Installing the GNU C Library
Before you do anything else, you should read the FAQ at
<http://sourceware.org/glibc/wiki/FAQ>. It answers common questions and
describes problems you may experience with compilation and installation.
Features can be added to the GNU C Library via "add-on" bundles.
These are separate tar files, which you unpack into the top level of the
source tree. Then you give 'configure' the '--enable-add-ons' option to
activate them, and they will be compiled into the library.
You will need recent versions of several GNU tools: definitely GCC
and GNU Make, and possibly others. *Note Tools for Compilation::,
Configuring and compiling the GNU C Library
The GNU C Library cannot be compiled in the source directory. You must
build it in a separate build directory. For example, if you have
unpacked the GNU C Library sources in '/src/gnu/glibc-VERSION', create a
directory '/src/gnu/glibc-build' to put the object files in. This
allows removing the whole build directory in case an error occurs, which
is the safest way to get a fresh start and should always be done.
From your object directory, run the shell script 'configure' located
at the top level of the source tree. In the scenario above, you'd type
$ ../glibc-VERSION/configure ARGS...
Please note that even though you're building in a separate build
directory, the compilation may need to create or modify files and
directories in the source directory.
'configure' takes many options, but the only one that is usually
mandatory is '--prefix'. This option tells 'configure' where you want
the GNU C Library installed. This defaults to '/usr/local', but the
normal setting to install as the standard system library is
'--prefix=/usr' for GNU/Linux systems and '--prefix=' (an empty prefix)
for GNU/Hurd systems.
It may also be useful to set the CC and CFLAGS variables in the
environment when running 'configure'. CC selects the C compiler that
will be used, and CFLAGS sets optimization options for the compiler.
The following list describes all of the available options for
Install machine-independent data files in subdirectories of
'DIRECTORY'. The default is to install in '/usr/local'.
Install the library and other machine-dependent files in
subdirectories of 'DIRECTORY'. The default is to the '--prefix'
directory if that option is specified, or '/usr/local' otherwise.
Look for kernel header files in DIRECTORY, not '/usr/include'. The
GNU C Library needs information from the kernel's header files
describing the interface to the kernel. The GNU C Library will
normally look in '/usr/include' for them, but if you specify this
option, it will look in DIRECTORY instead.
This option is primarily of use on a system where the headers in
'/usr/include' come from an older version of the GNU C Library.
Conflicts can occasionally happen in this case. You can also use
this option if you want to compile the GNU C Library with a newer
set of kernel headers than the ones found in '/usr/include'.
Specify add-on packages to include in the build. If this option is
specified with no list, it enables all the add-on packages it finds
in the main source directory; this is the default behavior. You
may specify an explicit list of add-ons to use in LIST, separated
by spaces or commas (if you use spaces, remember to quote them from
the shell). Each add-on in LIST can be an absolute directory name
or can be a directory name relative to the main source directory,
or relative to the build directory (that is, the current working
directory). For example,
This option is currently only useful on GNU/Linux systems. The
VERSION parameter should have the form X.Y.Z and describes the
smallest version of the Linux kernel the generated library is
expected to support. The higher the VERSION number is, the less
compatibility code is added, and the faster the code gets.
Use the binutils (assembler and linker) in 'DIRECTORY', not the
ones the C compiler would default to. You can use this option if
the default binutils on your system cannot deal with all the
constructs in the GNU C Library. In that case, 'configure' will
detect the problem and suppress these constructs, so that the
library will still be usable, but functionality may be lost--for
example, you can't build a shared libc with old binutils.
Use this option if your computer lacks hardware floating-point
support and your operating system does not emulate an FPU.
Don't build shared libraries even if it is possible. Not all
systems support shared libraries; you need ELF support and
(currently) the GNU linker.
Don't build libraries with profiling information. You may want to
use this option if you don't plan to do profiling.
Compile static versions of the NSS (Name Service Switch) libraries.
