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 should I do?
43 1.17. What is symbol versioning good for? Do I need it?
44 1.18. How can I compile on my fast ix86 machine a working libc for my slow
45 i386? After installing libc, programs abort with "Illegal
47 1.19. `make' complains about a missing dlfcn/libdl.so when building
48 malloc/libmemprof.so. How can I fix this?
49 1.20. Which tools should I use for MIPS?
51 2. Installation and configuration issues
53 2.1. Can I replace the libc on my Linux system with GNU libc?
54 2.2. How do I configure GNU libc so that the essential libraries
55 like libc.so go into /lib and the other into /usr/lib?
56 2.3. How should I avoid damaging my system when I install GNU libc?
57 2.4. Do I need to use GNU CC to compile programs that will use the
59 2.5. When linking with the new libc I get unresolved symbols
60 `crypt' and `setkey'. Why aren't these functions in the
62 2.6. When I use GNU libc on my Linux system by linking against
63 the libc.so which comes with glibc all I get is a core dump.
64 2.7. Looking through the shared libc file I haven't found the
65 functions `stat', `lstat', `fstat', and `mknod' and while
66 linking on my Linux system I get error messages. How is
67 this supposed to work?
68 2.8. When I run an executable on one system which I compiled on
69 another, I get dynamic linker errors. Both systems have the same
70 version of glibc installed. What's wrong?
71 2.9. How can I compile gcc 2.7.2.1 from the gcc source code using
73 2.10. The `gencat' utility cannot process the catalog sources which
74 were used on my Linux libc5 based system. Why?
75 2.11. Programs using libc have their messages translated, but other
76 behavior is not localized (e.g. collating order); why?
77 2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS
78 works great. But the glibc NIS+ doesn't seem to work.
79 2.13. I have killed ypbind to stop using NIS, but glibc
81 2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call:
82 RPC: Unable to receive; errno = Connection refused" when using NIS.
83 2.15. After installing glibc name resolving doesn't work properly.
84 2.16. How do I create the databases for NSS?
85 2.17. I have /usr/include/net and /usr/include/scsi as symlinks
86 into my Linux source tree. Is that wrong?
87 2.18. Programs like `logname', `top', `uptime' `users', `w' and
88 `who', show incorrect information about the (number of)
89 users on my system. Why?
90 2.19. After upgrading to glibc 2.1 with symbol versioning I get
91 errors about undefined symbols. What went wrong?
92 2.20. When I start the program XXX after upgrading the library
94 XXX: Symbol `_sys_errlist' has different size in shared
95 object, consider re-linking
96 Why? What should I do?
97 2.21. What do I need for C++ development?
98 2.22. Even statically linked programs need some shared libraries
99 which is not acceptable for me. What can I do?
100 2.23. I just upgraded my Linux system to glibc and now I get
101 errors whenever I try to link any program.
102 2.24. When I use nscd the machine freezes.
103 2.25. I need lots of open files. What do I have to do?
104 2.26. How do I get the same behavior on parsing /etc/passwd and
105 /etc/group as I have with libc5 ?
106 2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc
108 2.28. Why is extracting files via tar so slow?
109 2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error
110 before `_IO_seekoff'"). How should I fix this?
111 2.30. After upgrading to glibc 2.1, libraries that were compiled against
112 glibc 2.0.x don't work anymore.
113 2.31. What happened to the Berkeley DB libraries? Can I still use db
114 in /etc/nsswitch.conf?
115 2.32. What has do be done when upgrading to glibc 2.2?
116 2.33. The makefiles want to do a CVS commit.
117 2.34. When compiling C++ programs, I get a compilation error in streambuf.h.
118 2.35. When recompiling GCC, I get compilation errors in libio.
120 3. Source and binary incompatibilities, and what to do about them
122 3.1. I expect GNU libc to be 100% source code compatible with
123 the old Linux based GNU libc. Why isn't it like this?
124 3.2. Why does getlogin() always return NULL on my Linux box?
125 3.3. Where are the DST_* constants found in <sys/time.h> on many
127 3.4. The prototypes for `connect', `accept', `getsockopt',
128 `setsockopt', `getsockname', `getpeername', `send',
129 `sendto', and `recvfrom' are different in GNU libc from
130 any other system I saw. This is a bug, isn't it?
131 3.5. On Linux I've got problems with the declarations in Linux
133 3.6. I don't include any kernel headers myself but the compiler
134 still complains about redeclarations of types in the kernel
136 3.7. Why don't signals interrupt system calls anymore?
137 3.8. I've got errors compiling code that uses certain string
139 3.9. I get compiler messages "Initializer element not constant" with
140 stdin/stdout/stderr. Why?
141 3.10. I can't compile with gcc -traditional (or
142 -traditional-cpp). Why?
143 3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible?
144 3.12. I can't access some functions anymore. nm shows that they do
145 exist but linking fails nevertheless.
