FAQ GNU C Library

Этот документ пытается ответить на вопросы, которые возникают у пользователя, когда тот инсталлирует и использует glibc.

Библиотека GNU C library многогранна. Инсталляционный процесс как правило всегда не проходит гладко, и на то существует множество причин. Неправильная ее установка вообще может погубить вашу систему.
--drepper@redhat.com

1.1. В каких системах работает GNU C Library ?

1.2. Какой компилятор нужен для сборки GNU libc?

1.3. При компиляции glibc вылетают ошибки. Где я неправ?

1.4. Нужен ли мне специальный линкер или ассемблер?

1.5. Какой компилятор нужен для powerpc?

1.6. Что нужно для ARM?

1.7. Нужно что-то еще для сборки GNU C Library?

1.8. Какую версию Linux kernel нужно использовать ?

1.9. Компилятор зависает при сборке модулей - что делать ?

1.10. При выполнении команды `nm -u libc.so' находятся ошибочные символы. Это нормально?

1.11. Что это такое - `add-ons'?

1.12. Моя версия ядра эмулирует floating-point сопроцессор. Нужно ли мне включить опцию --with-fp?

1.13. При сборке я получаю кучу ошибок, которые говорят , что функции в glibc дублируются в libgcc.

1.14. Я получаю сообщения об ошибках при попытке использования librt. Я не могу даже использовать треды..

1.15. Что это за проблема при конфигурировании --enable-omitfp?

1.16. Получена ошибка при `make check'. Что делать?

1.17. Зачем нужен symbol versioning?

1.18. Как собрать на быстрой машине версию libc для медленной машины?

1.19. `make' выдает,что отсутствует dlfcn/libdl.so при сборке malloc/libmemprof.so. Как победить?

1.20. Что нужно для использования MIPS?

1.21. Какой комптлятор нужен для powerpc64?

2. Инсталляция и конфигурация

2.1. Можно ли перезаписать libc поверх существующей GNU libc?

2.2. Как сконфигурировать GNU libc ,чтобы библиотеки типа libc.so легли в /lib и в /usr/lib?

2.3. Что нужно сделать , чтобы избежать разрушения своей системы при инсталляции GNU libc?

2.4. Нужно ли использовать GNU CC для компиляции программ, которые будут использовать GNU C Library?

2.5. При линковке с новой libc я получаю unresolved symbols `crypt' и `setkey'. Почему этих функций нет нигде в libc?

2.6. При использовании GNU libc с libc.so , которая входит в glibc , я получаю core dump.

2.7. Я не нахожу в shared libc file функций `stat', `lstat', `fstat', `mknod' и получаю ошибки при линковке.

2.8. При запуске исполняемого файла на другой машине я аолучаю dynamic linker errors.

2.9. Как собрать gcc 2.7.2.1 из из исходников gcc с использованием glibc 2.x?

2.10. Утилита `gencat' не может найти каталог с исходниками , которые используются в Linux libc5 .

2.11. Программы,использующие glibc,выдают сообщения в другом переводе, который не локализован.

2.12. Я поставил /etc/nis.conf, и Linux libc 5 с NYS отлично работает. Чего нельзя сказать о glibc NIS+ .

2.13. Я убил ypbind ,но glibc продолжает использовать NIS.

2.14. Под Linux/Alpha, я всегда получаю "do_ypcall: clnt_call: RPC: Unable to receive; errno = Connection refused" при использовании NIS.

2.15. После инсталляции glibc не работает name resolving.

2.16. Как создать базу данных для NSS?

2.17. У меня /usr/include/net и /usr/include/scsi - симлинки . Это неверно?

2.18. Программы типа `logname', `top', `uptime' `users', `w' , `who' показывают неправду о пользователях моей системы.

2.19. После апгрейда glibc 2.1 я получаю ошибки.

2.20. Когда я запускаю программу XXX после апгрэйда library, я получаю
XXX: Symbol `_sys_errlist' has different size in shared object, consider re-linking

2.21. Что мне нужно для C++ development?

2.22. Статически залинкованным прогаммам нужны shared libraries, которых у меня нет.

2.23. Я проапгрэйдил glibc и теперь получаю ошибки при линковке любой программы.

2.24. При использовании nscd машина виснет.

2.25. Мне нужно открыть много файлов.

2.26. Как мне отпарсить /etc/passwd и /etc/group с использованием libc5 ?

2.27. Что нужно для апгрэйда с glibc 2.0 до 2.1?

2.28. Почему разархивация tar тормозит?

2.29. При компиляции программы я получаю ошибки в libio.h ( "parse error before `_IO_seekoff'").

2.30. После апгрэйда до glibc 2.1, библиотеки перестали работать.

2.31. Что случилось с Berkeley DB libraries? Можно ли использовать db в /etc/nsswitch.conf?

2.32. Что нужно делать при апгрэйде до glibc 2.2?

2.33. makefiles требует сделать CVS commit.

2.34. При компиляции C++ programs, я получаю ошибку в streambuf.h.

2.35. При рекомпиляции GCC, я получаю ошибку в libio.

2.36. Почему glibc не хокет устанавливаться в /usr/local?

2.37. При рекомпиляции GCC, я получаю ошибки в libstdc++.

3.Бинарная несовместимость

3.1. Я думал,что GNU libc на 100% со старой GNU libc. Почему это не так?

3.2. Почему у меня getlogin() всегда возвращает NULL?

3.3. Где можно найти константы DST_* ?

3.4. Прототипы для `connect', `accept', `getsockopt', `setsockopt', `getsockname', `getpeername', `send', `sendto', `recvfrom' в разных GNU libc отличаются в зависимости от системы. Это почему?

3.5. У меня проблемы с декларацией Linux kernel headers.

3.6. Я не включил kernel headers,но компилятор ссылается на них.

3.7. Почему прерывания перестали работать ?

3.8. Я получил ошибки компиляции при использовании определенных символьных функций.

