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20 <B>µ C l i b c</B>
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33 <A NAME="notworking"> <BIG><B>
34 uClibc Frequently Asked Questions (FAQ)
38 <TR><TD BGCOLOR="#eeeee0">
41 This is a collection of some of the frequently asked questions
42 about uClibc. Some of the questions even have answers. If you
43 have additions to this FAQ document, we would love to add them,
45 When you are done, <a href="http://uclibc.org/">you can click here to return
46 to the uClibc home page.</a>
49 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
51 What platforms does uClibc run on?
54 <TR><TD BGCOLOR="#eeeee0">
56 Currently uClibc runs on alpha, ARM, i386, i960, h8300, m68k, mips/mipsel,
57 PowerPC, SH, SPARC, and v850 processors.
61 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
63 Why is it called uClibc?
66 <TR><TD BGCOLOR="#eeeee0">
68 The letter 'u' is short for µ (the greek letter "mu"). µ is commonly used
69 as the abbreviation for the word "micro". The capital "C" is short for
70 "controller". So the name uClibc is sortof an abbreviation for "the
71 microcontroller C library". For simplicity, uClibc is pronounced
74 The name is partly historical, since uClibc was originally
75 created to support <a href="http://www.uclinux.org">µClinux</a>, a port of
76 Linux for MMU-less microcontrollers such as the Dragonball, Coldfire, and
77 ARM7TDMI. These days, uClibc also works just fine on normal Linux systems
78 (such as i386, ARM, and PowerPC), but we couldn't think of a better name.
81 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
83 Why are you doing this? What's wrong with glibc?
86 <TR><TD BGCOLOR="#eeeee0">
88 Initially, the project began since the GNU C library lacks support for
89 MMU-less systems, and because glibc is very large. The GNU C library is
90 designed with a very different set of goals then uClibc. The GNU C library
91 is a great piece of software, make no mistake. It is compliant with just
92 about every standard ever created, and runs on just about every operating
93 system and architecture -- no small task! But there is a price to be paid
94 for that. It is quite a large library, and keeps getting larger with each
95 release. It does not even pretend to target embedded systems. To quote
96 from Ulrich Drepper, the maintainer of GNU libc: "...glibc is not the right
97 thing for [an embedded OS]. It is designed as a native library (as opposed
98 to embedded). Many functions (e.g., printf) contain functionality which is
99 not wanted in embedded systems." 24 May 1999
104 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
106 So uClibc is smaller then glibc? Doesn't that mean it completely sucks?
107 How could it be smaller and not suck?
110 <TR><TD BGCOLOR="#eeeee0">
112 uClibc has been designed from the ground up to be a C library for
113 embedded Linux. We don't need to worry about things like MS-DOS
114 support, or BeOS, or AmigaOs any other system. This lets us cut out
115 a lot of complexity and very carefully optimize for Linux. By very
116 careful design, we can also take a few shortcuts. For example, glibc
117 contains an implementation of the wordexp() function, in compliance
118 with the Single Unix Specification, version 3. Well, standards are
119 important. But so is pragmatism. The wordexp function is huge, yet I
120 am not aware of even one Linux application that uses it! So uClibc
121 doesn't provide wordexp(). There are many similar examples. In other
122 cases, uClibc leaves certain features (such as full C99 Math library
123 support, IPV6, and RPC support) disabled by default. Those features
124 can be enabled for people that need them, but are otherwise disabled to
129 Glibc is a general purpose C library, and so as policy things are optimized
130 for speed. Most of uClibc's routines have been very carefully written to
131 optimize them for size instead.
135 The end result is a C library that will compile just about everything you
136 throw at it, that looks like glibc to application programs when you
137 compile, but is many times smaller.
142 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
144 Why should I use uClibc?
147 <TR><TD BGCOLOR="#eeeee0">
149 I don't know if you should use uClibc or not. It depends on your needs.
150 If you are building an embedded Linux system and you are tight on space, then
151 using uClibc instead if glibc may be a very good idea.
