INSTALL

   1 Installing the GNU C Library
   2 ****************************
   3
   4 Before you do anything else, you should read the FAQ at
   5 <http://sourceware.org/glibc/wiki/FAQ>.  It answers common questions and
   6 describes problems you may experience with compilation and installation.
   7
   8    You will need recent versions of several GNU tools: definitely GCC
   9 and GNU Make, and possibly others.  *Note Tools for Compilation::,
  10 below.
  11
  12 Configuring and compiling the GNU C Library
  13 ===========================================
  14
  15 The GNU C Library cannot be compiled in the source directory.  You must
  16 build it in a separate build directory.  For example, if you have
  17 unpacked the GNU C Library sources in '/src/gnu/glibc-VERSION', create a
  18 directory '/src/gnu/glibc-build' to put the object files in.  This
  19 allows removing the whole build directory in case an error occurs, which
  20 is the safest way to get a fresh start and should always be done.
  21
  22    From your object directory, run the shell script 'configure' located
  23 at the top level of the source tree.  In the scenario above, you'd type
  24
  25      $ ../glibc-VERSION/configure ARGS...
  26
  27    Please note that even though you're building in a separate build
  28 directory, the compilation may need to create or modify files and
  29 directories in the source directory.
  30
  31 'configure' takes many options, but the only one that is usually
  32 mandatory is '--prefix'.  This option tells 'configure' where you want
  33 the GNU C Library installed.  This defaults to '/usr/local', but the
  34 normal setting to install as the standard system library is
  35 '--prefix=/usr' for GNU/Linux systems and '--prefix=' (an empty prefix)
  36 for GNU/Hurd systems.
  37
  38    It may also be useful to set the CC and CFLAGS variables in the
  39 environment when running 'configure'.  CC selects the C compiler that
  40 will be used, and CFLAGS sets optimization options for the compiler.
  41
  42    The following list describes all of the available options for
  43 'configure':
  44
  45 '--prefix=DIRECTORY'
  46      Install machine-independent data files in subdirectories of
  47      'DIRECTORY'.  The default is to install in '/usr/local'.
  48
  49 '--exec-prefix=DIRECTORY'
  50      Install the library and other machine-dependent files in
  51      subdirectories of 'DIRECTORY'.  The default is to the '--prefix'
  52      directory if that option is specified, or '/usr/local' otherwise.
  53
  54 '--with-headers=DIRECTORY'
  55      Look for kernel header files in DIRECTORY, not '/usr/include'.  The
  56      GNU C Library needs information from the kernel's header files
  57      describing the interface to the kernel.  The GNU C Library will
  58      normally look in '/usr/include' for them, but if you specify this
  59      option, it will look in DIRECTORY instead.
  60
  61      This option is primarily of use on a system where the headers in
  62      '/usr/include' come from an older version of the GNU C Library.
  63      Conflicts can occasionally happen in this case.  You can also use
  64      this option if you want to compile the GNU C Library with a newer
  65      set of kernel headers than the ones found in '/usr/include'.
  66
  67 '--enable-kernel=VERSION'
  68      This option is currently only useful on GNU/Linux systems.  The
  69      VERSION parameter should have the form X.Y.Z and describes the
  70      smallest version of the Linux kernel the generated library is
  71      expected to support.  The higher the VERSION number is, the less
  72      compatibility code is added, and the faster the code gets.
  73
  74 '--with-binutils=DIRECTORY'
  75      Use the binutils (assembler and linker) in 'DIRECTORY', not the
  76      ones the C compiler would default to.  You can use this option if
  77      the default binutils on your system cannot deal with all the
  78      constructs in the GNU C Library.  In that case, 'configure' will
  79      detect the problem and suppress these constructs, so that the
  80      library will still be usable, but functionality may be lost--for
  81      example, you can't build a shared libc with old binutils.
  82
  83 '--without-fp'
  84      Use this option if your computer lacks hardware floating-point
  85      support and your operating system does not emulate an FPU.
