14 FAQ 

14.1 General questions 

14.1.1 How does Poky differ from OpenEmbedded?

The term Poky refers to the specific reference build system that the Yocto Project provides. Poky is based on OpenEmbedded-Core (OE-Core) and 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.

14.1.2 How can you claim Poky / OpenEmbedded-Core is stable?

There are three areas that help with stability;

The Yocto Project team keeps 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.

14.1.3 Are there any products built using the OpenEmbedded build system?

See Products that use the Yocto Project in the Yocto Project Wiki. Don’t hesitate to contribute to this page if you know other such products.

14.2 Building environment 

14.2.1 Missing dependencies on the development system?

If your development system does not meet the required Git, tar, and Python versions, you can get the required tools on your host development system in different ways (i.e. building a tarball or downloading a tarball). See the “Required Git, tar, Python, make and gcc Versions” section for steps on how to update your build tools.

14.2.2 How does OpenEmbedded fetch source code? Will it work through a firewall or proxy server?

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 PREMIRRORS, the upstream source, and then 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://.*/.* https://downloads.yoctoproject.org/mirror/sources/ \
    ftp://.*/.* https://downloads.yoctoproject.org/mirror/sources/ \
    http://.*/.* https://downloads.yoctoproject.org/mirror/sources/ \
    https://.*/.* https://downloads.yoctoproject.org/mirror/sources/"

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.

Another option is to set:

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 yet 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 = "\
    git://.*/.* https://downloads.yoctoproject.org/mirror/sources/ \
    ftp://.*/.* https://downloads.yoctoproject.org/mirror/sources/ \
    http://.*/.* https://downloads.yoctoproject.org/mirror/sources/ \
    https://.*/.* https://downloads.yoctoproject.org/mirror/sources/"
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.

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.

Here 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 build system also accepts http_proxy, ftp_proxy, https_proxy, and all_proxy set as to standard shell environment variables to redirect requests through proxy servers.

The Yocto Project also includes a meta-poky/conf/templates/default/site.conf.sample file that shows how to configure CVS and Git proxy servers if needed.

Note

You can find more information on the “Working Behind a Network Proxy” Wiki page.

14.3 Using the OpenEmbedded Build system 

14.3.1 How do I use an external toolchain?

See the “Optionally Using an External Toolchain” section in the Development Task manual.

14.3.2 Why do I get chmod permission issues?

If you see the error chmod: XXXXX new permissions are r-xrwxrwx, not r-xr-xr-x, you are probably running the build on an NTFS filesystem. Instead, run the build system on a partition with a modern Linux filesystem such as ext4, btrfs or xfs.

14.3.3 I see many 404 errors trying to download sources. Is anything wrong?

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. This can also allow builds to continue to work if an upstream source disappears.

14.3.4 Why do I get random build failures?

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.

14.3.5 Why does the build fail with `iconv.h` problems?

When you try to build a native recipe, you may get an error message that indicates that GNU libiconv is not in use but iconv.h has been included from libiconv:

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

When this happens, you need to check whether you have a previously installed version of the header file in /usr/local/include/. If that’s the case, 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. Make sure that leakage cannot occur from /usr/local/include and /opt locations.

14.3.6 Why don’t other recipes find the files provided by my `*-native` recipe?

Files provided by your native recipe could be missing from the native sysroot, your recipe could also be installing to the wrong place, or you could be getting permission errors during the do_install task in your recipe.

This situation happens when the build system used by a package does not recognize the environment variables supplied to it by 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, permission errors might be caused by a Makefile that ignores DESTDIR or uses a different name for that environment variable. Check the build system of the package to see if these kinds of issues exist.

14.3.7 Can I get rid of build output so I can start over?

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. oe-init-build-env). By default, this 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.

14.3.8 Why isn’t there a way to append bbclass files like bbappend for recipes?

The Yocto Project has consciously chosen not to implement such functionality. Class code is designed to be shared and reused, and exposes some level of configuration to its users. We want to encourage people to share these changes so we can build the best classes.

If the append functionality was available for classes, our evidence and experience suggest that people would create their custom changes in their layer instead of sharing and discussing the issues and/or limitations they encountered. This would lead to bizarre class interactions when new layers are included. We therefore consciously choose to have a natural pressure to share class code improvements or fixes.

There are also technical considerations like which recipes a class append would apply to and how that would fit within the layer model. These are complications we think we can live without!

14.4 Customizing generated images 

14.4.1 What does the OpenEmbedded build system produce as output?

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.

14.4.2 How do I make the Yocto Project support my board?

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 “Understanding and Creating Layers” section in the Yocto Project Development Tasks Manual and the Yocto Project Board Support Package Developer’s Guide.

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

14.4.3 How do I make the Yocto Project support my package?

To add a package, you need to create a BitBake recipe. For information on how to create a BitBake recipe, see the “Writing a New Recipe” section in the Yocto Project Development Tasks Manual.

14.4.4 What do I need to ship for license compliance?

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 “Licensing” section in the Yocto Project Overview and Concepts Manual and also in the “Maintaining Open Source License Compliance During Your Product’s Lifecycle” section in the Yocto Project Development Tasks Manual.

14.4.5 Do I have to make a full reflash after recompiling one package?

The OpenEmbedded build system can build packages in various formats such as IPK for OPKG, Debian package (.deb), or RPM. You can then upgrade only the modified 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.

14.4.6 How to prevent my package from being marked as machine specific?

If you have machine-specific data in a package for one machine only but the package is being marked as machine-specific in all cases, you can set SRC_URI_OVERRIDES_PACKAGE_ARCH = “0” in the .bb file. However, 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-global/base.bbclass file.

14.4.7 What’s the difference between `target` and `target-native`?

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.

14.4.8 Why do `${bindir}` and `${libdir}` have strange values for `-native` recipes?

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 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 (artificially broken across lines for readability) where the first is relatively normal and the second is not:

/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.

14.4.9 How do I create images with more free space?

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 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 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 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.

14.4.10 Why aren’t spaces in path names supported?

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.

14.4.11 I’m adding a binary in a recipe. Why is it different in the image?

The first most obvious change is the system stripping debug symbols from it. Setting INHIBIT_PACKAGE_STRIP to stop debug symbols being stripped and/or INHIBIT_PACKAGE_DEBUG_SPLIT to stop debug symbols being split into a separate file will ensure the binary is unchanged.

14.5 Issues on the running system 

14.5.1 How do I disable the cursor on my touchscreen device?

You need to create a form factor file as described in the “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

14.5.2 How to always bring up connected network interfaces?

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 “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