QEMU/KVM, Proxmox, and
+similar x86_64 virtual machines. Use production-like resources where possible:
+
+- Allocate **8 GB RAM or more** for Desktop Only. Node and Server + Desktop
+  should follow the normal 16 GB / 32 GB recommendations.
+- Create a **256 GB or larger virtual OS disk**. Thin-provisioned / dynamically
+  allocated disks are fine; they do not consume the full size immediately.
+- Use NAT or bridged networking with internet access before opening the
+  installer.
+- UEFI/EFI firmware is preferred. In UEFI VMs, the installer avoids depending
+  on VM NVRAM boot-entry writes. If a VM boots the ISO in legacy BIOS mode,
+  the installer automatically switches the installed system to GRUB.
+- For Node or Server + Desktop, attach a **second 2 TB virtual data disk**.
+  If you only attach one disk, choose **Desktop Only**.
+- Present the install target as a normal virtual disk such as VirtIO, SATA,
+  SCSI, or NVMe. USB-attached target disks are intentionally hidden by the
+  installer to avoid erasing the installer USB by mistake.
+
 ### 5. Install
 
 Follow the on-screen installer. Before confirming:
diff --git a/iso/installer.py b/iso/installer.py
index 98c5865..88d57ab 100644
--- a/iso/installer.py
+++ b/iso/installer.py
@@ -103,25 +103,81 @@ def human_size(nbytes):
     return f"{nbytes:.1f} PB"
 
 def check_internet():
-    """Return True if the machine can reach the internet."""
+    """Return True if the machine can reach the internet.
+
+    Some VM NAT setups and managed networks block ICMP even when HTTPS works,
+    so keep the existing ping checks but fall back to small HTTPS requests.
+    """
+    checks = [
+        ["ping", "-c", "1", "-W", "5", "nixos.org"],
+        ["curl", "--location", "--fail", "--silent", "--show-error", "--connect-timeout", "5", "--max-time", "10", "--output", "/dev/null", "https://cache.nixos.org/nix-cache-info"],
+        ["curl", "--location", "--fail", "--silent", "--show-error", "--connect-timeout", "5", "--max-time", "10", "--output", "/dev/null", "https://nixos.org/"],
+        ["ping", "-c", "1", "-W", "5", "1.1.1.1"],
+    ]
+
+    for cmd in checks:
+        try:
+            result = subprocess.run(cmd, capture_output=True, text=True)
+            if result.returncode == 0:
+                return True
+            log(f"Connectivity check failed ({' '.join(cmd)}): {result.stderr.strip() or result.stdout.strip()}")
+        except Exception as e:
+            log(f"Connectivity check failed ({' '.join(cmd)}): {e}")
+
+    return False
+
+def detect_virtualization():
+    """Return the VM technology name when running inside a VM, else None."""
     try:
         result = subprocess.run(
-            ["ping", "-c", "1", "-W", "5", "nixos.org"],
+            ["systemd-detect-virt", "--vm"],
             capture_output=True, text=True
         )
         if result.returncode == 0:
-            return True
+            name = result.stdout.strip()
+            if name == "none":
+                return None
+            return name or "virtual machine"
     except Exception:
         pass
-    # Fallback: try a second host in case DNS for nixos.org is down
-    try:
-        result = subprocess.run(
-            ["ping", "-c", "1", "-W", "5", "1.1.1.1"],
-            capture_output=True, text=True
-        )
-        return result.returncode == 0
-    except Exception:
-        return False
+
+    # Fallback for minimal environments where systemd-detect-virt is absent.
+    dmi_paths = [
+        "/sys/class/dmi/id/product_name",
+        "/sys/class/dmi/id/sys_vendor",
+        "/sys/class/dmi/id/board_vendor",
+    ]
+    markers = (
+        "kvm", "qemu", "virtualbox", "vmware", "hyper-v",
+        "bhyve", "parallels", "xen", "bochs", "virtual",
+    )
+    for dmi_path in dmi_paths:
+        try:
+            value = open(dmi_path, "r", encoding="utf-8", errors="ignore").read().strip()
+        except OSError:
+            continue
+        lowered = value.lower()
+        if any(marker in lowered for marker in markers):
+            return value or "virtual machine"
+
+    return None
+
+def detect_boot_mode():
+    """Return the firmware mode used to boot the installer ISO."""
+    return "uefi" if os.path.isdir("/sys/firmware/efi") else "bios"
+
+def boot_mode_label(mode):
+    if mode == "uefi":
+        return "UEFI (systemd-boot)"
+    return "Legacy BIOS (GRUB)"
+
+def nix_string(value):
+    """Quote a Python string for a simple Nix string literal."""
+    escaped = value.replace("\\", "\\\\")
+    escaped = escaped.replace('"', '\\"')
+    escaped = escaped.replace("\n", "\\n").replace("\r", "\\r").replace("\t", "\\t")
+    escaped = escaped.replace("${", "\\${")
+    return f'"{escaped}"'
 