  86
  87 '--disable-shared'
  88      Don't build shared libraries even if it is possible.  Not all
  89      systems support shared libraries; you need ELF support and
  90      (currently) the GNU linker.
  91
  92 '--disable-profile'
  93      Don't build libraries with profiling information.  You may want to
  94      use this option if you don't plan to do profiling.
  95
  96 '--enable-static-nss'
  97      Compile static versions of the NSS (Name Service Switch) libraries.
  98      This is not recommended because it defeats the purpose of NSS; a
  99      program linked statically with the NSS libraries cannot be
 100      dynamically reconfigured to use a different name database.
 101
 102 '--enable-hardcoded-path-in-tests'
 103      By default, dynamic tests are linked to run with the installed C
 104      library.  This option hardcodes the newly built C library path in
 105      dynamic tests so that they can be invoked directly.
 106
 107 '--disable-timezone-tools'
 108      By default, timezone related utilities ('zic', 'zdump', and
 109      'tzselect') are installed with the GNU C Library.  If you are
 110      building these independently (e.g.  by using the 'tzcode' package),
 111      then this option will allow disabling the install of these.
 112
 113      Note that you need to make sure the external tools are kept in sync
 114      with the versions that the GNU C Library expects as the data
 115      formats may change over time.  Consult the 'timezone' subdirectory
 116      for more details.
 117
 118 '--enable-lock-elision=yes'
 119      Enable lock elision for pthread mutexes by default.
 120
 121 '--enable-stack-protector'
 122 '--enable-stack-protector=strong'
 123 '--enable-stack-protector=all'
 124      Compile the C library and all other parts of the glibc package
 125      (including the threading and math libraries, NSS modules, and
 126      transliteration modules) using the GCC '-fstack-protector',
 127      '-fstack-protector-strong' or '-fstack-protector-all' options to
 128      detect stack overruns.  Only the dynamic linker and a small number
 129      of routines called directly from assembler are excluded from this
 130      protection.
 131
 132 '--enable-bind-now'
 133      Disable lazy binding for installed shared objects.  This provides
 134      additional security hardening because it enables full RELRO and a
 135      read-only global offset table (GOT), at the cost of slightly
 136      increased program load times.
 137
 138 '--enable-pt_chown'
 139      The file 'pt_chown' is a helper binary for 'grantpt' (*note
 140      Pseudo-Terminals: Allocation.) that is installed setuid root to fix
 141      up pseudo-terminal ownership.  It is not built by default because
 142      systems using the Linux kernel are commonly built with the 'devpts'
 143      filesystem enabled and mounted at '/dev/pts', which manages
 144      pseudo-terminal ownership automatically.  By using
 145      '--enable-pt_chown', you may build 'pt_chown' and install it setuid
 146      and owned by 'root'.  The use of 'pt_chown' introduces additional
 147      security risks to the system and you should enable it only if you
 148      understand and accept those risks.
 149
 150 '--disable-werror'
 151      By default, the GNU C Library is built with '-Werror'.  If you wish
 152      to build without this option (for example, if building with a newer
 153      version of GCC than this version of the GNU C Library was tested
 154      with, so new warnings cause the build with '-Werror' to fail), you
 155      can configure with '--disable-werror'.
 156
 157 '--disable-mathvec'
 158      By default for x86_64, the GNU C Library is built with the vector
 159      math library.  Use this option to disable the vector math library.
 160
 161 '--enable-tunables'
 162      Tunables support allows additional library parameters to be
 163      customized at runtime.  This feature is enabled by default.  This
 164      option can take the following values:
 165
 166      'yes'
 167           This is the default if no option is passed to configure.  This
 168           enables tunables and selects the default frontend (currently
 169           'valstring').
 170
 171      'no'
 172           This option disables tunables.
 173
 174      'valstring'
 175           This enables tunables and selects the 'valstring' frontend for
 176           tunables.  This frontend allows users to specify tunables as a
 177           colon-separated list in a single environment variable
 178           'GLIBC_TUNABLES'.