153 If you are trying to build a huge fileserver for your company that will
154 have 12 Terabytes of storage, then using glibc may make more sense.
155 Unless, for example, that 12 Terabytes will be Network Attached Storage
156 and you plan to burn Linux into the system's firmware...
161 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
163 If I use uClibc, do I have to release all my source code to the world for
164 free? I want to create a closed source commercial application and I want
165 to protect my intellectual property.
168 <TR><TD BGCOLOR="#eeeee0">
170 No, you do not need to give away your application source code just because
171 you use uClibc and/or run on Linux. uClibc is licensed under the <a
172 href="http://www.gnu.org/copyleft/lesser.html">Lesser GPL</a> licence, just
173 like the GNU C library (glibc). Please read this licence, or have a lawyer
174 read this licence if you have any questions. Here is my brief summary...
175 Using shared libraries makes complying with the license easy. You can
176 distribute a closed source application which is linked with an unmodified
177 uClibc shared library. In this case, you do not need to give away any
178 source code for your application or for the uClibc library. Please
179 consider sharing some of the money you make with us! :-)
182 If you make any changes to uClibc, and distribute uClibc or distribute any
183 applications using your modified version, you must also distribute the
184 source code for uClibc containing all of your changes.
187 If you distribute an application which has uClibc statically linked, you
188 must also make your application available as an object file which can later
189 be re-linked against updated versions of uClibc. This will (in theory)
190 allow your customers to apply uClibc bug fixes to your application. You do
191 not need to make the application object file available to everyone, just to
192 those you gave the fully linked application.
196 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
198 Can I use it on my desktop i386 system?
201 <TR><TD BGCOLOR="#eeeee0">
203 Sure! In fact, this can be very nice during development. By
204 installing uClibc on your development system, you can be sure that
205 the code you are working on will actually run when you deploy it
211 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
213 Does uClibc support shared libraries?
216 <TR><TD BGCOLOR="#eeeee0">
218 Yes. uClibc has native shared library support on i386, ARM, mips/mipsel,
219 SH, CRIS, and PowerPC processors. Other architectures can use shared libraries
220 but will need to use the GNU libc shared library loader.
222 Shared Libraries are not currently supported by uClibc on MMU-less systems.
223 <a href="http://www.snapgear.com/">SnapGear</a> has implemented
224 shared library support for MMU-less systems, however, so if you need MMU-less
225 shared library support they may be able to help.
229 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
231 How do I compile programs with uClibc?
234 <TR><TD BGCOLOR="#eeeee0">
236 The easiest way is to use the compiler wrapper built by uClibc. Instead of
237 using your usual compiler or cross compiler, you can use i386-uclibc-gcc,
238 (or whatever is appropriate for your target architecture) and your
239 applications will auto-magically link against uClibc. You can also
240 build your own native uClibc toolchain. Just download the uClibc toolchain
242 <a href="/cgi-bin/cvsweb/toolchain/">uClibc toolchain builder</a>,
243 or the uClibc buildroot system from
244 <a href="/cgi-bin/cvsweb/buildroot/">uClibc buildroot system</a>,
245 adjust the Makefile settings to match your target system, and then run 'make'.
247 If you want to be <em>really</em> lazy and start using uClibc right
248 away without needing to compile your own toolchain or anything, you can
249 grab a copy of the uClibc development systems, currently available for
250 <a href="http://www.uclibc.org/downloads/root_fs-i386.bz2">i386</a>,
251 <a href="http://www.uclibc.org/downloads/root_fs-powerpc.bz2">powerpc</a>,
253 <a href="http://www.uclibc.org/downloads/root_fs-arm.bz2">arm</a>.
