path: root/documentation/ref-manual/faq.rst

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

***
FAQ
***

**Q:** How does Poky differ from :oe_home:`OpenEmbedded <>`?

**A:** The term ``Poky`` refers to the specific reference build
system that the Yocto Project provides. Poky is based on
:term:`OpenEmbedded-Core (OE-Core)` and :term:`BitBake`. Thus, the
generic term used here for the build system is the "OpenEmbedded build
system." Development in the Yocto Project using Poky is closely tied to
OpenEmbedded, with changes always being merged to OE-Core or BitBake
first before being pulled back into Poky. This practice benefits both
projects immediately.

**Q:** My development system does not meet the required Git, tar, and
Python versions. In particular, I do not have Python 3.5.0 or greater.
Can I still use the Yocto Project?

**A:** You can get the required tools on your host development system a
couple different ways (i.e. building a tarball or downloading a
tarball). See the
":ref:`ref-manual/system-requirements:required git, tar, python and gcc versions`"
section for steps on how to update your build tools.

**Q:** How can you claim Poky / OpenEmbedded-Core is stable?

**A:** There are three areas that help with stability;

-  The Yocto Project team keeps :term:`OpenEmbedded-Core (OE-Core)` small and
   focused, containing around 830 recipes as opposed to the thousands
   available in other OpenEmbedded community layers. Keeping it small
   makes it easy to test and maintain.

-  The Yocto Project team runs manual and automated tests using a small,
   fixed set of reference hardware as well as emulated targets.

-  The Yocto Project uses an autobuilder, which provides continuous
   build and integration tests.

**Q:** How do I get support for my board added to the Yocto Project?

**A:** Support for an additional board is added by creating a Board
Support Package (BSP) layer for it. For more information on how to
create a BSP layer, see the
":ref:`dev-manual/common-tasks:understanding and creating layers`"
section in the Yocto Project Development Tasks Manual and the
:doc:`/bsp-guide/index`.

Usually, if the board is not completely exotic, adding support in the
Yocto Project is fairly straightforward.

**Q:** Are there any products built using the OpenEmbedded build system?

**A:** The software running on the `Vernier
LabQuest <https://vernier.com/labquest/>`__ is built using the
OpenEmbedded build system. See the `Vernier
LabQuest <https://www.vernier.com/products/interfaces/labq/>`__ website
for more information. There are a number of pre-production devices using
the OpenEmbedded build system and the Yocto Project team announces them
as soon as they are released.

**Q:** What does the OpenEmbedded build system produce as output?

**A:** Because you can use the same set of recipes to create output of
various formats, the output of an OpenEmbedded build depends on how you
start it. Usually, the output is a flashable image ready for the target
device.

**Q:** How do I add my package to the Yocto Project?

**A:** To add a package, you need to create a BitBake recipe. For
information on how to create a BitBake recipe, see the
":ref:`dev-manual/common-tasks:writing a new recipe`"
section in the Yocto Project Development Tasks Manual.

**Q:** Do I have to reflash my entire board with a new Yocto Project
image when recompiling a package?

**A:** The OpenEmbedded build system can build packages in various
formats such as IPK for OPKG, Debian package (``.deb``), or RPM. You can
then upgrade the packages using the package tools on the device, much
like on a desktop distribution such as Ubuntu or Fedora. However,
package management on the target is entirely optional.

**Q:** I see the error
'``chmod: XXXXX new permissions are r-xrwxrwx, not r-xr-xr-x``'. What is
wrong?

**A:** You are probably running the build on an NTFS filesystem. Use
``ext2``, ``ext3``, or ``ext4`` instead.

**Q:** I see lots of 404 responses for files when the OpenEmbedded build
system is trying to download sources. Is something wrong?

**A:** Nothing is wrong. The OpenEmbedded build system checks any
configured source mirrors before downloading from the upstream sources.
The build system does this searching for both source archives and
pre-checked out versions of SCM-managed software. These checks help in
large installations because it can reduce load on the SCM servers
themselves. The address above is one of the default mirrors configured
into the build system. Consequently, if an upstream source disappears,
the team can place sources there so builds continue to work.

**Q:** I have machine-specific data in a package for one machine only
but the package is being marked as machine-specific in all cases, how do
I prevent this?

**A:** Set ``SRC_URI_OVERRIDES_PACKAGE_ARCH`` = "0" in the ``.bb`` file
but make sure the package is manually marked as machine-specific for the
case that needs it. The code that handles
``SRC_URI_OVERRIDES_PACKAGE_ARCH`` is in the
``meta/classes/base.bbclass`` file.

