uclibc-ng/docs/uclibc.org/FAQ.html

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<h3>Frequently Asked Questions</h3>

This is a collection of some of the most frequently asked questions
about uClibc.  Some of the questions even have answers. If you
have additions to this FAQ document, we would love to add them,

<ol>
  <li><a href="#naming">Why is it called uClibc?</a>
  <li><a href="#platforms">What platforms does uClibc run on?</a>
  <li><a href="#why">Why are you doing this?  What's wrong with glibc?</a>
  <li><a href="#doesnt_suck">So uClibc is smaller then glibc?  Doesn't that mean it 
	completely sucks?  How could it be smaller and not suck?</a>
  <li><a href="#why_should_i">Why should I use uClibc?</a>
  <li><a href="#licensing">If I use uClibc, do I have to release all my source code to the world for
	free?  I want to create a closed source commercial application and I want
	to protect my intellectual property.</a>
  <li><a href="#development">Can I use it on my x86 development system?</a>
  <li><a href="#shared"> Does uClibc support shared libraries?</a>

    <li><a href="#compiling">How do I compile programs with uClibc?</a>
    <li><a href="#dev_systems">Is a pre-compiled uClibc development system available?</a>
    <li><a href="#job_control">Why do I keep getting "sh: can't access tty; job control 
	    turned off" errors?  Why doesn't Control-C work within my shell?</a>
    <li><a href="#autoconf">How do I make autoconf and automake behave?</a>
    <li><a href="#ldd">When I run 'ldd' to get a list of the library dependencies 
	    for a uClibc binary, ldd segfaults!  What should I do?</a>
    <li><a href="#timezones">Why does localtime() return times in UTC even when I have my timezone set?</a>
    <li><a href="#history">What is the history of uClibc?  Where did it come from?</a>
    <li><a href="#demanding">I demand that you to add &lt;favorite feature&gt; right now!   How come 
	    you don't answer all my questions on the mailing list instantly?  I demand 
	    that you help me with all of my problems <em>Right Now</em>!</a>
    <li><a href="#contracts">I need you to add &lt;favorite feature&gt;!  Are the uClibc developers willing to 
	    be paid in order to fix bugs or add in &lt;favorite feature&gt;?  Are you willing to provide
	    support contracts?</a>
    <li><a href="#support">I think you guys are great and I want to help support your work!</a>


</ol>


<hr />
<p>
<h2><a name="naming">Why is it called uClibc?</a></h2>
<p>

    The letter 'u' is short for µ (the greek letter "mu").  µ is commonly used
    as the abbreviation for the word "micro".  The capital "C" is short for
    "controller".  So the name uClibc is sortof an abbreviation for "the
    microcontroller C library".  For simplicity, uClibc is pronounced
    "yew-see-lib-see".  
    <p>
    The name is partly historical, since uClibc was originally
    created to support <a href="http://www.uclinux.org">µClinux</a>, a port of
    Linux for MMU-less microcontrollers such as the Dragonball, Coldfire, and
    ARM7TDMI.  These days, uClibc also works just fine on normal Linux systems
    (such as i386, ARM, and PowerPC), but we couldn't think of a better name.

<hr />
<p>
<h2><a name="platforms">What platforms does uClibc run on?</a></h2>
<p>


    Currently uClibc runs on alpha, ARM, cris, i386, i960, h8300, 
    m68k, mips/mipsel, PowerPC, SH, SPARC, and v850 processors.
    

<hr />
<p>
<h2><a name="why">Why are you doing this?  What's wrong with glibc?</a></h2>
<p>

    Initially, the project began since the GNU C library lacked support for
    MMU-less systems, and because glibc is very large.  The GNU C library is
    designed with a very different set of goals then uClibc.  The GNU C library
    is a great piece of software, make no mistake.  It is compliant with just
    about every standard ever created, and runs on just about every operating
    system and architecture -- no small task!  But there is a price to be paid
    for that.  It is quite a large library, and keeps getting larger with each
    release.  It does not even pretend to target embedded systems.  To quote
    from Ulrich Drepper, the maintainer of GNU libc: "...glibc is not the right
    thing for [an embedded OS]. It is designed as a native library (as opposed
    to embedded).  Many functions (e.g., printf) contain functionality which is
    not wanted in embedded systems." 24 May 1999



<hr />
<p>
<h2><a name="doesnt_suck">So uClibc is smaller then glibc?  Doesn't that mean it completely sucks?
How could it be smaller and not suck?</a></h2>
<p>
<p>

    uClibc and glibc have different goals.  glibc strives for features
    and performance, and is targeted for desktops and servers with
    (these days) lots of resources.  It also strives for ABI stability.