3.9. Я получил сообщение "Initializer element not constant" из stdin/stdout/stderr.

3.10. Не могу использовать опцию компиляции gcc -traditional (-traditional-cpp). Why?

3.11. Получил ошибки при использовании опции `gcc -ansi'.

3.12. У меня нет доступа к некоторым функциям. nm говорит,что эти функции есть.

3.13. При использовании библиотеки db-2 , которая используется в модуле Perl db , ошибка.

3.14. Функция pow() с использованием <math.h> вылетает. Я получил segmentation faults.

3.15. sys/sem.h file выдает `union semun'.

3.16. Почему исчез <netinet/ip_fw.h> ?

3.17. Я получил много варнингов при использовании -Wconversion и включении <string.h> or <math.h>.

3.18. После апгрэйда до glibc 2.1, я получил unresolved symbols, типа `_dl_initial_searchlist' и не могу выполнить ни один бинарник.

3.19. Тесты показывают,что char i/o в glibc 2 значительно медленнее,чем libc5.

3.20. Программы,откомпилированные с glibc 2.1 , не могут прочитать db files , собранный с glibc 2.0.

3.21. Макрос AC_CHECK_FUNC говорит,что функция существует, но при использовании всегда выдает ENOSYS.

3.22. Моя программа делает , когда я вызываю fclose() из setmntent().

3.23. Я получил "undefined reference to `atexit'"

4. Разное

4.1. Я изменил configure.in и получил `Autoconf version X.Y. or higher is required for this script'.

4.2. Когда я пытаюсь скомпилировать код, который испльзует IPv6 headers ,у меня проблемы. Ничего не работает.

4.3. Когда я устанавливаю timezone и переменную TZ = EST5EDT, glibc начинает неправильно вычислять время.

4.4. Какая документация о glibc доступна еще?

4.5. timezone string для Sydney/Australia неверна.

4.6. Использую make 3.77 , glibc 2.1 , и получаю segmentation faults.

4.7. Почему многие программы,использующие math functions, падают на моей AlphaStation?

4.8. Таблица символов не соответствует.

4.9. как определить версию glibc ?

4.10. Переключение контекста setcontext() не работает .

1. Compiling glibc

1.1. What systems does the GNU C Library run on?

The systems glibc is known to work on as of this release, and most probably in the future, are:

	*-*-gnu			GNU Hurd
 	i[3456]86-*-linux-gnu	Linux-2.x on Intel
 	m68k-*-linux-gnu	Linux-2.x on Motorola 680x0
 	alpha*-*-linux-gnu	Linux-2.x on DEC Alpha
 	powerpc-*-linux-gnu     Linux and MkLinux on PowerPC systems
 	powerpc64-*-linux-gnu	Linux-2.4+ on 64-bit PowerPC systems
 	sparc-*-linux-gnu	Linux-2.x on SPARC
 	sparc64-*-linux-gnu	Linux-2.x on UltraSPARC
 	arm-*-none		ARM standalone systems
 	arm-*-linux		Linux-2.x on ARM
 	arm-*-linuxaout		Linux-2.x on ARM using a.out binaries
 	mips*-*-linux-gnu	Linux-2.x on MIPS
 	ia64-*-linux-gnu	Linux-2.x on ia64
 	s390-*-linux-gnu	Linux-2.x on IBM S/390
 	s390x-*-linux-gnu	Linux-2.x on IBM S/390 64-bit
 	cris-*-linux-gnu	Linux-2.4+ on CRIS
 

Ports to other Linux platforms are in development, and may in fact work already, but no one has sent us success reports for them. Currently no ports to other operating systems are underway, although a few people have expressed interest.

If you have a system not listed above (or in the `README' file) and you are really interested in porting it, contact

	<bug-glibc@gnu.org>
 

1.2. What compiler do I need to build GNU libc?

GNU CC is found, like all other GNU packages, on

	ftp://ftp.gnu.org/pub/gnu
 

and the many mirror sites. ftp.gnu.org is always overloaded, so try to find a local mirror first.

You should always try to use the latest official release. Older versions may not have all the features GNU libc requires. The current releases of gcc (3.2 or newer) should work with the GNU C library (for MIPS see question 1.20).

Please note that gcc 2.95 and 2.95.x cannot compile glibc on Alpha due to problems in the complex float support.

1.3. When I try to compile glibc I get only error messages. What's wrong?

We recommend version GNU make version 3.79 or newer. Older versions have bugs and/or are missing features.

1.4. Do I need a special linker or assembler?

For Linux or Hurd, you want binutils 2.13 or higher. These are the only versions we've tested and found reliable. Other versions may work but we don't recommend them, especially not when C++ is involved.

Other operating systems may come with system tools that have all the necessary features, but this is moot because glibc hasn't been ported to them.

1.5. Which compiler should I use for powerpc?

1.6. Which tools should I use for ARM?

1.7. Do I need some more things to compile the GNU C Library?

• GNU gettext. This package contains the tools needed to construct `message catalog' files containing translated versions of system messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror site. (We distribute compiled message catalogs, but they may not be updated in patches.)

• Some files are built with special tools. E.g., files ending in .gperf need a `gperf' program. The GNU version (now available in a separate package, formerly only as part of libg++) is known to work while some vendor versions do not.

  You should not need these tools unless you change the source files.

• Perl 5 is needed if you wish to test an installation of GNU libc as the primary C library.

• When compiling for Linux, the header files of the Linux kernel must be available to the compiler as <linux/*.h> and <asm/*.h>.

• lots of disk space (~400MB for i?86-linux; more for RISC platforms).

• plenty of time. Compiling just the shared and static libraries for 35mins on a 2xPIII@550Mhz w/ 512MB RAM. On a 2xUltraSPARC-II@360Mhz w/ 1GB RAM it takes about 14 minutes. Multiply this by 1.5 or 2.0 if you build profiling and/or the highly optimized version as well. For Hurd systems times are much higher.

  You should avoid compiling in a NFS mounted filesystem. This is very slow.