**Q:** I'm behind a firewall and need to use a proxy server. How do I do
that?

**A:** Most source fetching by the OpenEmbedded build system is done by
``wget`` and you therefore need to specify the proxy settings in a
``.wgetrc`` file, which can be in your home directory if you are a
single user or can be in ``/usr/local/etc/wgetrc`` as a global user
file.

Following is the applicable code for setting various proxy types in the
``.wgetrc`` file. By default, these settings are disabled with comments.
To use them, remove the comments: ::

   # You can set the default proxies for Wget to use for http, https, and ftp.
   # They will override the value in the environment.
   #https_proxy = http://proxy.yoyodyne.com:18023/
   #http_proxy = http://proxy.yoyodyne.com:18023/
   #ftp_proxy = http://proxy.yoyodyne.com:18023/

   # If you do not want to use proxy at all, set this to off.
   #use_proxy = on

The Yocto Project also includes a
``meta-poky/conf/site.conf.sample`` file that shows how to configure CVS
and Git proxy servers if needed. For more information on setting up
various proxy types and configuring proxy servers, see the
":yocto_wiki:`Working Behind a Network Proxy </Working_Behind_a_Network_Proxy>`"
Wiki page.

**Q:** What's the difference between target and target\ ``-native``?

**A:** The ``*-native`` targets are designed to run on the system being
used for the build. These are usually tools that are needed to assist
the build in some way such as ``quilt-native``, which is used to apply
patches. The non-native version is the one that runs on the target
device.

**Q:** I'm seeing random build failures. Help?!

**A:** If the same build is failing in totally different and random
ways, the most likely explanation is:

-  The hardware you are running the build on has some problem.

-  You are running the build under virtualization, in which case the
   virtualization probably has bugs.

The OpenEmbedded build system processes a massive amount of data that
causes lots of network, disk and CPU activity and is sensitive to even
single-bit failures in any of these areas. True random failures have
always been traced back to hardware or virtualization issues.

**Q:** When I try to build a native recipe, the build fails with
``iconv.h`` problems.

**A:** If you get an error message that indicates GNU ``libiconv`` is
not in use but ``iconv.h`` has been included from ``libiconv``, you need
to check to see if you have a previously installed version of the header
file in ``/usr/local/include``.
::

   #error GNU libiconv not in use but included iconv.h is from libiconv

If you find a previously installed
file, you should either uninstall it or temporarily rename it and try
the build again.

This issue is just a single manifestation of "system leakage" issues
caused when the OpenEmbedded build system finds and uses previously
installed files during a native build. This type of issue might not be
limited to ``iconv.h``. Be sure that leakage cannot occur from
``/usr/local/include`` and ``/opt`` locations.

**Q:** What do we need to ship for license compliance?

**A:** This is a difficult question and you need to consult your lawyer
for the answer for your specific case. It is worth bearing in mind that
for GPL compliance, there needs to be enough information shipped to
allow someone else to rebuild and produce the same end result you are
shipping. This means sharing the source code, any patches applied to it,
and also any configuration information about how that package was
configured and built.

You can find more information on licensing in the
":ref:`overview-manual/development-environment:licensing`"
section in the Yocto
Project Overview and Concepts Manual and also in the
":ref:`dev-manual/common-tasks:maintaining open source license compliance during your product's lifecycle`"
section in the Yocto Project Development Tasks Manual.

**Q:** How do I disable the cursor on my touchscreen device?

**A:** You need to create a form factor file as described in the
":ref:`bsp-guide/bsp:miscellaneous bsp-specific recipe files`" section in
the Yocto Project Board Support Packages (BSP) Developer's Guide. Set
the ``HAVE_TOUCHSCREEN`` variable equal to one as follows:
::

   HAVE_TOUCHSCREEN=1

**Q:** How do I make sure connected network interfaces are brought up by
default?

**A:** The default interfaces file provided by the netbase recipe does
not automatically bring up network interfaces. Therefore, you will need
to add a BSP-specific netbase that includes an interfaces file. See the
":ref:`bsp-guide/bsp:miscellaneous bsp-specific recipe files`" section in
the Yocto Project Board Support Packages (BSP) Developer's Guide for
information on creating these types of miscellaneous recipe files.

For example, add the following files to your layer: ::

   meta-MACHINE/recipes-bsp/netbase/netbase/MACHINE/interfaces
   meta-MACHINE/recipes-bsp/netbase/netbase_5.0.bbappend

**Q:** How do I create images with more free space?

**A:** By default, the OpenEmbedded build system creates images that are
1.3 times the size of the populated root filesystem. To affect the image
size, you need to set various configurations:

-  *Image Size:* The OpenEmbedded build system uses the
   :term:`IMAGE_ROOTFS_SIZE` variable to define
   the size of the image in Kbytes. The build system determines the size
   by taking into account the initial root filesystem size before any
   modifications such as requested size for the image and any requested
   additional free disk space to be added to the image.

