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,
17 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
21 1.1. What systems does the GNU C Library run on?
22 1.2. What compiler do I need to build GNU libc?
23 1.3. When I try to compile glibc I get only error messages.
25 1.4. Do I need a special linker or assembler?
26 1.5. Which compiler should I use for powerpc?
27 1.6. Which tools should I use for ARM?
28 1.7. Do I need some more things to compile the GNU C Library?
29 1.8. What version of the Linux kernel headers should be used?
30 1.9. The compiler hangs while building iconvdata modules. What's
32 1.10. When I run `nm -u libc.so' on the produced library I still
33 find unresolved symbols. Can this be ok?
34 1.11. What are these `add-ons'?
35 1.12. My XXX kernel emulates a floating-point coprocessor for me.
36 Should I enable --with-fp?
37 1.13. When compiling GNU libc I get lots of errors saying functions
38 in glibc are duplicated in libgcc.
39 1.14. Why do I get messages about missing thread functions when I use
40 librt? I don't even use threads.
41 1.15. What's the problem with configure --enable-omitfp?
42 1.16. I get failures during `make check'. What shall I do?
43 1.17. What is symbol versioning good for? Do I need it?
45 2. Installation and configuration issues
47 2.1. Can I replace the libc on my Linux system with GNU libc?
48 2.2. How do I configure GNU libc so that the essential libraries
49 like libc.so go into /lib and the other into /usr/lib?
50 2.3. How should I avoid damaging my system when I install GNU libc?
51 2.4. Do I need to use GNU CC to compile programs that will use the
53 2.5. When linking with the new libc I get unresolved symbols
54 `crypt' and `setkey'. Why aren't these functions in the
56 2.6. When I use GNU libc on my Linux system by linking against
57 the libc.so which comes with glibc all I get is a core dump.
58 2.7. Looking through the shared libc file I haven't found the
59 functions `stat', `lstat', `fstat', and `mknod' and while
60 linking on my Linux system I get error messages. How is
61 this supposed to work?
62 2.8. When I run an executable on one system which I compiled on
63 another, I get dynamic linker errors. Both systems have the same
64 version of glibc installed. What's wrong?
65 2.9. How can I compile gcc 2.7.2.1 from the gcc source code using
67 2.10. The `gencat' utility cannot process the catalog sources which
68 were used on my Linux libc5 based system. Why?
69 2.11. Programs using libc have their messages translated, but other
70 behavior is not localized (e.g. collating order); why?
71 2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS
72 works great. But the glibc NIS+ doesn't seem to work.
73 2.13. I have killed ypbind to stop using NIS, but glibc
75 2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call:
76 RPC: Unable to receive; errno = Connection refused" when using NIS.
77 2.15. After installing glibc name resolving doesn't work properly.
78 2.16. How do I create the databases for NSS?
79 2.17. I have /usr/include/net and /usr/include/scsi as symlinks
80 into my Linux source tree. Is that wrong?
81 2.18. Programs like `logname', `top', `uptime' `users', `w' and
82 `who', show incorrect information about the (number of)
83 users on my system. Why?
84 2.19. After upgrading to glibc 2.1 with symbol versioning I get
85 errors about undefined symbols. What went wrong?
86 2.20. When I start the program XXX after upgrading the library
88 XXX: Symbol `_sys_errlist' has different size in shared
89 object, consider re-linking
90 Why? What should I do?
91 2.21. What do I need for C++ development?
92 2.22. Even statically linked programs need some shared libraries
93 which is not acceptable for me. What can I do?
94 2.23. I just upgraded my Linux system to glibc and now I get
95 errors whenever I try to link any program.
96 2.24. When I use nscd the machine freezes.
97 2.25. I need lots of open files. What do I have to do?
99 3. Source and binary incompatibilities, and what to do about them
101 3.1. I expect GNU libc to be 100% source code compatible with
102 the old Linux based GNU libc. Why isn't it like this?
103 3.2. Why does getlogin() always return NULL on my Linux box?
104 3.3. Where are the DST_* constants found in <sys/time.h> on many
106 3.4. The prototypes for `connect', `accept', `getsockopt',
107 `setsockopt', `getsockname', `getpeername', `send',
108 `sendto', and `recvfrom' are different in GNU libc from
109 any other system I saw. This is a bug, isn't it?
110 3.5. On Linux I've got problems with the declarations in Linux
112 3.6. I don't include any kernel headers myself but the compiler
113 still complains about redeclarations of types in the kernel
115 3.7. Why don't signals interrupt system calls anymore?
116 3.8. I've got errors compiling code that uses certain string
118 3.9. I get compiler messages "Initializer element not constant" with
119 stdin/stdout/stderr. Why?
120 3.10. I can't compile with gcc -traditional (or
121 -traditional-cpp). Why?
122 3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible?
123 3.12. I can't access some functions anymore. nm shows that they do
124 exist but linking fails nevertheless.
125 3.13. When using the db-2 library which comes with glibc is used in
126 the Perl db modules the testsuite is not passed. This did not
127 happen with db-1, gdbm, or ndbm.
128 3.14. The pow() inline function I get when including <math.h> is broken.
129 I get segmentation faults when I run the program.
130 3.15. The sys/sem.h file lacks the definition of `union semun'.
131 3.16. Why has <netinet/ip_fw.h> disappeared?
132 3.17. I get floods of warnings when I use -Wconversion and include
133 <string.h> or <math.h>.
137 4.1. After I changed configure.in I get `Autoconf version X.Y.
138 or higher is required for this script'. What can I do?
139 4.2. When I try to compile code which uses IPv6 headers and
140 definitions on my Linux 2.x.y system I am in trouble.
141 Nothing seems to work.
142 4.3. When I set the timezone by setting the TZ environment variable
143 to EST5EDT things go wrong since glibc computes the wrong time
144 from this information.
145 4.4. What other sources of documentation about glibc are available?
146 4.5. The timezone string for Sydney/Australia is wrong since even when
147 daylight saving time is in effect the timezone string is EST.
150 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
154 1.1. What systems does the GNU C Library run on?
156 {UD} This is difficult to answer. The file `README' lists the architectures
157 GNU libc was known to run on *at some time*. This does not mean that it
158 still can be compiled and run on them now.