 def symbolic_icon(name):
     """Create a crisp symbolic icon suitable for use as an ActionRow prefix."""
@@ -159,6 +215,10 @@ class InstallerWindow(Adw.ApplicationWindow):
         self.data_size = None
         self.data_drive_has_timechain = False
         self.free_password = None
+        self.virtualization = detect_virtualization()
+        self.boot_mode = detect_boot_mode()
+
+        log(f"Installer environment: boot_mode={self.boot_mode}, virtualization={self.virtualization or 'none'}")
 
         # Root navigation view
         self.nav = Adw.NavigationView()
@@ -343,7 +403,7 @@ class InstallerWindow(Adw.ApplicationWindow):
         if os.path.exists(LOGO):
             try:
                 img = Gtk.Image.new_from_file(LOGO)
-                img.set_pixel_size(480)
+                img.set_pixel_size(320 if self.virtualization else 480)
                 hero.append(img)
             except Exception:
                 pass
@@ -397,6 +457,42 @@ class InstallerWindow(Adw.ApplicationWindow):
         notice_frame.set_child(notice_box)
         outer.append(notice_frame)
 
+        if self.virtualization:
+            vm_frame = Gtk.Frame()
+            vm_frame.add_css_class("card")
+            vm_frame.set_margin_start(40)
+            vm_frame.set_margin_end(40)
+            vm_frame.set_margin_top(12)
+            vm_frame.set_margin_bottom(4)
+
+            vm_box = Gtk.Box(orientation=Gtk.Orientation.HORIZONTAL, spacing=12)
+            vm_box.set_margin_top(12)
+            vm_box.set_margin_bottom(12)
+            vm_box.set_margin_start(16)
+            vm_box.set_margin_end(16)
+
+            vm_icon = symbolic_icon("computer-symbolic")
+            vm_icon.set_valign(Gtk.Align.START)
+            vm_box.append(vm_icon)
+
+            vm_lbl = Gtk.Label()
+            vm_lbl.set_use_markup(True)
+            vm_lbl.set_wrap(True)
+            vm_lbl.set_xalign(0)
+            vm_lbl.set_halign(Gtk.Align.FILL)
+            vm_lbl.set_markup(
+                f"<span weight='bold'>Virtual machine detected: {GLib.markup_escape_text(self.virtualization)}</span>\n"
+                f"Boot mode: <span weight='bold'>{boot_mode_label(self.boot_mode)}</span>. "
+                "For the smoothest VM test, use 8+ GB RAM, NAT/bridged networking, "
+                "and a thin-provisioned virtual OS disk of at least 256 GB. "
+                "For Node or Server + Desktop, attach a second 2 TB virtual data disk; "
+                "otherwise choose Desktop Only."
+            )
+            vm_box.append(vm_lbl)
+
+            vm_frame.set_child(vm_box)
+            outer.append(vm_frame)
+
         # Role label
         role_lbl = Gtk.Label()
         role_lbl.set_markup("<span size='medium' weight='bold'>Choose your installation type:</span>")
@@ -448,7 +544,10 @@ class InstallerWindow(Adw.ApplicationWindow):
 
