.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

Creating Partitioned Images Using Wic
*************************************

Creating an image for a particular hardware target using the
OpenEmbedded build system does not necessarily mean you can boot that
image as is on your device. Physical devices accept and boot images in
various ways depending on the specifics of the device. Usually,
information about the hardware can tell you what image format the device
requires. Should your device require multiple partitions on an SD card,
flash, or an HDD, you can use the OpenEmbedded Image Creator, Wic, to
create the properly partitioned image.

The ``wic`` command generates partitioned images from existing
OpenEmbedded build artifacts. Image generation is driven by partitioning
commands contained in an OpenEmbedded kickstart file (``.wks``)
specified either directly on the command line or as one of a selection
of canned kickstart files as shown with the ``wic list images`` command
in the
":ref:`dev-manual/wic:generate an image using an existing kickstart file`"
section. When you apply the command to a given set of build artifacts, the
result is an image or set of images that can be directly written onto media and
used on a particular system.

.. note::

   For a kickstart file reference, see the
   ":ref:`ref-manual/kickstart:openembedded kickstart (\`\`.wks\`\`) reference`"
   Chapter in the Yocto Project Reference Manual.

The ``wic`` command and the infrastructure it is based on is by
definition incomplete. The purpose of the command is to allow the
generation of customized images, and as such, was designed to be
completely extensible through a plugin interface. See the
":ref:`dev-manual/wic:using the wic plugin interface`" section
for information on these plugins.

This section provides some background information on Wic, describes what
you need to have in place to run the tool, provides instruction on how
to use the Wic utility, provides information on using the Wic plugins
interface, and provides several examples that show how to use Wic.

Background
==========

This section provides some background on the Wic utility. While none of
this information is required to use Wic, you might find it interesting.

-  The name "Wic" is derived from OpenEmbedded Image Creator (oeic). The
   "oe" diphthong in "oeic" was promoted to the letter "w", because
   "oeic" is both difficult to remember and to pronounce.

-  Wic is loosely based on the Meego Image Creator (``mic``) framework.
   The Wic implementation has been heavily modified to make direct use
   of OpenEmbedded build artifacts instead of package installation and
   configuration, which are already incorporated within the OpenEmbedded
   artifacts.

-  Wic is a completely independent standalone utility that initially
   provides easier-to-use and more flexible replacements for an existing
   functionality in OE-Core's :ref:`ref-classes-image-live`
   class. The difference between Wic and those examples is that with Wic
   the functionality of those scripts is implemented by a
   general-purpose partitioning language, which is based on Redhat
   kickstart syntax.

Requirements
============

In order to use the Wic utility with the OpenEmbedded Build system, your
system needs to meet the following requirements:

-  The Linux distribution on your development host must support the
   Yocto Project. See the ":ref:`detailed-supported-distros`"
   section in the Yocto Project Reference Manual for the list of
   distributions that support the Yocto Project.

-  The standard system utilities, such as ``cp``, must be installed on
   your development host system.

-  You must have sourced the build environment setup script (i.e.
   :ref:`structure-core-script`) found in the :term:`Build Directory`.

-  You need to have the build artifacts already available, which
   typically means that you must have already created an image using the
   OpenEmbedded build system (e.g. ``core-image-minimal``). While it
   might seem redundant to generate an image in order to create an image
   using Wic, the current version of Wic requires the artifacts in the
   form generated by the OpenEmbedded build system.

-  You must build several native tools, which are built to run on the
   build system::

      $ bitbake parted-native dosfstools-native mtools-native

-  Include "wic" as part of the
   :term:`IMAGE_FSTYPES`
   variable.

-  Include the name of the :ref:`wic kickstart file <openembedded-kickstart-wks-reference>`
   as part of the :term:`WKS_FILE` variable. If multiple candidate files can
   be provided by different layers, specify all the possible names through the
   :term:`WKS_FILES` variable instead.

