diff --git a/install.ps1 b/install.ps1
index 19f51c43..eb5abf7d 100644
--- a/install.ps1
+++ b/install.ps1
@@ -11,7 +11,7 @@
 
     $ErrorActionPreference = "Stop"
     $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-    $defaultInstallSha256 = "e85a34efb84620b8c65858d209c9741a715f8ff6a61397f9ee161c0931a9a049"
+    $defaultInstallSha256 = "5ed37d4dabc5a6b28a9093f38a25506b20ec2f49c3587692efd695b017d1caf4"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }
diff --git a/install.py b/install.py
index fdd3f467..73bfd482 100644
--- a/install.py
+++ b/install.py
@@ -717,6 +717,28 @@ _BOARD_SOURCES: dict[str, tuple[str, str]] = {
 }
 
 
+# A derivative installed under a platform's name, with its own board file.
+# Knulli moves /usr/share/batocera to /usr/share/knulli (knulli-linux
+# 57afa662, board/scripts/post-build-script.sh:264-278) and writes its board
+# to knulli.arch (package/system/knulli-system/knulli-system.mk:98-99). Its
+# packages are its own, so Batocera's per-board core lists do not apply.
+_DERIVATIVE_BOARDS: dict[str, tuple[str, str]] = {
+    "batocera": ("Knulli", "/usr/share/knulli/knulli.arch"),
+}
+
+
+def derivative_board(platform: str) -> tuple[str, str] | None:
+    """(derivative, board) when a derivative of the platform names its board."""
+    name, where = _DERIVATIVE_BOARDS.get(platform, ("", ""))
+    if not where:
+        return None
+    try:
+        board = Path(where).read_text(encoding="utf-8", errors="replace").strip().lower()
+    except OSError:
+        return None
+    return (name, board) if board else None
+
+
 def detect_board(platform: str) -> str | None:
     """The board this system was built for, or None where it names none."""
     kind, where = _BOARD_SOURCES.get(platform, ("", ""))
@@ -767,16 +789,22 @@ def _parse_ps1_var(path: Path, key: str) -> str | None:
     return None
 
