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+Release 2.4 (rocko)
+===================
+
+This section provides migration information for moving to the Yocto
+Project 2.4 Release (codename "rocko") from the prior release.
+
+.. _migration-2.4-memory-resident-mode:
+
+Memory Resident Mode
+--------------------
+
+A persistent mode is now available in BitBake's default operation,
+replacing its previous "memory resident mode" (i.e.
+``oe-init-build-env-memres``). Now you only need to set
+:term:`BB_SERVER_TIMEOUT` to a timeout (in
+seconds) and BitBake's server stays resident for that amount of time
+between invocations. The ``oe-init-build-env-memres`` script has been
+removed since a separate environment setup script is no longer needed.
+
+.. _migration-2.4-packaging-changes:
+
+Packaging Changes
+-----------------
+
+This section provides information about packaging changes that have
+occurred:
+
+-  ``python3`` Changes:
+
+   -  The main "python3" package now brings in all of the standard
+      Python 3 distribution rather than a subset. This behavior matches
+      what is expected based on traditional Linux distributions. If you
+      wish to install a subset of Python 3, specify ``python-core`` plus
+      one or more of the individual packages that are still produced.
+
+   -  ``python3``: The ``bz2.py``, ``lzma.py``, and
+      ``_compression.py`` scripts have been moved from the
+      ``python3-misc`` package to the ``python3-compression`` package.
+
+-  ``binutils``: The ``libbfd`` library is now packaged in a separate
+   "libbfd" package. This packaging saves space when certain tools (e.g.
+   ``perf``) are installed. In such cases, the tools only need
+   ``libbfd`` rather than all the packages in ``binutils``.
+
+-  ``util-linux`` Changes:
+
+   -  The ``su`` program is now packaged in a separate "util-linux-su"
+      package, which is only built when "pam" is listed in the
+      :term:`DISTRO_FEATURES` variable.
+      ``util-linux`` should not be installed unless it is needed because
+      ``su`` is normally provided through the shadow file format. The
+      main ``util-linux`` package has runtime dependencies (i.e.
+      :term:`RDEPENDS`) on the ``util-linux-su`` package
+      when "pam" is in ``DISTRO_FEATURES``.
+
+   -  The ``switch_root`` program is now packaged in a separate
+      "util-linux-switch-root" package for small initramfs images that
+      do not need the whole ``util-linux`` package or the busybox
+      binary, which are both much larger than ``switch_root``. The main
+      ``util-linux`` package has a recommended runtime dependency (i.e.
+      :term:`RRECOMMENDS`) on the
+      ``util-linux-switch-root`` package.
+
+   -  The ``ionice`` program is now packaged in a separate
+      "util-linux-ionice" package. The main ``util-linux`` package has a
+      recommended runtime dependency (i.e. ``RRECOMMENDS``) on the
+      ``util-linux-ionice`` package.
+
+-  ``initscripts``: The ``sushell`` program is now packaged in a
+   separate "initscripts-sushell" package. This packaging change allows
+   systems to pull ``sushell`` in when ``selinux`` is enabled. The
+   change also eliminates needing to pull in the entire ``initscripts``
+   package. The main ``initscripts`` package has a runtime dependency
+   (i.e. ``RDEPENDS``) on the ``sushell`` package when "selinux" is in
+   ``DISTRO_FEATURES``.
+
+-  ``glib-2.0``: The ``glib-2.0`` package now has a recommended
+   runtime dependency (i.e. ``RRECOMMENDS``) on the ``shared-mime-info``
+   package, since large portions of GIO are not useful without the MIME
+   database. You can remove the dependency by using the
+   :term:`BAD_RECOMMENDATIONS` variable if
+   ``shared-mime-info`` is too large and is not required.
+
+-  *Go Standard Runtime:* The Go standard runtime has been split out
+   from the main ``go`` recipe into a separate ``go-runtime`` recipe.
+
+.. _migration-2.4-removed-recipes:
+
+Removed Recipes
+---------------
+
+The following recipes have been removed:
+
+-  ``acpitests``: This recipe is not maintained.
+
+-  ``autogen-native``: No longer required by Grub, oe-core, or
+   meta-oe.
+
+-  ``bdwgc``: Nothing in OpenEmbedded-Core requires this recipe. It
+   has moved to meta-oe.
+
+-  ``byacc``: This recipe was only needed by rpm 5.x and has moved to
+   meta-oe.
+
+-  ``gcc (5.4)``: The 5.4 series dropped the recipe in favor of 6.3 /
+   7.2.
