1 Frequently Asked Questions about the GNU C Library
3 This document tries to answer questions a user might have when installing
4 and using glibc. Please make sure you read this before sending questions or
5 bug reports to the maintainers.
7 The GNU C library is very complex. The installation process has not been
8 completely automated; there are too many variables. You can do substantial
9 damage to your system by installing the library incorrectly. Make sure you
10 understand what you are undertaking before you begin.
12 If you have any questions you think should be answered in this document,
19 ?? What systems does the GNU C Library run on?
21 {UD} This is difficult to answer. The file `README' lists the architectures
22 GNU libc was known to run on *at some time*. This does not mean that it
23 still can be compiled and run on them now.
25 The systems glibc is known to work on as of this release, and most probably
29 i[3456]86-*-linux-gnu Linux-2.x on Intel
30 m68k-*-linux-gnu Linux-2.x on Motorola 680x0
31 alpha-*-linux-gnu Linux-2.x on DEC Alpha
32 powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems
33 sparc-*-linux-gnu Linux-2.x on SPARC
34 sparc64-*-linux-gnu Linux-2.x on UltraSPARC
35 arm-*-none ARM standalone systems
36 arm-*-linux Linux-2.x on ARM
37 arm-*-linuxaout Linux-2.x on ARM using a.out binaries
39 Ports to other Linux platforms are in development, and may in fact work
40 already, but no one has sent us success reports for them. Currently no
41 ports to other operating systems are underway, although a few people have
44 If you have a system not listed above (or in the `README' file) and you are
45 really interested in porting it, contact
49 ?? What compiler do I need to build GNU libc?
51 {UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC
52 are used to increase portability and speed.
54 GNU CC is found, like all other GNU packages, on
56 ftp://ftp.gnu.org/pub/gnu
58 and the many mirror sites. ftp.gnu.org is always overloaded, so try to find
61 You should always try to use the latest official release. Older versions
62 may not have all the features GNU libc requires. The current releases of
63 egcs (1.0.3 and 1.1.1) should work with the GNU C library (for powerpc see
64 ?powerpc; for ARM see ?arm).
66 {ZW} Due to problems with C++ exception handling, you must use EGCS (any
67 version) to compile version 2.1 of GNU libc. See ?exception for details.
69 ?? When I try to compile glibc I get only error messages.
72 {UD} You definitely need GNU make to build GNU libc. No other make
73 program has the needed functionality.
75 We recommend version GNU make version 3.75 or 3.77. Versions before 3.75
76 have bugs and/or are missing features. Version 3.76 has bugs which
77 appear when building big projects like GNU libc. 3.76.1 appears to work but
78 some people have reported problems. If you build GNU make 3.77 from source,
79 please read ?make first.
81 ?? Do I need a special linker or assembler?
83 {ZW} If you want a shared library, you need a linker and assembler that
84 understand all the features of ELF, including weak and versioned symbols.
85 The static library can be compiled with less featureful tools, but lacks key
88 For Linux or Hurd, you want binutils 2.8.1.0.23, 2.9.1, or 2.9.1.0.15 or
89 higher. These are the only versions we've tested and found reliable. Other
90 versions after 2.8.1.0.23 may work but we don't recommend them, especially
91 not when C++ is involved. Earlier versions do not work at all.
93 Other operating systems may come with system tools that have all the
94 necessary features, but this is moot because glibc hasn't been ported to
97 ??powerpc Which compiler should I use for powerpc?
99 {GK} You want to use egcs 1.1 or later (together with the right versions
100 of all the other tools, of course).
102 In fact, egcs 1.1 has a bug that causes linuxthreads to be
103 miscompiled, resulting in segmentation faults when using condition
104 variables. There is a temporary patch at:
106 <http://discus.anu.edu.au/~geoffk/egcs-3.diff>
108 Later versions of egcs may fix this problem.
110 ??arm Which tools should I use for ARM?
112 {PB} You should use egcs 1.1 or a later version. For ELF systems some
113 changes are needed to the compiler; a patch against egcs-1.1.x can be found
116 <ftp://ftp.netwinder.org/users/p/philb/egcs-1.1.1pre2-diff-981126>
118 Binutils 2.9.1.0.16 or later is also required.
120 ?? Do I need some more things to compile the GNU C Library?
122 {UD} Yes, there are some more :-).
124 * GNU gettext. This package contains the tools needed to construct
125 `message catalog' files containing translated versions of system
126 messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror
127 site. (We distribute compiled message catalogs, but they may not be
130 * Some files are built with special tools. E.g., files ending in .gperf
131 need a `gperf' program. The GNU version (now available in a separate
132 package, formerly only as part of libg++) is known to work while some
133 vendor versions do not.
135 You should not need these tools unless you change the source files.
137 * Perl 5 is needed if you wish to test an installation of GNU libc
138 as the primary C library.
140 * When compiling for Linux, the header files of the Linux kernel must
141 be available to the compiler as <linux/*.h> and <asm/*.h>.
143 * lots of disk space (~170MB for i?86-linux; more for RISC platforms,
146 * plenty of time. Compiling just the shared and static libraries for
147 i?86-linux takes approximately 1h on an i586@133, or 2.5h on
148 i486@66, or 4.5h on i486@33. Multiply this by 1.5 or 2.0 if you
149 build profiling and/or the highly optimized version as well. For
150 Hurd systems times are much higher.
152 You should avoid compiling in a NFS mounted filesystem. This is
155 James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time of
156 45h34m for a full build (shared, static, and profiled) on Atari
157 Falcon (Motorola 68030 @ 16 Mhz, 14 Mb memory) and Jan Barte
158 <yann@plato.uni-paderborn.de> reports 22h48m on Atari TT030
159 (Motorola 68030 @ 32 Mhz, 34 Mb memory)
161 If you have some more measurements let me know.
163 ?? What version of the Linux kernel headers should be used?
165 {AJ,UD} The headers from the most recent Linux kernel should be used. The
166 headers used while compiling the GNU C library and the kernel binary used
167 when using the library do not need to match. The GNU C library runs without
168 problems on kernels that are older than the kernel headers used. The other
169 way round (compiling the GNU C library with old kernel headers and running
170 on a recent kernel) does not necessarily work. For example you can't use
171 new kernel features if you used old kernel headers to compile the GNU C
174 {ZW} Even if you are using a 2.0 kernel on your machine, we recommend you
175 compile GNU libc with 2.2 kernel headers. That way you won't have to
176 recompile libc if you ever upgrade to kernel 2.2. To tell libc which
177 headers to use, give configure the --with-headers switch
178 (e.g. --with-headers=/usr/src/linux-2.2.0/include).