This is not recommended because it defeats the purpose of NSS; a
program linked statically with the NSS libraries cannot be
dynamically reconfigured to use a different name database.
By default, dynamic tests are linked to run with the installed C
library. This option hardcodes the newly built C library path in
dynamic tests so that they can be invoked directly.
By default, timezone related utilities ('zic', 'zdump', and
'tzselect') are installed with the GNU C Library. If you are
building these independently (e.g. by using the 'tzcode' package),
then this option will allow disabling the install of these.
Note that you need to make sure the external tools are kept in sync
with the versions that the GNU C Library expects as the data
formats may change over time. Consult the 'timezone' subdirectory
for more details.
Enable lock elision for pthread mutexes by default.
The file 'pt_chown' is a helper binary for 'grantpt' (*note
Pseudo-Terminals: Allocation.) that is installed setuid root to fix
up pseudo-terminal ownership. It is not built by default because
systems using the Linux kernel are commonly built with the 'devpts'
filesystem enabled and mounted at '/dev/pts', which manages
pseudo-terminal ownership automatically. By using
'--enable-pt_chown', you may build 'pt_chown' and install it setuid
and owned by 'root'. The use of 'pt_chown' introduces additional
security risks to the system and you should enable it only if you
understand and accept those risks.
By default, the GNU C Library is built with '-Werror'. If you wish
to build without this option (for example, if building with a newer
version of GCC than this version of the GNU C Library was tested
with, so new warnings cause the build with '-Werror' to fail), you
can configure with '--disable-werror'.
By default for x86_64, the GNU C Library is built with vector math
library. Use this option to disable vector math library.
These options are for cross-compiling. If you specify both options
and BUILD-SYSTEM is different from HOST-SYSTEM, 'configure' will
prepare to cross-compile the GNU C Library from BUILD-SYSTEM to be
used on HOST-SYSTEM. You'll probably need the '--with-headers'
option too, and you may have to override CONFIGURE's selection of
the compiler and/or binutils.
If you only specify '--host', 'configure' will prepare for a native
compile but use what you specify instead of guessing what your
system is. This is most useful to change the CPU submodel. For
example, if 'configure' guesses your machine as 'i686-pc-linux-gnu'
but you want to compile a library for 586es, give
'--host=i586-pc-linux-gnu' or just '--host=i586-linux' and add the
appropriate compiler flags ('-mcpu=i586' will do the trick) to
If you specify just '--build', 'configure' will get confused.
Specify a description, possibly including a build number or build
date, of the binaries being built, to be included in '--version'
output from programs installed with the GNU C Library. For
example, '--with-pkgversion='FooBar GNU/Linux glibc build 123''.
The default value is 'GNU libc'.
Specify the URL that users should visit if they wish to report a
bug, to be included in '--help' output from programs installed with
the GNU C Library. The default value refers to the main
bug-reporting information for the GNU C Library.
To build the library and related programs, type 'make'. This will
produce a lot of output, some of which may look like errors from 'make'
but isn't. Look for error messages from 'make' containing '***'. Those
indicate that something is seriously wrong.
The compilation process can take a long time, depending on the
configuration and the speed of your machine. Some complex modules may
take a very long time to compile, as much as several minutes on slower
machines. Do not panic if the compiler appears to hang.
If you want to run a parallel make, simply pass the '-j' option with
an appropriate numeric parameter to 'make'. You need a recent GNU
'make' version, though.
To build and run test programs which exercise some of the library
facilities, type 'make check'. If it does not complete successfully, do
not use the built library, and report a bug after verifying that the
problem is not already known. *Note Reporting Bugs::, for instructions
on reporting bugs. Note that some of the tests assume they are not
being run by 'root'. We recommend you compile and test the GNU C
Library as an unprivileged user.
Before reporting bugs make sure there is no problem with your system.