+
+-  ``gnome-common``: Deprecated upstream and no longer needed.
+
+-  ``go-bootstrap-native``: Go 1.9 does its own bootstrapping so this
+   recipe has been removed.
+
+-  ``guile``: This recipe was only needed by ``autogen-native`` and
+   ``remake``. The recipe is no longer needed by either of these
+   programs.
+
+-  ``libclass-isa-perl``: This recipe was previously needed for LSB 4,
+   no longer needed.
+
+-  ``libdumpvalue-perl``: This recipe was previously needed for LSB 4,
+   no longer needed.
+
+-  ``libenv-perl``: This recipe was previously needed for LSB 4, no
+   longer needed.
+
+-  ``libfile-checktree-perl``: This recipe was previously needed for
+   LSB 4, no longer needed.
+
+-  ``libi18n-collate-perl``: This recipe was previously needed for LSB
+   4, no longer needed.
+
+-  ``libiconv``: This recipe was only needed for ``uclibc``, which was
+   removed in the previous release. ``glibc`` and ``musl`` have their
+   own implementations. ``meta-mingw`` still needs ``libiconv``, so it
+   has been moved to ``meta-mingw``.
+
+-  ``libpng12``: This recipe was previously needed for LSB. The
+   current ``libpng`` is 1.6.x.
+
+-  ``libpod-plainer-perl``: This recipe was previously needed for LSB
+   4, no longer needed.
+
+-  ``linux-yocto (4.1)``: This recipe was removed in favor of 4.4,
+   4.9, 4.10 and 4.12.
+
+-  ``mailx``: This recipe was previously only needed for LSB
+   compatibility, and upstream is defunct.
+
+-  ``mesa (git version only)``: The git version recipe was stale with
+   respect to the release version.
+
+-  ``ofono (git version only)``: The git version recipe was stale with
+   respect to the release version.
+
+-  ``portmap``: This recipe is obsolete and is superseded by
+   ``rpcbind``.
+
+-  ``python3-pygpgme``: This recipe is old and unmaintained. It was
+   previously required by ``dnf``, which has switched to official
+   ``gpgme`` Python bindings.
+
+-  ``python-async``: This recipe has been removed in favor of the
+   Python 3 version.
+
+-  ``python-gitdb``: This recipe has been removed in favor of the
+   Python 3 version.
+
+-  ``python-git``: This recipe was removed in favor of the Python 3
+   version.
+
+-  ``python-mako``: This recipe was removed in favor of the Python 3
+   version.
+
+-  ``python-pexpect``: This recipe was removed in favor of the Python
+   3 version.
+
+-  ``python-ptyprocess``: This recipe was removed in favor of Python
+   the 3 version.
+
+-  ``python-pycurl``: Nothing is using this recipe in
+   OpenEmbedded-Core (i.e. ``meta-oe``).
+
+-  ``python-six``: This recipe was removed in favor of the Python 3
+   version.
+
+-  ``python-smmap``: This recipe was removed in favor of the Python 3
+   version.
+
+-  ``remake``: Using ``remake`` as the provider of ``virtual/make`` is
+   broken. Consequently, this recipe is not needed in OpenEmbedded-Core.
+
+.. _migration-2.4-kernel-device-tree-move:
+
+Kernel Device Tree Move
+-----------------------
+
+Kernel Device Tree support is now easier to enable in a kernel recipe.
+The Device Tree code has moved to a
+:ref:`kernel-devicetree <ref-classes-kernel-devicetree>` class.
+Functionality is automatically enabled for any recipe that inherits the
+:ref:`kernel <ref-classes-kernel>` class and sets the
+:term:`KERNEL_DEVICETREE` variable. The
+previous mechanism for doing this,
+``meta/recipes-kernel/linux/linux-dtb.inc``, is still available to avoid
+breakage, but triggers a deprecation warning. Future releases of the
+Yocto Project will remove ``meta/recipes-kernel/linux/linux-dtb.inc``.
+It is advisable to remove any ``require`` statements that request
+``meta/recipes-kernel/linux/linux-dtb.inc`` from any custom kernel
+recipes you might have. This will avoid breakage in post 2.4 releases.
+
+.. _migration-2.4-package-qa-changes:
+
+Package QA Changes
+------------------
+
+The following package QA changes took place:
+
+-  The "unsafe-references-in-scripts" QA check has been removed.