180 Note that you must configure the 2.2 kernel if you do this, otherwise libc
181 will be unable to find <linux/version.h>. Just change the current directory
182 to the root of the 2.2 tree and do `make include/linux/version.h'.
184 ?? The compiler hangs while building iconvdata modules. What's
187 {ZW} This is a problem with old versions of GCC. Initialization of large
188 static arrays is very slow. The compiler will eventually finish; give it
191 The problem is fixed in egcs 1.1.
193 ?? When I run `nm -u libc.so' on the produced library I still
194 find unresolved symbols. Can this be ok?
196 {UD} Yes, this is ok. There can be several kinds of unresolved symbols:
198 * magic symbols automatically generated by the linker. These have names
199 like __start_* and __stop_*
201 * symbols starting with _dl_* come from the dynamic linker
203 * weak symbols, which need not be resolved at all (fabs for example)
205 Generally, you should make sure you find a real program which produces
206 errors while linking before deciding there is a problem.
208 ??addon What are these `add-ons'?
210 {UD} To avoid complications with export rules or external source code some
211 optional parts of the libc are distributed as separate packages (e.g., the
212 crypt package, see ?crypt).
214 To use these packages as part of GNU libc, just unpack the tarfiles in the
215 libc source directory and tell the configuration script about them using the
216 --enable-add-ons option. If you give just --enable-add-ons configure tries
217 to find all the add-on packages in your source tree. This may not work. If
218 it doesn't, or if you want to select only a subset of the add-ons, give a
219 comma-separated list of the add-ons to enable:
221 configure --enable-add-ons=crypt,linuxthreads
225 Add-ons can add features (including entirely new shared libraries), override
226 files, provide support for additional architectures, and just about anything
227 else. The existing makefiles do most of the work; only some few stub rules
228 must be written to get everything running.
230 ?? My XXX kernel emulates a floating-point coprocessor for me.
231 Should I enable --with-fp?
233 {ZW} An emulated FPU is just as good as a real one, as far as the C library
234 is concerned. You only need to say --without-fp if your machine has no way
235 to execute floating-point instructions.
237 People who are interested in squeezing the last drop of performance
238 out of their machine may wish to avoid the trap overhead, but this is
239 far more trouble than it's worth: you then have to compile
240 *everything* this way, including the compiler's internal libraries
241 (libgcc.a for GNU C), because the calling conventions change.
243 ?? When compiling GNU libc I get lots of errors saying functions
244 in glibc are duplicated in libgcc.
246 {EY} This is *exactly* the same problem that I was having. The problem was
247 due to the fact that configure didn't correctly detect that the linker flag
248 --no-whole-archive was supported in my linker. In my case it was because I
249 had run ./configure with bogus CFLAGS, and the test failed.
251 One thing that is particularly annoying about this problem is that once this
252 is misdetected, running configure again won't fix it unless you first delete
255 {UD} Starting with glibc-2.0.3 there should be a better test to avoid some
256 problems of this kind. The setting of CFLAGS is checked at the very
257 beginning and if it is not usable `configure' will bark.
259 ?? Why do I get messages about missing thread functions when I use
260 librt? I don't even use threads.
262 {UD} In this case you probably mixed up your installation. librt uses
263 threads internally and has implicit references to the thread library.
264 Normally these references are satisfied automatically but if the thread
265 library is not in the expected place you must tell the linker where it is.
266 When using GNU ld it works like this:
268 gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt
270 The `/some/other/dir' should contain the thread library. `ld' will use the
271 given path to find the implicitly referenced library while not disturbing
274 ?? What's the problem with configure --enable-omitfp?
276 {AJ} When --enable-omitfp is set the libraries are built without frame
277 pointers. Some compilers produce buggy code for this model and therefore we
278 don't advise using it at the moment.
280 If you use --enable-omitfp, you're on your own. If you encounter problems
281 with a library that was build this way, we advise you to rebuild the library
282 without --enable-omitfp. If the problem vanishes consider tracking the
283 problem down and report it as compiler failure.
285 Since a library built with --enable-omitfp is undebuggable on most systems,
286 debuggable libraries are also built - you can use them by appending "_g" to
289 The compilation of these extra libraries and the compiler optimizations slow
290 down the build process and need more disk space.
292 ?? I get failures during `make check'. What should I do?
294 {AJ} The testsuite should compile and run cleanly on your system; every
295 failure should be looked into. Depending on the failures, you probably
296 should not install the library at all.
298 You should consider using the `glibcbug' script to report the failure,
299 providing as much detail as possible. If you run a test directly, please
300 remember to set up the environment correctly. You want to test the compiled
301 library - and not your installed one. The best way is to copy the exact
302 command line which failed and run the test from the subdirectory for this
305 There are some failures which are not directly related to the GNU libc:
306 - Some compilers produce buggy code. No compiler gets single precision
307 complex numbers correct on Alpha. Otherwise, the egcs 1.1 release should be
308 ok; gcc 2.8.1 might cause some failures; gcc 2.7.2.x is so buggy that
309 explicit checks have been used so that you can't build with it.
310 - The kernel might have bugs. For example on Linux/Alpha 2.0.34 the
311 floating point handling has quite a number of bugs and therefore most of
312 the test cases in the math subdirectory will fail. Linux 2.2 has
313 fixes for the floating point support on Alpha. The Linux/SPARC kernel has
314 also some bugs in the FPU emulation code (as of Linux 2.2.0).
316 ?? What is symbol versioning good for? Do I need it?
318 {AJ} Symbol versioning solves problems that are related to interface
319 changes. One version of an interface might have been introduced in a
320 previous version of the GNU C library but the interface or the semantics of
321 the function has been changed in the meantime. For binary compatibility
322 with the old library, a newer library needs to still have the old interface
323 for old programs. On the other hand, new programs should use the new
324 interface. Symbol versioning is the solution for this problem. The GNU
325 libc version 2.1 uses symbol versioning by default if the installed binutils
328 We don't advise building without symbol versioning, since you lose binary
329 compatibility - forever! The binary compatibility you lose is not only
330 against the previous version of the GNU libc (version 2.0) but also against
334 ? Installation and configuration issues
336 ?? Can I replace the libc on my Linux system with GNU libc?
338 {UD} You cannot replace any existing libc for Linux with GNU libc. It is
339 binary incompatible and therefore has a different major version. You can,
340 however, install it alongside your existing libc.
