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".
The name is partly historical, since uClibc was originally created to support µClinux, 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.
Currently uClibc runs on alpha, ARM, cris, i386, i960, h8300, m68k, mips/mipsel, PowerPC, SH, SPARC, and v850 processors.
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
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.
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.
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.
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!!!
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.
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.
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...
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 Lesser GPL 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! :-)
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.
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.
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.
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.
Shared Libraries are not currently supported by uClibc on MMU-less systems. SnapGear 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.
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 uClibc toolchain builder, or the uClibc buildroot system from uClibc buildroot system. Simply adjust the Makefile settings to match your target system, and then run 'make'.
If you want to be really 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 i386, powerpc, mipsel, and arm. These are pre-built uClibc only development systems (created using buildroot), 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.
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 REALLY 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...
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.
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.
The uClibc time functions get timezone information from the TZ environment variable, as described in the Single Unix Specification Version 3. See http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap08.html for details on valid settings of TZ. For some additional examples, read http://www.uclibc.org/lists/uclibc/2002-August/006261.html 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.
The history and origin of uClibc is long and twisty. In the beginning, there was GNU libc. 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 Linux-8086 C library, which is part of the elks project, 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 µClinux.
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.
To start with, (with some initial help from D. Jeff Dionne), 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.
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.
These days, uClibc is being developed and enhanced by Erik Andersen and Manuel Novoa III of CodePoet Consulting along with the rest of the embedded Linux community.
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.
Sure! Now you have our attention! What you should do is contact Erik Andersen of CodePoet Consulting 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.
Wow, that would be great! You can click here to help support uClibc and/or request features.