 179
 180 '--enable-obsolete-nsl'
 181      By default, libnsl is only built as shared library for backward
 182      compatibility and the NSS modules libnss_compat, libnss_nis and
 183      libnss_nisplus are not built at all.  Use this option to enable
 184      libnsl with all depending NSS modules and header files.
 185
 186 '--disable-experimental-malloc'
 187      By default, a per-thread cache is enabled in 'malloc'.  While this
 188      cache can be disabled on a per-application basis using tunables
 189      (set glibc.malloc.tcache_count to zero), this option can be used to
 190      remove it from the build completely.
 191
 192 '--build=BUILD-SYSTEM'
 193 '--host=HOST-SYSTEM'
 194      These options are for cross-compiling.  If you specify both options
 195      and BUILD-SYSTEM is different from HOST-SYSTEM, 'configure' will
 196      prepare to cross-compile the GNU C Library from BUILD-SYSTEM to be
 197      used on HOST-SYSTEM.  You'll probably need the '--with-headers'
 198      option too, and you may have to override CONFIGURE's selection of
 199      the compiler and/or binutils.
 200
 201      If you only specify '--host', 'configure' will prepare for a native
 202      compile but use what you specify instead of guessing what your
 203      system is.  This is most useful to change the CPU submodel.  For
 204      example, if 'configure' guesses your machine as 'i686-pc-linux-gnu'
 205      but you want to compile a library for 586es, give
 206      '--host=i586-pc-linux-gnu' or just '--host=i586-linux' and add the
 207      appropriate compiler flags ('-mcpu=i586' will do the trick) to
 208      CFLAGS.
 209
 210      If you specify just '--build', 'configure' will get confused.
 211
 212 '--with-pkgversion=VERSION'
 213      Specify a description, possibly including a build number or build
 214      date, of the binaries being built, to be included in '--version'
 215      output from programs installed with the GNU C Library.  For
 216      example, '--with-pkgversion='FooBar GNU/Linux glibc build 123''.
 217      The default value is 'GNU libc'.
 218
 219 '--with-bugurl=URL'
 220      Specify the URL that users should visit if they wish to report a
 221      bug, to be included in '--help' output from programs installed with
 222      the GNU C Library.  The default value refers to the main
 223      bug-reporting information for the GNU C Library.
 224
 225    To build the library and related programs, type 'make'.  This will
 226 produce a lot of output, some of which may look like errors from 'make'
 227 but aren't.  Look for error messages from 'make' containing '***'.
 228 Those indicate that something is seriously wrong.
 229
 230    The compilation process can take a long time, depending on the
 231 configuration and the speed of your machine.  Some complex modules may
 232 take a very long time to compile, as much as several minutes on slower
 233 machines.  Do not panic if the compiler appears to hang.
 234
 235    If you want to run a parallel make, simply pass the '-j' option with
 236 an appropriate numeric parameter to 'make'.  You need a recent GNU
 237 'make' version, though.
 238
 239    To build and run test programs which exercise some of the library
 240 facilities, type 'make check'.  If it does not complete successfully, do
 241 not use the built library, and report a bug after verifying that the
 242 problem is not already known.  *Note Reporting Bugs::, for instructions
 243 on reporting bugs.  Note that some of the tests assume they are not
 244 being run by 'root'.  We recommend you compile and test the GNU C
 245 Library as an unprivileged user.
 246
 247    Before reporting bugs make sure there is no problem with your system.
 248 The tests (and later installation) use some pre-existing files of the
 249 system such as '/etc/passwd', '/etc/nsswitch.conf' and others.  These
 250 files must all contain correct and sensible content.
 251
 252    Normally, 'make check' will run all the tests before reporting all
 253 problems found and exiting with error status if any problems occurred.
 254 You can specify 'stop-on-test-failure=y' when running 'make check' to
 255 make the test run stop and exit with an error status immediately when a
 256 failure occurs.
