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uClibc - a Small C Library for Linux
Erik Andersen <>
uClibc (aka µClibc/pronounced yew-see-lib-see) is a C library for
developing embedded Linux systems. It is much smaller than the
GNU C Library, but nearly all applications supported by glibc
also work perfectly with uClibc. Porting applications from glibc
to uClibc typically involves just recompiling the source code.
uClibc even supports shared libraries and threading. It currently
runs on standard Linux and MMU-less (also known as µClinux)
systems with support for alpha, ARM, cris, e1, h8300, i386, i960,
m68k, microblaze, mips/mipsel, PowerPC, SH, SPARC, and v850
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...
uClibc is maintained by Erik Andersen and is licensed under the
GNU LESSER GENERAL PUBLIC LICENSE. This license allows you to
make closed source commercial applications using an unmodified
version of uClibc (Please consider sharing some of the money you
make ;-). You do not need to give away all your source code just
because you use uClibc and/or run on Linux. You should, however,
carefuly review the license and make certain you understand and
abide by it strictly.
For installation instructions, see the file INSTALL.
uClibc strives to be standards compliant, which means that most
documentation written for SuSv3, or for glibc also applies to
uClibc functions. However, many GNU extensions are not supported
because they have not been ported, or more importantly, would
increase the size of uClibc disproportional to the added
functionality. There is some discussion of these differences
in the "docs" directory.
Additional information (recent releases, FAQ, mailing list, bugs,
etc.) can be found at
uClibc may be freely modified and distributed under the terms of
the GNU Lesser General Public License, which can be found in the
Please Note:
There is an unwholesomely huge amount of code out there
that depends on the presence of GNU libc header files.
We have GNU libc compatible header files. So we have
committed a horrible sin in uClibc. We _lie_ and claim
to be GNU libc in order to force these applications to
work as their developers intended. This is IMHO,
pardonable, since these defines are not really intended
to check for the presence of a particular library, but
rather are used to define an _interface_. Some programs
are especially chummy with glibc, and may need this
behavior disabled by adding CFLAGS+=-D__FORCE_NOGLIBC
If you want to make special exceptions in your code which are
specifically for uClibc, you can make certain to include features.h,
and then have your code check for uClibc as follows:
#ifdef __UCLIBC__
And most of all, be sure to have some fun! :-)