  James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time for an earlier (and smaller!) version of glibc of 45h34m for a full build (shared, static, and profiled) on Atari Falcon (Motorola 68030 @ 16 Mhz, 14 Mb memory) and Jan Barte <yann@plato.uni-paderborn.de> reports 22h48m on Atari TT030 (Motorola 68030 @ 32 Mhz, 34 Mb memory)

  A full build of the PowerPC library took 1h on a PowerPC 750@400Mhz w/ 64MB of RAM, and about 9h on a 601@60Mhz w/ 72Mb.

  If you have some more measurements let me know.

1.8. What version of the Linux kernel headers should be used?

{ZW} Even if you are using a 2.0 kernel on your machine, we recommend you compile GNU libc with 2.2 kernel headers. That way you won't have to recompile libc if you ever upgrade to kernel 2.2. To tell libc which headers to use, give configure the --with-headers switch (e.g. --with-headers=/usr/src/linux-2.2.0/include).

Note that you must configure the 2.2 kernel if you do this, otherwise libc will be unable to find <linux/version.h>. Just change the current directory to the root of the 2.2 tree and do `make include/linux/version.h'.

1.9. The compiler hangs while building iconvdata modules. What's wrong?

1.10. When I run `nm -u libc.so' on the produced library I still find unresolved symbols. Can this be ok?

• magic symbols automatically generated by the linker. These have names like __start_* and __stop_*

• symbols starting with _dl_* come from the dynamic linker

• weak symbols, which need not be resolved at all (fabs for example)

1.11. What are these `add-ons'?

To use these packages as part of GNU libc, just unpack the tarfiles in the libc source directory and tell the configuration script about them using the --enable-add-ons option. If you give just --enable-add-ons configure tries to find all the add-on packages in your source tree. This may not work. If it doesn't, or if you want to select only a subset of the add-ons, give a comma-separated list of the add-ons to enable:

	configure --enable-add-ons=linuxthreads
 

for example.

Add-ons can add features (including entirely new shared libraries), override files, provide support for additional architectures, and just about anything else. The existing makefiles do most of the work; only some few stub rules must be written to get everything running.

Most add-ons are tightly coupled to a specific GNU libc version. Please check that the add-ons work with the GNU libc. For example the linuxthreads add-on has the same numbering scheme as the libc and will in general only work with the corresponding libc.

{AJ} With glibc 2.2 the crypt add-on and with glibc 2.1 the localedata add-on have been integrated into the normal glibc distribution, crypt and localedata are therefore not anymore add-ons.

1.12. My XXX kernel emulates a floating-point coprocessor for me. Should I enable --with-fp?

People who are interested in squeezing the last drop of performance out of their machine may wish to avoid the trap overhead, but this is far more trouble than it's worth: you then have to compile *everything* this way, including the compiler's internal libraries (libgcc.a for GNU C), because the calling conventions change.

1.13. When compiling GNU libc I get lots of errors saying functions in glibc are duplicated in libgcc.

One thing that is particularly annoying about this problem is that once this is misdetected, running configure again won't fix it unless you first delete config.cache.

{UD} Starting with glibc-2.0.3 there should be a better test to avoid some problems of this kind. The setting of CFLAGS is checked at the very beginning and if it is not usable `configure' will bark.

1.14. Why do I get messages about missing thread functions when I use librt? I don't even use threads.

	gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt
 

The `/some/other/dir' should contain the thread library. `ld' will use the given path to find the implicitly referenced library while not disturbing any other link path.

1.15. What's the problem with configure --enable-omitfp?

If you use --enable-omitfp, you're on your own. If you encounter problems with a library that was build this way, we advise you to rebuild the library without --enable-omitfp. If the problem vanishes consider tracking the problem down and report it as compiler failure.

Since a library built with --enable-omitfp is undebuggable on most systems, debuggable libraries are also built - you can use them by appending "_g" to the library names.

The compilation of these extra libraries and the compiler optimizations slow down the build process and need more disk space.

1.16. I get failures during `make check'. What should I do?

You should consider using the `glibcbug' script to report the failure, providing as much detail as possible. If you run a test directly, please remember to set up the environment correctly. You want to test the compiled library - and not your installed one. The best way is to copy the exact command line which failed and run the test from the subdirectory for this test in the sources.

There are some failures which are not directly related to the GNU libc:

• Some compilers produce buggy code. No compiler gets single precision complex numbers correct on Alpha. Otherwise, gcc-3.2 should be ok.
• The kernel might have bugs. For example on Linux/Alpha 2.0.34 the floating point handling has quite a number of bugs and therefore most of the test cases in the math subdirectory will fail. Linux 2.2 has fixes for the floating point support on Alpha. The Linux/SPARC kernel has also some bugs in the FPU emulation code (as of Linux 2.2.0).
• Other tools might have problems. For example bash 2.03 gives a segmentation fault running the tst-rpmatch.sh test script.

1.17. What is symbol versioning good for? Do I need it?

We don't advise building without symbol versioning, since you lose binary compatibility - forever! The binary compatibility you lose is not only against the previous version of the GNU libc (version 2.0) but also against all future versions.

1.18. How can I compile on my fast ix86 machine a working libc for my slow i386? After installing libc, programs abort with "Illegal Instruction".

	../configure --prefix=/usr i386-pc-linux-gnu
 

And you need to tell gcc to only generate i386 code, just add `-mcpu=i386' (just -m386 doesn't work) to your CFLAGS.

{UD} This applies not only to the i386. Compiling on a i686 for any older model will also fail if the above methods are not used.

1.19. `make' complains about a missing dlfcn/libdl.so when building malloc/libmemprof.so. How can I fix this?

After upgrading make, you should remove the file sysd-sorted in your build directory. The problem is that the broken make creates a wrong order for one list in that file. The list has to be recreated with the new make - which happens if you remove the file.

You might encounter this bug also in other situations where make scans directories. I strongly advise to upgrade your make version to 3.79 or newer.

