Installing the GNU C Library
****************************

Before you do anything else, you should read the file FAQ found at the top level of the source tree.  This file answers common questions and describes problems you may experience with compilation and installation.  It is updated more frequently than this manual.

Features can be added to GNU Libc via add-on bundles.  These are separate tarfiles 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.  As of the 2.1 release, two important components of glibc are distributed as ``official'' add-ons.  Unless you are doing an unusual installation, you should get them both.

Support for POSIX threads is maintained by someone else, so it's in a separate package.  It is only available for Linux systems, but this will change in the future.  Get it from the same place you got the main bundle; the file is glibc-linuxthreads-VERSION.tar.gz.

You will need recent versions of several GNU tools: definitely GCC and GNU Make, and possibly others.  See Tools for Compilation, below.

Configuring and compiling GNU Libc
==================================

GNU libc can be compiled in the source directory, but we strongly advise to build it in a separate build directory.  For example, if you have unpacked the glibc sources in /src/gnu/glibc-2.1.0, 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 found at the top level of the source tree.  In the scenario above, you'd type

     $ ../glibc-2.1.0/configure ARGS...

Please note that even if you're building in a separate build directory, the compilation needs to modify a few files in the source directory, especially some files in the manual subdirectory.

configure takes many options, but you can get away with knowing only two: --prefix and --enable-add-ons.  The --prefix option tells configure where you want glibc installed. This defaults to /usr/local.  The --enable-add-ons option tells configure to use all the add-on bundles it finds in the source directory.  Since important functionality is provided in add-ons, you should always specify this option.

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 configure:

--prefix=DIRECTORY
     Install machine-independent data files in subdirectories of DIRECTORY.  The default is to install in /usr/local.

--exec-prefix=DIRECTORY
     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.

--with-headers=DIRECTORY
     Look for kernel header files in DIRECTORY, not /usr/include.  Glibc needs information from the kernel's private header files.  It 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 glibc.  Conflicts can occasionally happen in this case.  Note that Linux libc5 qualifies as an older version of glibc.  You can also use this option if you want to compile glibc with a newer set of kernel headers than the ones found in /usr/include.

--enable-add-ons[=LIST]
     Enable add-on packages in your source tree.  If this option is specified with no list, it enables all the add-on packages it finds.  If you do not wish to use some add-on package that you have present in your source tree, give this option a list of the add-ons that you do want used, like this: --enable-add-ons=linuxthreads

--with-binutils=DIRECTORY
     Use the binutils (assembler and linker) in DIRECTORY, not the ones the C compiler would default to.  You could 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.

--without-fp
     Use this option if your computer lacks hardware floating-point support and your operating system does not emulate an FPU.

--disable-shared
     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.

--disable-profile
     Don't build libraries with profiling information.  You may want to use this option if you don't plan to do profiling.

--enable-omitfp
     Use maximum optimization for the normal (static and shared) libraries, and compile separate static libraries with debugging information and no optimisation.  We recommend against this.  The extra optimization doesn't gain you much, it may provoke compiler bugs, and you won't be able to trace bugs through the C library.

--disable-versioning
     Don't compile the shared libraries with symbol version information. Doing this will make the resulting library incompatible with old binaries, so it's not recommended.

--enable-static-nss
     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.

--build=BUILD-SYSTEM
--host=HOST-SYSTEM
     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 glibc 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 i586-pc-linux-gnu but you want to compile a library for 386es, give --host=i386-pc-linux-gnu or just --host=i386-linux and add the appropriate compiler flags (-mcpu=i386 will do the trick) to CFLAGS.

     If you specify just --build, configure will get confused.

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 really wrong.

The compilation process takes several hours even on fast hardware. Expect at least two hours for the default configuration on i586 for Linux.  For Hurd times are much longer.  Except for EGCS 1.1 and GCC 2.95 (and later versions of GCC), all supported versions of GCC have a problem which causes them to take several minutes to compile certain files in the iconvdata directory.  Do not panic if the compiler appears to hang.

If you want to run a parallel make, you can't just give make the -j option, because it won't be passed down to the sub-makes. Instead, edit the generated Makefile and uncomment the line

     # PARALLELMFLAGS = -j 4

You can change the 4 to some other number as appropriate for your system.  Instead of changing the Makefile, you could give this option directly to make and call it as, for example, make PARALLELMFLAGS=-j4.  If you're building in the source directory, you must use the latter approach since in this case no new Makefile is generated for you to change.

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.  See 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 glibc as an unprivileged user.