342 For Linux there are three major libc versions:
344 libc-5 original ELF libc
347 You can have any combination of these three installed. For more information
348 consult documentation for shared library handling. The Makefiles of GNU
349 libc will automatically generate the needed symbolic links which the linker
352 ?? How do I configure GNU libc so that the essential libraries
353 like libc.so go into /lib and the other into /usr/lib?
355 {UD,AJ} Like all other GNU packages GNU libc is designed to use a base
356 directory and install all files relative to this. The default is
357 /usr/local, because this is safe (it will not damage the system if installed
358 there). If you wish to install GNU libc as the primary C library on your
359 system, set the base directory to /usr (i.e. run configure --prefix=/usr
360 <other_options>). Note that this can damage your system; see ?safety for
363 Some systems like Linux have a filesystem standard which makes a difference
364 between essential libraries and others. Essential libraries are placed in
365 /lib because this directory is required to be located on the same disk
366 partition as /. The /usr subtree might be found on another
367 partition/disk. If you configure for Linux with --prefix=/usr, then this
368 will be done automatically.
370 To install the essential libraries which come with GNU libc in /lib on
371 systems other than Linux one must explicitly request it. Autoconf has no
372 option for this so you have to use a `configparms' file (see the `INSTALL'
373 file for details). It should contain:
378 The first line specifies the directory for the essential libraries, the
379 second line the directory for system configuration files.
381 ??safety How should I avoid damaging my system when I install GNU libc?
383 {ZW} If you wish to be cautious, do not configure with --prefix=/usr. If
384 you don't specify a prefix, glibc will be installed in /usr/local, where it
385 will probably not break anything. (If you wish to be certain, set the
386 prefix to something like /usr/local/glibc2 which is not used for anything.)
388 The dangers when installing glibc in /usr are twofold:
390 * glibc will overwrite the headers in /usr/include. Other C libraries
391 install a different but overlapping set of headers there, so the
392 effect will probably be that you can't compile anything. You need to
393 rename /usr/include out of the way first. (Do not throw it away; you
394 will then lose the ability to compile programs against your old libc.)
396 * None of your old libraries, static or shared, can be used with a
397 different C library major version. For shared libraries this is not a
398 problem, because the filenames are different and the dynamic linker
399 will enforce the restriction. But static libraries have no version
400 information. You have to evacuate all the static libraries in
401 /usr/lib to a safe location.
403 The situation is rather similar to the move from a.out to ELF which
404 long-time Linux users will remember.
406 ?? Do I need to use GNU CC to compile programs that will use the
409 {ZW} In theory, no; the linker does not care, and the headers are supposed
410 to check for GNU CC before using its extensions to the C language.
412 However, there are currently no ports of glibc to systems where another
413 compiler is the default, so no one has tested the headers extensively
414 against another compiler. You may therefore encounter difficulties. If you
415 do, please report them as bugs.
417 Also, in several places GNU extensions provide large benefits in code
418 quality. For example, the library has hand-optimized, inline assembly
419 versions of some string functions. These can only be used with GCC. See
422 ??crypt When linking with the new libc I get unresolved symbols
423 `crypt' and `setkey'. Why aren't these functions in the
426 {UD} The US places restrictions on exporting cryptographic programs and
427 source code. Until this law gets abolished we cannot ship the cryptographic
428 functions together with glibc.
430 The functions are available, as an add-on (see ?addon). People in the US
431 may get it from the same place they got GNU libc from. People outside the
432 US should get the code from ftp://ftp.ifi.uio.no/pub/gnu, or another archive
433 site outside the USA. The README explains how to install the sources.
435 If you already have the crypt code on your system the reason for the failure
436 is probably that you did not link with -lcrypt. The crypto functions are in
437 a separate library to make it possible to export GNU libc binaries from the
440 ?? When I use GNU libc on my Linux system by linking against
441 the libc.so which comes with glibc all I get is a core dump.
443 {UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the
444 user specifies a -dynamic-linker argument. This is the name of the libc5
445 dynamic linker, which does not work with glibc.
447 For casual use of GNU libc you can just specify to the linker
448 --dynamic-linker=/lib/ld-linux.so.2
450 which is the glibc dynamic linker, on Linux systems. On other systems the
451 name is /lib/ld.so.1. When linking via gcc, you've got to add
452 -Wl,--dynamic-linker=/lib/ld-linux.so.2
454 to the gcc command line.
456 To change your environment to use GNU libc for compiling you need to change
457 the `specs' file of your gcc. This file is normally found at
459 /usr/lib/gcc-lib/<arch>/<version>/specs
461 In this file you have to change a few things:
463 - change `ld-linux.so.1' to `ld-linux.so.2'
465 - remove all expression `%{...:-lgmon}'; there is no libgmon in glibc
467 - fix a minor bug by changing %{pipe:-} to %|
469 Here is what the gcc-2.7.2 specs file should look like when GNU libc is
472 -----------------------------------------------------------------------
474 %{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*}
480 %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}
489 %{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s
492 -m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}}
495 %{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}}
501 %{!shared: %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} %{!p:%{profile:gcrt1.o%s} %{!profile:crt1.o%s}}}} crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s}
503 *switches_need_spaces:
507 %{funsigned-char:-D__CHAR_UNSIGNED__}
510 -D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386)
518 -----------------------------------------------------------------------
520 Things get a bit more complicated if you have GNU libc installed in some
521 other place than /usr, i.e., if you do not want to use it instead of the old
522 libc. In this case the needed startup files and libraries are not found in
523 the regular places. So the specs file must tell the compiler and linker
526 Version 2.7.2.3 does and future versions of GCC will automatically
527 provide the correct specs.
529 ?? Looking through the shared libc file I haven't found the
530 functions `stat', `lstat', `fstat', and `mknod' and while
531 linking on my Linux system I get error messages. How is
532 this supposed to work?
534 {RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed
535 to be undefined references in libc.so.6! Your problem is probably a missing
536 or incorrect /usr/lib/libc.so file; note that this is a small text file now,
537 not a symlink to libc.so.6. It should look something like this:
539 GROUP ( libc.so.6 libc_nonshared.a )
541 ??exception When I run an executable on one system which I compiled on
542 another, I get dynamic linker errors. Both systems have the same
543 version of glibc installed. What's wrong?
545 {ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the
546 other with egcs (any version). Egcs has functions in its internal
547 `libgcc.a' to support exception handling with C++. They are linked into
548 any program or dynamic library compiled with egcs, whether it needs them or
549 not. Dynamic libraries then turn around and export those functions again
550 unless special steps are taken to prevent them.