1.20. Which tools should I use for MIPS?

You need also recent binutils, anything before and including 2.11 will not work correctly. Either try the Linux binutils 2.11.90.0.5 from HJ Lu or the current development version of binutils from CVS.

Please note that `make check' might fail for a number of the math tests because of problems of the FPU emulation in the Linux kernel (the MIPS FPU doesn't handle all cases and needs help from the kernel).

For details check also my page http://www.suse.de/~aj/glibc-mips.html.

1.21. Which compiler should I use for powerpc64?

2. Installation and configuration issues

2.1. Can I replace the libc on my Linux system with GNU libc?

For Linux there are three major libc versions:

	libc-4		a.out libc
 	libc-5		original ELF libc
 	libc-6		GNU libc
 

You can have any combination of these three installed. For more information consult documentation for shared library handling. The Makefiles of GNU libc will automatically generate the needed symbolic links which the linker will use.

2.2. How do I configure GNU libc so that the essential libraries like libc.so go into /lib and the other into /usr/lib?

Some systems like Linux have a filesystem standard which makes a difference between essential libraries and others. Essential libraries are placed in /lib because this directory is required to be located on the same disk partition as /. The /usr subtree might be found on another partition/disk. If you configure for Linux with --prefix=/usr, then this will be done automatically.

To install the essential libraries which come with GNU libc in /lib on systems other than Linux one must explicitly request it. Autoconf has no option for this so you have to use a `configparms' file (see the `INSTALL' file for details). It should contain:

slibdir=/lib sysconfdir=/etc

The first line specifies the directory for the essential libraries, the second line the directory for system configuration files.

2.3. How should I avoid damaging my system when I install GNU libc?

The dangers when installing glibc in /usr are twofold:

• glibc will overwrite the headers in /usr/include. Other C libraries install a different but overlapping set of headers there, so the effect will probably be that you can't compile anything. You need to rename /usr/include out of the way before running `make install'. (Do not throw it away; you will then lose the ability to compile programs against your old libc.)

• None of your old libraries, static or shared, can be used with a different C library major version. For shared libraries this is not a problem, because the filenames are different and the dynamic linker will enforce the restriction. But static libraries have no version information. You have to evacuate all the static libraries in /usr/lib to a safe location.

2.4. Do I need to use GNU CC to compile programs that will use the GNU C Library?

However, there are currently no ports of glibc to systems where another compiler is the default, so no one has tested the headers extensively against another compiler. You may therefore encounter difficulties. If you do, please report them as bugs.

Also, in several places GNU extensions provide large benefits in code quality. For example, the library has hand-optimized, inline assembly versions of some string functions. These can only be used with GCC. See question 3.8 for details.

2.5. When linking with the new libc I get unresolved symbols `crypt' and `setkey'. Why aren't these functions in the libc anymore?

2.6. When I use GNU libc on my Linux system by linking against the libc.so which comes with glibc all I get is a core dump.

For casual use of GNU libc you can just specify to the linker

    --dynamic-linker=/lib/ld-linux.so.2
 

which is the glibc dynamic linker, on Linux systems. On other systems the name is /lib/ld.so.1. When linking via gcc, you've got to add

    -Wl,--dynamic-linker=/lib/ld-linux.so.2
 

to the gcc command line.

To change your environment to use GNU libc for compiling you need to change the `specs' file of your gcc. This file is normally found at

	/usr/lib/gcc-lib/<arch>/<version>/specs
 

In this file you have to change a few things:

• change `ld-linux.so.1' to `ld-linux.so.2'

• remove all expression `%{...:-lgmon}'; there is no libgmon in glibc

• fix a minor bug by changing %{pipe:-} to %|

*asm_final: %|

*cpp: %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}

*cc1: %{profile:-p}

*cc1plus:

*endfile: %{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s

*link: -m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}}

*lib: %{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}}

*libgcc: -lgcc

*startfile: %{!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}

*switches_need_spaces:

*signed_char: %{funsigned-char:-D__CHAR_UNSIGNED__}

*predefines: -D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386)

*cross_compile: 0

*multilib: . ;

Things get a bit more complicated if you have GNU libc installed in some other place than /usr, i.e., if you do not want to use it instead of the old libc. In this case the needed startup files and libraries are not found in the regular places. So the specs file must tell the compiler and linker exactly what to use.

Version 2.7.2.3 does and future versions of GCC will automatically provide the correct specs.

2.7. Looking through the shared libc file I haven't found the functions `stat', `lstat', `fstat', and `mknod' and while linking on my Linux system I get error messages. How is this supposed to work?

GROUP ( libc.so.6 libc_nonshared.a )

2.8. When I run an executable on one system which I compiled on another, I get dynamic linker errors. Both systems have the same version of glibc installed. What's wrong?

When you link your program, it resolves its references to the exception functions to the ones exported accidentally by libc.so. That works fine as long as libc has those functions. On the other system, libc doesn't have those functions because it was compiled by gcc 2.8, and you get undefined symbol errors. The symbols in question are named things like `__register_frame_info'.

For glibc 2.0, the workaround is to not compile libc with egcs. We've also incorporated a patch which should prevent the EH functions sneaking into libc. It doesn't matter what compiler you use to compile your program.

For glibc 2.1, we've chosen to do it the other way around: libc.so explicitly provides the EH functions. This is to prevent other shared libraries from doing it.

{UD} Starting with glibc 2.1.1 you can compile glibc with gcc 2.8.1 or newer since we have explicitly add references to the functions causing the problem. But you nevertheless should use EGCS for other reasons (see question 1.2).

{GK} On some Linux distributions for PowerPC, you can see this when you have built gcc or egcs from the Web sources (gcc versions 2.95 or earlier), then re-built glibc. This happens because in these versions of gcc, exception handling is implemented using an older method; the people making the distributions are a little ahead of their time.