254 These are pre-built uClibc only development systems (created using
255 <a href="/cgi-bin/cvsweb/buildroot/">buildroot</a>), and provide a
256 really really easy way to get started. These are about 20 MB bzip2
257 compressed ext2 filesystems containing all the development software you
258 need to build your own uClibc applications. With bash, awk, make, gcc, g++,
259 autoconf, automake, ncurses, zlib, openssl, openssh, gdb, strace, busybox,
260 GNU coreutils, GNU tar, GNU grep, etc, these should have pretty much everything
261 you need to get started building your own applications linked against
262 uClibc. You can boot into them, loop mount them, dd them to a spare drive
263 and use resize2fs to make them fill a partition... Whatever works best
267 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
269 Why do I keep getting "sh: can't access tty; job control turned off" errors?
270 Why doesn't Control-C work within my shell?
273 <TR><TD BGCOLOR="#eeeee0">
275 This isn't really a uClibc question, but I'll answer it here anyways. Job
276 control will be turned off since your shell can not obtain a controlling
277 terminal. This typically happens when you run your shell on /dev/console.
278 The kernel will not provide a controlling terminal on the /dev/console
279 device. Your should run your shell on a normal tty such as tty1 or ttyS0
280 and everything will work perfectly. If you <em>REALLY</em> want your shell
281 to run on /dev/console, then you can hack your kernel (if you are into that
282 sortof thing) by changing drivers/char/tty_io.c to change the lines where
283 it sets "noctty = 1;" to instead set it to "0". I recommend you instead
284 run your shell on a real console...
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290 How do I make autoconf and automake behave?
293 <TR><TD BGCOLOR="#eeeee0">
296 <pre>export PATH=/usr/i386-linux-uclibc/bin:$PATH</pre>
297 (or similar adjusted for your target architecture) then run you can simply
298 run autoconf/automake and it should _just work_. Unfortunately, a large
299 number of configure scripts (such as the one from openssh) try to execute
300 test applications using your target C library, even if you are cross-
301 compiling. This is bad, since it will prevent these programs from compiling.
302 You need to complain to the authors of these programs and ask them to fix
303 their broken configure scripts.
309 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
311 When I run 'ldd' to get a list of the library dependencies for a uClibc
312 binary, ldd segfaults! What should I do?
315 <TR><TD BGCOLOR="#eeeee0">
317 Use the ldd that is built by uClibc, not your system's one. When your
318 system's ldd looks for library dependencies, it actually _runs_ that
319 program. This works fine -- usually. It generally will not work at all
320 when you have been cross compiling (which is why ldd segfaults). The ldd
321 program created by uClibc is cross platform and doesn't even try to run
322 the target program (like your system one does). So use the uClibc one
323 and it will do the right thing, and it won't segfault even when you are
328 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
330 Why does localtime() return times in UTC even when I have my timezone set?
333 <TR><TD BGCOLOR="#eeeee0">
336 The uClibc time functions get timezone information from the TZ environment
337 variable, as described in the Single Unix Specification Version 3. See
338 <a href="http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html">
339 http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html</a>
340 for details on valid settings of TZ. For some additional examples, read
341 <a href="http://www.uclibc.org/lists/uclibc/2002-August/006261.html">
342 http://www.uclibc.org/lists/uclibc/2002-August/006261.html</a> in the uClibc
343 mailing list archive.
344 You can store the value of TZ in the file '/etc/TZ' and uClibc will then
345 automagically use the specified setting.
349 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
351 What is the history of uClibc? Where did it come from?
354 <TR><TD BGCOLOR="#eeeee0">
356 The history and origin of uClibc is long and twisty.
357 In the beginning, there was <a href="http://www.gnu.org/software/libc/libc.html">GNU libc</a>. Then, libc4
358 (which later became linux libc 5) forked from GNU libc version 1.07.4, with
359 additions from 4.4BSD, in order to support Linux. Later, the <a
360 href="http://www.cix.co.uk/~mayday/">Linux-8086 C library</a>, which is part of
361 the <a href="http://www.elks.ecs.soton.ac.uk/">elks project</a>, was created,
362 which was, apparently, largely written from scratch but also borrowed code from
363 libc4, glibc, some Atari library code, with bits and pieces from about 20 other
364 places. Then uClibc forked off from the Linux-8086 C library in order to run
365 on <a href="http://www.uclinux.org">µClinux</a>.