-  *Overhead:* Use the
   :term:`IMAGE_OVERHEAD_FACTOR` variable
   to define the multiplier that the build system applies to the initial
   image size, which is 1.3 by default.

-  *Additional Free Space:* Use the
   :term:`IMAGE_ROOTFS_EXTRA_SPACE`
   variable to add additional free space to the image. The build system
   adds this space to the image after it determines its
   ``IMAGE_ROOTFS_SIZE``.

**Q:** Why don't you support directories with spaces in the pathnames?

**A:** The Yocto Project team has tried to do this before but too many
of the tools the OpenEmbedded build system depends on, such as
``autoconf``, break when they find spaces in pathnames. Until that
situation changes, the team will not support spaces in pathnames.

**Q:** How do I use an external toolchain?

**A:** The toolchain configuration is very flexible and customizable. It
is primarily controlled with the ``TCMODE`` variable. This variable
controls which ``tcmode-*.inc`` file to include from the
``meta/conf/distro/include`` directory within the :term:`Source Directory`.

The default value of ``TCMODE`` is "default", which tells the
OpenEmbedded build system to use its internally built toolchain (i.e.
``tcmode-default.inc``). However, other patterns are accepted. In
particular, "external-\*" refers to external toolchains. One example is
the Sourcery G++ Toolchain. The support for this toolchain resides in
the separate ``meta-sourcery`` layer at
https://github.com/MentorEmbedded/meta-sourcery/.

In addition to the toolchain configuration, you also need a
corresponding toolchain recipe file. This recipe file needs to package
up any pre-built objects in the toolchain such as ``libgcc``,
``libstdcc++``, any locales, and ``libc``.

**Q:** How does the OpenEmbedded build system obtain source code and
will it work behind my firewall or proxy server?

**A:** The way the build system obtains source code is highly
configurable. You can setup the build system to get source code in most
environments if HTTP transport is available.

When the build system searches for source code, it first tries the local
download directory. If that location fails, Poky tries
:term:`PREMIRRORS`, the upstream source, and then
:term:`MIRRORS` in that order.

Assuming your distribution is "poky", the OpenEmbedded build system uses
the Yocto Project source ``PREMIRRORS`` by default for SCM-based
sources, upstreams for normal tarballs, and then falls back to a number
of other mirrors including the Yocto Project source mirror if those
fail.

As an example, you could add a specific server for the build system to
attempt before any others by adding something like the following to the
``local.conf`` configuration file: ::

   PREMIRRORS_prepend = "\
       git://.*/.* http://www.yoctoproject.org/sources/ \n \
       ftp://.*/.* http://www.yoctoproject.org/sources/ \n \
       http://.*/.* http://www.yoctoproject.org/sources/ \n \
       https://.*/.* http://www.yoctoproject.org/sources/ \n"

These changes cause the build system to intercept Git, FTP, HTTP, and
HTTPS requests and direct them to the ``http://`` sources mirror. You
can use ``file://`` URLs to point to local directories or network shares
as well.

Aside from the previous technique, these options also exist:
::

   BB_NO_NETWORK = "1"

This statement tells BitBake to issue an error
instead of trying to access the Internet. This technique is useful if
you want to ensure code builds only from local sources.

Here is another technique:
::

   BB_FETCH_PREMIRRORONLY = "1"

This statement
limits the build system to pulling source from the ``PREMIRRORS`` only.
Again, this technique is useful for reproducing builds.

Here is another technique:
::

   BB_GENERATE_MIRROR_TARBALLS = "1"

This
statement tells the build system to generate mirror tarballs. This
technique is useful if you want to create a mirror server. If not,
however, the technique can simply waste time during the build.

Finally, consider an example where you are behind an HTTP-only firewall.
You could make the following changes to the ``local.conf`` configuration
file as long as the ``PREMIRRORS`` server is current: ::

   PREMIRRORS_prepend = "\
       ftp://.*/.* http://www.yoctoproject.org/sources/ \n \
       http://.*/.* http://www.yoctoproject.org/sources/ \n \
       https://.*/.* http://www.yoctoproject.org/sources/ \n"
   BB_FETCH_PREMIRRORONLY = "1"

These changes would cause the build system to successfully fetch source
over HTTP and any network accesses to anything other than the
``PREMIRRORS`` would fail.