A quick solution to this is to find the libgcc.a file that came with the distribution (it would have been installed under /usr/lib/gcc-lib), do `ar x libgcc.a frame.o' to get the frame.o file out, and add a line saying `LDLIBS-c.so += frame.o' to the file `configparms' in the directory you're building in. You can check you've got the right `frame.o' file by running `nm frame.o' and checking that it has the symbols defined that you're missing.

This will let you build glibc with the C compiler. The C++ compiler will still be binary incompatible with any C++ shared libraries that you got with your distribution.

2.9. How can I compile gcc 2.7.2.1 from the gcc source code using glibc 2.x?

2.10. The `gencat' utility cannot process the catalog sources which were used on my Linux libc5 based system. Why?

To ease the transition from the Linux version some of the non-standard features are also present in the `gencat' program of GNU libc. This mainly includes the use of symbols for the message number and the automatic generation of header files which contain the needed #defines to map the symbols to integers.

Here is a simple SED script to convert at least some Linux specific catalog files to the XPG4 form:

# Change catalog source in Linux specific format to standard XPG format.
 # Ulrich Drepper <drepper@redhat.com>, 1996.
 #
 /^\$ #/ {
   h
   s/\$ #\([^ ]*\).*/\1/
   x
   s/\$ #[^ ]* *\(.*\)/\$ \1/
 }
 

/^# / {
   s/^# \(.*\)/\1/
   G
   s/\(.*\)\n\(.*\)/\2 \1/
 }
 

2.11. Programs using libc have their messages translated, but other behavior is not localized (e.g. collating order); why?

    localedef -i fr_CA -f ISO-8859-1 fr_CA
 

Please see localedata/README in the source tree for further details.

2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS works great. But the glibc NIS+ doesn't seem to work.

    http://www.suse.de/~kukuk/linux/nisplus.html
 

2.13. I have killed ypbind to stop using NIS, but glibc continues using NIS.

    ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz
 

2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call: RPC: Unable to receive; errno = Connection refused" when using NIS.

2.15. After installing glibc name resolving doesn't work properly.

2.16. How do I create the databases for NSS?

2.17. I have /usr/include/net and /usr/include/scsi as symlinks into my Linux source tree. Is that wrong?

2.18. Programs like `logname', `top', `uptime' `users', `w' and `who', show incorrect information about the (number of) users on my system. Why?

2.19. After upgrading to glibc 2.1 with symbol versioning I get errors about undefined symbols. What went wrong?

The only way to fix this is to recompile your program. Sorry, that's the price you might have to pay once for quite a number of advantages with symbol versioning.

2.20. When I start the program XXX after upgrading the library I get XXX: Symbol `_sys_errlist' has different size in shared object, consider re-linking Why? What should I do?

Such symbols should normally not be used at all. There are mechanisms to avoid using them. In the case of _sys_errlist, there is the strerror() function which should _always_ be used instead. So the correct fix is to rewrite that part of the application.

In some situations (especially when testing a new library release) it might be possible that a symbol changed size when that should not have happened. So in case of doubt report such a warning message as a problem.

2.21. What do I need for C++ development?

	ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz
 

Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work very well with the GNU C library due to vtable thunks. If you're upgrading from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library compiled for 2.0 is not compatible due to the new Large File Support (LFS) in version 2.1.

{UD} But since in the case of a shared libstdc++ the version numbers should be different existing programs will continue to work.

2.22. Even statically linked programs need some shared libraries which is not acceptable for me. What can I do?

A solution is to configure glibc with --enable-static-nss. In this case you can create a static binary that will use only the services dns and files (change /etc/nsswitch.conf for this). You need to link explicitly against all these services. For example:

  gcc -static test-netdb.c -o test-netdb \
     -Wl,--start-group -lc -lnss_files -lnss_dns -lresolv -Wl,--end-group
 

The problem with this approach is that you've got to link every static program that uses NSS routines with all those libraries.

{UD} In fact, one cannot say anymore that a libc compiled with this option is using NSS. There is no switch anymore. Therefore it is *highly* recommended *not* to use --enable-static-nss since this makes the behaviour of the programs on the system inconsistent.

2.23. I just upgraded my Linux system to glibc and now I get errors whenever I try to link any program.

The most common case is that glibc put its `libc.so' in /usr/lib, but there was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the problem, just delete /lib/libc.so. You may also need to delete other symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5.

{AJ} The perl script test-installation.pl which is run as last step during an installation of glibc that is configured with --prefix=/usr should help detect these situations. If the script reports problems, something is really screwed up.

2.24. When I use nscd the machine freezes.

If you need nscd, you have to use at least a 2.1 kernel.

Note that I have at this point no information about any other platform.

2.25. I need lots of open files. What do I have to do?

The GNU C library is now select free. This means it internally has no limits imposed by the `fd_set' type. Instead all places where the functionality is needed the `poll' function is used.

If you increase the number of file descriptors in the kernel you don't need to recompile the C library.

{UD} You can always get the maximum number of file descriptors a process is allowed to have open at any time using

	number = sysconf (_SC_OPEN_MAX);
 

This will work even if the kernel limits change.

2.26. How do I get the same behavior on parsing /etc/passwd and /etc/group as I have with libc5 ?

passwd: compat
 group:  compat
 shadow: compat
 

passwd_compat: nis
 group_compat: nis
 shadow_compat: nis
 

2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc 2.1?

If you compile your own binaries against glibc 2.1, you also need to recompile some other libraries. The problem is that libio had to be changed and therefore libraries that are based or depend on the libio of glibc, e.g. ncurses, slang and most C++ libraries, need to be recompiled. If you experience strange segmentation faults in your programs linked against glibc 2.1, you might need to recompile your libraries.

Another problem is that older binaries that were linked statically against glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled static libraries (libfoo.a) which happen to depend on the older libio behavior will be broken by the glibc 2.1 upgrade. We plan to produce a compatibility library that people will be able to link in if they want to compile a static library generated against glibc 2.0 into a program on a glibc 2.1 system. You just add -lcompat and you should be fine.