+
+-  If you refer to ``${COREBASE}/LICENSE`` within
+   :term:`LIC_FILES_CHKSUM` you receive a
+   warning because this file is a description of the license for
+   OE-Core. Use ``${COMMON_LICENSE_DIR}/MIT`` if your recipe is
+   MIT-licensed and you cannot use the preferred method of referring to
+   a file within the source tree.
+
+.. _migration-2.4-readme-changes:
+
+``README`` File Changes
+-----------------------
+
+The following are changes to ``README`` files:
+
+-  The main Poky ``README`` file has been moved to the ``meta-poky``
+   layer and has been renamed ``README.poky``. A symlink has been
+   created so that references to the old location work.
+
+-  The ``README.hardware`` file has been moved to ``meta-yocto-bsp``. A
+   symlink has been created so that references to the old location work.
+
+-  A ``README.qemu`` file has been created with coverage of the
+   ``qemu*`` machines.
+
+.. _migration-2.4-miscellaneous-changes:
+
+Miscellaneous Changes
+---------------------
+
+The following are additional changes:
+
+-  The ``ROOTFS_PKGMANAGE_BOOTSTRAP`` variable and any references to it
+   have been removed. You should remove this variable from any custom
+   recipes.
+
+-  The ``meta-yocto`` directory has been removed.
+
+   .. note::
+
+      In the Yocto Project 2.1 release
+      meta-yocto
+      was renamed to
+      meta-poky
+      and the
+      meta-yocto
+      subdirectory remained to avoid breaking existing configurations.
+
+-  The ``maintainers.inc`` file, which tracks maintainers by listing a
+   primary person responsible for each recipe in OE-Core, has been moved
+   from ``meta-poky`` to OE-Core (i.e. from
+   ``meta-poky/conf/distro/include`` to ``meta/conf/distro/include``).
+
+-  The :ref:`buildhistory <ref-classes-buildhistory>` class now makes
+   a single commit per build rather than one commit per subdirectory in
+   the repository. This behavior assumes the commits are enabled with
+   :term:`BUILDHISTORY_COMMIT` = "1", which
+   is typical. Previously, the ``buildhistory`` class made one commit
+   per subdirectory in the repository in order to make it easier to see
+   the changes for a particular subdirectory. To view a particular
+   change, specify that subdirectory as the last parameter on the
+   ``git show`` or ``git diff`` commands.
+
+-  The ``x86-base.inc`` file, which is included by all x86-based machine
+   configurations, now sets :term:`IMAGE_FSTYPES`
+   using ``?=`` to "live" rather than appending with ``+=``. This change
+   makes the default easier to override.
+
+-  BitBake fires multiple "BuildStarted" events when multiconfig is
+   enabled (one per configuration). For more information, see the
+   ":ref:`Events <bitbake:bitbake-user-manual/bitbake-user-manual-metadata:events>`" section in the BitBake User
+   Manual.
+
+-  By default, the ``security_flags.inc`` file sets a
+   :term:`GCCPIE` variable with an option to enable
+   Position Independent Executables (PIE) within ``gcc``. Enabling PIE
+   in the GNU C Compiler (GCC), makes Return Oriented Programming (ROP)
+   attacks much more difficult to execute.
+
+-  OE-Core now provides a ``bitbake-layers`` plugin that implements a
+   "create-layer" subcommand. The implementation of this subcommand has
+   resulted in the ``yocto-layer`` script being deprecated and will
+   likely be removed in the next Yocto Project release.
+
+-  The ``vmdk``, ``vdi``, and ``qcow2`` image file types are now used in
+   conjunction with the "wic" image type through ``CONVERSION_CMD``.
+   Consequently, the equivalent image types are now ``wic.vmdk``,
+   ``wic.vdi``, and ``wic.qcow2``, respectively.
+
+-  ``do_image_<type>[depends]`` has replaced ``IMAGE_DEPENDS_<type>``.
+   If you have your own classes that implement custom image types, then
+   you need to update them.
+
+-  OpenSSL 1.1 has been introduced. However, the default is still 1.0.x
+   through the :term:`PREFERRED_VERSION`
+   variable. This preference is set is due to the remaining
+   compatibility issues with other software. The
+   :term:`PROVIDES` variable in the openssl 1.0 recipe
+   now includes "openssl10" as a marker that can be used in
+   :term:`DEPENDS` within recipes that build software
+   that still depend on OpenSSL 1.0.
+
+-  To ensure consistent behavior, BitBake's "-r" and "-R" options (i.e.
+   prefile and postfile), which are used to read or post-read additional
+   configuration files from the command line, now only affect the
+   current BitBake command. Before these BitBake changes, these options
+   would "stick" for future executions.
+
+