The build system also honors the standard shell environment variables
``http_proxy``, ``ftp_proxy``, ``https_proxy``, and ``all_proxy`` to
redirect requests through proxy servers.

.. note::

   You can find more information on the
   ":yocto_wiki:`Working Behind a Network Proxy </Working_Behind_a_Network_Proxy>`"
   Wiki page.

**Q:** Can I get rid of build output so I can start over?

**A:** Yes - you can easily do this. When you use BitBake to build an
image, all the build output goes into the directory created when you run
the build environment setup script (i.e.
:ref:`structure-core-script`). By default, this :term:`Build Directory`
is named ``build`` but can be named
anything you want.

Within the Build Directory, is the ``tmp`` directory. To remove all the
build output yet preserve any source code or downloaded files from
previous builds, simply remove the ``tmp`` directory.

**Q:** Why do ``${bindir}`` and ``${libdir}`` have strange values for
``-native`` recipes?

**A:** Executables and libraries might need to be used from a directory
other than the directory into which they were initially installed.
Complicating this situation is the fact that sometimes these executables
and libraries are compiled with the expectation of being run from that
initial installation target directory. If this is the case, moving them
causes problems.

This scenario is a fundamental problem for package maintainers of
mainstream Linux distributions as well as for the OpenEmbedded build
system. As such, a well-established solution exists. Makefiles,
Autotools configuration scripts, and other build systems are expected to
respect environment variables such as ``bindir``, ``libdir``, and
``sysconfdir`` that indicate where executables, libraries, and data
reside when a program is actually run. They are also expected to respect
a ``DESTDIR`` environment variable, which is prepended to all the other
variables when the build system actually installs the files. It is
understood that the program does not actually run from within
``DESTDIR``.

When the OpenEmbedded build system uses a recipe to build a
target-architecture program (i.e. one that is intended for inclusion on
the image being built), that program eventually runs from the root file
system of that image. Thus, the build system provides a value of
"/usr/bin" for ``bindir``, a value of "/usr/lib" for ``libdir``, and so
forth.

Meanwhile, ``DESTDIR`` is a path within the :term:`Build Directory`.
However, when the recipe builds a
native program (i.e. one that is intended to run on the build machine),
that program is never installed directly to the build machine's root
file system. Consequently, the build system uses paths within the Build
Directory for ``DESTDIR``, ``bindir`` and related variables. To better
understand this, consider the following two paths where the first is
relatively normal and the second is not:

.. note::

   Due to these lengthy examples, the paths are artificially broken
   across lines for readability.

::

   /home/maxtothemax/poky-bootchart2/build/tmp/work/i586-poky-linux/zlib/
      1.2.8-r0/sysroot-destdir/usr/bin

   /home/maxtothemax/poky-bootchart2/build/tmp/work/x86_64-linux/
      zlib-native/1.2.8-r0/sysroot-destdir/home/maxtothemax/poky-bootchart2/
      build/tmp/sysroots/x86_64-linux/usr/bin

Even if the paths look unusual,
they both are correct - the first for a target and the second for a
native recipe. These paths are a consequence of the ``DESTDIR``
mechanism and while they appear strange, they are correct and in
practice very effective.

**Q:** The files provided by my ``*-native`` recipe do not appear to be
available to other recipes. Files are missing from the native sysroot,
my recipe is installing to the wrong place, or I am getting permissions
errors during the do_install task in my recipe! What is wrong?

**A:** This situation results when a build system does not recognize the
environment variables supplied to it by :term:`BitBake`. The
incident that prompted this FAQ entry involved a Makefile that used an
environment variable named ``BINDIR`` instead of the more standard
variable ``bindir``. The makefile's hardcoded default value of
"/usr/bin" worked most of the time, but not for the recipe's ``-native``
variant. For another example, permissions errors might be caused by a
Makefile that ignores ``DESTDIR`` or uses a different name for that
environment variable. Check the the build system to see if these kinds
of issues exist.

**Q:** I'm adding a binary in a recipe but it's different in the image, what is
changing it?

**A:** The first most obvious change is the system stripping debug symbols from
it. Setting :term:`INHIBIT_PACKAGE_STRIP` to stop debug symbols being stripped and/or
:term:`INHIBIT_PACKAGE_DEBUG_SPLIT` to stop debug symbols being split into a separate
file will ensure the binary is unchanged. The other less obvious thing that can
happen is prelinking of the image. This is set by default in local.conf via
:term:`USER_CLASSES` which can contain 'image-prelink'. If you remove that, the
image will not be prelinked meaning the binaries would be unchanged.