The glibc-compat add-on will provide the libcompat.a library, the older nss modules, and a few other files. Together, they should make it possible to do development with old static libraries on a glibc 2.1 system. This add-on is still in development. You can get it from

	ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz
 

2.28. Why is extracting files via tar so slow?

• do you really need NIS/NIS+ (some Linux distributions add by default nis/nisplus even if it's not needed)? If not, just remove the entries.

• if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes with glibc 2.1.

2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error before `_IO_seekoff'"). How should I fix this?

  In file included from /usr/include/stdio.h:57,
                    from ...
   /usr/include/libio.h:335: parse error before `_IO_seekoff'
   /usr/include/libio.h:335: parse error before `_G_off64_t'
   /usr/include/libio.h:336: parse error before `_IO_seekpos'
   /usr/include/libio.h:336: parse error before `_G_fpos64_t'
 

The problem is a wrong _G_config.h file in your include path. The _G_config.h file that comes with glibc 2.1 should be used and not one from libc5 or from a compiler directory. To check which _G_config.h file the compiler uses, compile your program with `gcc -E ...|grep G_config.h' and remove that file. Your compiler should pick up the file that has been installed by glibc 2.1 in your include directory.

2.30. After upgrading to glibc 2.1, libraries that were compiled against glibc 2.0.x don't work anymore.

2.31. What happened to the Berkeley DB libraries? Can I still use db in /etc/nsswitch.conf?

The NSS db module has been rewritten to support a number of different versions of Berkeley DB for the NSS db module. Currently the releases 2.x and 3.x of Berkeley DB are supported. The older db 1.85 library is not supported. You can use the version from glibc 2.1.x or download a version from Sleepycat Software (http://www.sleepycat.com). The library has to be compiled as shared library and installed in the system lib directory (normally /lib). The library needs to have a special soname to be found by the NSS module.

If public structures change in a new Berkeley db release, this needs to be reflected in glibc.

Currently the code searches for libraries with a soname of "libdb.so.3" (that's the name from db 2.4.14 which comes with glibc 2.1.x) and "libdb-3.0.so" (the name used by db 3.0.55 as default).

The nss_db module is now in a separate package since it requires a database library being available.

2.32. What has do be done when upgrading to glibc 2.2?

• The utmp daemon has been removed and is not supported by glibc anymore. If it has been in use, it should be switched off.
• Programs using IPv6 have to be recompiled due to incompatible changes in sockaddr_in6 by the IPv6 working group.
• The Berkeley db libraries have been removed (for details see question 2.31).
• The format of the locale files has changed, all locales should be regenerated with localedef. All statically linked applications which use i18n should be recompiled, otherwise they'll not be localized.
• glibc comes with a number of new applications. For example ldconfig has been implemented for glibc, the libc5 version of ldconfig is not needed anymore.
• There's no more K&R compatibility in the glibc headers. The GNU C library requires a C compiler that handles especially prototypes correctly. Especially gcc -traditional will not work with glibc headers.

2.33. The makefiles want to do a CVS commit.

2.34. When compiling C++ programs, I get a compilation error in streambuf.h.

  http://www.haible.de/bruno/gccinclude-glibc-2.2-compat.diff
 

2.35. When recompiling GCC, I get compilation errors in libio.

2.36. Why shall glibc never get installed on GNU/Linux systems in /usr/local?

2.37. When recompiling GCC, I get compilation errors in libstdc++.

  http://www.haible.de/bruno/gcc-3.2-glibc-2.3-compat.diff
 

3. Source and binary incompatibilities, and what to do about them

3.1. I expect GNU libc to be 100% source code compatible with the old Linux based GNU libc. Why isn't it like this?

• _GNU_SOURCE: glibc does not make the GNU extensions available automatically. If a program depends on GNU extensions or some other non-standard functionality, it is necessary to compile it with the C compiler option -D_GNU_SOURCE, or better, to put `#define _GNU_SOURCE' at the beginning of your source files, before any C library header files are included. This difference normally manifests itself in the form of missing prototypes and/or data type definitions. Thus, if you get such errors, the first thing you should do is try defining _GNU_SOURCE and see if that makes the problem go away.

  For more information consult the file `NOTES' in the GNU C library sources.

• reboot(): GNU libc sanitizes the interface of reboot() to be more compatible with the interface used on other OSes. reboot() as implemented in glibc takes just one argument. This argument corresponds to the third argument of the Linux reboot system call. That is, a call of the form reboot(a, b, c) needs to be changed into reboot(c). Beside this the header <sys/reboot.h> defines the needed constants for the argument. These RB_* constants should be used instead of the cryptic magic numbers.

• swapon(): the interface of this function didn't change, but the prototype is in a separate header file <sys/swap.h>. This header file also provides the SWAP_* constants defined by <linux/swap.h>; you should use them for the second argument to swapon().

• errno: If a program uses the variable "errno", then it _must_ include <errno.h>. The old libc often (erroneously) declared this variable implicitly as a side-effect of including other libc header files. glibc is careful to avoid such namespace pollution, which, in turn, means that you really need to include the header files that you depend on. This difference normally manifests itself in the form of the compiler complaining about references to an undeclared symbol "errno".

• Linux-specific syscalls: All Linux system calls now have appropriate library wrappers and corresponding declarations in various header files. This is because the syscall() macro that was traditionally used to work around missing syscall wrappers are inherently non-portable and error-prone. The following table lists all the new syscall stubs, the header-file declaring their interface and the system call name.

         syscall name:	wrapper name:	declaring header file:
          -------------	-------------	----------------------
          bdflush		bdflush		<sys/kdaemon.h>
          syslog		ksyslog_ctl	<sys/klog.h>
   

• lpd: Older versions of lpd depend on a routine called _validuser(). The library does not provide this function, but instead provides __ivaliduser() which has a slightly different interface. Simply upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD lpd is known to be working).

• resolver functions/BIND: like on many other systems the functions of the resolver library are not included in libc itself. There is a separate library libresolv. If you get undefined symbol errors for symbols starting with `res_*' simply add -lresolv to your linker command line.