    <p>

    On the other hand, the goal of uClibc is to provide as much functionality
    as possible in a small amount of space, and it is intended primarily for
    embedded use.  It is also highly configurable in supported features, at the
    cost of ABI differences for different configurations.  uClibc has been
    designed from the ground up to be a C library for embedded Linux.  We don't
    need to worry about things like MS-DOS support, or BeOS, or AmigaOs any
    other system.  This lets us cut out a lot of complexity and very carefully
    optimize for Linux.

    <p>

    In other cases, uClibc
    leaves certain features (such as full C99 Math library support, wordexp, 
    IPV6, and RPC support) disabled by default.  Those features can be enabled 
    for people that need them, but are otherwise disabled to save space.

    <p>
    
    Some of the space savings in uClibc is obtained at the cost of performance,
    and some is due to sacrificing features.  Much of it comes from aggressive
    refactoring of code to eliminate redundancy.  In regards to locale data,
    elimination of redundant data storage resulted in substantial space
    savings.  The result is a libc that currently includes the features needed
    by nearly all applications and yet is considerably smaller than glibc.  To
    compare "apples to apples", if you take uClibc and compile in locale data
    for about 170 UTF-8 locales, then uClibc will take up about 570k.  If you
    take glibc and add in locale data for the same 170 UTF-8 locales, you will
    need over 30MB!!!

    <p>

    The end result is a C library that will compile just about everything you
    throw at it, that looks like glibc to application programs when you
    compile, and is many times smaller.

    

<hr />
<p>
<h2><a name="why_should_i">Why should I use uClibc?</a></h2>
<p>

    I don't know if you should use uClibc or not.  It depends on your needs.
    If you are building an embedded Linux system and you are tight on space, then
    using uClibc instead if glibc may be a very good idea.

    <p>

    If you are building an embedded Linux system and you find that
    glibc is eating up too much space, you should consider using
    uClibc.  If you are building a huge fileserver with 12 Terabytes
    of storage, then using glibc may make more sense.  Unless, for
    example, that 12 Terabytes will be Network Attached Storage and
    you plan to burn Linux into the system's firmware...



<hr />
<p>
<h2><a name="licensing">If I use uClibc, do I have to release all my source code to the world for
	free?  I want to create a closed source commercial application and I want
	to protect my intellectual property.</a></h2>
<p>

    No, you do not need to give away your application source code just because
    you use uClibc and/or run on Linux.  uClibc is licensed under the <a
    href="http://www.gnu.org/copyleft/lesser.html">Lesser GPL</a> licence, just
    like the GNU C library (glibc).  Please read this licence, or have a lawyer
    read this licence if you have any questions.  Here is my brief summary...
    Using shared libraries makes complying with the license easy.  You can
    distribute a closed source application which is linked with an unmodified
    uClibc shared library.  In this case, you do not need to give away any
    source code for your application.  Please consider sharing some of the
    money you make with us!  :-)
    <p>

    If you make any changes to uClibc, and distribute uClibc or distribute any
    applications using your modified version, you must also distribute the
    source code for uClibc containing all of your changes.
    <p>

    If you distribute an application which has uClibc statically linked, you
    must also make your application available as an object file which can later
    be re-linked against updated versions of uClibc.  This will (in theory)
    allow your customers to apply uClibc bug fixes to your application.  You do
    not need to make the application object file available to everyone, just to
    those you gave the fully linked application.


<hr />
<p>
<h2><a name="development">Can I use it on my x86 development system?</a></h2>
<p>

    Sure!  In fact, this can be very nice during development.  By
    installing uClibc on your development system, you can be sure that
    the code you are working on will actually run when you deploy it on
    your target system.



<hr />
<p>
<h2><a name="shared"> Does uClibc support shared libraries?</a></h2>
<p>
    
    Yes.  uClibc has native shared library support on i386, ARM, mips, 
    SH, CRIS, and PowerPC processors.  Other architectures can use shared
    libraries but will need to use the GNU libc shared library loader.
    <p>
    Shared Libraries are not currently supported by uClibc on MMU-less systems.  
    <a href="http://www.snapgear.com/">SnapGear</a> has implemented
    shared library support for MMU-less systems, however, so if you need MMU-less 
    shared library support they may be able to help.


<hr />
<p>
<h2><a name="compiling">How do I compile programs with uClibc?</a></h2>
<p>

    You will need to have your own uClibc toolchain (i.e. GNU binutils and
    gcc configured to produce binaries linked with uClibc).
    You can build your own native uClibc toolchain using the uClibc
    toolchain builder from 
    <a href="/cgi-bin/cvsweb/toolchain/">uClibc toolchain builder</a>,
    or the uClibc buildroot system from
    <a href="/cgi-bin/cvsweb/buildroot/">uClibc buildroot system</a>.
    Simply adjust the Makefile settings to match your target system,
    and then run 'make'.