552 When you link your program, it resolves its references to the exception
553 functions to the ones exported accidentally by libc.so. That works fine as
554 long as libc has those functions. On the other system, libc doesn't have
555 those functions because it was compiled by gcc 2.8, and you get undefined
556 symbol errors. The symbols in question are named things like
557 `__register_frame_info'.
559 For glibc 2.0, the workaround is to not compile libc with egcs. We've also
560 incorporated a patch which should prevent the EH functions sneaking into
561 libc. It doesn't matter what compiler you use to compile your program.
563 For glibc 2.1, we've chosen to do it the other way around: libc.so
564 explicitly provides the EH functions. This is to prevent other shared
565 libraries from doing it. You must therefore compile glibc 2.1 with EGCS.
566 Again, it doesn't matter what compiler you use for your programs.
568 ?? How can I compile gcc 2.7.2.1 from the gcc source code using
571 {AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later.
572 But you should get at least gcc 2.8.1 or egcs 1.0.2 (or later versions)
575 ?? The `gencat' utility cannot process the catalog sources which
576 were used on my Linux libc5 based system. Why?
578 {UD} The `gencat' utility provided with glibc complies to the XPG standard.
579 The older Linux version did not obey the standard, so they are not
582 To ease the transition from the Linux version some of the non-standard
583 features are also present in the `gencat' program of GNU libc. This mainly
584 includes the use of symbols for the message number and the automatic
585 generation of header files which contain the needed #defines to map the
588 Here is a simple SED script to convert at least some Linux specific catalog
589 files to the XPG4 form:
591 -----------------------------------------------------------------------
592 # Change catalog source in Linux specific format to standard XPG format.
593 # Ulrich Drepper <drepper@cygnus.com>, 1996.
597 s/\$ #\([^ ]*\).*/\1/
599 s/\$ #[^ ]* *\(.*\)/\$ \1/
605 s/\(.*\)\n\(.*\)/\2 \1/
607 -----------------------------------------------------------------------
609 ?? Programs using libc have their messages translated, but other
610 behavior is not localized (e.g. collating order); why?
612 {ZW} Translated messages are automatically installed, but the locale
613 database that controls other behaviors is not. You need to run localedef to
614 install this database, after you have run `make install'. For example, to
615 set up the French Canadian locale, simply issue the command
617 localedef -i fr_CA -f ISO-8859-1 fr_CA
619 Please see localedata/README in the source tree for further details.
621 ?? I have set up /etc/nis.conf, and the Linux libc 5 with NYS
622 works great. But the glibc NIS+ doesn't seem to work.
624 {TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for
625 storing information about the NIS+ server and their public keys, because the
626 nis.conf file does not contain all the necessary information. You have to
627 copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is
628 byte order independent) or generate it with nisinit from the nis-tools
629 package; available at
631 http://www-vt.uni-paderborn.de/~kukuk/linux/nisplus.html
633 ?? I have killed ypbind to stop using NIS, but glibc
636 {TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from
637 ypbind. ypbind 3.3 and older versions don't always remove these files, so
638 glibc will continue to use them. Other BSD versions seem to work correctly.
639 Until ypbind 3.4 is released, you can find a patch at
641 ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz
643 ?? Under Linux/Alpha, I always get "do_ypcall: clnt_call:
644 RPC: Unable to receive; errno = Connection refused" when using NIS.
646 {TK} You need a ypbind version which is 64bit clean. Some versions are not
647 64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3,
648 you need the patch from ftp.kernel.org (See the previous question). I don't
649 know about other versions.
652 ?? After installing glibc name resolving doesn't work properly.
654 {AJ} You probably should read the manual section describing nsswitch.conf
655 (just type `info libc "NSS Configuration File"'). The NSS configuration
656 file is usually the culprit.
659 ?? How do I create the databases for NSS?
661 {AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create
662 the database files. The glibc sources contain a Makefile which does the
663 necessary conversion and calls to create those files. The file is
664 `db-Makefile' in the subdirectory `nss' and you can call it with `make -f
665 db-Makefile'. Please note that not all services are capable of using a
666 database. Currently passwd, group, ethers, protocol, rpc, services shadow
667 and netgroup are implemented.
669 ?? I have /usr/include/net and /usr/include/scsi as symlinks
670 into my Linux source tree. Is that wrong?
672 {PB} This was necessary for libc5, but is not correct when using glibc.
673 Including the kernel header files directly in user programs usually does not
674 work (see ?kerhdr). glibc provides its own <net/*> and <scsi/*> header
675 files to replace them, and you may have to remove any symlink that you have
676 in place before you install glibc. However, /usr/include/asm and
677 /usr/include/linux should remain as they were.
679 ?? Programs like `logname', `top', `uptime' `users', `w' and
680 `who', show incorrect information about the (number of)
681 users on my system. Why?
685 ?? After upgrading to glibc 2.1 with symbol versioning I get
686 errors about undefined symbols. What went wrong?
688 {AJ} The problem is caused either by wrong program code or tools. In the
689 versioned libc a lot of symbols are now local that were global symbols in
690 previous versions. It seems that programs linked against older versions
691 often accidentally used libc global variables -- something that should not
694 The only way to fix this is to recompile your program. Sorry, that's the
695 price you might have to pay once for quite a number of advantages with
698 ?? When I start the program XXX after upgrading the library
700 XXX: Symbol `_sys_errlist' has different size in shared
701 object, consider re-linking
702 Why? What should I do?
704 {UD} As the message says, relink the binary. The problem is that a few
705 symbols from the library can change in size and there is no way to avoid
706 this. _sys_errlist is a good example. Occasionally there are new error
707 numbers added to the kernel and this must be reflected at user level,
708 breaking programs that refer to them directly.
710 Such symbols should normally not be used at all. There are mechanisms to
711 avoid using them. In the case of _sys_errlist, there is the strerror()
712 function which should _always_ be used instead. So the correct fix is to
713 rewrite that part of the application.
715 In some situations (especially when testing a new library release) it might
716 be possible that a symbol changed size when that should not have happened.
717 So in case of doubt report such a warning message as a problem.
719 ?? What do I need for C++ development?
721 {HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or
722 gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++
723 support and works directly with glibc 2.1. If you use gcc-2.8.1 with
724 libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available
726 ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz
728 Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work
729 very well with the GNU C library due to vtable thunks. If you're upgrading
730 from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library
731 compiled for 2.0 is not compatible due to the new Large File Support (LFS)
734 {UD} But since in the case of a shared libstdc++ the version numbers should
735 be different existing programs will continue to work.
737 ?? Even statically linked programs need some shared libraries
738 which is not acceptable for me. What can I do?