Getting Help
============

You can get general help for the ``wic`` command by entering the ``wic``
command by itself or by entering the command with a help argument as
follows::

   $ wic -h
   $ wic --help
   $ wic help

Currently, Wic supports seven commands: ``cp``, ``create``, ``help``,
``list``, ``ls``, ``rm``, and ``write``. You can get help for all these
commands except "help" by using the following form::

   $ wic help command

For example, the following command returns help for the ``write``
command::

   $ wic help write

Wic supports help for three topics: ``overview``, ``plugins``, and
``kickstart``. You can get help for any topic using the following form::

   $ wic help topic

For example, the following returns overview help for Wic::

   $ wic help overview

There is one additional level of help for Wic. You can get help on
individual images through the ``list`` command. You can use the ``list``
command to return the available Wic images as follows::

   $ wic list images
     genericx86                    		Create an EFI disk image for genericx86*
     edgerouter                    		Create SD card image for Edgerouter
     beaglebone-yocto              		Create SD card image for Beaglebone
     qemux86-directdisk            		Create a qemu machine 'pcbios' direct disk image
     systemd-bootdisk              		Create an EFI disk image with systemd-boot
     mkhybridiso                   		Create a hybrid ISO image
     mkefidisk                     		Create an EFI disk image
     sdimage-bootpart              		Create SD card image with a boot partition
     directdisk-multi-rootfs       		Create multi rootfs image using rootfs plugin
     directdisk                    		Create a 'pcbios' direct disk image
     directdisk-bootloader-config  		Create a 'pcbios' direct disk image with custom bootloader config
     qemuriscv                     		Create qcow2 image for RISC-V QEMU machines
     directdisk-gpt                		Create a 'pcbios' direct disk image
     efi-bootdisk

Once you know the list of available
Wic images, you can use ``help`` with the command to get help on a
particular image. For example, the following command returns help on the
"beaglebone-yocto" image::

   $ wic list beaglebone-yocto help

   Creates a partitioned SD card image for Beaglebone.
   Boot files are located in the first vfat partition.

Operational Modes
=================

You can use Wic in two different modes, depending on how much control
you need for specifying the OpenEmbedded build artifacts that are used
for creating the image: Raw and Cooked:

-  *Raw Mode:* You explicitly specify build artifacts through Wic
   command-line arguments.

-  *Cooked Mode:* The current
   :term:`MACHINE` setting and image
   name are used to automatically locate and provide the build
   artifacts. You just supply a kickstart file and the name of the image
   from which to use artifacts.

Regardless of the mode you use, you need to have the build artifacts
ready and available.

Raw Mode
--------

Running Wic in raw mode allows you to specify all the partitions through
the ``wic`` command line. The primary use for raw mode is if you have
built your kernel outside of the Yocto Project :term:`Build Directory`.
In other words, you can point to arbitrary kernel, root filesystem locations,
and so forth. Contrast this behavior with cooked mode where Wic looks in the
:term:`Build Directory` (e.g. ``tmp/deploy/images/``\ machine).

The general form of the ``wic`` command in raw mode is::

   $ wic create wks_file options ...

     Where:

        wks_file:
           An OpenEmbedded kickstart file.  You can provide
           your own custom file or use a file from a set of
           existing files as described by further options.

        optional arguments:
          -h, --help            show this help message and exit
          -o OUTDIR, --outdir OUTDIR
                                name of directory to create image in
          -e IMAGE_NAME, --image-name IMAGE_NAME
                                name of the image to use the artifacts from e.g. core-
                                image-sato
          -r ROOTFS_DIR, --rootfs-dir ROOTFS_DIR
                                path to the /rootfs dir to use as the .wks rootfs
                                source
          -b BOOTIMG_DIR, --bootimg-dir BOOTIMG_DIR
                                path to the dir containing the boot artifacts (e.g.
                                /EFI or /syslinux dirs) to use as the .wks bootimg
                                source
          -k KERNEL_DIR, --kernel-dir KERNEL_DIR
                                path to the dir containing the kernel to use in the
                                .wks bootimg
          -n NATIVE_SYSROOT, --native-sysroot NATIVE_SYSROOT
                                path to the native sysroot containing the tools to use
                                to build the image
          -s, --skip-build-check
                                skip the build check
          -f, --build-rootfs    build rootfs
          -c {gzip,bzip2,xz}, --compress-with {gzip,bzip2,xz}
                                compress image with specified compressor
          -m, --bmap            generate .bmap
          --no-fstab-update     Do not change fstab file.
          -v VARS_DIR, --vars VARS_DIR
                                directory with <image>.env files that store bitbake
                                variables
          -D, --debug           output debug information

.. note::

   You do not need root privileges to run Wic. In fact, you should not
   run as root when using the utility.

Cooked Mode
-----------

Running Wic in cooked mode leverages off artifacts in the
:term:`Build Directory`. In other words, you do not have to specify kernel or
root filesystem locations as part of the command. All you need to provide is
a kickstart file and the name of the image from which to use artifacts
by using the "-e" option. Wic looks in the :term:`Build Directory` (e.g.
``tmp/deploy/images/``\ machine) for artifacts.