160 The systems glibc is known to work on as of this release, and most probably
164 i[3456]86-*-linux-gnu Linux-2.x on Intel
165 m68k-*-linux-gnu Linux-2.x on Motorola 680x0
166 alpha-*-linux-gnu Linux-2.x on DEC Alpha
167 powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems
168 sparc-*-linux-gnu Linux-2.x on SPARC
169 sparc64-*-linux-gnu Linux-2.x on UltraSPARC
170 arm-*-none ARM standalone systems
171 arm-*-linux Linux-2.x on ARM
172 arm-*-linuxaout Linux-2.x on ARM using a.out binaries
174 Ports to other Linux platforms are in development, and may in fact work
175 already, but no one has sent us success reports for them. Currently no
176 ports to other operating systems are underway, although a few people have
179 If you have a system not listed above (or in the `README' file) and you are
180 really interested in porting it, contact
185 1.2. What compiler do I need to build GNU libc?
187 {UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC
188 are used to increase portability and speed.
190 GNU CC is found, like all other GNU packages, on
192 ftp://ftp.gnu.org/pub/gnu
194 and the many mirror sites. ftp.gnu.org is always overloaded, so try to find
195 a local mirror first.
197 You should always try to use the latest official release. Older versions
198 may not have all the features GNU libc requires. The current releases of
199 egcs (1.0.3 and 1.1) and GNU CC (2.8.1) should work with the GNU C library
200 (for powerpc see question question 1.5; for ARM see question question 1.6).
202 {ZW} You may have problems if you try to mix code compiled with
203 EGCS and with GCC 2.8.1. See question 2.8 for details.
206 1.3. When I try to compile glibc I get only error messages.
209 {UD} You definitely need GNU make to translate GNU libc. No other make
210 program has the needed functionality.
212 We recommend version GNU make version 3.75 or 3.77. Versions before 3.75
213 have bugs and/or are missing features. Version 3.76 has bugs which
214 appear when building big projects like GNU libc. 3.76.1 appears to work but
215 some people have reported problems.
218 1.4. Do I need a special linker or assembler?
220 {ZW} If you want a shared library, you need a linker and assembler that
221 understand all the features of ELF, including weak and versioned symbols.
222 The static library can be compiled with less featureful tools, but lacks key
223 features such as NSS.
225 For Linux or Hurd, you want binutils 2.8.1.0.23, 2.9.1, or 2.9.1.0.15 or
226 higher. These are the only versions we've tested and found reliable. Other
227 versions after 2.8.1.0.23 may work but we don't recommend them, especially
228 not when C++ is involved. Earlier versions do not work at all.
230 Other operating systems may come with system tools that have all the
231 necessary features, but this is moot because glibc hasn't been ported to
235 1.5. Which compiler should I use for powerpc?
237 {GK} You want to use egcs 1.1 or later (together with the right versions
238 of all the other tools, of course).
240 In fact, egcs 1.1 has a bug that causes linuxthreads to be
241 miscompiled, resulting in segmentation faults when using condition
242 variables. There is a temporary patch at:
244 <http://discus.anu.edu.au/~geoffk/egcs-3.diff>
246 Later versions of egcs may fix this problem.
249 1.6. Which tools should I use for ARM?
251 {PB} You should use egcs 1.1 or a later version. For ELF systems some
252 changes are needed to the compiler; a patch against egcs-1.1.x can be found
255 <ftp://ftp.netwinder.org/users/p/philb/egcs-1.1.1pre2-diff-981126>
257 Binutils 2.9.1.0.16 or later is also required.
260 1.7. Do I need some more things to compile the GNU C Library?
262 {UD} Yes, there are some more :-).
264 * GNU gettext. This package contains the tools needed to construct
265 `message catalog' files containing translated versions of system
266 messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror
267 site. (We distribute compiled message catalogs, but they may not be
270 * Some files are built with special tools. E.g., files ending in .gperf
271 need a `gperf' program. The GNU version (now available in a separate
272 package, formerly only as part of libg++) is known to work while some
273 vendor versions do not.
275 You should not need these tools unless you change the source files.
277 * Perl 5 is needed if you wish to test an installation of GNU libc
278 as the primary C library.
280 * When compiling for Linux, the header files of the Linux kernel must
281 be available to the compiler as <linux/*.h> and <asm/*.h>.
283 * lots of disk space (~170MB for i?86-linux; more for RISC platforms,
286 * plenty of time. Compiling just the shared and static libraries for
287 i?86-linux takes approximately 1h on an i586@133, or 2.5h on
288 i486@66, or 4.5h on i486@33. Multiply this by 1.5 or 2.0 if you
289 build profiling and/or the highly optimized version as well. For
290 Hurd systems times are much higher.
292 You should avoid compiling in a NFS mounted filesystem. This is
295 James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time of
296 45h34m for a full build (shared, static, and profiled) on Atari
297 Falcon (Motorola 68030 @ 16 Mhz, 14 Mb memory) and Jan Barte
298 <yann@plato.uni-paderborn.de> reports 22h48m on Atari TT030
299 (Motorola 68030 @ 32 Mhz, 34 Mb memory)
301 If you have some more measurements let me know.
304 1.8. What version of the Linux kernel headers should be used?
306 {AJ,UD} The headers from the most recent Linux kernel should be used. The
307 headers used while compiling the GNU C library and the kernel binary used
308 when using the library do not need to match. The GNU C library runs without
309 problems on kernels that are older than the kernel headers used. The other
310 way round (compiling the GNU C library with old kernel headers and running
311 on a recent kernel) does not necessarily work. For example you can't use
312 new kernel features when using old kernel headers for compiling the GNU C
315 {ZW} Even if you are using a 2.0 kernel on your machine, we recommend you
316 compile GNU libc with 2.1 kernel headers. That way you won't have to
317 recompile libc if you ever upgrade to kernel 2.1 or 2.2. To tell libc which
318 headers to use, give configure the --with-headers switch
319 (e.g. --with-headers=/usr/src/linux-2.1.107/include).
321 Note that you must configure the 2.1 kernel if you do this, otherwise libc
322 will be unable to find <linux/version.h>. Just change the current directory
323 to the root of the 2.1 tree and do `make include/linux/version.h'.
326 1.9. The compiler hangs while building iconvdata modules. What's
329 {ZW} This is a problem with old versions of GCC. Initialization of large
330 static arrays is very slow. The compiler will eventually finish; give it
333 The problem is fixed in egcs 1.1 but not in earlier releases.
336 1.10. When I run `nm -u libc.so' on the produced library I still
337 find unresolved symbols. Can this be ok?
339 {UD} Yes, this is ok. There can be several kinds of unresolved symbols:
341 * magic symbols automatically generated by the linker. These have names
342 like __start_* and __stop_*
344 * symbols starting with _dl_* come from the dynamic linker
346 * weak symbols, which need not be resolved at all (fabs for example)
348 Generally, you should make sure you find a real program which produces
349 errors while linking before deciding there is a problem.
352 1.11. What are these `add-ons'?