740 {AJ} NSS (for details just type `info libc "Name Service Switch"') won't
741 work properly without shared libraries. NSS allows using different services
742 (e.g. NIS, files, db, hesiod) by just changing one configuration file
743 (/etc/nsswitch.conf) without relinking any programs. The only disadvantage
744 is that now static libraries need to access shared libraries. This is
745 handled transparently by the GNU C library.
747 A solution is to configure glibc with --enable-static-nss. In this case you
748 can create a static binary that will use only the services dns and files
749 (change /etc/nsswitch.conf for this). You need to link explicitly against
750 all these services. For example:
752 gcc -static test-netdb.c -o test-netdb.c \
753 -lc -lnss_files -lnss_dns -lresolv
755 The problem with this approach is that you've got to link every static
756 program that uses NSS routines with all those libraries.
758 {UD} In fact, one cannot say anymore that a libc compiled with this
759 option is using NSS. There is no switch anymore. Therefore it is
760 *highly* recommended *not* to use --enable-static-nss since this makes
761 the behaviour of the programs on the system inconsistent.
763 ?? I just upgraded my Linux system to glibc and now I get
764 errors whenever I try to link any program.
766 {ZW} This happens when you have installed glibc as the primary C library but
767 have stray symbolic links pointing at your old C library. If the first
768 `libc.so' the linker finds is libc 5, it will use that. Your program
769 expects to be linked with glibc, so the link fails.
771 The most common case is that glibc put its `libc.so' in /usr/lib, but there
772 was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the
773 problem, just delete /lib/libc.so. You may also need to delete other
774 symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5.
776 {AJ} The perl script test-installation.pl which is run as last step during
777 an installation of glibc that is configured with --prefix=/usr should help
778 detect these situations. If the script reports problems, something is
781 ?? When I use nscd the machine freezes.
783 {UD} You cannot use nscd with Linux 2.0.*. There is functionality missing
784 in the kernel and work-arounds are not suitable. Besides, some parts of the
785 kernel are too buggy when it comes to using threads.
787 If you need nscd, you have to use at least a 2.1 kernel.
789 Note that I have at this point no information about any other platform.
791 ?? I need lots of open files. What do I have to do?
793 {AJ} This is at first a kernel issue. The kernel defines limits with
794 OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the
795 number of used file descriptors. You need to change these values in your
796 kernel and recompile the kernel so that the kernel allows to use more open
797 files. You don't necessarily need to recompile the GNU C library since the
798 only place where OPEN_MAX and FD_SETSIZE is really needed in the library
799 itself is the size of fd_set which is used by select.
801 The GNU C library is now (nearly) select free. This means it internally has
802 no limits imposed by the `fd_set' type. Instead almost all places where the
803 functionality is needed the `poll' function is used.
805 If you increase the number of file descriptors in the kernel you don't need
806 to recompile the C library. The remaining select calls are in the RPC code.
807 If your RPC daemons don't need more than FD_SETSIZE file descriptors, you
808 don't need to change anything at all.
810 {UD} You can always get the maximum number of file descriptors a process is
811 allowed to have open at any time using
813 number = sysconf (_SC_OPEN_MAX);
815 This will work even if the kernel limits change.
817 ?? How do I get the same behavior on parsing /etc/passwd and
818 /etc/group as I have with libc5 ?
820 {TK} The name switch setup in /etc/nsswitch.conf selected by most Linux
821 distributions does not support +/- and netgroup entries in the files like
822 /etc/passwd. Though this is the preferred setup some people might have
823 setups coming over from the libc5 days where it was the default to recognize
824 lines like this. To get back to the old behaviour one simply has to change
825 the rules for passwd, group, and shadow in the nsswitch.conf file as
836 ?? What needs to be recompiled when upgrading from glibc 2.0 to glibc
839 {AJ,CG} If you just upgrade the glibc from 2.0.x (x <= 7) to 2.1, binaries
840 that have been linked against glibc 2.0 will continue to work.
842 If you compile your own binaries against glibc 2.1, you also need to
843 recompile some other libraries. The problem is that libio had to be
844 changed and therefore libraries that are based or depend on the libio
845 of glibc, e.g. ncurses or slang, need to be recompiled. If you
846 experience strange segmentation faults in your programs linked against
847 glibc 2.1, you might need to recompile your libraries.
849 Another problem is that older binaries that were linked statically against
850 glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of
851 libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled
852 static libraries (libfoo.a) which happen to depend on the older libio
853 behavior will be broken by the glibc 2.1 upgrade. We plan to produce a
854 compatibility library that people will be able to link in if they want
855 to compile a static library generated against glibc 2.0 into a program
856 on a glibc 2.1 system. You just add -lcompat and you should be fine.
858 The glibc-compat add-on will provide the libcompat.a library, the older
859 nss modules, and a few other files. Together, they should make it
860 possible to do development with old static libraries on a glibc 2.1
861 system. This add-on is still in development. You can get it from
862 ftp://alpha.gnu.org/gnu/glibc-compat-2.1.tar.gz
863 but please keep in mind that it is experimental.
865 ?? Why is extracting files via tar so slow?
867 {AJ} Extracting of tar archives might be quite slow since tar has to look up
868 userid and groupids and doesn't cache negative results. If you have nis or
869 nisplus in your /etc/nsswitch.conf for the passwd and/or group database,
870 each file extractions needs a network connection. There are two possible
873 - do you really need NIS/NIS+ (some Linux distributions add by default
874 nis/nisplus even if it's not needed)? If not, just remove the entries.
876 - if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes
879 ? Source and binary incompatibilities, and what to do about them
881 ?? I expect GNU libc to be 100% source code compatible with
882 the old Linux based GNU libc. Why isn't it like this?
884 {DMT,UD} Not every extension in Linux libc's history was well thought-out.
885 In fact it had a lot of problems with standards compliance and with
886 cleanliness. With the introduction of a new version number these errors can
887 now be corrected. Here is a list of the known source code
890 * _GNU_SOURCE: glibc does not make the GNU extensions available
891 automatically. If a program depends on GNU extensions or some
892 other non-standard functionality, it is necessary to compile it
893 with the C compiler option -D_GNU_SOURCE, or better, to put
894 `#define _GNU_SOURCE' at the beginning of your source files, before
895 any C library header files are included. This difference normally
896 manifests itself in the form of missing prototypes and/or data type
897 definitions. Thus, if you get such errors, the first thing you
898 should do is try defining _GNU_SOURCE and see if that makes the
901 For more information consult the file `NOTES' in the GNU C library
904 * reboot(): GNU libc sanitizes the interface of reboot() to be more
905 compatible with the interface used on other OSes. reboot() as
906 implemented in glibc takes just one argument. This argument
907 corresponds to the third argument of the Linux reboot system call.