The general form of the ``wic`` command using Cooked Mode is as follows::

   $ wic create wks_file -e IMAGE_NAME

     Where:

        wks_file:
           An OpenEmbedded kickstart file.  You can provide
           your own custom file or use a file from a set of
           existing files provided with the Yocto Project
           release.

        required argument:
           -e IMAGE_NAME, --image-name IMAGE_NAME
                                name of the image to use the artifacts from e.g. core-
                                image-sato

Using an Existing Kickstart File
================================

If you do not want to create your own kickstart file, you can use an
existing file provided by the Wic installation. As shipped, kickstart
files can be found in the :ref:`overview-manual/development-environment:yocto project source repositories` in the
following two locations::

   poky/meta-yocto-bsp/wic
   poky/scripts/lib/wic/canned-wks

Use the following command to list the available kickstart files::

   $ wic list images
     genericx86                    		Create an EFI disk image for genericx86*
     beaglebone-yocto              		Create SD card image for Beaglebone
     edgerouter                    		Create SD card image for Edgerouter
     qemux86-directdisk            		Create a QEMU machine 'pcbios' direct disk image
     directdisk-gpt                		Create a 'pcbios' direct disk image
     mkefidisk                     		Create an EFI disk image
     directdisk                    		Create a 'pcbios' direct disk image
     systemd-bootdisk              		Create an EFI disk image with systemd-boot
     mkhybridiso                   		Create a hybrid ISO image
     sdimage-bootpart              		Create SD card image with a boot partition
     directdisk-multi-rootfs       		Create multi rootfs image using rootfs plugin
     directdisk-bootloader-config  		Create a 'pcbios' direct disk image with custom bootloader config

When you use an existing file, you
do not have to use the ``.wks`` extension. Here is an example in Raw
Mode that uses the ``directdisk`` file::

   $ wic create directdisk -r rootfs_dir -b bootimg_dir \
         -k kernel_dir -n native_sysroot

Here are the actual partition language commands used in the
``genericx86.wks`` file to generate an image::

   # short-description: Create an EFI disk image for genericx86*
   # long-description: Creates a partitioned EFI disk image for genericx86* machines
   part /boot --source bootimg-efi --sourceparams="loader=grub-efi" --ondisk sda --label msdos --active --align 1024
   part / --source rootfs --ondisk sda --fstype=ext4 --label platform --align 1024 --use-uuid
   part swap --ondisk sda --size 44 --label swap1 --fstype=swap

   bootloader --ptable gpt --timeout=5 --append="rootfstype=ext4 console=ttyS0,115200 console=tty0"

Using the Wic Plugin Interface
==============================

You can extend and specialize Wic functionality by using Wic plugins.
This section explains the Wic plugin interface.

.. note::

   Wic plugins consist of "source" and "imager" plugins. Imager plugins
   are beyond the scope of this section.

Source plugins provide a mechanism to customize partition content during
the Wic image generation process. You can use source plugins to map
values that you specify using ``--source`` commands in kickstart files
(i.e. ``*.wks``) to a plugin implementation used to populate a given
partition.

.. note::

   If you use plugins that have build-time dependencies (e.g. native
   tools, bootloaders, and so forth) when building a Wic image, you need
   to specify those dependencies using the :term:`WKS_FILE_DEPENDS`
   variable.

Source plugins are subclasses defined in plugin files. As shipped, the
Yocto Project provides several plugin files. You can see the source
plugin files that ship with the Yocto Project
:yocto_git:`here </poky/tree/scripts/lib/wic/plugins/source>`.
Each of these plugin files contains source plugins that are designed to
populate a specific Wic image partition.

Source plugins are subclasses of the ``SourcePlugin`` class, which is
defined in the ``poky/scripts/lib/wic/pluginbase.py`` file. For example,
the ``BootimgEFIPlugin`` source plugin found in the ``bootimg-efi.py``
file is a subclass of the ``SourcePlugin`` class, which is found in the
``pluginbase.py`` file.

You can also implement source plugins in a layer outside of the Source
Repositories (external layer). To do so, be sure that your plugin files
are located in a directory whose path is
``scripts/lib/wic/plugins/source/`` within your external layer. When the
plugin files are located there, the source plugins they contain are made
available to Wic.

When the Wic implementation needs to invoke a partition-specific
implementation, it looks for the plugin with the same name as the
``--source`` parameter used in the kickstart file given to that
partition. For example, if the partition is set up using the following
command in a kickstart file::

   part /boot --source bootimg-pcbios --ondisk sda --label boot --active --align 1024

The methods defined as class
members of the matching source plugin (i.e. ``bootimg-pcbios``) in the
``bootimg-pcbios.py`` plugin file are used.