354 {UD} To avoid complications with export rules or external source code some
355 optional parts of the libc are distributed as separate packages (e.g., the
356 crypt package, see question 2.5).
358 To use these packages as part of GNU libc, just unpack the tarfiles in the
359 libc source directory and tell the configuration script about them using the
360 --enable-add-ons option. If you give just --enable-add-ons configure tries
361 to find all the add-on packages in your source tree. This may not work. If
362 it doesn't, or if you want to select only a subset of the add-ons, give a
363 comma-separated list of the add-ons to enable:
365 configure --enable-add-ons=crypt,linuxthreads
369 Add-ons can add features (including entirely new shared libraries), override
370 files, provide support for additional architectures, and just about anything
371 else. The existing makefiles do most of the work; only some few stub rules
372 must be written to get everything running.
375 1.12. My XXX kernel emulates a floating-point coprocessor for me.
376 Should I enable --with-fp?
378 {ZW} An emulated FPU is just as good as a real one, as far as the C library
379 is concerned. You only need to say --without-fp if your machine has no way
380 to execute floating-point instructions.
382 People who are interested in squeezing the last drop of performance
383 out of their machine may wish to avoid the trap overhead, but this is
384 far more trouble than it's worth: you then have to compile
385 *everything* this way, including the compiler's internal libraries
386 (libgcc.a for GNU C), because the calling conventions change.
389 1.13. When compiling GNU libc I get lots of errors saying functions
390 in glibc are duplicated in libgcc.
392 {EY} This is *exactly* the same problem that I was having. The problem was
393 due to the fact that configure didn't correctly detect that the linker flag
394 --no-whole-archive was supported in my linker. In my case it was because I
395 had run ./configure with bogus CFLAGS, and the test failed.
397 One thing that is particularly annoying about this problem is that once this
398 is misdetected, running configure again won't fix it unless you first delete
401 {UD} Starting with glibc-2.0.3 there should be a better test to avoid some
402 problems of this kind. The setting of CFLAGS is checked at the very
403 beginning and if it is not usable `configure' will bark.
406 1.14. Why do I get messages about missing thread functions when I use
407 librt? I don't even use threads.
409 {UD} In this case you probably mixed up your installation. librt uses
410 threads internally and has implicit references to the thread library.
411 Normally these references are satisfied automatically but if the thread
412 library is not in the expected place you must tell the linker where it is.
413 When using GNU ld it works like this:
415 gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt
417 The `/some/other/dir' should contain the thread library. `ld' will use the
418 given path to find the implicitly referenced library while not disturbing
422 1.15. What's the problem with configure --enable-omitfp?
424 {AJ} When --enable-omitfp is set the libraries are built without frame
425 pointers. Some compilers produce buggy code for this model and therefore we
426 don't advise using it at the moment.
428 If you use --enable-omitfp, you're on your own. If you encounter problems
429 with a library that was build this way, we advise you to rebuild the library
430 without --enable-omitfp. If the problem vanishes consider tracking the
431 problem down and report it as compiler failure.
433 Since a library build with --enable-omitfp is undebuggable on most systems,
434 debuggable libraries are also built - you can use it by appending "_g" to
437 The compilation of these extra libraries and the compiler optimizations slow
438 down the build process and need more disk space.
441 1.16. I get failures during `make check'. What shall I do?
443 {AJ} The testsuite should compile and run cleanly on your system, every
444 failure should be looked into. Depending on the failure I wouldn't advise
445 installing the library at all.
447 You should consider using the `glibcbug' script to report the failure,
448 providing as much detail as possible. If you run a test directly, please
449 remember to set up the environment correctly. You want to test the compiled
450 library - and not your installed one. The best way is to copy the exact
451 command line which failed and run the test from the subdirectory for this
454 There are some failures which are not directly related to the GNU libc:
455 - Some compiler produce buggy code. The egcs 1.1 release should be ok. gcc
456 2.8.1 might cause some failures, gcc 2.7.2.x is so buggy, that explicit
457 checks have been used so that you can't build with it.
458 - The kernel might have bugs. For example on Linux/Alpha 2.0.34 the
459 floating point handling has quite a number of bugs and therefore most of
460 the test cases in the math subdirectory will fail. The current Linux 2.1
461 development kernels have fixes for the floating point support on Alpha.
464 1.17. What is symbol versioning good for? Do I need it?
466 {AJ} Symbol versioning solves problems that are related to interface
467 changes. One version of an interface might have been introduced in a
468 previous version of the GNU C library but the interface or the semantics of
469 the function has been changed in the meantime. For binary compatibility
470 with the old library, a newer library needs to still have the old interface
471 for old programs. On the other hand new programs should use the new
472 interface. Symbol versioning is the solution for this problem. The GNU
473 libc version 2.1 uses by default symbol versioning if the binutils support
476 We don't advise to build without symbol versioning since you lose binary
477 compatibility if you do - for ever! The binary compatibility you lose is
478 not only against the previous version of the GNU libc (version 2.0) but also
479 against future versions.
482 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
484 2. Installation and configuration issues
486 2.1. Can I replace the libc on my Linux system with GNU libc?
488 {UD} You cannot replace any existing libc for Linux with GNU libc. It is
489 binary incompatible and therefore has a different major version. You can,
490 however, install it alongside your existing libc.
492 For Linux there are three major libc versions:
494 libc-5 original ELF libc
497 You can have any combination of these three installed. For more information
498 consult documentation for shared library handling. The Makefiles of GNU
499 libc will automatically generate the needed symbolic links which the linker
503 2.2. How do I configure GNU libc so that the essential libraries
504 like libc.so go into /lib and the other into /usr/lib?
506 {UD,AJ} Like all other GNU packages GNU libc is designed to use a base
507 directory and install all files relative to this. The default is
508 /usr/local, because this is safe (it will not damage the system if installed
509 there). If you wish to install GNU libc as the primary C library on your
510 system, set the base directory to /usr (i.e. run configure --prefix=/usr
511 <other_options>). Note that this can damage your system; see question 2.3 for
514 Some systems like Linux have a filesystem standard which makes a difference
515 between essential libraries and others. Essential libraries are placed in
516 /lib because this directory is required to be located on the same disk
517 partition as /. The /usr subtree might be found on another
518 partition/disk. If you configure for Linux with --prefix=/usr, then this
519 will be done automatically.
521 To install the essential libraries which come with GNU libc in /lib on
522 systems other than Linux one must explicitly request it. Autoconf has no
523 option for this so you have to use a `configparms' file (see the `INSTALL'
524 file for details). It should contain:
529 The first line specifies the directory for the essential libraries, the
530 second line the directory for system configuration files.
