// -*- mode:doc; -*- // vim: set syntax=asciidoc: == Frequently Asked Questions & Troubleshooting [[faq-boot-hang-after-starting]] === The boot hangs after 'Starting network...' If the boot process seems to hang after the following messages (messages not necessarily exactly similar, depending on the list of packages selected): ------------------------ Freeing init memory: 3972K Initializing random number generator... done. Starting network... Starting dropbear sshd: generating rsa key... generating dsa key... OK ------------------------ then it means that your system is running, but didn't start a shell on the serial console. In order to have the system start a shell on your serial console, you have to go into the Buildroot configuration, in +System configuration+, modify +Run a getty (login prompt) after boot+ and set the appropriate port and baud rate in the +getty options+ submenu. This will automatically tune the +/etc/inittab+ file of the generated system so that a shell starts on the correct serial port. [[faq-no-compiler-on-target]] === Why is there no compiler on the target? It has been decided that support for the _native compiler on the target_ would be stopped from the Buildroot-2012.11 release because: * this feature was neither maintained nor tested, and often broken; * this feature was only available for Buildroot toolchains; * Buildroot mostly targets _small_ or _very small_ target hardware with limited resource onboard (CPU, ram, mass-storage), for which compiling on the target does not make much sense; * Buildroot aims at easing the cross-compilation, making native compilation on the target unnecessary. If you need a compiler on your target anyway, then Buildroot is not suitable for your purpose. In such case, you need a _real distribution_ and you should opt for something like: * http://www.openembedded.org[openembedded] * https://www.yoctoproject.org[yocto] * https://www.debian.org/ports/[Debian] * https://fedoraproject.org/wiki/Architectures[Fedora] * http://en.opensuse.org/Portal:ARM[openSUSE ARM] * http://archlinuxarm.org[Arch Linux ARM] * ... [[faq-no-dev-files-on-target]] === Why are there no development files on the target? Since there is no compiler available on the target (see xref:faq-no-compiler-on-target[]), it does not make sense to waste space with headers or static libraries. Therefore, those files are always removed from the target since the Buildroot-2012.11 release. [[faq-no-doc-on-target]] === Why is there no documentation on the target? Because Buildroot mostly targets _small_ or _very small_ target hardware with limited resource onboard (CPU, ram, mass-storage), it does not make sense to waste space with the documentation data. If you need documentation data on your target anyway, then Buildroot is not suitable for your purpose, and you should look for a _real distribution_ (see: xref:faq-no-compiler-on-target[]). [[faq-why-not-visible-package]] === Why are some packages not visible in the Buildroot config menu? If a package exists in the Buildroot tree and does not appear in the config menu, this most likely means that some of the package's dependencies are not met. To know more about the dependencies of a package, search for the package symbol in the config menu (see xref:make-tips[]). Then, you may have to recursively enable several options (which correspond to the unmet dependencies) to finally be able to select the package. If the package is not visible due to some unmet toolchain options, then you should certainly run a full rebuild (see xref:make-tips[] for more explanations). [[faq-why-not-use-target-as-chroot]] === Why not use the target directory as a chroot directory? There are plenty of reasons to *not* use the target directory a chroot one, among these: * file ownerships, modes and permissions are not correctly set in the target directory; * device nodes are not created in the target directory. For these reasons, commands run through chroot, using the target directory as the new root, will most likely fail. If you want to run the target filesystem inside a chroot, or as an NFS root, then use the tarball image generated in +images/+ and extract it as root. [[faq-no-binary-packages]] === Why doesn't Buildroot generate binary packages (.deb, .ipkg...)? One feature that is often discussed on the Buildroot list is the general topic of "package management". To summarize, the idea would be to add some tracking of which Buildroot package installs what files, with the goals of: * being able to remove files installed by a package when this package gets unselected from the menuconfig; * being able to generate binary packages (ipk or other format) that can be installed on the target without re-generating a new root filesystem image. In general, most people think it is easy to do: just track which package installed what and remove it when the package is unselected. However, it is much more complicated than that: * It is not only about the +target/+ directory, but also the sysroot in +host//sysroot+ and the +host/+ directory itself. All files installed in those directories by various packages must be tracked. * When a package is unselected from the configuration, it is not sufficient to remove just the files it installed. One must also remove all its reverse dependencies (i.e. packages relying on it) and rebuild all those packages. For example, package A depends optionally on the OpenSSL library. Both are selected, and Buildroot is built. Package A is