• the `signal' function's behavior corresponds to the BSD semantic and not the SysV semantic as it was in libc-5. The interface on all GNU systems shall be the same and BSD is the semantic of choice. To use the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE. See question 3.7 for details.

3.2. Why does getlogin() always return NULL on my Linux box?

3.3. Where are the DST_* constants found in <sys/time.h> on many systems?

Instead GNU libc contains zone database support and compatibility code for POSIX TZ environment variable handling. For former is very much preferred (see question 4.3).

3.4. The prototypes for `connect', `accept', `getsockopt', `setsockopt', `getsockname', `getpeername', `send', `sendto', and `recvfrom' are different in GNU libc from any other system I saw. This is a bug, isn't it?

3.5. On Linux I've got problems with the declarations in Linux kernel headers.

For example, the sigset_t type is 32 or 64 bits wide in the kernel. In glibc it is 1024 bits wide. This guarantees that when the kernel gets a bigger sigset_t (for POSIX.1e realtime support, say) user programs will not have to be recompiled. Consult the header files for more information about the changes.

Therefore you shouldn't include Linux kernel header files directly if glibc has defined a replacement. Otherwise you might get undefined results because of type conflicts.

3.6. I don't include any kernel headers myself but the compiler still complains about redeclarations of types in the kernel headers.

There might be some problems left but 2.1.61/2.0.32 fix most of the known ones. See the BUGS file for other known problems.

3.7. Why don't signals interrupt system calls anymore?

There are three differences:

• BSD-style signals that occur in the middle of a system call do not affect the system call; System V signals cause the system call to fail and set errno to EINTR.

• BSD signal handlers remain installed once triggered. System V signal handlers work only once, so one must reinstall them each time.

• A BSD signal is blocked during the execution of its handler. In other words, a handler for SIGCHLD (for example) does not need to worry about being interrupted by another SIGCHLD. It may, however, be interrupted by other signals.

If you are porting an old program that relies on the old semantics, you can quickly fix the problem by changing signal() to sysv_signal() throughout. Alternatively, define _XOPEN_SOURCE before including <signal.h>.

For new programs, the sigaction() function allows you to specify precisely how you want your signals to behave. All three differences listed above are individually switchable on a per-signal basis with this function.

If all you want is for one specific signal to cause system calls to fail and return EINTR (for example, to implement a timeout) you can do this with siginterrupt().

3.8. I've got errors compiling code that uses certain string functions. Why?

The optimized string functions are only used when compiling with optimizations (-O1 or higher). The behavior can be changed with two feature macros:

• __NO_STRING_INLINES: Don't do any string optimizations.
• __USE_STRING_INLINES: Use assembly language inline functions (might increase code size dramatically).

{UD} Another problem in this area is that gcc still has problems on machines with very few registers (e.g., ix86). The inline assembler code can require almost all the registers and the register allocator cannot always handle this situation.

One can disable the string optimizations selectively. Instead of writing

	cp = strcpy (foo, "lkj");
 

one can write

	cp = (strcpy) (foo, "lkj");
 

This disables the optimization for that specific call.

3.9. I get compiler messages "Initializer element not constant" with stdin/stdout/stderr. Why?

   static FILE *InPtr = stdin;
 

lead to this message. This is correct behaviour with glibc since stdin is not a constant expression. Please note that a strict reading of ISO C does not allow above constructs.

One of the advantages of this is that you can assign to stdin, stdout, and stderr just like any other global variable (e.g. `stdout = my_stream;'), which can be very useful with custom streams that you can write with libio (but beware this is not necessarily portable). The reason to implement it this way were versioning problems with the size of the FILE structure.

To fix those programs you've got to initialize the variable at run time. This can be done, e.g. in main, like:

   static FILE *InPtr;
    int main(void)
    {
      InPtr = stdin;
    }
 

or by constructors (beware this is gcc specific):

   static FILE *InPtr;
    static void inPtr_construct (void) __attribute__((constructor));
    static void inPtr_construct (void) { InPtr = stdin; }
 

3.10. I can't compile with gcc -traditional (or -traditional-cpp). Why?

   enum {foo
    #define foo foo
    }
 

are useful for debugging purposes (you can use foo with your debugger that's why we need the enum) and for compatibility (other systems use defines and check with #ifdef).

3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible?

The GNU C library is conforming to ANSI/ISO C - if and only if you're only using the headers and library functions defined in the standard.

3.12. I can't access some functions anymore. nm shows that they do exist but linking fails nevertheless.

3.13. When using the db-2 library which comes with glibc is used in the Perl db modules the testsuite is not passed. This did not happen with db-1, gdbm, or ndbm.

3.14. The pow() inline function I get when including <math.h> is broken. I get segmentation faults when I run the program.

3.15. The sys/sem.h file lacks the definition of `union semun'.

3.16. Why has <netinet/ip_fw.h> disappeared?

3.17. I get floods of warnings when I use -Wconversion and include <string.h> or <math.h>.

-Wconversion isn't really intended for production use, only for shakedown compiles after converting an old program to standard C.

3.18. After upgrading to glibc 2.1, I receive errors about unresolved symbols, like `_dl_initial_searchlist' and can not execute any binaries. What went wrong?

The path /lib/ld-linux.so.2 is hardcoded in every glibc2 binary but libc.so.6 is searched via /etc/ld.so.cache and in some special directories like /lib and /usr/lib. If you run configure with another prefix than /usr and put this prefix before /lib in /etc/ld.so.conf, your system will break.

So what can you do? Either of the following should work:

• Run `configure' with the same prefix argument you've used for glibc 2.0.x so that the same paths are used.
• Replace /lib/ld-linux.so.2 with a link to the dynamic linker from glibc 2.1.