<hr />
<p>
<h2><a name="dev_systems">Is a pre-compiled uClibc development system available?</a></h2>
<p>

    If you want to be <em>really</em> lazy and start using uClibc right
    away without needing to compile your own toolchain or anything, you can
    grab a copy of the uClibc development systems, currently available for
    <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_i386.bz2">i386</a>,
    <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_powerpc.bz2">powerpc</a>,
    <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_arm.bz2">arm</a>,
    <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_mips.bz2">mips</a>,
    <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_mipsel.bz2">mipsel</a>, and
    <a href="http://www.kernel.org/pub/linux/libs/uclibc/root_fs_sh4.bz2">sh4</a>.
    The powerpc dev system mostly works, but there is still some sortof
    problem with the shared library loader that has not yet been resolved.

    <p>
    These are pre-built uClibc only development systems (created using 
    <a href="/cgi-bin/cvsweb/buildroot/">buildroot</a>), and provide a 
    really really easy way to get started.  These are about bzip2 compressed
    ext2 filesystems containing all the development software you need to build
    your own uClibc applications.  With bash, awk, make, gcc, g++, autoconf,
    automake, ncurses, zlib, openssl, openssh, gdb, strace, busybox, GNU
    coreutils, GNU tar, GNU grep, etc, these should have pretty much everything
    you need to get started building your own applications linked against
    uClibc.  You can boot into them, loop mount them, dd them to a spare drive
    and use resize2fs to make them fill a partition...  Whatever works best for
    you.

    <p>
    The quickest way to get started using a root_fs image (using the i386
    platform as an example) is:
    <ul>
    <li>Download root_fs_i386.bz2 from kernel.org</li>
    <li>bunzip2 root_fs_i386.bz2</li>
    <li>mkdir root_fs</li>
    <li>su root</li>
    <li>mount -o loop root_fs_i386 root_fs</li>
    <li>chroot root_fs /bin/sh</li>
    </ul>
    Type "exit" to end the chroot session and return to the host system.
    <p>



<hr />
<p>
<h2><a name="job_control">Why do I keep getting "sh: can't access tty; job control 
	turned off" errors?  Why doesn't Control-C work within my shell?</a></h2>
<p>

    This isn't really a uClibc question, but I'll answer it here anyways.  Job
    control will be turned off since your shell can not obtain a controlling
    terminal.  This typically happens when you run your shell on /dev/console.
    The kernel will not provide a controlling terminal on the /dev/console
    device.  Your should run your shell on a normal tty such as tty1 or ttyS0
    and everything will work perfectly.  If you <em>REALLY</em> want your shell
    to run on /dev/console, then you can hack your kernel (if you are into that
    sortof thing) by changing drivers/char/tty_io.c to change the lines where
    it sets "noctty = 1;" to instead set it to "0".  I recommend you instead
    run your shell on a real console...


<hr />
<p>
<h2><a name="autoconf">How do I make autoconf and automake behave?</a></h2>
<p>

    When you are cross-compiling, autoconf and automake are known to behave
    badly.  This is because a large number of configure scripts (such as the
    one from openssh) try to actually execute applications that were cross
    compiled for your target system.  This is bad, since of course these won't
    run, and this will also prevent your programs from compiling.  You need to
    complain to the authors of these programs and ask them to fix their broken
    configure scripts.


<hr />
<p>
<h2><a name="ldd">When I run 'ldd' to get a list of the library dependencies 
	for a uClibc binary, ldd segfaults!  What should I do?</a></h2>
<p>

    Use the ldd that is built by uClibc, not your system's one.  When your
    system's ldd looks for library dependencies, it actually _runs_ that
    program.  This works fine -- usually.  It generally will not work at all 
    when you have been cross compiling (which is why ldd segfaults).  The ldd
    program created by uClibc is cross platform and doesn't even try to run
    the target program (like your system one does).  So use the uClibc one
    and it will do the right thing, and it won't segfault even when you are
    cross compiling.


<hr />
<p>
<h2><a name="timezones">Why does localtime() return times in UTC even when I have my timezone set?</a></h2>
<p>


    The uClibc time functions get timezone information from the TZ environment
    variable, as described in the Single Unix Specification Version 3.  See
     <a href="http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html">
    http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html</a>
    for details on valid settings of TZ.  For some additional examples, read
    <a href="http://www.uclibc.org/lists/uclibc/2002-August/006261.html">
    http://www.uclibc.org/lists/uclibc/2002-August/006261.html</a> in the uClibc
    mailing list archive.
    You can store the value of TZ in the file '/etc/TZ' and uClibc will then
    automagically use the specified setting.


