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poky/documentation/dev-manual/device-manager.rst

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+.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
+
+.. _device-manager:
+
+Selecting a Device Manager
+**************************
+
+The Yocto Project provides multiple ways to manage the device manager
+(``/dev``):
+
+-  Persistent and Pre-Populated ``/dev``: For this case, the ``/dev``
+   directory is persistent and the required device nodes are created
+   during the build.
+
+-  Use ``devtmpfs`` with a Device Manager: For this case, the ``/dev``
+   directory is provided by the kernel as an in-memory file system and
+   is automatically populated by the kernel at runtime. Additional
+   configuration of device nodes is done in user space by a device
+   manager like ``udev`` or ``busybox-mdev``.
+
+Using Persistent and Pre-Populated ``/dev``
+===========================================
+
+To use the static method for device population, you need to set the
+:term:`USE_DEVFS` variable to "0"
+as follows::
+
+   USE_DEVFS = "0"
+
+The content of the resulting ``/dev`` directory is defined in a Device
+Table file. The
+:term:`IMAGE_DEVICE_TABLES`
+variable defines the Device Table to use and should be set in the
+machine or distro configuration file. Alternatively, you can set this
+variable in your ``local.conf`` configuration file.
+
+If you do not define the :term:`IMAGE_DEVICE_TABLES` variable, the default
+``device_table-minimal.txt`` is used::
+
+   IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
+
+The population is handled by the ``makedevs`` utility during image
+creation:
+
+Using ``devtmpfs`` and a Device Manager
+=======================================
+
+To use the dynamic method for device population, you need to use (or be
+sure to set) the :term:`USE_DEVFS`
+variable to "1", which is the default::
+
+   USE_DEVFS = "1"
+
+With this
+setting, the resulting ``/dev`` directory is populated by the kernel
+using ``devtmpfs``. Make sure the corresponding kernel configuration
+variable ``CONFIG_DEVTMPFS`` is set when building you build a Linux
+kernel.
+
+All devices created by ``devtmpfs`` will be owned by ``root`` and have
+permissions ``0600``.
+
+To have more control over the device nodes, you can use a device manager
+like ``udev`` or ``busybox-mdev``. You choose the device manager by
+defining the ``VIRTUAL-RUNTIME_dev_manager`` variable in your machine or
+distro configuration file. Alternatively, you can set this variable in
+your ``local.conf`` configuration file::
+
+   VIRTUAL-RUNTIME_dev_manager = "udev"
+
+   # Some alternative values
+   # VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
+   # VIRTUAL-RUNTIME_dev_manager = "systemd"
+