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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, cris, h8300, i386, i960, m68k,
57 mips/mipsel, 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 lacked 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 and glibc have different goals. glibc strives for features
113 and performance, and is targeted for desktops and servers with
114 (these days) lots of resources. It also strives for ABI stability.
118 On the other hand, the goal of uClibc is to provide as much functionality
119 as possible in a small amount of space, and it is intended primarily for
120 embedded use. It is also highly configurable in supported features, at the
121 cost of ABI differences for different configurations. uClibc has been
122 designed from the ground up to be a C library for embedded Linux. We don't
123 need to worry about things like MS-DOS support, or BeOS, or AmigaOs any
124 other system. This lets us cut out a lot of complexity and very carefully
129 In other cases, uClibc
130 leaves certain features (such as full C99 Math library support, wordexp,
131 IPV6, and RPC support) disabled by default. Those features can be enabled
132 for people that need them, but are otherwise disabled to save space.
136 Some of the space savings in uClibc is obtained at the cost of performance,
137 and some is due to sacrificing features. Much of it comes from aggressive
138 refactoring of code to eliminate redundancy. In regards to locale data,
139 elimination of redundant data storage resulted in substantial space
140 savings. The result is a libc that currently includes the features needed
141 by nearly all applications and yet is considerably smaller than glibc. To
142 compare "apples to apples", if you take uClibc and compile in locale data
143 for about 170 UTF-8 locales, then uClibc will take up about 570k. If you
144 take glibc and add in locale data for the same 170 UTF-8 locales, you will
149 The end result is a C library that will compile just about everything you
150 throw at it, that looks like glibc to application programs when you
151 compile, and is many times smaller.
156 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
158 Why should I use uClibc?
161 <TR><TD BGCOLOR="#eeeee0">
163 I don't know if you should use uClibc or not. It depends on your needs.
164 If you are building an embedded Linux system and you are tight on space, then
165 using uClibc instead if glibc may be a very good idea.
169 If you are building an embedded Linux system and you find that
170 glibc is eating up too much space, you should consider using
171 uClibc. If you are building a huge fileserver with 12 Terabytes
172 of storage, then using glibc may make more sense. Unless, for
173 example, that 12 Terabytes will be Network Attached Storage and
174 you plan to burn Linux into the system's firmware...
179 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
181 If I use uClibc, do I have to release all my source code to the world for
182 free? I want to create a closed source commercial application and I want
183 to protect my intellectual property.
186 <TR><TD BGCOLOR="#eeeee0">
188 No, you do not need to give away your application source code just because
189 you use uClibc and/or run on Linux. uClibc is licensed under the <a
190 href="http://www.gnu.org/copyleft/lesser.html">Lesser GPL</a> licence, just
191 like the GNU C library (glibc). Please read this licence, or have a lawyer
192 read this licence if you have any questions. Here is my brief summary...
193 Using shared libraries makes complying with the license easy. You can
194 distribute a closed source application which is linked with an unmodified
195 uClibc shared library. In this case, you do not need to give away any
196 source code for your application or for the uClibc library. Please
197 consider sharing some of the money you make with us! :-)
200 If you make any changes to uClibc, and distribute uClibc or distribute any
201 applications using your modified version, you must also distribute the
202 source code for uClibc containing all of your changes.
205 If you distribute an application which has uClibc statically linked, you
206 must also make your application available as an object file which can later
207 be re-linked against updated versions of uClibc. This will (in theory)
208 allow your customers to apply uClibc bug fixes to your application. You do
209 not need to make the application object file available to everyone, just to
210 those you gave the fully linked application.
214 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
216 Can I use it on my x86 development system?
219 <TR><TD BGCOLOR="#eeeee0">
221 Sure! In fact, this can be very nice during development. By
222 installing uClibc on your development system, you can be sure that
223 the code you are working on will actually run when you deploy it
229 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
231 Does uClibc support shared libraries?
234 <TR><TD BGCOLOR="#eeeee0">
236 Yes. uClibc has native shared library support on i386, ARM, mips/mipsel,
237 SH, CRIS, and PowerPC processors. Other architectures can use shared libraries
238 but will need to use the GNU libc shared library loader.
240 Shared Libraries are not currently supported by uClibc on MMU-less systems.
241 <a href="http://www.snapgear.com/">SnapGear</a> has implemented
242 shared library support for MMU-less systems, however, so if you need MMU-less
243 shared library support they may be able to help.