built with crypto support using OpenSSL. Later on, OpenSSL gets unselected from the configuration, but package A remains (since OpenSSL is an optional dependency, this is possible.) If only OpenSSL files are removed, then the files installed by package A are broken: they use a library that is no longer present on the target. Although this is technically doable, it adds a lot of complexity to Buildroot, which goes against the simplicity we try to stick to. * In addition to the previous problem, there is the case where the optional dependency is not even known to Buildroot. For example, package A in version 1.0 never used OpenSSL, but in version 2.0 it automatically uses OpenSSL if available. If the Buildroot .mk file hasn't been updated to take this into account, then package A will not be part of the reverse dependencies of OpenSSL and will not be removed and rebuilt when OpenSSL is removed. For sure, the .mk file of package A should be fixed to mention this optional dependency, but in the mean time, you can have non-reproducible behaviors. * The request is to also allow changes in the menuconfig to be applied on the output directory without having to rebuild everything from scratch. However, this is very difficult to achieve in a reliable way: what happens when the suboptions of a package are changed (we would have to detect this, and rebuild the package from scratch and potentially all its reverse dependencies), what happens if toolchain options are changed, etc. At the moment, what Buildroot does is clear and simple so its behaviour is very reliable and it is easy to support users. If configuration changes done in menuconfig are applied after the next make, then it has to work correctly and properly in all situations, and not have some bizarre corner cases. The risk is to get bug reports like "I have enabled package A, B and C, then ran make, then disabled package C and enabled package D and ran make, then re-enabled package C and enabled package E and then there is a build failure". Or worse "I did some configuration, then built, then did some changes, built, some more changes, built, some more changes, built, and now it fails, but I don't remember all the changes I did and in which order". This will be impossible to support. For all these reasons, the conclusion is that adding tracking of installed files to remove them when the package is unselected, or to generate a repository of binary packages, is something that is very hard to achieve reliably and will add a lot of complexity. On this matter, the Buildroot developers make this position statement: * Buildroot strives to make it easy to generate a root filesystem (hence the name, by the way.) That is what we want to make Buildroot good at: building root filesystems. * Buildroot is not meant to be a distribution (or rather, a distribution generator.) It is the opinion of most Buildroot developers that this is not a goal we should pursue. We believe that there are other tools better suited to generate a distro than Buildroot is. For example, http://openembedded.org/[Open Embedded], or https://openwrt.org/[openWRT], are such tools. * We prefer to push Buildroot in a direction that makes it easy (or even easier) to generate complete root filesystems. This is what makes Buildroot stands out in the crowd (among other things, of course!) * We believe that for most embedded Linux systems, binary packages are not necessary, and potentially harmful. When binary packages are used, it means that the system can be partially upgraded, which creates an enormous number of possible combinations of package versions that should be tested before doing the upgrade on the embedded device. On the other hand, by doing complete system upgrades by upgrading the entire root filesystem image at once, the image deployed to the embedded system is guaranteed to really be the one that has been tested and validated. [[faq-speeding-up-build]] === How to speed-up the build process? Since Buildroot often involves doing full rebuilds of the entire system that can be quite long, we provide below a number of tips to help reduce the build time: * Use a pre-built external toolchain instead of the default Buildroot internal toolchain. By using a pre-built Linaro toolchain (on ARM) or a Sourcery CodeBench toolchain (for ARM, x86, x86-64, MIPS, etc.), you will save the build time of the toolchain at each complete rebuild, approximately 15 to 20 minutes. Note that temporarily using an external toolchain does not prevent you to switch back to an internal toolchain (that may provide a higher level of customization) once the rest of your system is working; * Use the +ccache+ compiler cache (see: xref:ccache[]); * Learn about rebuilding only the few packages you actually care about (see xref:rebuild-pkg[]), but beware that sometimes full rebuilds are anyway necessary (see xref:full-rebuild[]); * Make sure you are not using a virtual machine for the Linux system used to run Buildroot. Most of the virtual machine technologies are known to cause a significant performance impact on I/O, which is really important for building source code; * Make sure that you're using only local files: do not attempt to do a build over NFS, which significantly slows down the build. Having the Buildroot download folder available locally also helps a bit. * Buy new hardware. SSDs and lots of RAM are key to speeding up the builds. * Experiment with top-level parallel build, see xref:top-level-parallel-build[].