533 2.3. How should I avoid damaging my system when I install GNU libc?
535 {ZW} If you wish to be cautious, do not configure with --prefix=/usr. If
536 you don't specify a prefix, glibc will be installed in /usr/local, where it
537 will probably not break anything. (If you wish to be certain, set the
538 prefix to something like /usr/local/glibc2 which is not used for anything.)
540 The dangers when installing glibc in /usr are twofold:
542 * glibc will overwrite the headers in /usr/include. Other C libraries
543 install a different but overlapping set of headers there, so the
544 effect will probably be that you can't compile anything. You need to
545 rename /usr/include out of the way first. (Do not throw it away; you
546 will then lose the ability to compile programs against your old libc.)
548 * None of your old libraries, static or shared, can be used with a
549 different C library major version. For shared libraries this is not a
550 problem, because the filenames are different and the dynamic linker
551 will enforce the restriction. But static libraries have no version
552 information. You have to evacuate all the static libraries in
553 /usr/lib to a safe location.
555 The situation is rather similar to the move from a.out to ELF which
556 long-time Linux users will remember.
559 2.4. Do I need to use GNU CC to compile programs that will use the
562 {ZW} In theory, no; the linker does not care, and the headers are supposed
563 to check for GNU CC before using its extensions to the C language.
565 However, there are currently no ports of glibc to systems where another
566 compiler is the default, so no one has tested the headers extensively
567 against another compiler. You may therefore encounter difficulties. If you
568 do, please report them as bugs.
570 Also, in several places GNU extensions provide large benefits in code
571 quality. For example, the library has hand-optimized, inline assembly
572 versions of some string functions. These can only be used with GCC. See
573 question 3.8 for details.
576 2.5. When linking with the new libc I get unresolved symbols
577 `crypt' and `setkey'. Why aren't these functions in the
580 {UD} The US places restrictions on exporting cryptographic programs and
581 source code. Until this law gets abolished we cannot ship the cryptographic
582 functions together with glibc.
584 The functions are available, as an add-on (see question 1.11). People in the US
585 may get it from the same place they got GNU libc from. People outside the
586 US should get the code from ftp://ftp.ifi.uio.no/pub/gnu, or another archive
587 site outside the USA. The README explains how to install the sources.
589 If you already have the crypt code on your system the reason for the failure
590 is probably that you did not link with -lcrypt. The crypto functions are in
591 a separate library to make it possible to export GNU libc binaries from the
595 2.6. When I use GNU libc on my Linux system by linking against
596 the libc.so which comes with glibc all I get is a core dump.
598 {UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the
599 user specifies a -dynamic-linker argument. This is the name of the libc5
600 dynamic linker, which does not work with glibc.
602 For casual use of GNU libc you can just specify to the linker
603 --dynamic-linker=/lib/ld-linux.so.2
605 which is the glibc dynamic linker, on Linux systems. On other systems the
606 name is /lib/ld.so.1. When linking via gcc, you've got to add
607 -Wl,--dynamic-linker=/lib/ld-linux.so.2
609 to the gcc command line.
611 To change your environment to use GNU libc for compiling you need to change
612 the `specs' file of your gcc. This file is normally found at
614 /usr/lib/gcc-lib/<arch>/<version>/specs
616 In this file you have to change a few things:
618 - change `ld-linux.so.1' to `ld-linux.so.2'
620 - remove all expression `%{...:-lgmon}'; there is no libgmon in glibc
622 - fix a minor bug by changing %{pipe:-} to %|
624 Here is what the gcc-2.7.2 specs file should look like when GNU libc is
627 -----------------------------------------------------------------------
629 %{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*}
635 %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}
644 %{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s
647 -m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}}
650 %{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}}
656 %{!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}
658 *switches_need_spaces:
662 %{funsigned-char:-D__CHAR_UNSIGNED__}
665 -D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386)
673 -----------------------------------------------------------------------
675 Things get a bit more complicated if you have GNU libc installed in some
676 other place than /usr, i.e., if you do not want to use it instead of the old
677 libc. In this case the needed startup files and libraries are not found in
678 the regular places. So the specs file must tell the compiler and linker
681 Version 2.7.2.3 does and future versions of GCC will automatically
682 provide the correct specs.
685 2.7. Looking through the shared libc file I haven't found the
686 functions `stat', `lstat', `fstat', and `mknod' and while
687 linking on my Linux system I get error messages. How is
688 this supposed to work?
690 {RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed
691 to be undefined references in libc.so.6! Your problem is probably a missing
692 or incorrect /usr/lib/libc.so file; note that this is a small text file now,
693 not a symlink to libc.so.6. It should look something like this:
695 GROUP ( libc.so.6 libc_nonshared.a )
698 2.8. When I run an executable on one system which I compiled on
699 another, I get dynamic linker errors. Both systems have the same
700 version of glibc installed. What's wrong?
702 {ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the
703 other with egcs (any version). Egcs has functions in its internal
704 `libgcc.a' to support exception handling with C++. They are linked into
705 any program or dynamic library compiled with egcs, whether it needs them or
706 not. Dynamic libraries then turn around and export those functions again
707 unless special steps are taken to prevent them.
709 When you link your program, it resolves its references to the exception
710 functions to the ones exported accidentally by libc.so. That works fine as
711 long as libc has those functions. On the other system, libc doesn't have
712 those functions because it was compiled by gcc 2.8, and you get undefined
713 symbol errors. The symbols in question are named things like
714 `__register_frame_info'.
716 For glibc 2.0, the workaround is to not compile libc with egcs. We've also
717 incorporated a patch which should prevent the EH functions sneaking into
718 libc. It doesn't matter what compiler you use to compile your program.
720 For glibc 2.1, we've chosen to do it the other way around: libc.so
721 explicitly provides the EH functions. This is to prevent other shared
722 libraries from doing it. You must therefore compile glibc 2.1 with EGCS
723 unless you don't care about ever importing binaries from other systems.
724 Again, it doesn't matter what compiler you use for your programs.
727 2.9. How can I compile gcc 2.7.2.1 from the gcc source code using
730 {AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later.
731 But you should get at least gcc 2.8.1 or egcs 1.0.2 (or later versions)
735 2.10. The `gencat' utility cannot process the catalog sources which
736 were used on my Linux libc5 based system. Why?
738 {UD} The `gencat' utility provided with glibc complies to the XPG standard.
739 The older Linux version did not obey the standard, so they are not
742 To ease the transition from the Linux version some of the non-standard
743 features are also present in the `gencat' program of GNU libc. This mainly
744 includes the use of symbols for the message number and the automatic
745 generation of header files which contain the needed #defines to map the
748 Here is a simple SED script to convert at least some Linux specific catalog
749 files to the XPG4 form:
751 -----------------------------------------------------------------------
752 # Change catalog source in Linux specific format to standard XPG format.