To format the GNU C Library Reference Manual for printing, type make dvi.  You need a working TeX installation to do this. The distribution already includes the on-line formatted version of the manual, as Info files.  You can regenerate those with make info, but it shouldn't be necessary.

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 makefiles.

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 for programs run on the build system as part of compiling the library.  You may need to set AR and RANLIB to cross-compiling versions of ar and ranlib if the native tools are not configured to work with object files for the target you configured for.

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 glibc 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.

If you're upgrading from Linux libc5 or some other C library, you need to replace the /usr/include with a fresh directory before installing it. The new /usr/include should contain the Linux headers, but nothing else.

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.

If you are upgrading from a previous installation of glibc 2.0 or 2.1, make install will do the entire job.  You do not need to remove the old includes -- if you want to do so anyway you must then follow the order given above.

You may also need to reconfigure GCC to work with the new library.  The easiest way to do that is to figure out the compiler switches to make it work again (-Wl,--dynamic-linker=/lib/ld-linux.so.2 should work on Linux systems) and use them to recompile gcc.  You can also edit the specs file (/usr/lib/gcc-lib/TARGET/VERSION/specs), but that is a bit of a black art.

You can install glibc somewhere other than where you configured it to go by setting the install_root 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.

Glibc 2.2 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 well.

One auxiliary program, /usr/libexec/pt_chown, is installed setuid root.  This program is invoked by the grantpt function; it sets the permissions on a pseudoterminal so it can be used by the calling process.  This means programs like xterm and screen do not have to be setuid to get a pty.  (There may be other reasons why they need privileges.)  If you are using a 2.1 or newer Linux kernel with the devptsfs or devfs filesystems providing pty slaves, you don't need this program; otherwise you do. The source for pt_chown is in login/programs/pt_chown.c.

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 glibc, you can issue from your build directory the command make localedata/install-locales.

To configure the locally used timezone, you can either 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 /etc/localtime.

Recommended Tools for Compilation
=================================

We recommend installing the following GNU tools before attempting to build the GNU C library:

  * GNU make 3.75

     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 version GNU make version 3.75 or 3.77.  All earlier versions have severe bugs or lack features. Version 3.76 is known to have bugs which only show up in big projects like GNU libc. Version 3.76.1 seems OK but some people have reported problems.

  * EGCS 1.1.1, 1.1 or 1.0.3, or GCC 2.8.1, 2.95 or newer

     The GNU C library can only be compiled with the GNU C compiler family. As of the 2.1 release, EGCS 1.0.3 or higher is required.  GCC 2.8.1 can also be used (but see the FAQ for reasons why you might not want to). Earlier versions simply are too buggy.  As of this writing, GCC 2.95.2 is the compiler we advise to use.

     You can use whatever compiler you like to compile programs that use GNU libc, but be aware that both GCC 2.7 and 2.8 have bugs in their floating-point support that may be triggered by the math library.

     On Alpha machines you need at least EGCS 1.1.1.  Earlier versions don't work reliably.

     For PPC you might need some patches even on top of the last EGCS version. See the FAQ.

  * GNU binutils 2.9.1, 2.9.1.0.16, or later 2.9.1.0.x release

     You must use GNU binutils (as and ld) if you want to build a shared library.  Even if you don't, we recommend you use them anyway.  No one has tested compilation with non-GNU binutils in a long time.

     The quality of binutils releases has varied a bit recently.  The bugs are in obscure features, but glibc uses quite a few of those.  2.9.1, 2.9.1.0.16, and later 2.9.1.0.x releases are known to work.  Versions after 2.8.1.0.23 may or may not work.  Older versions definitely don't. 2.9.1.0.16 or higher is required on some platforms, like PPC and Arm.

     For PPC you might need some patches even on top of the last binutils version.  See the FAQ.

  * GNU texinfo 3.12f

     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.

  * GNU awk 3.0, or some other POSIX awk

     Awk is used in several places to generate files.  The scripts should work with any POSIX-compliant awk implementation; gawk 3.0 and mawk 1.3 are known to work.

  * 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.  The known exception is the script po2test.sed in the intl subdirectory which is used to generate msgs.h for the testsuite.  This script works correctly only with GNU sed 3.02.  If you like to run the testsuite, you should definitly upgrade sed.

If you change any of the configure.in files you will also need

  * GNU autoconf 2.12 or higher

and if you change any of the message translation files you will need

  * GNU gettext 0.10.35 or later (version 0.10.35 is a alpha release and available via ftp from alpha.gnu.org/gnu)

You may also need these packages if you upgrade your source tree using patches, although we try to avoid this.