	LD_LIBRARY_PATH=<path-where-libc.so.6-lives> \
 	<path-where-corresponding-dynamic-linker-lives>/ld-linux.so.2 \
 	<path-to-binary>/binary
 

For example `LD_LIBRARY_PATH=/libold /libold/ld-linux.so.2 /bin/mv ...' might be useful in fixing a broken system (if /libold contains dynamic linker and corresponding libc).

With that command line no path is used. To further debug problems with the dynamic linker, use the LD_DEBUG environment variable, e.g. `LD_DEBUG=help echo' for the help text.

If you just want to test this release, don't put the lib directory in /etc/ld.so.conf. You can call programs directly with full paths (as above). When compiling new programs against glibc 2.1, you've got to specify the correct paths to the compiler (option -I with gcc) and linker (options --dynamic-linker, -L and --rpath).

3.19. bonnie reports that char i/o with glibc 2 is much slower than with libc5. What can be done?

3.20. Programs compiled with glibc 2.1 can't read db files made with glibc 2.0. What has changed that programs like rpm break?

3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but when I try to use it, it always returns -1 and sets errno to ENOSYS.

Your program should check at runtime whether the function works, and implement a fallback. Note that Autoconf cannot detect unimplemented functions in other systems' C libraries, so you need to do this anyway.

3.22. My program segfaults when I call fclose() on the FILE* returned from setmntent(). Is this a glibc bug?

In general, you should use the correct deallocation routine. For instance, if you open a file using fopen(), you should deallocate the FILE * using fclose(), not free(), even though the FILE * is also a pointer.

In the case of setmntent(), it may appear to work in most cases, but it won't always work. Unfortunately, for compatibility reasons, we can't change the return type of setmntent() to something other than FILE *.

3.23. I get "undefined reference to `atexit'"

If a similar message is issued at runtime this means that the application or DSO is not linked against libc. This can cause problems since 'atexit' is not exported anymore.

4. Miscellaneous

4.1. After I changed configure.in I get `Autoconf version X.Y. or higher is required for this script'. What can I do?

4.2. When I try to compile code which uses IPv6 headers and definitions on my Linux 2.x.y system I am in trouble. Nothing seems to work.

{PB} The 2.1 release of GNU libc aims to comply with the current versions of all the relevant standards. The IPv6 support libraries for older Linux systems used a different naming convention and so code written to work with them may need to be modified. If the standards make incompatible changes in the future then the libc may need to change again.

IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it should contain all the necessary support; until then you should use the latest 2.1.x release you can find. As of 98/11/26 the currently recommended kernel for IPv6 is 2.1.129.

Also, as of the 2.1 release the IPv6 API provided by GNU libc is not 100% complete.

4.3. When I set the timezone by setting the TZ environment variable to EST5EDT things go wrong since glibc computes the wrong time from this information.

The alternative approach to handle timezones which is implemented is the correct one to use: use the timezone database. This avoids all the problems the POSIX method has plus it is much easier to use. Simply run the tzselect shell script, answer the question and use the name printed in the end by making a symlink /etc/localtime pointing to /usr/share/zoneinfo/NAME (NAME is the returned value from tzselect). That's all. You never again have to worry.

So, please avoid sending bug reports about time related problems if you use the POSIX method and you have not verified something is really broken by reading the POSIX standards.

4.4. What other sources of documentation about glibc are available?

Please note that this is not a complete list.

4.5. The timezone string for Sydney/Australia is wrong since even when daylight saving time is in effect the timezone string is EST.

	Eastern Standard Time	= EST
 	Eastern Summer Time	= EST
 

Great! To get this bug fixed convince the authorities to change the laws and regulations of the country this effects. glibc behaves correctly.

4.6. I've build make 3.77 against glibc 2.1 and now make gets segmentation faults.

4.7. Why do so many programs using math functions fail on my AlphaStation?

4.8. The conversion table for character set XX does not match with what I expect.

Before doing this look through the list of known problem first:

• the GBK (simplified Chinese) encoding is based on Unicode tables. This is good. These tables, however, differ slightly from the tables used by the M$ people. The differences are these [+ Unicode, - M$]:

      +0xA1AA 0x2015
       +0xA844 0x2014
       -0xA1AA 0x2014
       -0xA844 0x2015
   

  In addition the Unicode tables contain mappings for the GBK characters 0xA8BC, 0xA8BF, 0xA989 to 0xA995, and 0xFE50 to 0xFEA0.

• when mapping from EUC-CN to GBK and vice versa we ignore the fact that the coded character at position 0xA1A4 maps to different Unicode characters. Since the iconv() implementation can do whatever it wants if it cannot directly map a character this is a perfectly good solution since the semantics and appearance of the character does not change.

4.9. How can I find out which version of glibc I am using in the moment?

	/lib/libc.so.6
 

This will produce all the information you need.

What always will work is to use the API glibc provides. Compile and run the following little program to get the version information:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 #include <stdio.h>
 #include <gnu/libc-version.h>
 int main (void) { puts (gnu_get_libc_version ()); return 0; }
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

This interface can also obviously be used to perform tests at runtime if this should be necessary.

4.10. Context switching with setcontext() does not work from within signal handlers.

• UNIX provides no other (portable) way of effecting a synchronous context switch (also known as co-routine switch). Some versions support this via setjmp()/longjmp() but this does not work universally.

• As defined by the UNIX '98 standard, the only way setcontext() could trigger an asychronous context switch is if this function were invoked on the ucontext_t pointer passed as the third argument to a signal handler. But according to draft 5, XPG6, XBD 2.4.3, setcontext() is not among the set of routines that may be called from a signal handler.

• If setcontext() were to be used for asynchronous context switches, all kinds of synchronization and re-entrancy issues could arise and these problems have already been solved by real multi-threading libraries (e.g., POSIX threads or Linux threads).

• Synchronous context switching can be implemented entirely in user-level and less state needs to be saved/restored than for an asynchronous context switch. It is therefore useful to distinguish between the two types of context switches. Indeed, some application vendors are known to use setcontext() to implement co-routines on top of normal (heavier-weight) pre-emptable threads.

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