753 # Ulrich Drepper <drepper@cygnus.com>, 1996.
757 s/\$ #\([^ ]*\).*/\1/
759 s/\$ #[^ ]* *\(.*\)/\$ \1/
765 s/\(.*\)\n\(.*\)/\2 \1/
767 -----------------------------------------------------------------------
770 2.11. Programs using libc have their messages translated, but other
771 behavior is not localized (e.g. collating order); why?
773 {ZW} Translated messages are automatically installed, but the locale
774 database that controls other behaviors is not. You need to run localedef to
775 install this database, after you have run `make install'. For example, to
776 set up the French Canadian locale, simply issue the command
778 localedef -i fr_CA -f ISO-8859-1 fr_CA
780 Please see localedata/README in the source tree for further details.
783 2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS
784 works great. But the glibc NIS+ doesn't seem to work.
786 {TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for
787 storing information about the NIS+ server and their public keys, because the
788 nis.conf file does not contain all the necessary information. You have to
789 copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is
790 byte order independent) or generate it with nisinit from the nis-tools
791 package; available at
793 http://www-vt.uni-paderborn.de/~kukuk/linux/nisplus.html
796 2.13. I have killed ypbind to stop using NIS, but glibc
799 {TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from
800 ypbind. ypbind 3.3 and older versions don't always remove these files, so
801 glibc will continue to use them. Other BSD versions seem to work correctly.
802 Until ypbind 3.4 is released, you can find a patch at
804 ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz
807 2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call:
808 RPC: Unable to receive; errno = Connection refused" when using NIS.
810 {TK} You need a ypbind version which is 64bit clean. Some versions are not
811 64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3,
812 you need the patch from ftp.kernel.org (See the previous question). I don't
813 know about other versions.
816 2.15. After installing glibc name resolving doesn't work properly.
818 {AJ} You probably should read the manual section describing nsswitch.conf
819 (just type `info libc "NSS Configuration File"'). The NSS configuration
820 file is usually the culprit.
823 2.16. How do I create the databases for NSS?
825 {AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create
826 the database files. The glibc sources contain a Makefile which does the
827 necessary conversion and calls to create those files. The file is
828 `db-Makefile' in the subdirectory `nss' and you can call it with `make -f
829 db-Makefile'. Please note that not all services are capable of using a
830 database. Currently passwd, group, ethers, protocol, rpc, services shadow
831 and netgroup are implemented.
834 2.17. I have /usr/include/net and /usr/include/scsi as symlinks
835 into my Linux source tree. Is that wrong?
837 {PB} This was necessary for libc5, but is not correct when using glibc.
838 Including the kernel header files directly in user programs usually does not
839 work (see question 3.5). glibc provides its own <net/*> and <scsi/*> header
840 files to replace them, and you may have to remove any symlink that you have
841 in place before you install glibc. However, /usr/include/asm and
842 /usr/include/linux should remain as they were.
845 2.18. Programs like `logname', `top', `uptime' `users', `w' and
846 `who', show incorrect information about the (number of)
847 users on my system. Why?
849 {MK} See question 3.2.
852 2.19. After upgrading to glibc 2.1 with symbol versioning I get
853 errors about undefined symbols. What went wrong?
855 {AJ} The problem is caused either by wrong program code or tools. In the
856 versioned libc a lot of symbols are now local that were global symbols in
857 previous versions. It seems that programs linked against older versions
858 often accidentally used libc global variables -- something that should not
861 The only way to fix this is to recompile your program. Sorry, that's the
862 price you might have to pay once for quite a number of advantages with
866 2.20. When I start the program XXX after upgrading the library
868 XXX: Symbol `_sys_errlist' has different size in shared
869 object, consider re-linking
870 Why? What should I do?
872 {UD} As the message says, relink the binary. The problem is that a few
873 symbols from the library can change in size and there is no way to avoid
874 this. _sys_errlist is a good example. Occasionally there are new error
875 numbers added to the kernel and this must be reflected at user level,
876 breaking programs that refer to them directly.
878 Such symbols should normally not be used at all. There are mechanisms to
879 avoid using them. In the case of _sys_errlist, there is the strerror()
880 function which should _always_ be used instead. So the correct fix is to
881 rewrite that part of the application.
883 In some situations (especially when testing a new library release) it might
884 be possible that a symbol changed size when that should not have happened.
885 So in case of doubt report such a warning message as a problem.
888 2.21. What do I need for C++ development?
890 {HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or
891 gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++
892 support and works directly with glibc 2.1. If you use gcc-2.8.1 with
893 libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available
895 ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz
897 Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work
898 very well with the GNU C library due to vtable thunks. If you're upgrading
899 from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library
900 compiled for 2.0 is not compatible due to the new Large File Support (LFS)
903 {UD} But since in the case of a shared libstdc++ the version numbers should
904 be different existing programs will continue to work.
907 2.22. Even statically linked programs need some shared libraries
908 which is not acceptable for me. What can I do?
910 {AJ} NSS (for details just type `info libc "Name Service Switch"') won't
911 work properly without shared libraries. NSS allows using different services
912 (e.g. NIS, files, db, hesiod) by just changing one configuration file
913 (/etc/nsswitch.conf) without relinking any programs. The only disadvantage
914 is that now static libraries need to access shared libraries. This is
915 handled transparently by the GNU C library.
917 A solution is to configure glibc with --enable-static-nss. In this case you
918 can create a static binary that will use only the services dns and files
919 (change /etc/nsswitch.conf for this). You need to link explicitly against
920 all these services. For example:
922 gcc -static test-netdb.c -o test-netdb.c \
923 -lc -lnss_files -lnss_dns -lresolv
925 The problem with this approach is that you've got to link every static
926 program that uses NSS routines with all those libraries.
928 {UD} In fact, one cannot say anymore that a libc compiled with this
929 option is using NSS. There is no switch anymore. Therefore it is
930 *highly* recommended *not* to use --enable-static-nss since this makes
931 the behaviour of the programs on the system inconsistent.
934 2.23. I just upgraded my Linux system to glibc and now I get
935 errors whenever I try to link any program.
937 {ZW} This happens when you have installed glibc as the primary C library but
938 have stray symbolic links pointing at your old C library. If the first
939 `libc.so' the linker finds is libc 5, it will use that. Your program
940 expects to be linked with glibc, so the link fails.