The tests (and later installation) use some pre-existing files of the
system such as '/etc/passwd', '/etc/nsswitch.conf' and others. These
files must all contain correct and sensible content.
Normally, 'make check' will run all the tests before reporting all
problems found and exiting with error status if any problems occurred.
You can specify 'stop-on-test-failure=y' when running 'make check' to
make the test run stop and exit with an error status immediately when a
To format the 'GNU C Library Reference Manual' for printing, type
'make dvi'. You need a working TeX installation to do this. The
distribution builds the on-line formatted version of the manual, as Info
files, as part of the build process. You can build them manually with
The library has a number of special-purpose configuration parameters
which you can find in 'Makeconfig'. These can be overwritten with the
file 'configparms'. To change them, create a 'configparms' in your
build directory and add values as appropriate for your system. The file
is included and parsed by 'make' and has to follow the conventions for
It is easy to configure the GNU C Library for cross-compilation by
setting a few variables in 'configparms'. Set 'CC' to the
cross-compiler for the target you configured the library for; it is
important to use this same 'CC' value when running 'configure', like
this: 'CC=TARGET-gcc configure TARGET'. Set 'BUILD_CC' to the compiler
to use for programs run on the build system as part of compiling the
library. You may need to set 'AR' to cross-compiling versions of 'ar'
if the native tools are not configured to work with object files for the
target you configured for. When cross-compiling the GNU C Library, it
may be tested using 'make check
test-wrapper="SRCDIR/scripts/cross-test-ssh.sh HOSTNAME"', where SRCDIR
is the absolute directory name for the main source directory and
HOSTNAME is the host name of a system that can run the newly built
binaries of the GNU C Library. The source and build directories must be
visible at the same locations on both the build system and HOSTNAME.
In general, when testing the GNU C Library, 'test-wrapper' may be set
to the name and arguments of any program to run newly built binaries.
This program must preserve the arguments to the binary being run, its
working directory and the standard input, output and error file
descriptors. If 'TEST-WRAPPER env' will not work to run a program with
environment variables set, then 'test-wrapper-env' must be set to a
program that runs a newly built program with environment variable
assignments in effect, those assignments being specified as 'VAR=VALUE'
before the name of the program to be run. If multiple assignments to
the same variable are specified, the last assignment specified must take
precedence. Similarly, if 'TEST-WRAPPER env -i' will not work to run a
program with an environment completely empty of variables except those
directly assigned, then 'test-wrapper-env-only' must be set; its use has
the same syntax as 'test-wrapper-env', the only difference in its
semantics being starting with an empty set of environment variables
rather than the ambient set.
Installing the C Library
To install the library and its header files, and the Info files of the
manual, type 'make install'. This will build things, if necessary,
before installing them; however, you should still compile everything
first. If you are installing the GNU C Library as your primary C
library, we recommend that you shut the system down to single-user mode
first, and reboot afterward. This minimizes the risk of breaking things
when the library changes out from underneath.
'make install' will do the entire job of upgrading from a previous
installation of the GNU C Library version 2.x. There may sometimes be
headers left behind from the previous installation, but those are
generally harmless. If you want to avoid leaving headers behind you can
do things in the following order.
You must first build the library ('make'), optionally check it ('make
check'), switch the include directories and then install ('make
install'). The steps must be done in this order. Not moving the
directory before install will result in an unusable mixture of header
files from both libraries, but configuring, building, and checking the
library requires the ability to compile and run programs against the old
library. The new '/usr/include', after switching the include
directories and before installing the library should contain the Linux
headers, but nothing else. If you do this, you will need to restore any
headers from libraries other than the GNU C Library yourself after
installing the library.
