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1 // -*- mode:doc; -*-
2 // vim: set syntax=asciidoc:
4 == Frequently Asked Questions & Troubleshooting
6 [[faq-boot-hang-after-starting]]
7 === The boot hangs after 'Starting network...'
9 If the boot process seems to hang after the following messages
10 (messages not necessarily exactly similar, depending on the list of
11 packages selected):
13 ------------------------
14 Freeing init memory: 3972K
15 Initializing random number generator... done.
16 Starting network...
17 Starting dropbear sshd: generating rsa key... generating dsa key... OK
18 ------------------------
20 then it means that your system is running, but didn't start a shell on
21 the serial console. In order to have the system start a shell on your
22 serial console, you have to go into the Buildroot configuration, in
23 +System configuration+, modify +Run a getty (login prompt) after boot+
24 and set the appropriate port and baud rate in the +getty options+
25 submenu. This will automatically tune the +/etc/inittab+ file of the
26 generated system so that a shell starts on the correct serial port.
28 [[faq-no-compiler-on-target]]
29 === Why is there no compiler on the target?
31 It has been decided that support for the _native compiler on the
32 target_ would be stopped from the Buildroot-2012.11 release because:
34 * this feature was neither maintained nor tested, and often broken;
35 * this feature was only available for Buildroot toolchains;
36 * Buildroot mostly targets _small_ or _very small_ target hardware
37 with limited resource onboard (CPU, ram, mass-storage), for which
38 compiling on the target does not make much sense;
39 * Buildroot aims at easing the cross-compilation, making native
40 compilation on the target unnecessary.
42 If you need a compiler on your target anyway, then Buildroot is not
43 suitable for your purpose. In such case, you need a _real
44 distribution_ and you should opt for something like:
46 * http://www.openembedded.org[openembedded]
47 * https://www.yoctoproject.org[yocto]
48 * http://www.emdebian.org[emdebian]
49 * https://fedoraproject.org/wiki/Architectures[Fedora]
50 * http://en.opensuse.org/Portal:ARM[openSUSE ARM]
51 * http://archlinuxarm.org[Arch Linux ARM]
52 * ...
54 [[faq-no-dev-files-on-target]]
55 === Why are there no development files on the target?
57 Since there is no compiler available on the target (see
58 xref:faq-no-compiler-on-target[]), it does not make sense to waste
59 space with headers or static libraries.
61 Therefore, those files are always removed from the target since the
62 Buildroot-2012.11 release.
64 [[faq-no-doc-on-target]]
65 === Why is there no documentation on the target?
67 Because Buildroot mostly targets _small_ or _very small_ target
68 hardware with limited resource onboard (CPU, ram, mass-storage), it
69 does not make sense to waste space with the documentation data.
71 If you need documentation data on your target anyway, then Buildroot
72 is not suitable for your purpose, and you should look for a _real
73 distribution_ (see: xref:faq-no-compiler-on-target[]).
75 [[faq-why-not-visible-package]]
76 === Why are some packages not visible in the Buildroot config menu?
78 If a package exists in the Buildroot tree and does not appear in the
79 config menu, this most likely means that some of the package's
80 dependencies are not met.
82 To know more about the dependencies of a package, search for the
83 package symbol in the config menu (see xref:make-tips[]).
85 Then, you may have to recursively enable several options (which
86 correspond to the unmet dependencies) to finally be able to select
87 the package.
89 If the package is not visible due to some unmet toolchain options,
90 then you should certainly run a full rebuild (see xref:make-tips[] for
91 more explanations).
93 [[faq-why-not-use-target-as-chroot]]
94 === Why not use the target directory as a chroot directory?
96 There are plenty of reasons to *not* use the target directory a chroot
97 one, among these:
99 * file ownerships, modes and permissions are not correctly set in the
100 target directory;
101 * device nodes are not created in the target directory.
103 For these reasons, commands run through chroot, using the target
104 directory as the new root, will most likely fail.
106 If you want to run the target filesystem inside a chroot, or as an NFS
107 root, then use the tarball image generated in +images/+ and extract it
108 as root.
110 [[faq-no-binary-packages]]
111 === Why doesn't Buildroot generate binary packages (.deb, .ipkg...)?
113 One feature that is often discussed on the Buildroot list is the
114 general topic of "package management". To summarize, the idea
115 would be to add some tracking of which Buildroot package installs
116 what files, with the goals of:
118 * being able to remove files installed by a package when this package
119 gets unselected from the menuconfig;
121 * being able to generate binary packages (ipk or other format) that
122 can be installed on the target without re-generating a new root
123 filesystem image.
125 In general, most people think it is easy to do: just track which package
126 installed what and remove it when the package is unselected. However, it
127 is much more complicated than that:
129 * It is not only about the +target/+ directory, but also the sysroot in
130 +host/usr/<tuple>/sysroot+ and the +host/+ directory itself. All files
131 installed in those directories by various packages must be tracked.