942 The most common case is that glibc put its `libc.so' in /usr/lib, but there
943 was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the
944 problem, just delete /lib/libc.so. You may also need to delete other
945 symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5.
947 {AJ} The perl script test-installation.pl which is run as last step during
948 an installation of glibc that is configured with --prefix=/usr should help
949 detect these situations. If the script reports problems, something is
953 2.24. When I use nscd the machine freezes.
955 {UD} You cannot use nscd with Linux 2.0.*. There is functionality missing
956 in the kernel and work-arounds are not suitable. Besides, some parts of the
957 kernel are too buggy when it comes to using threads.
959 If you need nscd, you have to use a 2.1 kernel.
961 Note that I have at this point no information about any other platform.
964 2.25. I need lots of open files. What do I have to do?
966 {AJ} This is at first a kernel issue. The kernel defines limits with
967 OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the
968 number of used file descriptors. You need to change these values in your
969 kernel and recompile the kernel so that the kernel allows to use more open
970 files. You don't necessarily need to recompile the GNU C library since the
971 only place where OPEN_MAX and FD_SETSIZE is really needed in the library
972 itself is the size of fd_set which is used by select.
974 The GNU C library is now (nearly) select free. This means it internally has
975 no limits imposed by the `fd_set' type. Instead almost all places where the
976 functionality is needed the `poll' function is used.
978 If you increase the number of file descriptors in the kernel you don't need
979 to recompile the C library. The remaining select calls are in the RPC code.
980 If your RPC daemons don't need more than FD_SETSIZE file descriptors, you
981 don't need to change anything at all.
983 {UD} You can always get the maximum number of file descriptors a process is
984 allowed to have open at any time using
986 number = sysconf (_SC_OPEN_MAX);
988 This will work even if the kernel limits change.
991 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
993 3. Source and binary incompatibilities, and what to do about them
995 3.1. I expect GNU libc to be 100% source code compatible with
996 the old Linux based GNU libc. Why isn't it like this?
998 {DMT,UD} Not every extension in Linux libc's history was well thought-out.
999 In fact it had a lot of problems with standards compliance and with
1000 cleanliness. With the introduction of a new version number these errors can
1001 now be corrected. Here is a list of the known source code
1004 * _GNU_SOURCE: glibc does not make the GNU extensions available
1005 automatically. If a program depends on GNU extensions or some
1006 other non-standard functionality, it is necessary to compile it
1007 with the C compiler option -D_GNU_SOURCE, or better, to put
1008 `#define _GNU_SOURCE' at the beginning of your source files, before
1009 any C library header files are included. This difference normally
1010 manifests itself in the form of missing prototypes and/or data type
1011 definitions. Thus, if you get such errors, the first thing you
1012 should do is try defining _GNU_SOURCE and see if that makes the
1015 For more information consult the file `NOTES' in the GNU C library
1018 * reboot(): GNU libc sanitizes the interface of reboot() to be more
1019 compatible with the interface used on other OSes. reboot() as
1020 implemented in glibc takes just one argument. This argument
1021 corresponds to the third argument of the Linux reboot system call.
1022 That is, a call of the form reboot(a, b, c) needs to be changed into
1023 reboot(c). Beside this the header <sys/reboot.h> defines the needed
1024 constants for the argument. These RB_* constants should be used
1025 instead of the cryptic magic numbers.
1027 * swapon(): the interface of this function didn't change, but the
1028 prototype is in a separate header file <sys/swap.h>. This header
1029 file also provides the SWAP_* constants defined by <linux/swap.h>;
1030 you should use them for the second argument to swapon().
1032 * errno: If a program uses the variable "errno", then it _must_
1033 include <errno.h>. The old libc often (erroneously) declared this
1034 variable implicitly as a side-effect of including other libc header
1035 files. glibc is careful to avoid such namespace pollution, which,
1036 in turn, means that you really need to include the header files that
1037 you depend on. This difference normally manifests itself in the
1038 form of the compiler complaining about references to an undeclared
1041 * Linux-specific syscalls: All Linux system calls now have appropriate
1042 library wrappers and corresponding declarations in various header files.
1043 This is because the syscall() macro that was traditionally used to
1044 work around missing syscall wrappers are inherently non-portable and
1045 error-prone. The following table lists all the new syscall stubs,
1046 the header-file declaring their interface and the system call name.
1048 syscall name: wrapper name: declaring header file:
1049 ------------- ------------- ----------------------
1050 bdflush bdflush <sys/kdaemon.h>
1051 syslog ksyslog_ctl <sys/klog.h>
1053 * lpd: Older versions of lpd depend on a routine called _validuser().
1054 The library does not provide this function, but instead provides
1055 __ivaliduser() which has a slightly different interface. Simply
1056 upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD
1057 lpd is known to be working).
1059 * resolver functions/BIND: like on many other systems the functions of
1060 the resolver library are not included in libc itself. There is a
1061 separate library libresolv. If you get undefined symbol errors for
1062 symbols starting with `res_*' simply add -lresolv to your linker
1065 * the `signal' function's behavior corresponds to the BSD semantic and
1066 not the SysV semantic as it was in libc-5. The interface on all GNU
1067 systems shall be the same and BSD is the semantic of choice. To use
1068 the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE.
1069 See question 3.7 for details.
1072 3.2. Why does getlogin() always return NULL on my Linux box?
1074 {UD} The GNU C library has a format for the UTMP and WTMP file which differs
1075 from what your system currently has. It was extended to fulfill the needs
1076 of the next years when IPv6 is introduced. The record size is different and
1077 some fields have different positions. The files written by functions from
1078 the one library cannot be read by functions from the other library. Sorry,
1079 but this is what a major release is for. It's better to have a cut now than
1080 having no means to support the new techniques later.
1082 {MK} There is however a (partial) solution for this problem. Please take a
1083 look at the file `login/README.utmpd'.
1086 3.3. Where are the DST_* constants found in <sys/time.h> on many
1089 {UD} These constants come from the old BSD days and are not used anymore
1090 (libc5 does not actually implement the handling although the constants are
1093 Instead GNU libc contains zone database support and compatibility code for
1094 POSIX TZ environment variable handling.
1097 3.4. The prototypes for `connect', `accept', `getsockopt',
1098 `setsockopt', `getsockname', `getpeername', `send',
1099 `sendto', and `recvfrom' are different in GNU libc from
1100 any other system I saw. This is a bug, isn't it?