 257
 258    The GNU C Library pretty printers come with their own set of scripts
 259 for testing, which run together with the rest of the testsuite through
 260 'make check'.  These scripts require the following tools to run
 261 successfully:
 262
 263    * Python 2.7.6/3.4.3 or later
 264
 265      Python is required for running the printers' test scripts.
 266
 267    * PExpect 4.0
 268
 269      The printer tests drive GDB through test programs and compare its
 270      output to the printers'.  PExpect is used to capture the output of
 271      GDB, and should be compatible with the Python version in your
 272      system.
 273
 274    * GDB 7.8 or later with support for Python 2.7.6/3.4.3 or later
 275
 276      GDB itself needs to be configured with Python support in order to
 277      use the pretty printers.  Notice that your system having Python
 278      available doesn't imply that GDB supports it, nor that your
 279      system's Python and GDB's have the same version.
 280
 281 If these tools are absent, the printer tests will report themselves as
 282 'UNSUPPORTED'.  Notice that some of the printer tests require the GNU C
 283 Library to be compiled with debugging symbols.
 284
 285    To format the 'GNU C Library Reference Manual' for printing, type
 286 'make dvi'.  You need a working TeX installation to do this.  The
 287 distribution builds the on-line formatted version of the manual, as Info
 288 files, as part of the build process.  You can build them manually with
 289 'make info'.
 290
 291    The library has a number of special-purpose configuration parameters
 292 which you can find in 'Makeconfig'.  These can be overwritten with the
 293 file 'configparms'.  To change them, create a 'configparms' in your
 294 build directory and add values as appropriate for your system.  The file
 295 is included and parsed by 'make' and has to follow the conventions for
 296 makefiles.
 297
 298    It is easy to configure the GNU C Library for cross-compilation by
 299 setting a few variables in 'configparms'.  Set 'CC' to the
 300 cross-compiler for the target you configured the library for; it is
 301 important to use this same 'CC' value when running 'configure', like
 302 this: 'CC=TARGET-gcc configure TARGET'.  Set 'BUILD_CC' to the compiler
 303 to use for programs run on the build system as part of compiling the
 304 library.  You may need to set 'AR' to cross-compiling versions of 'ar'
 305 if the native tools are not configured to work with object files for the
 306 target you configured for.  When cross-compiling the GNU C Library, it
 307 may be tested using 'make check
 308 test-wrapper="SRCDIR/scripts/cross-test-ssh.sh HOSTNAME"', where SRCDIR
 309 is the absolute directory name for the main source directory and
 310 HOSTNAME is the host name of a system that can run the newly built
 311 binaries of the GNU C Library.  The source and build directories must be
 312 visible at the same locations on both the build system and HOSTNAME.
 313
 314    In general, when testing the GNU C Library, 'test-wrapper' may be set
 315 to the name and arguments of any program to run newly built binaries.
 316 This program must preserve the arguments to the binary being run, its
 317 working directory and the standard input, output and error file
 318 descriptors.  If 'TEST-WRAPPER env' will not work to run a program with
 319 environment variables set, then 'test-wrapper-env' must be set to a
 320 program that runs a newly built program with environment variable
 321 assignments in effect, those assignments being specified as 'VAR=VALUE'
 322 before the name of the program to be run.  If multiple assignments to
 323 the same variable are specified, the last assignment specified must take
 324 precedence.  Similarly, if 'TEST-WRAPPER env -i' will not work to run a
 325 program with an environment completely empty of variables except those
 326 directly assigned, then 'test-wrapper-env-only' must be set; its use has
 327 the same syntax as 'test-wrapper-env', the only difference in its
 328 semantics being starting with an empty set of environment variables
 329 rather than the ambient set.