908 That is, a call of the form reboot(a, b, c) needs to be changed into
909 reboot(c). Beside this the header <sys/reboot.h> defines the needed
910 constants for the argument. These RB_* constants should be used
911 instead of the cryptic magic numbers.
913 * swapon(): the interface of this function didn't change, but the
914 prototype is in a separate header file <sys/swap.h>. This header
915 file also provides the SWAP_* constants defined by <linux/swap.h>;
916 you should use them for the second argument to swapon().
918 * errno: If a program uses the variable "errno", then it _must_
919 include <errno.h>. The old libc often (erroneously) declared this
920 variable implicitly as a side-effect of including other libc header
921 files. glibc is careful to avoid such namespace pollution, which,
922 in turn, means that you really need to include the header files that
923 you depend on. This difference normally manifests itself in the
924 form of the compiler complaining about references to an undeclared
927 * Linux-specific syscalls: All Linux system calls now have appropriate
928 library wrappers and corresponding declarations in various header files.
929 This is because the syscall() macro that was traditionally used to
930 work around missing syscall wrappers are inherently non-portable and
931 error-prone. The following table lists all the new syscall stubs,
932 the header-file declaring their interface and the system call name.
934 syscall name: wrapper name: declaring header file:
935 ------------- ------------- ----------------------
936 bdflush bdflush <sys/kdaemon.h>
937 syslog ksyslog_ctl <sys/klog.h>
939 * lpd: Older versions of lpd depend on a routine called _validuser().
940 The library does not provide this function, but instead provides
941 __ivaliduser() which has a slightly different interface. Simply
942 upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD
943 lpd is known to be working).
945 * resolver functions/BIND: like on many other systems the functions of
946 the resolver library are not included in libc itself. There is a
947 separate library libresolv. If you get undefined symbol errors for
948 symbols starting with `res_*' simply add -lresolv to your linker
951 * the `signal' function's behavior corresponds to the BSD semantic and
952 not the SysV semantic as it was in libc-5. The interface on all GNU
953 systems shall be the same and BSD is the semantic of choice. To use
954 the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE.
955 See ?signal for details.
957 ??getlog Why does getlogin() always return NULL on my Linux box?
959 {UD} The GNU C library has a format for the UTMP and WTMP file which differs
960 from what your system currently has. It was extended to fulfill the needs
961 of the next years when IPv6 is introduced. The record size is different and
962 some fields have different positions. The files written by functions from
963 the one library cannot be read by functions from the other library. Sorry,
964 but this is what a major release is for. It's better to have a cut now than
965 having no means to support the new techniques later.
967 {MK} There is however a (partial) solution for this problem. Please take a
968 look at the file `login/README.utmpd'.
970 ?? Where are the DST_* constants found in <sys/time.h> on many
973 {UD} These constants come from the old BSD days and are not used anymore
974 (libc5 does not actually implement the handling although the constants are
977 Instead GNU libc contains zone database support and compatibility code for
978 POSIX TZ environment variable handling. For former is very much preferred
981 ?? The prototypes for `connect', `accept', `getsockopt',
982 `setsockopt', `getsockname', `getpeername', `send',
983 `sendto', and `recvfrom' are different in GNU libc from
984 any other system I saw. This is a bug, isn't it?
986 {UD} No, this is no bug. This version of GNU libc already follows the new
987 Single Unix specifications (and I think the POSIX.1g draft which adopted the
988 solution). The type for a parameter describing a size is now `socklen_t', a
991 ??kerhdr On Linux I've got problems with the declarations in Linux
994 {UD,AJ} On Linux, the use of kernel headers is reduced to the minimum. This
995 gives Linus the ability to change the headers more freely. Also, user
996 programs are now insulated from changes in the size of kernel data
999 For example, the sigset_t type is 32 or 64 bits wide in the kernel. In
1000 glibc it is 1024 bits wide. This guarantees that when the kernel gets a
1001 bigger sigset_t (for POSIX.1e realtime support, say) user programs will not
1002 have to be recompiled. Consult the header files for more information about
1005 Therefore you shouldn't include Linux kernel header files directly if glibc
1006 has defined a replacement. Otherwise you might get undefined results because
1009 ?? I don't include any kernel headers myself but the compiler
1010 still complains about redeclarations of types in the kernel
1013 {UD} The kernel headers before Linux 2.1.61 and 2.0.32 don't work correctly
1014 with glibc. Compiling C programs is possible in most cases but C++ programs
1015 have (due to the change of the name lookups for `struct's) problems. One
1016 prominent example is `struct fd_set'.
1018 There might be some problems left but 2.1.61/2.0.32 fix most of the known
1019 ones. See the BUGS file for other known problems.
1021 ??signal Why don't signals interrupt system calls anymore?
1023 {ZW} By default GNU libc uses the BSD semantics for signal(), unlike Linux
1024 libc 5 which used System V semantics. This is partially for compatibility
1025 with other systems and partially because the BSD semantics tend to make
1026 programming with signals easier.
1028 There are three differences:
1030 * BSD-style signals that occur in the middle of a system call do not
1031 affect the system call; System V signals cause the system call to
1032 fail and set errno to EINTR.
1034 * BSD signal handlers remain installed once triggered. System V signal
1035 handlers work only once, so one must reinstall them each time.
1037 * A BSD signal is blocked during the execution of its handler. In other
1038 words, a handler for SIGCHLD (for example) does not need to worry about
1039 being interrupted by another SIGCHLD. It may, however, be interrupted
1042 There is general consensus that for `casual' programming with signals, the
1043 BSD semantics are preferable. You don't need to worry about system calls
1044 returning EINTR, and you don't need to worry about the race conditions
1045 associated with one-shot signal handlers.
1047 If you are porting an old program that relies on the old semantics, you can
1048 quickly fix the problem by changing signal() to sysv_signal() throughout.
1049 Alternatively, define _XOPEN_SOURCE before including <signal.h>.
1051 For new programs, the sigaction() function allows you to specify precisely
1052 how you want your signals to behave. All three differences listed above are
1053 individually switchable on a per-signal basis with this function.
1055 If all you want is for one specific signal to cause system calls to fail and
1056 return EINTR (for example, to implement a timeout) you can do this with
1060 ??string I've got errors compiling code that uses certain string
1063 {AJ} glibc 2.1 has special string functions that are faster than the normal
1064 library functions. Some of the functions are additionally implemented as
1065 inline functions and others as macros. This might lead to problems with
1066 existing codes but it is explicitly allowed by ISO C.