247 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
249 How do I compile programs with uClibc?
252 <TR><TD BGCOLOR="#eeeee0">
254 The easiest way is to use the compiler wrapper built by uClibc. Instead of
255 using your usual compiler or cross compiler, you can use i386-uclibc-gcc,
256 (or whatever is appropriate for your target architecture) and your
257 applications will auto-magically link against uClibc. You can also
258 build your own native uClibc toolchain. Just download the uClibc toolchain
260 <a href="/cgi-bin/cvsweb/toolchain/">uClibc toolchain builder</a>,
261 or the uClibc buildroot system from
262 <a href="/cgi-bin/cvsweb/buildroot/">uClibc buildroot system</a>,
263 adjust the Makefile settings to match your target system, and then run 'make'.
265 If you want to be <em>really</em> lazy and start using uClibc right
266 away without needing to compile your own toolchain or anything, you can
267 grab a copy of the uClibc development systems, currently available for
268 <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_i386.bz2">i386</a>,
269 <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_powerpc.bz2">powerpc</a>,
270 <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_mipsel.bz2">mipsel</a>,
272 <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_arm.bz2">arm</a>.
273 These are pre-built uClibc only development systems (created using
274 <a href="/cgi-bin/cvsweb/buildroot/">buildroot</a>), and provide a
275 really really easy way to get started. These are about 20 MB bzip2
276 compressed ext2 filesystems containing all the development software you
277 need to build your own uClibc applications. With bash, awk, make, gcc, g++,
278 autoconf, automake, ncurses, zlib, openssl, openssh, gdb, strace, busybox,
279 GNU coreutils, GNU tar, GNU grep, etc, these should have pretty much everything
280 you need to get started building your own applications linked against
281 uClibc. You can boot into them, loop mount them, dd them to a spare drive
282 and use resize2fs to make them fill a partition... Whatever works best
286 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
288 Why do I keep getting "sh: can't access tty; job control turned off" errors?
289 Why doesn't Control-C work within my shell?
292 <TR><TD BGCOLOR="#eeeee0">
294 This isn't really a uClibc question, but I'll answer it here anyways. Job
295 control will be turned off since your shell can not obtain a controlling
296 terminal. This typically happens when you run your shell on /dev/console.
297 The kernel will not provide a controlling terminal on the /dev/console
298 device. Your should run your shell on a normal tty such as tty1 or ttyS0
299 and everything will work perfectly. If you <em>REALLY</em> want your shell
300 to run on /dev/console, then you can hack your kernel (if you are into that
301 sortof thing) by changing drivers/char/tty_io.c to change the lines where
302 it sets "noctty = 1;" to instead set it to "0". I recommend you instead
303 run your shell on a real console...
307 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
309 How do I make autoconf and automake behave?
312 <TR><TD BGCOLOR="#eeeee0">
315 <pre>export PATH=/usr/i386-linux-uclibc/bin:$PATH</pre>
316 (or similar adjusted for your target architecture) then run you can simply
317 run autoconf/automake and it should _just work_. Unfortunately, a large
318 number of configure scripts (such as the one from openssh) try to execute
319 test applications using your target C library, even if you are cross-
320 compiling. This is bad, since it will prevent these programs from compiling.
321 You need to complain to the authors of these programs and ask them to fix
322 their broken configure scripts.
328 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
330 When I run 'ldd' to get a list of the library dependencies for a uClibc
331 binary, ldd segfaults! What should I do?
334 <TR><TD BGCOLOR="#eeeee0">
336 Use the ldd that is built by uClibc, not your system's one. When your
337 system's ldd looks for library dependencies, it actually _runs_ that
338 program. This works fine -- usually. It generally will not work at all
339 when you have been cross compiling (which is why ldd segfaults). The ldd
340 program created by uClibc is cross platform and doesn't even try to run
341 the target program (like your system one does). So use the uClibc one
342 and it will do the right thing, and it won't segfault even when you are
347 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
349 Why does localtime() return times in UTC even when I have my timezone set?
352 <TR><TD BGCOLOR="#eeeee0">
355 The uClibc time functions get timezone information from the TZ environment
356 variable, as described in the Single Unix Specification Version 3. See
357 <a href="http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html">
358 http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html</a>
359 for details on valid settings of TZ. For some additional examples, read
360 <a href="http://www.uclibc.org/lists/uclibc/2002-August/006261.html">
361 http://www.uclibc.org/lists/uclibc/2002-August/006261.html</a> in the uClibc
362 mailing list archive.
363 You can store the value of TZ in the file '/etc/TZ' and uClibc will then
364 automagically use the specified setting.