To be more concrete, here is the corresponding plugin definition from
the ``bootimg-pcbios.py`` file for the previous command along with an
example method called by the Wic implementation when it needs to prepare
a partition using an implementation-specific function::

                .
                .
                .
   class BootimgPcbiosPlugin(SourcePlugin):
       """
       Create MBR boot partition and install syslinux on it.
       """

      name = 'bootimg-pcbios'
                .
                .
                .
       @classmethod
       def do_prepare_partition(cls, part, source_params, creator, cr_workdir,
                                oe_builddir, bootimg_dir, kernel_dir,
                                rootfs_dir, native_sysroot):
           """
           Called to do the actual content population for a partition i.e. it
           'prepares' the partition to be incorporated into the image.
           In this case, prepare content for legacy bios boot partition.
           """
                .
                .
                .

If a
subclass (plugin) itself does not implement a particular function, Wic
locates and uses the default version in the superclass. It is for this
reason that all source plugins are derived from the ``SourcePlugin``
class.

The ``SourcePlugin`` class defined in the ``pluginbase.py`` file defines
a set of methods that source plugins can implement or override. Any
plugins (subclass of ``SourcePlugin``) that do not implement a
particular method inherit the implementation of the method from the
``SourcePlugin`` class. For more information, see the ``SourcePlugin``
class in the ``pluginbase.py`` file for details:

The following list describes the methods implemented in the
``SourcePlugin`` class:

-  ``do_prepare_partition()``: Called to populate a partition with
   actual content. In other words, the method prepares the final
   partition image that is incorporated into the disk image.

-  ``do_configure_partition()``: Called before
   ``do_prepare_partition()`` to create custom configuration files for a
   partition (e.g. syslinux or grub configuration files).

-  ``do_install_disk()``: Called after all partitions have been
   prepared and assembled into a disk image. This method provides a hook
   to allow finalization of a disk image (e.g. writing an MBR).

-  ``do_stage_partition()``: Special content-staging hook called
   before ``do_prepare_partition()``. This method is normally empty.

   Typically, a partition just uses the passed-in parameters (e.g. the
   unmodified value of ``bootimg_dir``). However, in some cases, things
   might need to be more tailored. As an example, certain files might
   additionally need to be taken from ``bootimg_dir + /boot``. This hook
   allows those files to be staged in a customized fashion.

   .. note::

      ``get_bitbake_var()`` allows you to access non-standard variables that
      you might want to use for this behavior.

You can extend the source plugin mechanism. To add more hooks, create
more source plugin methods within ``SourcePlugin`` and the corresponding
derived subclasses. The code that calls the plugin methods uses the
``plugin.get_source_plugin_methods()`` function to find the method or
methods needed by the call. Retrieval of those methods is accomplished
by filling up a dict with keys that contain the method names of
interest. On success, these will be filled in with the actual methods.
See the Wic implementation for examples and details.

Wic Examples
============

This section provides several examples that show how to use the Wic
utility. All the examples assume the list of requirements in the
":ref:`dev-manual/wic:requirements`" section have been met. The
examples assume the previously generated image is
``core-image-minimal``.

Generate an Image using an Existing Kickstart File
--------------------------------------------------

This example runs in Cooked Mode and uses the ``mkefidisk`` kickstart
file::

   $ wic create mkefidisk -e core-image-minimal
   INFO: Building wic-tools...
             .
             .
             .
   INFO: The new image(s) can be found here:
     ./mkefidisk-201804191017-sda.direct

   The following build artifacts were used to create the image(s):
     ROOTFS_DIR:                   /home/stephano/yocto/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR:                  /home/stephano/yocto/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
     KERNEL_DIR:                   /home/stephano/yocto/build/tmp-glibc/deploy/images/qemux86
     NATIVE_SYSROOT:               /home/stephano/yocto/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

   INFO: The image(s) were created using OE kickstart file:
     /home/stephano/yocto/openembedded-core/scripts/lib/wic/canned-wks/mkefidisk.wks

The previous example shows the easiest way to create an image by running
in cooked mode and supplying a kickstart file and the "-e" option to
point to the existing build artifacts. Your ``local.conf`` file needs to
have the :term:`MACHINE` variable set
to the machine you are using, which is "qemux86" in this example.

Once the image builds, the output provides image location, artifact use,
and kickstart file information.