             available = has_second_drive or key not in NEEDS_DATA_DRIVE
             if not available:
-                card.set_subtitle(desc + "\n⚠ Requires a second internal drive (not detected)")
+                drive_hint = "⚠ Requires a second internal drive (not detected)"
+                if self.virtualization:
+                    drive_hint += " — in a VM, attach a second virtual disk or choose Desktop Only"
+                card.set_subtitle(desc + f"\n{drive_hint}")
                 card.set_sensitive(False)
             else:
                 card.set_subtitle(desc)
@@ -531,9 +630,10 @@ class InstallerWindow(Adw.ApplicationWindow):
         # ── OS Drive group ────────────────────────────────────────────
         os_group = Adw.PreferencesGroup()
         os_group.set_title("OS Drive  (NixOS Boot + Root)")
-        os_group.set_description(
-            "Choose the drive for the NixOS installation.  Minimum 256 GB required."
-        )
+        os_description = "Choose the drive for the NixOS installation.  Minimum 256 GB required."
+        if self.virtualization:
+            os_description += " In a VM, a thin-provisioned virtual disk is OK."
+        os_group.set_description(os_description)
         os_group.set_margin_top(24)
         os_group.set_margin_start(40)
         os_group.set_margin_end(40)
@@ -546,6 +646,8 @@ class InstallerWindow(Adw.ApplicationWindow):
             row.set_title(f"/dev/{name}")
             type_label = tran.upper() if tran else "Disk"
             meets = "✓ Meets 256 GB minimum" if size >= BYTES_256GB else "✗ Below 256 GB minimum"
+            if self.virtualization and size < BYTES_256GB:
+                meets += " (expand the virtual disk)"
             row.set_subtitle(f"{human_size(size)}  ·  {type_label}  —  {meets}")
             row.add_prefix(symbolic_icon("drive-harddisk-symbolic"))
 
@@ -570,11 +672,14 @@ class InstallerWindow(Adw.ApplicationWindow):
         if self.role != "Desktop Only":
             data_group = Adw.PreferencesGroup()
             data_group.set_title("Bitcoin Timechain & Backups Drive")
-            data_group.set_description(
+            data_description = (
                 "💡 Tip: Always assign your LARGEST drive here.  "
                 "The full Bitcoin timechain is over 700 GB and grows continuously — "
                 "a 2 TB or larger drive is required."
             )
+            if self.virtualization:
+                data_description += " In a VM, attach a second 2 TB thin-provisioned virtual disk for Node or Server + Desktop."
+            data_group.set_description(data_description)
             data_group.set_margin_top(20)
             data_group.set_margin_start(40)
             data_group.set_margin_end(40)
@@ -599,6 +704,8 @@ class InstallerWindow(Adw.ApplicationWindow):
                 row.set_title(f"/dev/{name}")
                 type_label = tran.upper() if tran else "Disk"
                 meets = "✓ Meets 2 TB minimum" if size >= BYTES_2TB else "✗ Below 2 TB minimum"
+                if self.virtualization and size < BYTES_2TB:
+                    meets += " (use a 2 TB thin-provisioned virtual disk)"
                 row.set_subtitle(f"{human_size(size)}  ·  {type_label}  —  {meets}")
                 row.add_prefix(symbolic_icon("drive-harddisk-symbolic"))
 