You can install the GNU C Library somewhere other than where you
configured it to go by setting the 'DESTDIR' GNU standard make variable
on the command line for 'make install'. The value of this variable is
prepended to all the paths for installation. This is useful when
setting up a chroot environment or preparing a binary distribution. The
directory should be specified with an absolute file name. Installing
with the 'prefix' and 'exec_prefix' GNU standard make variables set is
The GNU C Library includes a daemon called 'nscd', which you may or
may not want to run. 'nscd' caches name service lookups; it can
dramatically improve performance with NIS+, and may help with DNS as
One auxiliary program, '/usr/libexec/pt_chown', is installed setuid
'root' if the '--enable-pt_chown' configuration option is used. This
program is invoked by the 'grantpt' function; it sets the permissions on
a pseudoterminal so it can be used by the calling process. If you are
using a Linux kernel with the 'devpts' filesystem enabled and mounted at
'/dev/pts', you don't need this program.
After installation you might want to configure the timezone and
locale installation of your system. The GNU C Library comes with a
locale database which gets configured with 'localedef'. For example, to
set up a German locale with name 'de_DE', simply issue the command
'localedef -i de_DE -f ISO-8859-1 de_DE'. To configure all locales that
are supported by the GNU C Library, you can issue from your build
directory the command 'make localedata/install-locales'.
To configure the locally used timezone, set the 'TZ' environment
variable. The script 'tzselect' helps you to select the right value.
As an example, for Germany, 'tzselect' would tell you to use
'TZ='Europe/Berlin''. For a system wide installation (the given paths
are for an installation with '--prefix=/usr'), link the timezone file
which is in '/usr/share/zoneinfo' to the file '/etc/localtime'. For
Germany, you might execute 'ln -s /usr/share/zoneinfo/Europe/Berlin
Recommended Tools for Compilation
We recommend installing the following GNU tools before attempting to
build the GNU C Library:
* GNU 'make' 3.79 or newer
You need the latest version of GNU 'make'. Modifying the GNU C
Library to work with other 'make' programs would be so difficult
that we recommend you port GNU 'make' instead. *Really.* We
recommend GNU 'make' version 3.79. All earlier versions have
severe bugs or lack features.
* GCC 4.7 or newer
GCC 4.7 or higher is required. In general it is recommended to use
the newest version of the compiler that is known to work for
building the GNU C Library, as newer compilers usually produce
better code. As of release time, GCC 5.3 is the newest compiler
verified to work to build the GNU C Library.
You can use whatever compiler you like to compile programs that use
the GNU C Library.
Check the FAQ for any special compiler issues on particular
* GNU 'binutils' 2.22 or later
You must use GNU 'binutils' (as and ld) to build the GNU C Library.
No other assembler or linker has the necessary functionality at the
moment. As of release time, GNU 'binutils' 2.25 is the newest
verified to work to build the GNU C Library.
* GNU 'texinfo' 4.7 or later
To correctly translate and install the Texinfo documentation you
need this version of the 'texinfo' package. Earlier versions do
not understand all the tags used in the document, and the
installation mechanism for the info files is not present or works
differently. As of release time, 'texinfo' 6.0 is the newest
verified to work to build the GNU C Library.
* GNU 'awk' 3.1.2, or higher
'awk' is used in several places to generate files. Some 'gawk'
extensions are used, including the 'asorti' function, which was
introduced in version 3.1.2 of 'gawk'. As of release time, 'gawk'
version 4.1.3 is the newest verified to work to build the GNU C
* Perl 5
Perl is not required, but it is used if present to test the
installation. We may decide to use it elsewhere in the future.
* GNU 'sed' 3.02 or newer
'Sed' is used in several places to generate files. Most scripts
work with any version of 'sed'. As of release time, 'sed' version
4.2.2 is the newest verified to work to build the GNU C Library.
If you change any of the 'configure.ac' files you will also need
* GNU 'autoconf' 2.69 (exactly)
and if you change any of the message translation files you will need
* GNU 'gettext' 0.10.36 or later
If you wish to regenerate the 'yacc' parser code in the 'intl'
subdirectory you will need
* GNU 'bison' 2.7 or later
You may also need these packages if you upgrade your source tree using
patches, although we try to avoid this.