1068 The optimized string functions are only used when compiling with
1069 optimizations (-O1 or higher). The behavior can be changed with two feature
1072 * __NO_STRING_INLINES: Don't do any string optimizations.
1073 * __USE_STRING_INLINES: Use assembly language inline functions (might
1074 increase code size dramatically).
1076 Since some of these string functions are now additionally defined as macros,
1077 code like "char *strncpy();" doesn't work anymore (and is unnecessary, since
1078 <string.h> has the necessary declarations). Either change your code or
1079 define __NO_STRING_INLINES.
1081 {UD} Another problem in this area is that gcc still has problems on machines
1082 with very few registers (e.g., ix86). The inline assembler code can require
1083 almost all the registers and the register allocator cannot always handle
1086 One can disable the string optimizations selectively. Instead of writing
1088 cp = strcpy (foo, "lkj");
1092 cp = (strcpy) (foo, "lkj");
1094 This disables the optimization for that specific call.
1096 ?? I get compiler messages "Initializer element not constant" with
1097 stdin/stdout/stderr. Why?
1099 {RM,AJ} Constructs like:
1100 static FILE *InPtr = stdin;
1102 lead to this message. This is correct behaviour with glibc since stdin is
1103 not a constant expression. Please note that a strict reading of ISO C does
1104 not allow above constructs.
1106 One of the advantages of this is that you can assign to stdin, stdout, and
1107 stderr just like any other global variable (e.g. `stdout = my_stream;'),
1108 which can be very useful with custom streams that you can write with libio
1109 (but beware this is not necessarily portable). The reason to implement it
1110 this way were versioning problems with the size of the FILE structure.
1112 To fix those programs you've got to initialize the variable at run time.
1113 This can be done, e.g. in main, like:
1121 or by constructors (beware this is gcc specific):
1124 static void inPtr_construct (void) __attribute__((constructor));
1125 static void inPtr_construct (void) { InPtr = stdin; }
1128 ?? I can't compile with gcc -traditional (or
1129 -traditional-cpp). Why?
1131 {AJ} glibc2 does break -traditional and -traditonal-cpp - and will continue
1132 to do so. For example constructs of the form:
1138 are useful for debugging purposes (you can use foo with your debugger that's
1139 why we need the enum) and for compatibility (other systems use defines and
1142 ?? I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible?
1144 {AJ} The GNU C library is compatible with the ANSI/ISO C standard. If
1145 you're using `gcc -ansi', the glibc includes which are specified in the
1146 standard follow the standard. The ANSI/ISO C standard defines what has to be
1147 in the include files - and also states that nothing else should be in the
1148 include files (btw. you can still enable additional standards with feature
1151 The GNU C library is conforming to ANSI/ISO C - if and only if you're only
1152 using the headers and library functions defined in the standard.
1154 ?? I can't access some functions anymore. nm shows that they do
1155 exist but linking fails nevertheless.
1157 {AJ} With the introduction of versioning in glibc 2.1 it is possible to
1158 export only those identifiers (functions, variables) that are really needed
1159 by application programs and by other parts of glibc. This way a lot of
1160 internal interfaces are now hidden. nm will still show those identifiers
1161 but marking them as internal. ISO C states that identifiers beginning with
1162 an underscore are internal to the libc. An application program normally
1163 shouldn't use those internal interfaces (there are exceptions,
1164 e.g. __ivaliduser). If a program uses these interfaces, it's broken. These
1165 internal interfaces might change between glibc releases or dropped
1168 ?? When using the db-2 library which comes with glibc is used in
1169 the Perl db modules the testsuite is not passed. This did not
1170 happen with db-1, gdbm, or ndbm.
1172 {UD} You are using an outdated copy of the DB_File Perl module. In fact db-2
1173 finally removed the handling of zero-sized keys which was one of the features
1174 tested by the old Perl testsuite and therefore you see an error. But this
1175 never was documented and guaranteed, only broken programs used this feature.
1177 Consequently db-2 does not need to support this feature and instead signals
1178 an error which leads to easier debugging. The DB_File module maintainer
1179 Paul Marquess <pmarquess@bfsec.bt.co.uk> acknowledged this change and fixed
1180 the testsuite so that if you use DB_File v1.60 or later you should not have
1181 any more problems with db-2.
1183 ?? The pow() inline function I get when including <math.h> is broken.
1184 I get segmentation faults when I run the program.
1186 {UD} Nope, the implementation is correct. The problem is with egcs version
1187 prior to 1.1. I.e., egcs 1.0 to 1.0.3 are all broken (at least on Intel).
1188 If you have to use this compiler you must define __NO_MATH_INLINES before
1189 including <math.h> to prevent the inline functions from being used. egcs 1.1
1190 fixes the problem. I don't know about gcc 2.8 and 2.8.1.
1192 ?? The sys/sem.h file lacks the definition of `union semun'.
1194 {UD} Nope. This union has to be provided by the user program. Former glibc
1195 versions defined this but it was an error since it does not make much sense
1196 when thinking about it. The standards describing the System V IPC functions
1197 define it this way and therefore programs must be adopted.
1199 ?? Why has <netinet/ip_fw.h> disappeared?
1201 {AJ} The corresponding Linux kernel data structures and constants are
1202 totally different in Linux 2.0 and Linux 2.2. This situation has to be
1203 taken care in user programs using the firewall structures and therefore
1204 those programs (ipfw is AFAIK the only one) should deal with this problem
1207 ?? I get floods of warnings when I use -Wconversion and include
1208 <string.h> or <math.h>.
1210 {ZW} <string.h> and <math.h> intentionally use prototypes to override
1211 argument promotion. -Wconversion warns about all these. You can safely
1212 ignore the warnings.
1214 -Wconversion isn't really intended for production use, only for shakedown
1215 compiles after converting an old program to standard C.
1218 ?? After upgrading to glibc 2.1, I receive errors about
1219 unresolved symbols, like `_dl_initial_searchlist' and can not
1220 execute any binaries. What went wrong?
1222 {AJ} This normally happens if your libc and ld (dynamic linker) are from
1223 different releases of glibc. For example, the dynamic linker
1224 /lib/ld-linux.so.2 comes from glibc 2.0.x, but the version of libc.so.6 is
1227 The path /lib/ld-linux.so.2 is hardcoded in every glibc2 binary but
1228 libc.so.6 is searched via /etc/ld.so.cache and in some special directories
1229 like /lib and /usr/lib. If you run configure with another prefix than /usr
1230 and put this prefix before /lib in /etc/ld.so.conf, your system will break.