<hr />
<p>
<h2><a name="history">What is the history of uClibc?  Where did it come from?</a></h2>
<p>


    The history and origin of uClibc is long and twisty.
    In the beginning, there was <a href="http://www.gnu.org/software/libc/libc.html">GNU libc</a>.  Then, libc4
    (which later became linux libc 5) forked from GNU libc version 1.07.4, with
    additions from 4.4BSD, in order to support Linux.  Later, the <a
    href="http://www.cix.co.uk/~mayday/">Linux-8086 C library</a>, which is part of
    the <a href="http://www.elks.ecs.soton.ac.uk/">elks project</a>, was created,
    which was, apparently, largely written from scratch but also borrowed code from
    libc4, glibc, some Atari library code, with bits and pieces from about 20 other
    places.  Then uClibc forked off from the Linux-8086 C library in order to run
    on <a href="http://www.uclinux.org">µClinux</a>.
    <p>

    I had for some time been despairing over the state of C libraries in Linux.
    GNU libc, the standard, is very poorly suited to embedded systems and
    has been getting bigger with every release.  I spent quite a bit of time looking over the
    available Open Source C libraries that I knew of, and none of them really
    impressed me.  I felt there was a real vacancy in the embedded Linux ecology.
    The closest library to what I imagined an embedded C library should be was
    uClibc.  But it had a lot of problems too -- not the least of which was that,
    traditionally, uClibc required a complete source tree fork in order to support
    each and every new platform.  This resulted in a big mess of twisty versions,
    all different.  I decided to fix it and the result is what you see here.

    <p>

    To start with, (with some initial help from <a
    href="http://www.uclinux.org/developers/">D. Jeff Dionne</a>), I
    ported uClibc to run on i386.  I then grafted in the header files from glibc
    and cleaned up the resulting breakage.  This (plus some additional work) has
    made it much less dependant on kernel headers, a large departure from
    its traditional tightly-coupled-to-the-kernel origins.  I have written and/or
    rewritten a number of things that were missing or broken, and sometimes grafted
    in bits of code from the current glibc and libc5.  I have also added a proper
    configuration system which allows you to easily select your target architecture
    and enable and disable various features.  Many people have helped by testing,
    contributing ports to new architectures, and adding support for missing features.

    <p>

    In particular, around the end of 2000, Manuel Novoa III got involved with
    uClibc.  One of his first contributions was the original gcc wrapper (which
    has since been removed).  Since then, he has written virtually all of the
    current uClibc stdio, time, string, ctype, locale, and wchar-related code,
    as well as much of stdlib and various other bits throught the library.

    <p>

    These days, uClibc is being developed and enhanced by Erik Andersen 
    and Manuel Novoa III of
    <a href="http://codepoet-consulting.com/">CodePoet Consulting</a> 
    along with the rest of the embedded Linux community.



<hr />
<p>
<h2><a name="demanding">I demand that you to add &lt;favorite feature&gt; right now!   How come 
	you don't answer all my questions on the mailing list instantly?  I demand 
	that you help me with all of my problems <em>Right Now</em>!</a></h2>
<p>

    You have not paid us a single cent and yet you still have the
    product of several years of work from Erik and Manuel and
    many other people.  We are not your slaves!  We work on uClibc
    because we find it interesting.  If you go off flaming us, we will
    ignore you.


    

<hr />
<p>
<h2><a name="contracts">I need you to add &lt;favorite feature&gt;!  Are the uClibc developers willing to 
	be paid in order to fix bugs or add in &lt;favorite feature&gt;?  Are you willing to provide
	support contracts?</a></h2>
<p>

    Sure!  Now you have our attention!  What you should do is contact <a
	href="mailto:andersen@codepoet.org">Erik Andersen</a> of <a
	href="http://codepoet-consulting.com/">CodePoet Consulting</a> to bid
    on your project.  If Erik is too busy to personally add your feature, there
    are several other active uClibc contributors who will almost certainly be able 
    to help you out.  Erik can contact them and ask them about their availability.
    

<hr />
<p>
<h2><a name="support">I think you guys are great and I want to help support your work!</a></h2>
<p>

    Wow, that would be great!  You can click here to help support uClibc and/or request features.
    
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    If you prefer to contact us directly for payments, hardware donations, 
    support requests, etc., you can contact 
    <a href="http://codepoet-consulting.com/">CodePoet Consulting</a> here.

<hr />


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