Specific advice for GNU/Linux systems
If you are installing the GNU C Library on GNU/Linux systems, you need
to have the header files from a 3.2 or newer kernel around for
reference. These headers must be installed using 'make
headers_install'; the headers present in the kernel source directory are
not suitable for direct use by the GNU C Library. You do not need to
use that kernel, just have its headers installed where the GNU C Library
can access them, referred to here as INSTALL-DIRECTORY. The easiest way
to do this is to unpack it in a directory such as
'/usr/src/linux-VERSION'. In that directory, run 'make headers_install
INSTALL_HDR_PATH=INSTALL-DIRECTORY'. Finally, configure the GNU C
Library with the option '--with-headers=INSTALL-DIRECTORY/include'. Use
the most recent kernel you can get your hands on. (If you are
cross-compiling the GNU C Library, you need to specify
'ARCH=ARCHITECTURE' in the 'make headers_install' command, where
ARCHITECTURE is the architecture name used by the Linux kernel, such as
'x86' or 'powerpc'.)
After installing the GNU C Library, you may need to remove or rename
directories such as '/usr/include/linux' and '/usr/include/asm', and
replace them with copies of directories such as 'linux' and 'asm' from
'INSTALL-DIRECTORY/include'. All directories present in
'INSTALL-DIRECTORY/include' should be copied, except that the GNU C
Library provides its own version of '/usr/include/scsi'; the files
provided by the kernel should be copied without replacing those provided
by the GNU C Library. The 'linux', 'asm' and 'asm-generic' directories
are required to compile programs using the GNU C Library; the other
directories describe interfaces to the kernel but are not required if
not compiling programs using those interfaces. You do not need to copy
kernel headers if you did not specify an alternate kernel header source
The Filesystem Hierarchy Standard for GNU/Linux systems expects some
components of the GNU C Library installation to be in '/lib' and some in
'/usr/lib'. This is handled automatically if you configure the GNU C
Library with '--prefix=/usr'. If you set some other prefix or allow it
to default to '/usr/local', then all the components are installed there.
There are probably bugs in the GNU C Library. There are certainly
errors and omissions in this manual. If you report them, they will get
fixed. If you don't, no one will ever know about them and they will
remain unfixed for all eternity, if not longer.
It is a good idea to verify that the problem has not already been
reported. Bugs are documented in two places: The file 'BUGS' describes
a number of well known bugs and the central GNU C Library bug tracking
system has a WWW interface at <http://sourceware.org/bugzilla/>. The
WWW interface gives you access to open and closed reports. A closed
report normally includes a patch or a hint on solving the problem.
To report a bug, first you must find it. With any luck, this will be
the hard part. Once you've found a bug, make sure it's really a bug. A
good way to do this is to see if the GNU C Library behaves the same way
some other C library does. If so, probably you are wrong and the
libraries are right (but not necessarily). If not, one of the libraries
is probably wrong. It might not be the GNU C Library. Many historical
Unix C libraries permit things that we don't, such as closing a file
If you think you have found some way in which the GNU C Library does
not conform to the ISO and POSIX standards (*note Standards and
Portability::), that is definitely a bug. Report it!
Once you're sure you've found a bug, try to narrow it down to the
smallest test case that reproduces the problem. In the case of a C
library, you really only need to narrow it down to one library function
call, if possible. This should not be too difficult.
The final step when you have a simple test case is to report the bug.
Do this at <http://www.gnu.org/software/libc/bugs.html>.
If you are not sure how a function should behave, and this manual
doesn't tell you, that's a bug in the manual. Report that too! If the
function's behavior disagrees with the manual, then either the library
or the manual has a bug, so report the disagreement. If you find any
errors or omissions in this manual, please report them to the bug
database. If you refer to specific sections of the manual, please
include the section names for easier identification.