.. note::

   You should always verify the details provided in the output to make
   sure that the image was indeed created exactly as expected.

Continuing with the example, you can now write the image from the
:term:`Build Directory` onto a USB stick, or whatever media for which you
built your image, and boot from the media. You can write the image by using
``bmaptool`` or ``dd``::

   $ oe-run-native bmap-tools-native bmaptool copy mkefidisk-201804191017-sda.direct /dev/sdX

or ::

   $ sudo dd if=mkefidisk-201804191017-sda.direct of=/dev/sdX

.. note::

   For more information on how to use the ``bmaptool``
   to flash a device with an image, see the
   ":ref:`dev-manual/bmaptool:flashing images using \`\`bmaptool\`\``"
   section.

Using a Modified Kickstart File
-------------------------------

Because partitioned image creation is driven by the kickstart file, it
is easy to affect image creation by changing the parameters in the file.
This next example demonstrates that through modification of the
``directdisk-gpt`` kickstart file.

As mentioned earlier, you can use the command ``wic list images`` to
show the list of existing kickstart files. The directory in which the
``directdisk-gpt.wks`` file resides is
``scripts/lib/image/canned-wks/``, which is located in the
:term:`Source Directory` (e.g. ``poky``).
Because available files reside in this directory, you can create and add
your own custom files to the directory. Subsequent use of the
``wic list images`` command would then include your kickstart files.

In this example, the existing ``directdisk-gpt`` file already does most
of what is needed. However, for the hardware in this example, the image
will need to boot from ``sdb`` instead of ``sda``, which is what the
``directdisk-gpt`` kickstart file uses.

The example begins by making a copy of the ``directdisk-gpt.wks`` file
in the ``scripts/lib/image/canned-wks`` directory and then by changing
the lines that specify the target disk from which to boot::

   $ cp /home/stephano/yocto/poky/scripts/lib/wic/canned-wks/directdisk-gpt.wks \
        /home/stephano/yocto/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks

Next, the example modifies the ``directdisksdb-gpt.wks`` file and
changes all instances of "``--ondisk sda``" to "``--ondisk sdb``". The
example changes the following two lines and leaves the remaining lines
untouched::

   part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024
   part / --source rootfs --ondisk sdb --fstype=ext4 --label platform --align 1024 --use-uuid

Once the lines are changed, the
example generates the ``directdisksdb-gpt`` image. The command points
the process at the ``core-image-minimal`` artifacts for the Next Unit of
Computing (nuc) :term:`MACHINE` the
``local.conf``::

   $ wic create directdisksdb-gpt -e core-image-minimal
   INFO: Building wic-tools...
              .
              .
              .
   Initialising tasks: 100% |#######################################| Time: 0:00:01
   NOTE: Executing SetScene Tasks
   NOTE: Executing RunQueue Tasks
   NOTE: Tasks Summary: Attempted 1161 tasks of which 1157 didn't need to be rerun and all succeeded.
   INFO: Creating image(s)...

   INFO: The new image(s) can be found here:
     ./directdisksdb-gpt-201710090938-sdb.direct

   The following build artifacts were used to create the image(s):
     ROOTFS_DIR:                   /home/stephano/yocto/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR:                  /home/stephano/yocto/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
     KERNEL_DIR:                   /home/stephano/yocto/build/tmp-glibc/deploy/images/qemux86
     NATIVE_SYSROOT:               /home/stephano/yocto/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

   INFO: The image(s) were created using OE kickstart file:
     /home/stephano/yocto/poky/scripts/lib/wic/canned-wks/directdisksdb-gpt.wks

Continuing with the example, you can now directly ``dd`` the image to a
USB stick, or whatever media for which you built your image, and boot
the resulting media::

   $ sudo dd if=directdisksdb-gpt-201710090938-sdb.direct of=/dev/sdb
   140966+0 records in
   140966+0 records out
   72174592 bytes (72 MB, 69 MiB) copied, 78.0282 s, 925 kB/s
   $ sudo eject /dev/sdb

Using a Modified Kickstart File and Running in Raw Mode
-------------------------------------------------------

This next example manually specifies each build artifact (runs in Raw
Mode) and uses a modified kickstart file. The example also uses the
``-o`` option to cause Wic to create the output somewhere other than the
default output directory, which is the current directory::

   $ wic create test.wks -o /home/stephano/testwic \
        --rootfs-dir /home/stephano/yocto/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/rootfs \
        --bootimg-dir /home/stephano/yocto/build/tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share \
        --kernel-dir /home/stephano/yocto/build/tmp/deploy/images/qemux86 \
        --native-sysroot /home/stephano/yocto/build/tmp/work/i586-poky-linux/wic-tools/1.0-r0/recipe-sysroot-native

   INFO: Creating image(s)...