1232 So what can you do? Either of the following should work:
1234 * Run `configure' with the same prefix argument you've used for glibc 2.0.x
1235 so that the same paths are used.
1236 * Replace /lib/ld-linux.so.2 with a link to the dynamic linker from glibc
1239 You can even call the dynamic linker by hand if everything fails. You've
1240 got to set LD_LIBRARY_PATH so that the corresponding libc is found and also
1241 need to provide an absolute path to your binary:
1243 LD_LIBRARY_PATH=<path-where-libc.so.6-lives> \
1244 <path-where-corresponding-dynamic-linker-lives>/ld-linux.so.2 \
1245 <path-to-binary>/binary
1247 For example `LD_LIBRARY_PATH=/libold /libold/ld-linux.so.2 /bin/mv ...'
1248 might be useful in fixing a broken system (if /libold contains dynamic
1249 linker and corresponding libc).
1251 With that command line no path is used. To further debug problems with the
1252 dynamic linker, use the LD_DEBUG environment variable, e.g.
1253 `LD_DEBUG=help echo' for the help text.
1255 If you just want to test this release, don't put the lib directory in
1256 /etc/ld.so.conf. You can call programs directly with full paths (as above).
1257 When compiling new programs against glibc 2.1, you've got to specify the
1258 correct paths to the compiler (option -I with gcc) and linker (options
1259 --dynamic-linker, -L and --rpath).
1264 ?? After I changed configure.in I get `Autoconf version X.Y.
1265 or higher is required for this script'. What can I do?
1267 {UD} You have to get the specified autoconf version (or a later one)
1268 from your favorite mirror of ftp.gnu.org.
1270 ?? When I try to compile code which uses IPv6 headers and
1271 definitions on my Linux 2.x.y system I am in trouble.
1272 Nothing seems to work.
1274 {UD} The problem is that IPv6 development still has not reached a point
1275 where the headers are stable. There are still lots of incompatible changes
1276 made and the libc headers have to follow.
1278 {PB} The 2.1 release of GNU libc aims to comply with the current versions of
1279 all the relevant standards. The IPv6 support libraries for older Linux
1280 systems used a different naming convention and so code written to work with
1281 them may need to be modified. If the standards make incompatible changes in
1282 the future then the libc may need to change again.
1284 IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it
1285 should contain all the necessary support; until then you should use the
1286 latest 2.1.x release you can find. As of 98/11/26 the currently recommended
1287 kernel for IPv6 is 2.1.129.
1289 Also, as of the 2.1 release the IPv6 API provided by GNU libc is not
1290 100% complete. In particular the getipnodebyname and getipnodebyaddr
1291 functions are not implemented.
1293 ??tzdb When I set the timezone by setting the TZ environment variable
1294 to EST5EDT things go wrong since glibc computes the wrong time
1295 from this information.
1297 {UD} The problem is that people still use the braindamaged POSIX method to
1298 select the timezone using the TZ environment variable with a format EST5EDT
1299 or whatever. People, if you insist on using TZ instead of the timezone
1300 database (see below), read the POSIX standard, the implemented behaviour is
1301 correct! What you see is in fact the result of the decisions made while
1302 POSIX.1 was created. We've only implemented the handling of TZ this way to
1303 be POSIX compliant. It is not really meant to be used.
1305 The alternative approach to handle timezones which is implemented is the
1306 correct one to use: use the timezone database. This avoids all the problems
1307 the POSIX method has plus it is much easier to use. Simply run the tzselect
1308 shell script, answer the question and use the name printed in the end by
1309 making a symlink /etc/localtime pointing to /usr/share/zoneinfo/NAME (NAME
1310 is the returned value from tzselect). That's all. You never again have to
1313 So, please avoid sending bug reports about time related problems if you use
1314 the POSIX method and you have not verified something is really broken by
1315 reading the POSIX standards.
1317 ?? What other sources of documentation about glibc are available?
1319 {AJ} The FSF has a page about the GNU C library at
1320 <http://www.gnu.org/software/libc/>. The problem data base of open and
1321 solved bugs in GNU libc is available at
1322 <http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl>. Eric Green has written
1323 a HowTo for converting from Linux libc5 to glibc2. The HowTo is accessable
1324 via the FSF page and at <http://www.imaxx.net/~thrytis/glibc>. Frodo
1325 Looijaard describes a different way installing glibc2 as secondary libc at
1326 <http://huizen.dds.nl/~frodol/glibc>.
1328 Please note that this is not a complete list.
1330 ?? The timezone string for Sydney/Australia is wrong since even when
1331 daylight saving time is in effect the timezone string is EST.
1333 {UD} The problem for some timezones is that the local authorities decided
1334 to use the term "summer time" instead of "daylight saving time". In this
1335 case the abbreviation character `S' is the same as the standard one. So,
1338 Eastern Standard Time = EST
1339 Eastern Summer Time = EST
1341 Great! To get this bug fixed convince the authorities to change the laws
1342 and regulations of the country this effects. glibc behaves correctly.
1344 ??make I've build make 3.77 against glibc 2.1 and now make gets
1345 segmentation faults.
1347 {AJ} GNU make 3.77 has support for 64 bit filesystems which is slightly
1348 broken (and one of the new features in the GNU C library 2.1 is 64 bit
1349 filesystem support :-( ). To get a working make you can use either make
1350 3.75 or patch 3.77. A working patch is available via RedHat's Rawhide server
1351 (ftp://rawhide.redhat.com/SRPMS/SRPMS/make-3.77-*src.rpm).
1354 Answers were given by:
1355 {UD} Ulrich Drepper, <drepper@cygnus.com>
1356 {DMT} David Mosberger-Tang, <davidm@AZStarNet.com>
1357 {RM} Roland McGrath, <roland@gnu.org>
1358 {AJ} Andreas Jaeger, <aj@arthur.rhein-neckar.de>
1359 {EY} Eric Youngdale, <eric@andante.jic.com>
1360 {PB} Phil Blundell, <Philip.Blundell@pobox.com>
1361 {MK} Mark Kettenis, <kettenis@phys.uva.nl>
1362 {ZW} Zack Weinberg, <zack@rabi.phys.columbia.edu>
1363 {TK} Thorsten Kukuk, <kukuk@vt.uni-paderborn.de>
1364 {GK} Geoffrey Keating, <geoffk@ozemail.com.au>
1365 {HJ} H.J. Lu, <hjl@gnu.org>
1366 {CG} Cristian Gafton, <gafton@redhat.com>
1370 outline-regexp:"\\?"