@@ -655,10 +762,16 @@ class InstallerWindow(Adw.ApplicationWindow):
             dlg = Adw.MessageDialog()
             dlg.set_transient_for(self)
             dlg.set_heading("OS Drive Too Small")
-            dlg.set_body(
+            body = (
                 f"The selected OS drive (/dev/{os_name}, {human_size(os_size)}) "
                 f"does not meet the 256 GB minimum.  Please choose a larger drive."
             )
+            if self.virtualization:
+                body += (
+                    "\n\nVM tip: expand the virtual OS disk to at least 256 GB. "
+                    "Thin-provisioned disks usually do not consume the full size immediately."
+                )
+            dlg.set_body(body)
             dlg.add_response("ok", "OK")
             dlg.present()
             return
@@ -668,12 +781,18 @@ class InstallerWindow(Adw.ApplicationWindow):
             dlg = Adw.MessageDialog()
             dlg.set_transient_for(self)
             dlg.set_heading("Bitcoin Drive Too Small")
-            dlg.set_body(
+            body = (
                 f"The selected Bitcoin Timechain & Backups drive "
                 f"(/dev/{data_name}, {human_size(data_size)}) "
                 f"does not meet the 2 TB minimum.  "
                 f"Please choose a larger drive or select \"None\"."
             )
+            if self.virtualization:
+                body += (
+                    "\n\nVM tip: attach a second 2 TB thin-provisioned virtual disk "
+                    "for Node or Server + Desktop test installs."
+                )
+            dlg.set_body(body)
             dlg.add_response("ok", "OK")
             dlg.present()
             return
@@ -829,7 +948,12 @@ class InstallerWindow(Adw.ApplicationWindow):
     # ── Worker: partition ─────────────────────────────────────────────────
 
     def partition_path(self, dev_path, num):
-        return f"{dev_path}p{num}" if "nvme" in dev_path else f"{dev_path}{num}"
+        base = os.path.basename(dev_path)
+        needs_p = (
+            base.startswith(("nvme", "mmcblk", "loop", "md")) or
+            (base[-1:].isdigit())
+        )
+        return f"{dev_path}p{num}" if needs_p else f"{dev_path}{num}"
 
     def detect_existing_timechain_data(self, data_path, buf=None):
         data_p1 = self.partition_path(data_path, 1)
@@ -900,12 +1024,19 @@ class InstallerWindow(Adw.ApplicationWindow):
 
         time.sleep(2)
 
-        # ── Partition boot disk: 512M ESP + rest as root ──
-        GLib.idle_add(append_text, buf, "\n=== Partitioning boot disk ===\n")
-        run_stream(["sudo", "sgdisk",
-                    "-n", "1:1M:+512M", "-t", "1:EF00", "-c", "1:ESP",
-                    "-n", "2:0:0",      "-t", "2:8300", "-c", "2:root",
-                    boot_path], buf)
+        # ── Partition boot disk ──
+        if self.boot_mode == "uefi":
+            GLib.idle_add(append_text, buf, "\n=== Partitioning boot disk (UEFI) ===\n")
+            run_stream(["sudo", "sgdisk",
+                        "-n", "1:1M:+512M", "-t", "1:EF00", "-c", "1:ESP",
+                        "-n", "2:0:0",      "-t", "2:8300", "-c", "2:root",
+                        boot_path], buf)
+        else:
+            GLib.idle_add(append_text, buf, "\n=== Partitioning boot disk (Legacy BIOS) ===\n")
+            run_stream(["sudo", "sgdisk",
+                        "-n", "1:1M:+1M", "-t", "1:EF02", "-c", "1:BIOS-boot",
+                        "-n", "2:0:0",    "-t", "2:8300", "-c", "2:root",
+                        boot_path], buf)
 
         run_stream(["sudo", "partprobe", boot_path], buf)
         time.sleep(2)
@@ -925,7 +1056,10 @@ class InstallerWindow(Adw.ApplicationWindow):
         boot_p1 = self.partition_path(boot_path, 1)
         boot_p2 = self.partition_path(boot_path, 2)
 