 
-# Embedded systems, first match wins: Knulli also carries the Batocera
-# markers. The registry publishes the same rules as each manifest's
-# `detect`, and a test holds the two equal. MiSTer is a path rule below.
+# Embedded systems, first match wins. The registry publishes the same rules
+# as each manifest's `detect`, and a test holds the two equal. MiSTer is a
+# path rule below.
 _EMBEDDED_RULES: tuple[tuple[str, str, tuple[str, ...], str], ...] = (
     # ROCKNIX writes OS_NAME and no ID since 2025 (scripts/image). Older
     # images wrote ID=rocknix.
     ("rocknix", "os_release", ("OS_NAME=rocknix", "ID=rocknix"), "/storage/roms/bios"),
-    ("batocera", "file_exists", ("/etc/knulli-release",), "/userdata/bios"),
+    # Knulli (knulli-linux 57afa662): OS_NAME in os-release
+    # (board/scripts/post-build-script.sh:233-236) and knulli.version
+    # (package/system/knulli-system/knulli-system.mk:98-102).
+    ("batocera", "os_release", ("OS_NAME=knulli",), "/userdata/bios"),
+    ("batocera", "file_exists", ("/usr/share/knulli/knulli.version",), "/userdata/bios"),
     ("lakka", "os_release", ("ID=lakka",), "/storage/system"),
-    ("batocera", "file_exists", ("/etc/batocera-version",), "/userdata/bios"),
+    # batocera.linux 38845725, batocera-system.mk:21-22 (the same lines in
+    # batocera-30): batocera.arch and batocera.version.
+    ("batocera", "file_exists", ("/usr/share/batocera/batocera.version",), "/userdata/bios"),
     ("recalbox", "file_exists", ("/recalbox/recalbox.version",), "/recalbox/share/bios"),
     ("recalbox", "file_exists", ("/usr/bin/recalbox-settings",), "/recalbox/share/bios"),
     ("retroarch", "file_exists", ("/opt/muos",), "/run/muos/storage/bios"),
@@ -4633,6 +4661,15 @@ def _install(args: argparse.Namespace, real_stdout: TextIO) -> None:
                 if board in known:
                     target = board
                     print(f"  Board {board} detected (--every-board installs all boards)")
+                else:
+                    print(f"  Board {board} has no {PLATFORM_NAMES.get(plat_name, plat_name)} "
+                          "core list: installing the files of every board")
+            else:
+                derived = derivative_board(plat_name)
+                if derived:
+                    print(f"  {derived[0]} board {derived[1]} detected. {derived[0]} "
+                          "builds its own set of cores and publishes no core list "
+                          "per board: installing the files of every board")
         if target:
             targets = target_lists.get(plat_name)
             if targets is None:
diff --git a/install.sh b/install.sh
index a9fb019f..094090f8 100755
--- a/install.sh
+++ b/install.sh
@@ -18,7 +18,7 @@ esac
 TEMP_INSTALLER=""
 TEMP_DIRECTORY=""
 DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-DEFAULT_INSTALL_SHA256="e85a34efb84620b8c65858d209c9741a715f8ff6a61397f9ee161c0931a9a049"
+DEFAULT_INSTALL_SHA256="5ed37d4dabc5a6b28a9093f38a25506b20ec2f49c3587692efd695b017d1caf4"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {
diff --git a/platforms/_registry.yml b/platforms/_registry.yml
index 819438d7..beb31913 100644
--- a/platforms/_registry.yml
+++ b/platforms/_registry.yml
@@ -313,14 +313,22 @@ platforms:
     target_source: https://github.com/batocera-linux/batocera.linux
     install:
       detect:
-      # Knulli is a Batocera derivative and carries its markers too.
+      # Knulli, a Batocera derivative (knulli-cfw/knulli-linux 57afa662):
+      # OS_NAME in os-release (board/scripts/post-build-script.sh:233-236),
+      # and knulli.version (package/system/knulli-system/knulli-system.mk:98-102).
       - os: linux
-        method: file_exists
-        file: /etc/knulli-release
+        method: os_release
+        match: [OS_NAME=knulli]
         bios_path: /userdata/bios
       - os: linux
         method: file_exists
-        file: /etc/batocera-version
+        file: /usr/share/knulli/knulli.version
+        bios_path: /userdata/bios
+      # batocera.linux 38845725, package/batocera/core/batocera-system/
+      # batocera-system.mk:21-22 writes batocera.arch and batocera.version.
+      - os: linux
+        method: file_exists
+        file: /usr/share/batocera/batocera.version
         bios_path: /userdata/bios
       standalone_copies: *standalone_copies
   recalbox:
diff --git a/tests/test_install.py b/tests/test_install.py
index 44db4d6f..fa44f502 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -1028,7 +1028,8 @@ class DetectionFollowsTheRegistry(unittest.TestCase):
         with unittest.mock.patch.object(install, "_parse_os_release", return_value={}), \
                 unittest.mock.patch.object(
                     Path, "exists",
-                    lambda p: str(p) in ("/etc/knulli-release", "/etc/batocera-version"),
+                    lambda p: str(p) in ("/usr/share/knulli/knulli.version",
+                                       "/usr/share/batocera/batocera.version"),
                 ):
             self.assertEqual(install._detect_embedded(), [("batocera", Path("/userdata/bios"))])
         # What ROCKNIX writes since 2025: OS_NAME and HW_DEVICE, no ID.
@@ -3952,5 +3953,43 @@ class MuOsIsReadFromItsRetroArchConfig(unittest.TestCase):
         self.assertEqual(rule[3], "/run/muos/storage/bios")
 