1102 {UD} No, this is no bug. This version of GNU libc already follows the new
1103 Single Unix specifications (and I think the POSIX.1g draft which adopted the
1104 solution). The type for a parameter describing a size is now `socklen_t', a
1108 3.5. On Linux I've got problems with the declarations in Linux
1111 {UD,AJ} On Linux, the use of kernel headers is reduced to the minimum. This
1112 gives Linus the ability to change the headers more freely. Also, user
1113 programs are now insulated from changes in the size of kernel data
1116 For example, the sigset_t type is 32 or 64 bits wide in the kernel. In
1117 glibc it is 1024 bits wide. This guarantees that when the kernel gets a
1118 bigger sigset_t (for POSIX.1e realtime support, say) user programs will not
1119 have to be recompiled. Consult the header files for more information about
1122 Therefore you shouldn't include Linux kernel header files directly if glibc
1123 has defined a replacement. Otherwise you might get undefined results because
1127 3.6. I don't include any kernel headers myself but the compiler
1128 still complains about redeclarations of types in the kernel
1131 {UD} The kernel headers before Linux 2.1.61 and 2.0.32 don't work correctly
1132 with glibc. Compiling C programs is possible in most cases but C++ programs
1133 have (due to the change of the name lookups for `struct's) problems. One
1134 prominent example is `struct fd_set'.
1136 There might be some problems left but 2.1.61/2.0.32 fix most of the known
1137 ones. See the BUGS file for other known problems.
1140 3.7. Why don't signals interrupt system calls anymore?
1142 {ZW} By default GNU libc uses the BSD semantics for signal(), unlike Linux
1143 libc 5 which used System V semantics. This is partially for compatibility
1144 with other systems and partially because the BSD semantics tend to make
1145 programming with signals easier.
1147 There are three differences:
1149 * BSD-style signals that occur in the middle of a system call do not
1150 affect the system call; System V signals cause the system call to
1151 fail and set errno to EINTR.
1153 * BSD signal handlers remain installed once triggered. System V signal
1154 handlers work only once, so one must reinstall them each time.
1156 * A BSD signal is blocked during the execution of its handler. In other
1157 words, a handler for SIGCHLD (for example) does not need to worry about
1158 being interrupted by another SIGCHLD. It may, however, be interrupted
1161 There is general consensus that for `casual' programming with signals, the
1162 BSD semantics are preferable. You don't need to worry about system calls
1163 returning EINTR, and you don't need to worry about the race conditions
1164 associated with one-shot signal handlers.
1166 If you are porting an old program that relies on the old semantics, you can
1167 quickly fix the problem by changing signal() to sysv_signal() throughout.
1168 Alternatively, define _XOPEN_SOURCE before including <signal.h>.
1170 For new programs, the sigaction() function allows you to specify precisely
1171 how you want your signals to behave. All three differences listed above are
1172 individually switchable on a per-signal basis with this function.
1174 If all you want is for one specific signal to cause system calls to fail and
1175 return EINTR (for example, to implement a timeout) you can do this with
1179 3.8. I've got errors compiling code that uses certain string
1182 {AJ} glibc 2.1 has special string functions that are faster than the normal
1183 library functions. Some of the functions are additionally implemented as
1184 inline functions and others as macros.
1186 The optimized string functions are only used when compiling with
1187 optimizations (-O1 or higher). The behavior can be changed with two feature
1190 * __NO_STRING_INLINES: Don't do any string optimizations.
1191 * __USE_STRING_INLINES: Use assembly language inline functions (might
1192 increase code size dramatically).
1194 Since some of these string functions are now additionally defined as macros,
1195 code like "char *strncpy();" doesn't work anymore (and is unnecessary, since
1196 <string.h> has the necessary declarations). Either change your code or
1197 define __NO_STRING_INLINES.
1199 {UD} Another problem in this area is that gcc still has problems on machines
1200 with very few registers (e.g., ix86). The inline assembler code can require
1201 almost all the registers and the register allocator cannot always handle
1204 One can disable the string optimizations selectively. Instead of writing
1206 cp = strcpy (foo, "lkj");
1210 cp = (strcpy) (foo, "lkj");
1212 This disables the optimization for that specific call.
1215 3.9. I get compiler messages "Initializer element not constant" with
1216 stdin/stdout/stderr. Why?
1218 {RM,AJ} Constructs like:
1219 static FILE *InPtr = stdin;
1221 lead to this message. This is correct behaviour with glibc since stdin is
1222 not a constant expression. Please note that a strict reading of ISO C does
1223 not allow above constructs.
1225 One of the advantages of this is that you can assign to stdin, stdout, and
1226 stderr just like any other global variable (e.g. `stdout = my_stream;'),
1227 which can be very useful with custom streams that you can write with libio
1228 (but beware this is not necessarily portable). The reason to implement it
1229 this way were versioning problems with the size of the FILE structure.
1231 To fix those programs you've got to initialize the variable at run time.
1232 This can be done, e.g. in main, like:
1240 or by constructors (beware this is gcc specific):
1243 static void inPtr_construct (void) __attribute__((constructor));
1244 static void inPtr_construct (void) { InPtr = stdin; }
1247 3.10. I can't compile with gcc -traditional (or
1248 -traditional-cpp). Why?
1250 {AJ} glibc2 does break -traditional and -traditonal-cpp - and will continue
1251 to do so. For example constructs of the form:
1257 are useful for debugging purposes (you can use foo with your debugger that's
1258 why we need the enum) and for compatibility (other systems use defines and
1262 3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible?
1264 {AJ} The GNU C library is compatible with the ANSI/ISO C standard. If
1265 you're using `gcc -ansi', the glibc includes which are specified in the
1266 standard follow the standard. The ANSI/ISO C standard defines what has to be
1267 in the include files - and also states that nothing else should be in the
1268 include files (btw. you can still enable additional standards with feature
1271 The GNU C library is conforming to ANSI/ISO C - if and only if you're only
1272 using the headers and library functions defined in the standard.
1275 3.12. I can't access some functions anymore. nm shows that they do
1276 exist but linking fails nevertheless.
1278 {AJ} With the introduction of versioning in glibc 2.1 it is possible to
1279 export only those identifiers (functions, variables) that are really needed
1280 by application programs and by other parts of glibc. This way a lot of
1281 internal interfaces are now hidden. nm will still show those identifiers
1282 but marking them as internal. ISO C states that identifiers beginning with
1283 an underscore are internal to the libc. An application program normally
1284 shouldn't use those internal interfaces (there are exceptions,
1285 e.g. __ivaliduser). If a program uses these interfaces, it's broken. These
1286 internal interfaces might change between glibc releases or dropped
1290 3.13. When using the db-2 library which comes with glibc is used in
1291 the Perl db modules the testsuite is not passed. This did not
1292 happen with db-1, gdbm, or ndbm.