-        run_stream(["sudo", "mkfs.vfat", "-F", "32", boot_p1], buf)
+        if self.boot_mode == "uefi":
+            run_stream(["sudo", "mkfs.vfat", "-F", "32", boot_p1], buf)
+        else:
+            GLib.idle_add(append_text, buf, "Skipping ESP format for Legacy BIOS install.\n")
         run_stream(["sudo", "mkfs.ext4", "-F", "-L", "sovran_systemsos", boot_p2], buf)
 
         if data_path and not self.data_drive_has_timechain:
@@ -935,8 +1069,11 @@ class InstallerWindow(Adw.ApplicationWindow):
         # ── Mount filesystems ──
         GLib.idle_add(append_text, buf, "\n=== Mounting filesystems ===\n")
         run_stream(["sudo", "mount", boot_p2, "/mnt"], buf)
-        run_stream(["sudo", "mkdir", "-p", "/mnt/boot/efi"], buf)
-        run_stream(["sudo", "mount", "-o", "umask=0077,defaults", boot_p1, "/mnt/boot/efi"], buf)
+        if self.boot_mode == "uefi":
+            run_stream(["sudo", "mkdir", "-p", "/mnt/boot/efi"], buf)
+            run_stream(["sudo", "mount", "-o", "umask=0077,defaults", boot_p1, "/mnt/boot/efi"], buf)
+        else:
+            GLib.idle_add(append_text, buf, "Legacy BIOS install: /boot/efi mount not required.\n")
 
         if data_path:
             data_p1 = self.partition_path(data_path, 1)
@@ -966,12 +1103,33 @@ class InstallerWindow(Adw.ApplicationWindow):
         is_server = str(self.role == "Server+Desktop").lower()
         is_desktop = str(self.role == "Desktop Only").lower()
         is_node = str(self.role == "Node (Bitcoin-only)").lower()
+        boot_overrides = ""
+        if self.boot_mode == "bios":
+            grub_device = nix_string(f"/dev/{self.boot_disk}")
+            boot_overrides = f"""
+
+  # The installer ISO was booted in Legacy BIOS mode, so install GRUB to the
+  # target disk instead of using the default UEFI systemd-boot configuration.
+  boot.loader.systemd-boot.enable = lib.mkForce false;
+  boot.loader.efi.canTouchEfiVariables = lib.mkForce false;
+  boot.loader.grub.enable = lib.mkForce true;
+  boot.loader.grub.device = lib.mkForce {grub_device};
+  fileSystems."/boot/efi".enable = lib.mkForce false;
+"""
+        elif self.virtualization:
+            boot_overrides = """
+
+  # VM UEFI firmware can reject or forget NVRAM boot-entry writes. Keep the
+  # normal UEFI systemd-boot layout, but use the fallback removable path instead
+  # of depending on EFI variable updates.
+  boot.loader.efi.canTouchEfiVariables = lib.mkForce false;
+"""
         content = f"""# THIS FILE IS AUTO-GENERATED BY THE INSTALLER. DO NOT EDIT.
 {{ config, lib, ... }}:
 {{
   sovran_systemsOS.roles.server_plus_desktop = lib.mkDefault {is_server};
   sovran_systemsOS.roles.desktop = lib.mkDefault {is_desktop};
-  sovran_systemsOS.roles.node = lib.mkDefault {is_node};
+  sovran_systemsOS.roles.node = lib.mkDefault {is_node};{boot_overrides}
 }}
 """
         proc = subprocess.run(
@@ -1008,6 +1166,11 @@ class InstallerWindow(Adw.ApplicationWindow):
         boot_row.set_subtitle(f"/dev/{self.boot_disk}  —  {human_size(self.boot_size)}")
         details.add(boot_row)
 