133 * When a package is unselected from the configuration, it is not
134 sufficient to remove just the files it installed. One must also
135 remove all its reverse dependencies (i.e. packages relying on it)
136 and rebuild all those packages. For example, package A depends
137 optionally on the OpenSSL library. Both are selected, and Buildroot
138 is built. Package A is built with crypto support using OpenSSL.
139 Later on, OpenSSL gets unselected from the configuration, but
140 package A remains (since OpenSSL is an optional dependency, this
141 is possible.) If only OpenSSL files are removed, then the files
142 installed by package A are broken: they use a library that is no
143 longer present on the target. Although this is technically doable,
144 it adds a lot of complexity to Buildroot, which goes against the
145 simplicity we try to stick to.
147 * In addition to the previous problem, there is the case where the
148 optional dependency is not even known to Buildroot. For example,
149 package A in version 1.0 never used OpenSSL, but in version 2.0 it
150 automatically uses OpenSSL if available. If the Buildroot .mk file
151 hasn't been updated to take this into account, then package A will
152 not be part of the reverse dependencies of OpenSSL and will not be
153 removed and rebuilt when OpenSSL is removed. For sure, the .mk file
154 of package A should be fixed to mention this optional dependency,
155 but in the mean time, you can have non-reproducible behaviors.
157 * The request is to also allow changes in the menuconfig to be
158 applied on the output directory without having to rebuild
159 everything from scratch. However, this is very difficult to achieve
160 in a reliable way: what happens when the suboptions of a package
161 are changed (we would have to detect this, and rebuild the package
162 from scratch and potentially all its reverse dependencies), what
163 happens if toolchain options are changed, etc. At the moment, what
164 Buildroot does is clear and simple so its behaviour is very
165 reliable and it is easy to support users. If configuration changes
166 done in menuconfig are applied after the next make, then it has to
167 work correctly and properly in all situations, and not have some
168 bizarre corner cases. The risk is to get bug reports like "I have
169 enabled package A, B and C, then ran make, then disabled package
170 C and enabled package D and ran make, then re-enabled package C
171 and enabled package E and then there is a build failure". Or worse
172 "I did some configuration, then built, then did some changes,
173 built, some more changes, built, some more changes, built, and now
174 it fails, but I don't remember all the changes I did and in which
175 order". This will be impossible to support.
177 For all these reasons, the conclusion is that adding tracking of
178 installed files to remove them when the package is unselected, or to
179 generate a repository of binary packages, is something that is very
180 hard to achieve reliably and will add a lot of complexity.
182 On this matter, the Buildroot developers make this position statement:
184 * Buildroot strives to make it easy to generate a root filesystem (hence
185 the name, by the way.) That is what we want to make Buildroot good at:
186 building root filesystems.
188 * Buildroot is not meant to be a distribution (or rather, a distribution
189 generator.) It is the opinion of most Buildroot developers that this
190 is not a goal we should pursue. We believe that there are other tools
191 better suited to generate a distro than Buildroot is. For example,
192 http://openembedded.org/[Open Embedded], or https://openwrt.org/[openWRT],
193 are such tools.
195 * We prefer to push Buildroot in a direction that makes it easy (or even
196 easier) to generate complete root filesystems. This is what makes
197 Buildroot stands out in the crowd (among other things, of course!)
199 * We believe that for most embedded Linux systems, binary packages are
200 not necessary, and potentially harmful. When binary packages are
201 used, it means that the system can be partially upgraded, which
202 creates an enormous number of possible combinations of package
203 versions that should be tested before doing the upgrade on the
204 embedded device. On the other hand, by doing complete system
205 upgrades by upgrading the entire root filesystem image at once,
206 the image deployed to the embedded system is guaranteed to really
207 be the one that has been tested and validated.
209 [[faq-speeding-up-build]]
210 === How to speed-up the build process?
212 Since Buildroot often involves doing full rebuilds of the entire
213 system that can be quite long, we provide below a number of tips to
214 help reduce the build time:
216 * Use a pre-built external toolchain instead of the default Buildroot
217 internal toolchain. By using a pre-built Linaro toolchain (on ARM)
218 or a Sourcery CodeBench toolchain (for ARM, x86, x86-64, MIPS,
219 etc.), you will save the build time of the toolchain at each
220 complete rebuild, approximately 15 to 20 minutes. Note that
221 temporarily using an external toolchain does not prevent you to
222 switch back to an internal toolchain (that may provide a higher
223 level of customization) once the rest of your system is working;
225 * Use the +ccache+ compiler cache (see: xref:ccache[]);
227 * Learn about rebuilding only the few packages you actually care
228 about (see xref:rebuild-pkg[]), but beware that sometimes full
229 rebuilds are anyway necessary (see xref:full-rebuild[]);
231 * Make sure you are not using a virtual machine for the Linux system
232 used to run Buildroot. Most of the virtual machine technologies are
233 known to cause a significant performance impact on I/O, which is
234 really important for building source code;
236 * Make sure that you're using only local files: do not attempt to do
237 a build over NFS, which significantly slows down the build. Having
238 the Buildroot download folder available locally also helps a bit.
240 * Buy new hardware. SSDs and lots of RAM are key to speeding up the
241 builds.