146 3.13. When using the db-2 library which comes with glibc is used in
147 the Perl db modules the testsuite is not passed. This did not
148 happen with db-1, gdbm, or ndbm.
149 3.14. The pow() inline function I get when including <math.h> is broken.
150 I get segmentation faults when I run the program.
151 3.15. The sys/sem.h file lacks the definition of `union semun'.
152 3.16. Why has <netinet/ip_fw.h> disappeared?
153 3.17. I get floods of warnings when I use -Wconversion and include
154 <string.h> or <math.h>.
155 3.18. After upgrading to glibc 2.1, I receive errors about
156 unresolved symbols, like `_dl_initial_searchlist' and can not
157 execute any binaries. What went wrong?
158 3.19. bonnie reports that char i/o with glibc 2 is much slower than with
159 libc5. What can be done?
160 3.20. Programs compiled with glibc 2.1 can't read db files made with glibc
161 2.0. What has changed that programs like rpm break?
162 3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but
163 when I try to use it, it always returns -1 and sets errno to ENOSYS.
164 3.22. My program segfaults when I call fclose() on the FILE* returned
165 from setmntent(). Is this a glibc bug?
166 3.23. I get "undefined reference to `atexit'"
170 4.1. After I changed configure.in I get `Autoconf version X.Y.
171 or higher is required for this script'. What can I do?
172 4.2. When I try to compile code which uses IPv6 headers and
173 definitions on my Linux 2.x.y system I am in trouble.
174 Nothing seems to work.
175 4.3. When I set the timezone by setting the TZ environment variable
176 to EST5EDT things go wrong since glibc computes the wrong time
177 from this information.
178 4.4. What other sources of documentation about glibc are available?
179 4.5. The timezone string for Sydney/Australia is wrong since even when
180 daylight saving time is in effect the timezone string is EST.
181 4.6. I've build make 3.77 against glibc 2.1 and now make gets
183 4.7. Why do so many programs using math functions fail on my AlphaStation?
184 4.8. The conversion table for character set XX does not match with
186 4.9. How can I find out which version of glibc I am using in the moment?
189 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
193 1.1. What systems does the GNU C Library run on?
195 {UD} This is difficult to answer. The file `README' lists the architectures
196 GNU libc was known to run on *at some time*. This does not mean that it
197 still can be compiled and run on them now.
199 The systems glibc is known to work on as of this release, and most probably
203 i[3456]86-*-linux-gnu Linux-2.x on Intel
204 m68k-*-linux-gnu Linux-2.x on Motorola 680x0
205 alpha*-*-linux-gnu Linux-2.x on DEC Alpha
206 powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems
207 sparc-*-linux-gnu Linux-2.x on SPARC
208 sparc64-*-linux-gnu Linux-2.x on UltraSPARC
209 arm-*-none ARM standalone systems
210 arm-*-linux Linux-2.x on ARM
211 arm-*-linuxaout Linux-2.x on ARM using a.out binaries
212 mips*-*-linux-gnu Linux-2.x on MIPS
213 ia64-*-linux-gnu Linux-2.x on ia64
214 s390-*-linux-gnu Linux-2.x on IBM S/390
215 s390x-*-linux-gnu Linux-2.x on IBM S/390 64-bit
217 Ports to other Linux platforms are in development, and may in fact work
218 already, but no one has sent us success reports for them. Currently no
219 ports to other operating systems are underway, although a few people have
222 If you have a system not listed above (or in the `README' file) and you are
223 really interested in porting it, contact
228 1.2. What compiler do I need to build GNU libc?
230 {UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC
231 are used to increase portability and speed.
233 GNU CC is found, like all other GNU packages, on
235 ftp://ftp.gnu.org/pub/gnu
237 and the many mirror sites. ftp.gnu.org is always overloaded, so try to find
238 a local mirror first.
240 You should always try to use the latest official release. Older versions
241 may not have all the features GNU libc requires. The current releases of
242 gcc (2.95 or newer) should work with the GNU C library (for powerpc see
243 question 1.5; for ARM see question 1.6; for MIPS see question 1.20).
245 Please note that gcc 2.95 and 2.95.x cannot compile glibc on Alpha due to
246 problems in the complex float support.
249 1.3. When I try to compile glibc I get only error messages.
252 {UD} You definitely need GNU make to build GNU libc. No other make
253 program has the needed functionality.
255 We recommend version GNU make version 3.79 or newer. Older versions have
256 bugs and/or are missing features.
259 1.4. Do I need a special linker or assembler?
261 {ZW} If you want a shared library, you need a linker and assembler that
262 understand all the features of ELF, including weak and versioned symbols.
263 The static library can be compiled with less featureful tools, but lacks key
264 features such as NSS.
266 For Linux or Hurd, you want binutils 2.10.1 or higher. These are the only
267 versions we've tested and found reliable. Other versions may work but we
268 don't recommend them, especially not when C++ is involved.