 
+class BatoceraAndKnulliByWhatTheirBuildsWrite(unittest.TestCase):
+    """No Batocera build writes /etc/batocera-version (batocera-system.mk
+    writes /usr/share/batocera/batocera.version), and Knulli writes no
+    /etc/knulli-release and removes /usr/share/batocera: neither was
+    detected, and a Knulli board got every board's files without a word."""
+
+    def _detect(self, release: dict, files: tuple[str, ...]):
+        with unittest.mock.patch.object(install, "_parse_os_release", return_value=release), \
+                unittest.mock.patch.object(Path, "exists", lambda p: str(p) in files):
+            return install._detect_embedded()
+
+    def test_batocera_by_its_version_file(self):
+        self.assertEqual(self._detect({}, ("/usr/share/batocera/batocera.version",)),
+                         [("batocera", Path("/userdata/bios"))])
+        self.assertEqual(self._detect({}, ("/etc/batocera-version",)), [])
+
+    def test_knulli_by_its_os_release_or_version_file(self):
+        self.assertEqual(self._detect({"OS_NAME": "knulli"}, ()),
+                         [("batocera", Path("/userdata/bios"))])
+        self.assertEqual(self._detect({}, ("/usr/share/knulli/knulli.version",)),
+                         [("batocera", Path("/userdata/bios"))])
+
+    def test_a_knulli_board_is_named_and_not_narrowed(self):
+        board = Path(_tempdir(self)) / "knulli.arch"
+        board.write_text("a133")
+        with unittest.mock.patch.dict(install._DERIVATIVE_BOARDS,
+                                      {"batocera": ("Knulli", str(board))}):
+            self.assertEqual(install.derivative_board("batocera"), ("Knulli", "a133"))
+            self.assertIsNone(install.derivative_board("recalbox"))
+
+    def test_the_run_says_why_every_board_is_installed(self):
+        source = (REPO_ROOT / "install.py").read_text(encoding="utf-8")
+        block = source[source.index("board = detect_board(plat_name)"):]
+        block = block[:block.index("if target:")]
+        self.assertIn("has no", block)
+        self.assertIn("derivative_board(plat_name)", block)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/wiki/installer.md b/wiki/installer.md
index 1937c0cb..190acfcc 100644
--- a/wiki/installer.md
+++ b/wiki/installer.md
@@ -279,9 +279,9 @@ wins, since a machine is only one of them.
 | Evidence | Platform | BIOS directory |
 |----------|----------|----------------|
 | `/etc/os-release` `OS_NAME=ROCKNIX` (or `ID=rocknix` on images before 2025) | ROCKNIX | `/storage/roms/bios` |
-| `/etc/knulli-release` | Batocera | `/userdata/bios` |
+| `/etc/os-release` `OS_NAME=knulli` or `/usr/share/knulli/knulli.version` | Batocera (Knulli) | `/userdata/bios` |
 | `/etc/os-release` `ID=lakka` | Lakka | `/storage/system` |
-| `/etc/batocera-version` | Batocera | `/userdata/bios` |
+| `/usr/share/batocera/batocera.version` | Batocera | `/userdata/bios` |
 | `/recalbox/recalbox.version` or `/usr/bin/recalbox-settings` | Recalbox | `/recalbox/share/bios` |
 | `/opt/muos` | RetroArch (muOS) | `system_directory` of `/opt/muos/share/info/config/retroarch.cfg`, else of the default it is copied from: `/run/muos/storage/bios`, which muOS binds to `MUOS/bios` on the second card when that card holds one, else the first. Cores are read from that config's `libretro_directory` (`/opt/muos/share/core`) |
 | `/mnt/mmc/MUOS/` | RetroArch | `/mnt/mmc/MUOS/bios` |
@@ -290,7 +290,10 @@ wins, since a machine is only one of them.
 
 Batocera, Recalbox, ROCKNIX and Lakka also name the board they were built for, and
 that board narrows the install unless `--target` or `--every-board` says
-otherwise (see the options above).
+otherwise (see the options above). A board with no core list of its own is
+named and gets the files of every board. Knulli names its board in
+`/usr/share/knulli/knulli.arch` but builds its own set of cores, so Batocera's
+per-board lists are not applied to it and the run says so.
 
 Some platforms keep their BIOS in a fixed directory, and that directory is the
 evidence. They are looked for after the configurations below, for a platform