+        boot_mode_row = Adw.ActionRow()
+        boot_mode_row.set_title("Boot Mode")
+        boot_mode_row.set_subtitle(boot_mode_label(self.boot_mode))
+        details.add(boot_mode_row)
+
         if self.data_disk:
             data_row = Adw.ActionRow()
             data_row.set_title("Data Disk")
diff --git a/iso/sovran-install-headless.sh b/iso/sovran-install-headless.sh
index b5d4840..ac8be22 100755
--- a/iso/sovran-install-headless.sh
+++ b/iso/sovran-install-headless.sh
@@ -12,6 +12,11 @@ Options:
   --deploy-key "ssh-ed25519 AAAA..."  SSH pubkey for remote access after install
   --headscale-server URL       Headscale login server for post-install Tailnet
   --headscale-key KEY          Headscale pre-auth key for the installed OS
+
+VM notes:
+  Desktop test installs still need a 256 GB OS disk (thin-provisioned is OK).
+  Node/server installs need a separate 2 TB data disk. UEFI is preferred; UEFI
+  VMs avoid NVRAM boot-entry writes, and legacy BIOS VMs use GRUB.
 USAGE
 }
 
@@ -25,6 +30,8 @@ DEPLOY_KEY=""
 HEADSCALE_SERVER=""
 HEADSCALE_KEY=""
 DATA_DISK_HAS_TIMECHAIN=false
+BOOT_MODE=""
+VIRTUALIZATION=""
 
 FLAKE="/etc/sovran/flake"
 LOG="/tmp/sovran-headless-install.log"
@@ -69,6 +76,22 @@ case "$ROLE" in
     *) die "--role must be one of: server, desktop, node" ;;
 esac
 
+# ── Detect firmware / VM environment ─────────────────────────────────────────
+if [[ -d /sys/firmware/efi ]]; then
+    BOOT_MODE="uefi"
+else
+    BOOT_MODE="bios"
+fi
+
+if command -v systemd-detect-virt >/dev/null 2>&1; then
+    if VIRT_RESULT=$(systemd-detect-virt --vm 2>/dev/null); then
+        [[ "$VIRT_RESULT" != "none" ]] && VIRTUALIZATION="$VIRT_RESULT"
+    fi
+fi
+
+log "Boot mode: ${BOOT_MODE} ($([[ "$BOOT_MODE" == uefi ]] && echo systemd-boot || echo GRUB))"
+[[ -n "$VIRTUALIZATION" ]] && log "Virtual machine detected: ${VIRTUALIZATION}"
+
 # ── Validate disk existence and size ─────────────────────────────────────────
 log "=== Validating disks ==="
 
@@ -96,13 +119,26 @@ fi
 # ── Helper: partition suffix ──────────────────────────────────────────────────
 part_suffix() {
     local dev="$1" n="$2"
-    if [[ "$dev" == *nvme* ]]; then
+    local base
+    base=$(basename "$dev")
+    if [[ "$base" == nvme* || "$base" == mmcblk* || "$base" == loop* || "$base" == md* || "$base" =~ [0-9]$ ]]; then
         echo "${dev}p${n}"
     else
         echo "${dev}${n}"
     fi
 }
 
+nix_string() {
+    local value="$1"
+    value="${value//\\/\\\\}"
+    value="${value//\"/\\\"}"
+    value="${value//$'\n'/\\n}"
+    value="${value//$'\r'/\\r}"
+    value="${value//$'\t'/\\t}"
+    value="${value//\$\{/\\\$\{}"
+    printf '"%s"' "$value"
+}
+
 # ── Detect existing Bitcoin timechain data on data disk ───────────────────────
 if [[ -n "$DATA_DISK" ]]; then
     DATA_P1=$(part_suffix "$DATA_DISK" 1)
@@ -142,12 +178,19 @@ partprobe "$DISK"
 sleep 2
 