368 I had for some time been despairing over the state of C libraries in Linux.
369 GNU libc, the standard, is very poorly suited to embedded systems and
370 has been getting bigger with every release. I spent quite a bit of time looking over the
371 available Open Source C libraries that I knew of (listed below), and none of them really
372 impressed me. I felt there was a real vacancy in the embedded Linux ecology.
373 The closest library to what I imagined an embedded C library should be was
374 uClibc. But it had a lot of problems too -- not the least of which was that,
375 traditionally, uClibc had a complete source tree fork in order to support each
376 and every new platform. This resulted in a big mess of twisty versions, all
377 different. I decided to fix it and the result is what you see here.
378 My source tree has now become the official uClibc source tree and it now lives
379 on cvs.uclinux.org and www.uclibc.org.
383 To start with, (with some initial help from <a
384 href="http://www.uclinux.org/developers/">D. Jeff Dionne</a>), I
385 ported it to run on i386. I then grafted in the header files from glibc 2.1.3
386 and cleaned up the resulting breakage. This (plus some additional work) has
387 made it almost completely independent of kernel headers, a large departure from
388 its traditional tightly-coupled-to-the-kernel origins. I have written and/or
389 rewritten a number of things that were missing or broken, and sometimes grafted
390 in bits of code from the current glibc and libc5. I have also built a proper
391 platform abstraction layer, so now you can simply edit the file "Config" and
392 use that to decide which architecture you will be compiling for, and whether or
393 not your target has an MMU, and FPU, etc. I have also added a test suite,
394 which, though incomplete, is a good start. Several people have helped by
395 contributing ports to new architectures, and a lot of work has been done on
396 adding support for missing features.
400 These days, uClibc is being developed and enhanced by Erik Andersen of
401 <a href="http://codepoet-consulting.com/">CodePoet Consulting</a> along
402 with the rest of the embedded Linux community.
407 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
409 I demand that you to add <favorite feature> right now! How come
410 you don't answer all my questions on the mailing list instantly? I demand
411 that you help me with all of my problems <em>Right Now</em>!
414 <TR><TD BGCOLOR="#eeeee0">
416 You have not paid us a single cent and yet you still have the
417 product of nearly two years of work from Erik and Manuel and
418 many other people. We are not your slaves! We work on uClibc
419 because we find it interesting. If you go off flaming us, we will
424 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
426 I need you to add <favorite feature>! Are the uClibc developers willing to
427 be paid in order to fix bugs or add in <favorite feature>? Are you willing to provide
431 <TR><TD BGCOLOR="#eeeee0">
433 Sure! Now you have our attention! What you should do is contact <a
434 href="mailto:andersen@codepoet.org">Erik Andersen</a> of <a
435 href="http://codepoet-consulting.com/">CodePoet Consulting</a> to bid
436 on your project. If Erik is too busy to personally add your feature, there
437 are several other active uClibc contributors who will almost certainly be able
438 to help you out. Erik can contact them and ask them about their availability.
442 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
444 I think you guys are great and I want to help support your work!
447 <TR><TD BGCOLOR="#eeeee0">
449 Wow, that would be great! You can click here to help support uClibc and/or request features.
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466 <a href="http://codepoet-consulting.com/">CodePoet Consulting</a> here.
469 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
471 Ok, I'm done reading all these questions.
474 <TR><TD BGCOLOR="#eeeee0">
476 <a href="http://uclibc.org/">Well then, click here to return to the uClibc home page.</a>
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494 Mail all comments, insults, suggestions and bribes to
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