 330
 331 Installing the C Library
 332 ========================
 333
 334 To install the library and its header files, and the Info files of the
 335 manual, type 'make install'.  This will build things, if necessary,
 336 before installing them; however, you should still compile everything
 337 first.  If you are installing the GNU C Library as your primary C
 338 library, we recommend that you shut the system down to single-user mode
 339 first, and reboot afterward.  This minimizes the risk of breaking things
 340 when the library changes out from underneath.
 341
 342    'make install' will do the entire job of upgrading from a previous
 343 installation of the GNU C Library version 2.x.  There may sometimes be
 344 headers left behind from the previous installation, but those are
 345 generally harmless.  If you want to avoid leaving headers behind you can
 346 do things in the following order.
 347
 348    You must first build the library ('make'), optionally check it ('make
 349 check'), switch the include directories and then install ('make
 350 install').  The steps must be done in this order.  Not moving the
 351 directory before install will result in an unusable mixture of header
 352 files from both libraries, but configuring, building, and checking the
 353 library requires the ability to compile and run programs against the old
 354 library.  The new '/usr/include', after switching the include
 355 directories and before installing the library should contain the Linux
 356 headers, but nothing else.  If you do this, you will need to restore any
 357 headers from libraries other than the GNU C Library yourself after
 358 installing the library.
 359
 360    You can install the GNU C Library somewhere other than where you
 361 configured it to go by setting the 'DESTDIR' GNU standard make variable
 362 on the command line for 'make install'.  The value of this variable is
 363 prepended to all the paths for installation.  This is useful when
 364 setting up a chroot environment or preparing a binary distribution.  The
 365 directory should be specified with an absolute file name.  Installing
 366 with the 'prefix' and 'exec_prefix' GNU standard make variables set is
 367 not supported.
 368
 369    The GNU C Library includes a daemon called 'nscd', which you may or
 370 may not want to run.  'nscd' caches name service lookups; it can
 371 dramatically improve performance with NIS+, and may help with DNS as
 372 well.
 373
 374    One auxiliary program, '/usr/libexec/pt_chown', is installed setuid
 375 'root' if the '--enable-pt_chown' configuration option is used.  This
 376 program is invoked by the 'grantpt' function; it sets the permissions on
 377 a pseudoterminal so it can be used by the calling process.  If you are
 378 using a Linux kernel with the 'devpts' filesystem enabled and mounted at
 379 '/dev/pts', you don't need this program.
 380
 381    After installation you might want to configure the timezone and
 382 locale installation of your system.  The GNU C Library comes with a
 383 locale database which gets configured with 'localedef'.  For example, to
 384 set up a German locale with name 'de_DE', simply issue the command
 385 'localedef -i de_DE -f ISO-8859-1 de_DE'.  To configure all locales that
 386 are supported by the GNU C Library, you can issue from your build
 387 directory the command 'make localedata/install-locales'.
 388
 389    To configure the locally used timezone, set the 'TZ' environment
 390 variable.  The script 'tzselect' helps you to select the right value.
 391 As an example, for Germany, 'tzselect' would tell you to use
 392 'TZ='Europe/Berlin''.  For a system wide installation (the given paths
 393 are for an installation with '--prefix=/usr'), link the timezone file
 394 which is in '/usr/share/zoneinfo' to the file '/etc/localtime'.  For
 395 Germany, you might execute 'ln -s /usr/share/zoneinfo/Europe/Berlin
 396 /etc/localtime'.
 397
 398 Recommended Tools for Compilation
 399 =================================
 400
 401 We recommend installing the following GNU tools before attempting to
 402 build the GNU C Library:
 403
 404    * GNU 'make' 3.79 or newer
 405
 406      You need the latest version of GNU 'make'.  Modifying the GNU C
 407      Library to work with other 'make' programs would be so difficult
 408      that we recommend you port GNU 'make' instead.  *Really.*  We
 409      recommend GNU 'make' version 3.79.  All earlier versions have
 410      severe bugs or lack features.