1294 {UD} You are using an outdated copy of the DB_File Perl module. In fact db-2
1295 finally removed the handling of zero-sized keys which was one of the features
1296 tested by the old Perl testsuite and therefore you see an error. But this
1297 never was documented and guaranteed, only broken programs used this feature.
1299 Consequently db-2 does not need to support this feature and instead signals
1300 an error which leads to easier debugging. The DB_File module maintainer
1301 Paul Marquess <pmarquess@bfsec.bt.co.uk> acknowledged this change and fixed
1302 the testsuite so that if you use DB_File v1.60 or later you should not have
1303 any more problems with db-2.
1306 3.14. The pow() inline function I get when including <math.h> is broken.
1307 I get segmentation faults when I run the program.
1309 {UD} Nope, the implementation is correct. The problem is with egcs version
1310 prior to 1.1. I.e., egcs 1.0 to 1.0.3 are all broken (at least on Intel).
1311 If you have to use this compiler you must define __NO_MATH_INLINES before
1312 including <math.h> to prevent the inline functions from being used. egcs 1.1
1313 fixes the problem. I don't know about gcc 2.8 and 2.8.1.
1316 3.15. The sys/sem.h file lacks the definition of `union semun'.
1318 {UD} Nope. This union has to be provided by the user program. Former glibc
1319 versions defined this but it was an error since it does not make much sense
1320 when thinking about it. The standards describing the System V IPC functions
1321 define it this way and therefore programs must be adopted.
1324 3.16. Why has <netinet/ip_fw.h> disappeared?
1326 {AJ} The corresponding Linux kernel data structures and constants are
1327 totally different in Linux 2.0 and Linux 2.1. This situation has to be
1328 taken care in user programs using the firewall structures and therefore
1329 those programs (ipfw is AFAIK the only one) should deal with this problem
1333 3.17. I get floods of warnings when I use -Wconversion and include
1334 <string.h> or <math.h>.
1336 {ZW} <string.h> and <math.h> intentionally use prototypes to override
1337 argument promotion. -Wconversion warns about all these. You can safely
1338 ignore the warnings.
1340 -Wconversion isn't really intended for production use, only for shakedown
1341 compiles after converting an old program to standard C.
1344 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1348 4.1. After I changed configure.in I get `Autoconf version X.Y.
1349 or higher is required for this script'. What can I do?
1351 {UD} You have to get the specified autoconf version (or a later one)
1352 from your favorite mirror of ftp.gnu.org.
1355 4.2. When I try to compile code which uses IPv6 headers and
1356 definitions on my Linux 2.x.y system I am in trouble.
1357 Nothing seems to work.
1359 {UD} The problem is that IPv6 development still has not reached a point
1360 where the headers are stable. There are still lots of incompatible changes
1361 made and the libc headers have to follow.
1363 {PB} The 2.1 release of GNU libc aims to comply with the current versions of
1364 all the relevant standards. The IPv6 support libraries for older Linux
1365 systems used a different naming convention and so code written to work with
1366 them may need to be modified. If the standards make incompatible changes in
1367 the future then the libc may need to change again.
1369 IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it
1370 should contain all the necessary support; until then you should use the
1371 latest 2.1.x release you can find. As of 98/11/26 the currently recommended
1372 kernel for IPv6 is 2.1.129.
1374 Also, as of the 2.1 release the IPv6 API provided by GNU libc is not
1375 100% complete. In particular the getipnodebyname and getipnodebyaddr
1376 functions are not implemented.
1379 4.3. When I set the timezone by setting the TZ environment variable
1380 to EST5EDT things go wrong since glibc computes the wrong time
1381 from this information.
1383 {UD} The problem is that people still use the braindamaged POSIX method to
1384 select the timezone using the TZ environment variable with a format EST5EDT
1385 or whatever. People, read the POSIX standard, the implemented behaviour is
1386 correct! What you see is in fact the result of the decisions made while
1387 POSIX.1 was created. We've only implemented the handling of TZ this way to
1388 be POSIX compliant. It is not really meant to be used.
1390 The alternative approach to handle timezones which is implemented is the
1391 correct one to use: use the timezone database. This avoids all the problems
1392 the POSIX method has plus it is much easier to use. Simply run the tzselect
1393 shell script, answer the question and use the name printed in the end by
1394 making a symlink to /usr/share/zoneinfo/NAME (NAME is the returned value
1395 from tzselect) from the file /etc/localtime. That's all. You never again
1398 So, please avoid sending bug reports about time related problems if you use
1399 the POSIX method and you have not verified something is really broken by
1400 reading the POSIX standards.
1403 4.4. What other sources of documentation about glibc are available?
1405 {AJ} The FSF has a page about the GNU C library at
1406 <http://www.gnu.org/software/libc/>. The problem data base of open and
1407 solved bugs in GNU libc is available at
1408 <http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl>. Eric Green has written
1409 a HowTo for converting from Linux libc5 to glibc2. The HowTo is accessable
1410 via the FSF page and at <http://www.imaxx.net/~thrytis/glibc>. Frodo
1411 Looijaard describes a different way installing glibc2 as secondary libc at
1412 <http://huizen.dds.nl/~frodol/glibc>.
1414 Please note that this is not a complete list.
1417 4.5. The timezone string for Sydney/Australia is wrong since even when
1418 daylight saving time is in effect the timezone string is EST.
1420 {UD} The problem for some timezones is that the local authorities decided
1421 to use the term "summer time" instead of "daylight saving time". In this
1422 case the abbreviation character `S' is the same as the standard one. So,
1425 Eastern Standard Time = EST
1426 Eastern Summer Time = EST
1428 Great! To get this bug fixed convince the authorities to change the laws
1429 and regulations of the country this effects. glibc behaves correctly.
1432 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
1434 Answers were given by:
1435 {UD} Ulrich Drepper, <drepper@cygnus.com>
1436 {DMT} David Mosberger-Tang, <davidm@AZStarNet.com>
1437 {RM} Roland McGrath, <roland@gnu.org>
1438 {AJ} Andreas Jaeger, <aj@arthur.rhein-neckar.de>
1439 {EY} Eric Youngdale, <eric@andante.jic.com>
1440 {PB} Phil Blundell, <Philip.Blundell@pobox.com>
1441 {MK} Mark Kettenis, <kettenis@phys.uva.nl>
1442 {ZW} Zack Weinberg, <zack@rabi.phys.columbia.edu>
1443 {TK} Thorsten Kukuk, <kukuk@vt.uni-paderborn.de>
1444 {GK} Geoffrey Keating, <geoffk@ozemail.com.au>
1445 {HJ} H.J. Lu, <hjl@gnu.org>
1449 outline-regexp:"\\?"