// -*- 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]
  * http://www.emdebian.org[emdebian]
  * 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/usr/<tuple>/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.