 411
 412    * GCC 4.9 or newer
 413
 414      GCC 4.9 or higher is required.  In general it is recommended to use
 415      the newest version of the compiler that is known to work for
 416      building the GNU C Library, as newer compilers usually produce
 417      better code.  As of release time, GCC 7.1 is the newest compiler
 418      verified to work to build the GNU C Library.
 419
 420      For PowerPC 64-bits little-endian (powerpc64le), GCC 6.2 or higher
 421      is required.  This compiler version is the first to provide the
 422      features required for building the GNU C Library with support for
 423      '_Float128'.
 424
 425      For multi-arch support it is recommended to use a GCC which has
 426      been built with support for GNU indirect functions.  This ensures
 427      that correct debugging information is generated for functions
 428      selected by IFUNC resolvers.  This support can either be enabled by
 429      configuring GCC with '--enable-gnu-indirect-function', or by
 430      enabling it by default by setting 'default_gnu_indirect_function'
 431      variable for a particular architecture in the GCC source file
 432      'gcc/config.gcc'.
 433
 434      You can use whatever compiler you like to compile programs that use
 435      the GNU C Library.
 436
 437      Check the FAQ for any special compiler issues on particular
 438      platforms.
 439
 440    * GNU 'binutils' 2.25 or later
 441
 442      You must use GNU 'binutils' (as and ld) to build the GNU C Library.
 443      No other assembler or linker has the necessary functionality at the
 444      moment.  As of release time, GNU 'binutils' 2.27 is the newest
 445      verified to work to build the GNU C Library.
 446
 447    * GNU 'texinfo' 4.7 or later
 448
 449      To correctly translate and install the Texinfo documentation you
 450      need this version of the 'texinfo' package.  Earlier versions do
 451      not understand all the tags used in the document, and the
 452      installation mechanism for the info files is not present or works
 453      differently.  As of release time, 'texinfo' 6.0 is the newest
 454      verified to work to build the GNU C Library.
 455
 456    * GNU 'awk' 3.1.2, or higher
 457
 458      'awk' is used in several places to generate files.  Some 'gawk'
 459      extensions are used, including the 'asorti' function, which was
 460      introduced in version 3.1.2 of 'gawk'.  As of release time, 'gawk'
 461      version 4.1.3 is the newest verified to work to build the GNU C
 462      Library.
 463
 464    * Perl 5
 465
 466      Perl is not required, but it is used if present to test the
 467      installation.  We may decide to use it elsewhere in the future.
 468
 469    * GNU 'sed' 3.02 or newer
 470
 471      'Sed' is used in several places to generate files.  Most scripts
 472      work with any version of 'sed'.  As of release time, 'sed' version
 473      4.2.2 is the newest verified to work to build the GNU C Library.
 474
 475 If you change any of the 'configure.ac' files you will also need
 476
 477    * GNU 'autoconf' 2.69 (exactly)
 478
 479 and if you change any of the message translation files you will need
 480
 481    * GNU 'gettext' 0.10.36 or later
 482
 483 If you wish to regenerate the 'yacc' parser code in the 'intl'
 484 subdirectory you will need
 485
 486    * GNU 'bison' 2.7 or later
 487
 488 You may also need these packages if you upgrade your source tree using
 489 patches, although we try to avoid this.
 490
 491 Specific advice for GNU/Linux systems
 492 =====================================
 493
 494 If you are installing the GNU C Library on GNU/Linux systems, you need
 495 to have the header files from a 3.2 or newer kernel around for
 496 reference.  (For the ia64 architecture, you need version 3.2.18 or newer
 497 because this is the first version with support for the 'accept4' system
 498 call.)  These headers must be installed using 'make headers_install';
 499 the headers present in the kernel source directory are not suitable for
 500 direct use by the GNU C Library.  You do not need to use that kernel,
 501 just have its headers installed where the GNU C Library can access them,
 502 referred to here as INSTALL-DIRECTORY.  The easiest way to do this is to
 503 unpack it in a directory such as '/usr/src/linux-VERSION'.  In that
 504 directory, run 'make headers_install
 505 INSTALL_HDR_PATH=INSTALL-DIRECTORY'.  Finally, configure the GNU C
 506 Library with the option '--with-headers=INSTALL-DIRECTORY/include'.  Use
 507 the most recent kernel you can get your hands on.  (If you are
 508 cross-compiling the GNU C Library, you need to specify
 509 'ARCH=ARCHITECTURE' in the 'make headers_install' command, where
 510 ARCHITECTURE is the architecture name used by the Linux kernel, such as
 511 'x86' or 'powerpc'.)