   INFO: The new image(s) can be found here:
     /home/stephano/testwic/test-201710091445-sdb.direct

   The following build artifacts were used to create the image(s):
     ROOTFS_DIR:                   /home/stephano/yocto/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR:                  /home/stephano/yocto/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share
     KERNEL_DIR:                   /home/stephano/yocto/build/tmp-glibc/deploy/images/qemux86
     NATIVE_SYSROOT:               /home/stephano/yocto/build/tmp-glibc/work/i586-oe-linux/wic-tools/1.0-r0/recipe-sysroot-native

   INFO: The image(s) were created using OE kickstart file:
     test.wks

For this example,
:term:`MACHINE` did not have to be
specified in the ``local.conf`` file since the artifact is manually
specified.

Using Wic to Manipulate an Image
--------------------------------

Wic image manipulation allows you to shorten turnaround time during
image development. For example, you can use Wic to delete the kernel
partition of a Wic image and then insert a newly built kernel. This
saves you time from having to rebuild the entire image each time you
modify the kernel.

.. note::

   In order to use Wic to manipulate a Wic image as in this example,
   your development machine must have the ``mtools`` package installed.

The following example examines the contents of the Wic image, deletes
the existing kernel, and then inserts a new kernel:

#. *List the Partitions:* Use the ``wic ls`` command to list all the
   partitions in the Wic image::

      $ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic
      Num     Start        End          Size      Fstype
       1       1048576     25041919     23993344  fat16
       2      25165824     72157183     46991360  ext4

   The previous output shows two partitions in the
   ``core-image-minimal-qemux86.wic`` image.

#. *Examine a Particular Partition:* Use the ``wic ls`` command again
   but in a different form to examine a particular partition.

   .. note::

      You can get command usage on any Wic command using the following
      form::

              $ wic help command


      For example, the following command shows you the various ways to
      use the
      wic ls
      command::

              $ wic help ls


   The following command shows what is in partition one::

        $ wic ls tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1
        Volume in drive : is boot
         Volume Serial Number is E894-1809
        Directory for ::/

        libcom32 c32    186500 2017-10-09  16:06
        libutil  c32     24148 2017-10-09  16:06
        syslinux cfg       220 2017-10-09  16:06
        vesamenu c32     27104 2017-10-09  16:06
        vmlinuz        6904608 2017-10-09  16:06
                5 files           7 142 580 bytes
                                 16 582 656 bytes free

   The previous output shows five files, with the
   ``vmlinuz`` being the kernel.

   .. note::

      If you see the following error, you need to update or create a
      ``~/.mtoolsrc`` file and be sure to have the line "mtools_skip_check=1"
      in the file. Then, run the Wic command again::

              ERROR: _exec_cmd: /usr/bin/mdir -i /tmp/wic-parttfokuwra ::/ returned '1' instead of 0
               output: Total number of sectors (47824) not a multiple of sectors per track (32)!
               Add mtools_skip_check=1 to your .mtoolsrc file to skip this test


#. *Remove the Old Kernel:* Use the ``wic rm`` command to remove the
   ``vmlinuz`` file (kernel)::

      $ wic rm tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz

#. *Add In the New Kernel:* Use the ``wic cp`` command to add the
   updated kernel to the Wic image. Depending on how you built your
   kernel, it could be in different places. If you used ``devtool`` and
   an SDK to build your kernel, it resides in the ``tmp/work`` directory
   of the extensible SDK. If you used ``make`` to build the kernel, the
   kernel will be in the ``workspace/sources`` area.

   The following example assumes ``devtool`` was used to build the
   kernel::

      $ wic cp poky_sdk/tmp/work/qemux86-poky-linux/linux-yocto/4.12.12+git999-r0/linux-yocto-4.12.12+git999/arch/x86/boot/bzImage \
               poky/build/tmp/deploy/images/qemux86/core-image-minimal-qemux86.wic:1/vmlinuz

   Once the new kernel is added back into the image, you can use the
   ``dd`` command or :ref:`bmaptool
   <dev-manual/bmaptool:flashing images using \`\`bmaptool\`\`>`
   to flash your wic image onto an SD card or USB stick and test your
   target.

   .. note::

      Using ``bmaptool`` is generally 10 to 20 times faster than using ``dd``.