Supported Configurations
========================

The GNU C Library currently supports configurations that match the following patterns:

     alpha-*-linux
     arm-*-linux
     arm-*-linuxaout
     arm-*-none
     iX86-*-gnu
     iX86-*-linux
     m68k-*-linux
     powerpc-*-linux
     sparc-*-linux
     sparc64-*-linux

Former releases of this library (version 1.09.1 and perhaps earlier versions) used to run on the following configurations:

     alpha-dec-osf1
     alpha-*-linuxecoff
     iX86-*-bsd4.3
     iX86-*-isc2.2
     iX86-*-isc3.N
     iX86-*-sco3.2
     iX86-*-sco3.2v4
     iX86-*-sysv
     iX86-*-sysv4
     iX86-force_cpu386-none
     iX86-sequent-bsd
     i960-nindy960-none
     m68k-hp-bsd4.3
     m68k-mvme135-none
     m68k-mvme136-none
     m68k-sony-newsos3
     m68k-sony-newsos4
     m68k-sun-sunos4.N
     mips-dec-ultrix4.N
     mips-sgi-irix4.N
     sparc-sun-solaris2.N
     sparc-sun-sunos4.N

Since no one has volunteered to test and fix these configurations, they are not supported at the moment.  They probably don't compile; they definitely don't work anymore.  Porting the library is not hard. If you are interested in doing a port, please contact the glibc maintainers by sending electronic mail to bug-glibc@gnu.org.

Valid cases of iX86 include i386, i486, i586, and i686.  All of those configurations produce a library that can run on this processor and newer processors.  The GCC compiler by default generates code that's optimized for the machine it's configured for and will use the instructions available on that machine. For example if your GCC is configured for i686, gcc will optimize for i686 and might issue some i686 specific instructions. To generate code for other models, you have to configure for that model and give GCC the appropriate -march= and -mcpu= compiler switches via CFLAGS.

Specific advice for Linux systems
=================================

If you are installing GNU libc on a Linux system, you need to have the header files from a 2.2 kernel around for reference.  You do not need to use the 2.2 kernel, just have its headers where glibc can access at them.  The easiest way to do this is to unpack it in a directory such as /usr/src/linux-2.2.1.  In that directory, run make config and accept all the defaults.  Then run make include/linux/version.h.  Finally, configure glibc with the option --with-headers=/usr/src/linux-2.2.1/include.  Use the most recent kernel you can get your hands on.

An alternate tactic is to unpack the 2.2 kernel and run make config as above.  Then rename or delete /usr/include, create a new /usr/include, and make the usual symbolic links of /usr/include/linux and /usr/include/asm into the 2.2 kernel sources.  You can then configure glibc with no special options. This tactic is recommended if you are upgrading from libc5, since you need to get rid of the old header files anyway.

Note that /usr/include/net and /usr/include/scsi should not be symlinks into the kernel sources.  GNU libc provides its own versions of these files.

Linux expects some components of the libc installation to be in /lib and some in /usr/lib.  This is handled automatically if you configure glibc with --prefix=/usr.  If you set some other prefix or allow it to default to /usr/local, then all the components are installed there.

If you are upgrading from libc5, you need to recompile every shared library on your system against the new library for the sake of new code, but keep the old libraries around for old binaries to use.  This is complicated and difficult.  Consult the Glibc2 HOWTO at http://www.imaxx.net/~thrytis/glibc for details.

You cannot use nscd with 2.0 kernels, due to bugs in the kernel-side thread support.  nscd happens to hit these bugs particularly hard, but you might have problems with any threaded program.

Reporting Bugs
==============

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 bug tracking system has a WWW interface at http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl.  The WWW interface gives you access to open and closed reports.  The closed reports normally include a patch or a hint on solving the problem.

To report a bug, first you must find it.  Hopefully, 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 library.  Many historical Unix C libraries permit things that we don't, such as closing a file twice.

If you think you have found some way in which the GNU C library does not conform to the ISO and POSIX standards (see 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 using the glibcbug script.  It is installed with libc, or if you haven't installed it, will be in your build directory.  Send your test case, the results you got, the results you expected, and what you think the problem might be (if you've thought of anything). glibcbug will insert the configuration information we need to see, and ship the report off to bugs@gnu.org.  Don't send a message there directly; it is fed to a program that expects mail to be formatted in a particular way.  Use the script.

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 Internet address bug-glibc-manual@gnu.org.  If you refer to specific sections of the manual, please include the section names for easier identification.