 512
 513    After installing the GNU C Library, you may need to remove or rename
 514 directories such as '/usr/include/linux' and '/usr/include/asm', and
 515 replace them with copies of directories such as 'linux' and 'asm' from
 516 'INSTALL-DIRECTORY/include'.  All directories present in
 517 'INSTALL-DIRECTORY/include' should be copied, except that the GNU C
 518 Library provides its own version of '/usr/include/scsi'; the files
 519 provided by the kernel should be copied without replacing those provided
 520 by the GNU C Library.  The 'linux', 'asm' and 'asm-generic' directories
 521 are required to compile programs using the GNU C Library; the other
 522 directories describe interfaces to the kernel but are not required if
 523 not compiling programs using those interfaces.  You do not need to copy
 524 kernel headers if you did not specify an alternate kernel header source
 525 using '--with-headers'.
 526
 527    The Filesystem Hierarchy Standard for GNU/Linux systems expects some
 528 components of the GNU C Library installation to be in '/lib' and some in
 529 '/usr/lib'.  This is handled automatically if you configure the GNU C
 530 Library with '--prefix=/usr'.  If you set some other prefix or allow it
 531 to default to '/usr/local', then all the components are installed there.
 532
 533 Reporting Bugs
 534 ==============
 535
 536 There are probably bugs in the GNU C Library.  There are certainly
 537 errors and omissions in this manual.  If you report them, they will get
 538 fixed.  If you don't, no one will ever know about them and they will
 539 remain unfixed for all eternity, if not longer.
 540
 541    It is a good idea to verify that the problem has not already been
 542 reported.  Bugs are documented in two places: The file 'BUGS' describes
 543 a number of well known bugs and the central GNU C Library bug tracking
 544 system has a WWW interface at <http://sourceware.org/bugzilla/>.  The
 545 WWW interface gives you access to open and closed reports.  A closed
 546 report normally includes a patch or a hint on solving the problem.
 547
 548    To report a bug, first you must find it.  With any luck, this will be
 549 the hard part.  Once you've found a bug, make sure it's really a bug.  A
 550 good way to do this is to see if the GNU C Library behaves the same way
 551 some other C library does.  If so, probably you are wrong and the
 552 libraries are right (but not necessarily).  If not, one of the libraries
 553 is probably wrong.  It might not be the GNU C Library.  Many historical
 554 Unix C libraries permit things that we don't, such as closing a file
 555 twice.
 556
 557    If you think you have found some way in which the GNU C Library does
 558 not conform to the ISO and POSIX standards (*note Standards and
 559 Portability::), that is definitely a bug.  Report it!
 560
 561    Once you're sure you've found a bug, try to narrow it down to the
 562 smallest test case that reproduces the problem.  In the case of a C
 563 library, you really only need to narrow it down to one library function
 564 call, if possible.  This should not be too difficult.
 565
 566    The final step when you have a simple test case is to report the bug.
 567 Do this at <http://www.gnu.org/software/libc/bugs.html>.
 568
 569    If you are not sure how a function should behave, and this manual
 570 doesn't tell you, that's a bug in the manual.  Report that too!  If the
 571 function's behavior disagrees with the manual, then either the library
 572 or the manual has a bug, so report the disagreement.  If you find any
 573 errors or omissions in this manual, please report them to the bug
 574 database.  If you refer to specific sections of the manual, please
 575 include the section names for easier identification.