368 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
370 What is the history of uClibc? Where did it come from?
373 <TR><TD BGCOLOR="#eeeee0">
375 The history and origin of uClibc is long and twisty.
376 In the beginning, there was <a href="http://www.gnu.org/software/libc/libc.html">GNU libc</a>. Then, libc4
377 (which later became linux libc 5) forked from GNU libc version 1.07.4, with
378 additions from 4.4BSD, in order to support Linux. Later, the <a
379 href="http://www.cix.co.uk/~mayday/">Linux-8086 C library</a>, which is part of
380 the <a href="http://www.elks.ecs.soton.ac.uk/">elks project</a>, was created,
381 which was, apparently, largely written from scratch but also borrowed code from
382 libc4, glibc, some Atari library code, with bits and pieces from about 20 other
383 places. Then uClibc forked off from the Linux-8086 C library in order to run
384 on <a href="http://www.uclinux.org">µClinux</a>.
387 I had for some time been despairing over the state of C libraries in Linux.
388 GNU libc, the standard, is very poorly suited to embedded systems and
389 has been getting bigger with every release. I spent quite a bit of time looking over the
390 available Open Source C libraries that I knew of (listed below), and none of them really
391 impressed me. I felt there was a real vacancy in the embedded Linux ecology.
392 The closest library to what I imagined an embedded C library should be was
393 uClibc. But it had a lot of problems too -- not the least of which was that,
394 traditionally, uClibc had a complete source tree fork in order to support each
395 and every new platform. This resulted in a big mess of twisty versions, all
396 different. I decided to fix it and the result is what you see here.
397 My source tree has now become the official uClibc source tree and it now lives
398 on cvs.uclinux.org and www.uclibc.org.
402 To start with, (with some initial help from <a
403 href="http://www.uclinux.org/developers/">D. Jeff Dionne</a>), I
404 ported it to run on i386. I then grafted in the header files from glibc 2.1.3
405 and cleaned up the resulting breakage. This (plus some additional work) has
406 made it almost completely independent of kernel headers, a large departure from
407 its traditional tightly-coupled-to-the-kernel origins. I have written and/or
408 rewritten a number of things that were missing or broken, and sometimes grafted
409 in bits of code from the current glibc and libc5. I have also built a proper
410 platform abstraction layer, so now you can simply edit the file "Config" and
411 use that to decide which architecture you will be compiling for, and whether or
412 not your target has an MMU, and FPU, etc. I have also added a test suite,
413 which, though incomplete, is a good start. Several people have helped by
414 contributing ports to new architectures, and a lot of work has been done on
415 adding support for missing features.
419 In particular, around the end of 2000, Manuel Novoa III got involved with
420 uClibc. One of his first contributions was the original gcc wrapper.
421 Since then, he has written virtually all of the current uClibc stdio, time,
422 string, ctype, locale, and wchar-related code, as well as much of stdlib
423 and various other bits throught the library.
427 These days, uClibc is being developed and enhanced by Erik Andersen
428 and Manuel Novoa III of
429 <a href="http://codepoet-consulting.com/">CodePoet Consulting</a>
430 along with the rest of the embedded Linux community.
435 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
437 I demand that you to add <favorite feature> right now! How come
438 you don't answer all my questions on the mailing list instantly? I demand
439 that you help me with all of my problems <em>Right Now</em>!
442 <TR><TD BGCOLOR="#eeeee0">
444 You have not paid us a single cent and yet you still have the
445 product of nearly two years of work from Erik and Manuel and
446 many other people. We are not your slaves! We work on uClibc
447 because we find it interesting. If you go off flaming us, we will
452 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
454 I need you to add <favorite feature>! Are the uClibc developers willing to
455 be paid in order to fix bugs or add in <favorite feature>? Are you willing to provide
459 <TR><TD BGCOLOR="#eeeee0">
461 Sure! Now you have our attention! What you should do is contact <a
462 href="mailto:andersen@codepoet.org">Erik Andersen</a> of <a
463 href="http://codepoet-consulting.com/">CodePoet Consulting</a> to bid
464 on your project. If Erik is too busy to personally add your feature, there
465 are several other active uClibc contributors who will almost certainly be able
466 to help you out. Erik can contact them and ask them about their availability.
470 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
472 I think you guys are great and I want to help support your work!
475 <TR><TD BGCOLOR="#eeeee0">
477 Wow, that would be great! You can click here to help support uClibc and/or request features.
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494 <a href="http://codepoet-consulting.com/">CodePoet Consulting</a> here.
497 <TR><TD BGCOLOR="#ccccc0" ALIGN=left>
499 Ok, I'm done reading all these questions.
502 <TR><TD BGCOLOR="#eeeee0">
504 <a href="http://uclibc.org/">Well then, click here to return to the uClibc home page.</a>
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522 Mail all comments, insults, suggestions and bribes to
523 <a href="mailto:andersen@codepoet.org">Erik Andersen</a><BR>
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