 # ── Step 2: Partition OS disk ─────────────────────────────────────────────────
-log "=== Partitioning OS disk ==="
-
-sgdisk \
-    -n "1:1M:+512M" -t "1:EF00" -c "1:ESP" \
-    -n "2:0:0"      -t "2:8300" -c "2:root" \
-    "$DISK"
+if [[ "$BOOT_MODE" == "uefi" ]]; then
+    log "=== Partitioning OS disk (UEFI) ==="
+    sgdisk \
+        -n "1:1M:+512M" -t "1:EF00" -c "1:ESP" \
+        -n "2:0:0"      -t "2:8300" -c "2:root" \
+        "$DISK"
+else
+    log "=== Partitioning OS disk (Legacy BIOS) ==="
+    sgdisk \
+        -n "1:1M:+1M" -t "1:EF02" -c "1:BIOS-boot" \
+        -n "2:0:0"    -t "2:8300" -c "2:root" \
+        "$DISK"
+fi
 
 partprobe "$DISK"
 sleep 2
@@ -168,7 +211,11 @@ log "=== Formatting partitions ==="
 BOOT_P1=$(part_suffix "$DISK" 1)
 BOOT_P2=$(part_suffix "$DISK" 2)
 
-mkfs.vfat -F 32 "$BOOT_P1"
+if [[ "$BOOT_MODE" == "uefi" ]]; then
+    mkfs.vfat -F 32 "$BOOT_P1"
+else
+    log "Skipping ESP format for Legacy BIOS install"
+fi
 mkfs.ext4 -F -L sovran_systemsos "$BOOT_P2"
 
 if [[ -n "$DATA_DISK" && "$DATA_DISK_HAS_TIMECHAIN" != true ]]; then
@@ -180,8 +227,12 @@ fi
 log "=== Mounting filesystems ==="
 
 mount "$BOOT_P2" /mnt
-mkdir -p /mnt/boot/efi
-mount -o umask=0077,defaults "$BOOT_P1" /mnt/boot/efi
+if [[ "$BOOT_MODE" == "uefi" ]]; then
+    mkdir -p /mnt/boot/efi
+    mount -o umask=0077,defaults "$BOOT_P1" /mnt/boot/efi
+else
+    log "Legacy BIOS install: /boot/efi mount not required"
+fi
 
 if [[ -n "$DATA_DISK" ]]; then
     DATA_P1=$(part_suffix "$DATA_DISK" 1)
@@ -219,16 +270,41 @@ case "$ROLE" in
         IS_SERVER=false; IS_DESKTOP=false; IS_NODE=true ;;
 esac
 
-cat > /mnt/etc/nixos/role-state.nix <<EOF
+{
+    cat <<EOF
 # THIS FILE IS AUTO-GENERATED BY THE INSTALLER. DO NOT EDIT.
 { config, lib, ... }:
 {
   sovran_systemsOS.roles.server_plus_desktop = lib.mkDefault ${IS_SERVER};
   sovran_systemsOS.roles.desktop = lib.mkDefault ${IS_DESKTOP};
   sovran_systemsOS.roles.node = lib.mkDefault ${IS_NODE};
-}
 EOF
 
+    if [[ "$BOOT_MODE" == "bios" ]]; then
+        GRUB_DEVICE=$(nix_string "$DISK")
+        cat <<EOF
+
+  # The installer ISO was booted in Legacy BIOS mode, so install GRUB to the
+  # target disk instead of using the default UEFI systemd-boot configuration.
+  boot.loader.systemd-boot.enable = lib.mkForce false;
+  boot.loader.efi.canTouchEfiVariables = lib.mkForce false;
+  boot.loader.grub.enable = lib.mkForce true;
+  boot.loader.grub.device = lib.mkForce ${GRUB_DEVICE};
+  fileSystems."/boot/efi".enable = lib.mkForce false;
+EOF
+    elif [[ -n "$VIRTUALIZATION" ]]; then
+        cat <<EOF
+
+  # VM UEFI firmware can reject or forget NVRAM boot-entry writes. Keep the
+  # normal UEFI systemd-boot layout, but use the fallback removable path instead
+  # of depending on EFI variable updates.
+  boot.loader.efi.canTouchEfiVariables = lib.mkForce false;
+EOF
+    fi
+
+    echo "}"
+} > /mnt/etc/nixos/role-state.nix
+
 # ── Step 10: Write custom.nix with deploy config ──────────────────────────────
 log "=== Writing custom.nix ==="