270 Other operating systems may come with system tools that have all the
271 necessary features, but this is moot because glibc hasn't been ported to
275 1.5. Which compiler should I use for powerpc?
277 {GK} You want to use at least gcc 2.95 (together with the right versions
278 of all the other tools, of course). See also question 2.8.
281 1.6. Which tools should I use for ARM?
283 {PB} You should use egcs 1.1 or a later version. For ELF systems some
284 changes are needed to the compiler; a patch against egcs-1.1.x can be found
287 <ftp://ftp.netwinder.org/users/p/philb/egcs-1.1.1pre2-diff-981126>
289 Binutils 2.10.1 or later is also required.
292 1.7. Do I need some more things to compile the GNU C Library?
294 {UD} Yes, there are some more :-).
296 * GNU gettext. This package contains the tools needed to construct
297 `message catalog' files containing translated versions of system
298 messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror
299 site. (We distribute compiled message catalogs, but they may not be
300 updated in patches.) Please note that the required minimal version
301 (0.10.35) of gettext is alpha software and available from
302 ftp://alpha.gnu.org/gnu .
304 * Some files are built with special tools. E.g., files ending in .gperf
305 need a `gperf' program. The GNU version (now available in a separate
306 package, formerly only as part of libg++) is known to work while some
307 vendor versions do not.
309 You should not need these tools unless you change the source files.
311 * Perl 5 is needed if you wish to test an installation of GNU libc
312 as the primary C library.
314 * When compiling for Linux, the header files of the Linux kernel must
315 be available to the compiler as <linux/*.h> and <asm/*.h>.
317 * lots of disk space (~400MB for i?86-linux; more for RISC platforms).
319 * plenty of time. Compiling just the shared and static libraries for
320 35mins on a 2xPIII@550Mhz w/ 512MB RAM. On a 2xUltraSPARC-II@360Mhz
321 w/ 1GB RAM it takes about 14 minutes. Multiply this by 1.5 or 2.0
322 if you build profiling and/or the highly optimized version as well.
323 For Hurd systems times are much higher.
325 You should avoid compiling in a NFS mounted filesystem. This is
328 James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time for
329 an earlier (and smaller!) version of glibc of 45h34m for a full build
330 (shared, static, and profiled) on Atari Falcon (Motorola 68030 @ 16 Mhz,
331 14 Mb memory) and Jan Barte <yann@plato.uni-paderborn.de> reports
332 22h48m on Atari TT030 (Motorola 68030 @ 32 Mhz, 34 Mb memory)
334 A full build of the PowerPC library took 1h on a PowerPC 750@400Mhz w/
335 64MB of RAM, and about 9h on a 601@60Mhz w/ 72Mb.
337 If you have some more measurements let me know.
340 1.8. What version of the Linux kernel headers should be used?
342 {AJ,UD} The headers from the most recent Linux kernel should be used. The
343 headers used while compiling the GNU C library and the kernel binary used
344 when using the library do not need to match. The GNU C library runs without
345 problems on kernels that are older than the kernel headers used. The other
346 way round (compiling the GNU C library with old kernel headers and running
347 on a recent kernel) does not necessarily work. For example you can't use
348 new kernel features if you used old kernel headers to compile the GNU C
351 {ZW} Even if you are using a 2.0 kernel on your machine, we recommend you
352 compile GNU libc with 2.2 kernel headers. That way you won't have to
353 recompile libc if you ever upgrade to kernel 2.2. To tell libc which
354 headers to use, give configure the --with-headers switch
355 (e.g. --with-headers=/usr/src/linux-2.2.0/include).
357 Note that you must configure the 2.2 kernel if you do this, otherwise libc
358 will be unable to find <linux/version.h>. Just change the current directory
359 to the root of the 2.2 tree and do `make include/linux/version.h'.
362 1.9. The compiler hangs while building iconvdata modules. What's
365 {} Removed. Does not apply anymore.
368 1.10. When I run `nm -u libc.so' on the produced library I still
369 find unresolved symbols. Can this be ok?
371 {UD} Yes, this is ok. There can be several kinds of unresolved symbols:
373 * magic symbols automatically generated by the linker. These have names
374 like __start_* and __stop_*
376 * symbols starting with _dl_* come from the dynamic linker
378 * weak symbols, which need not be resolved at all (fabs for example)
380 Generally, you should make sure you find a real program which produces
381 errors while linking before deciding there is a problem.
384 1.11. What are these `add-ons'?
386 {UD} To avoid complications with export rules or external source code some
387 optional parts of the libc are distributed as separate packages, e.g., the
388 linuxthreads package.
390 To use these packages as part of GNU libc, just unpack the tarfiles in the
391 libc source directory and tell the configuration script about them using the
392 --enable-add-ons option. If you give just --enable-add-ons configure tries
393 to find all the add-on packages in your source tree. This may not work. If
394 it doesn't, or if you want to select only a subset of the add-ons, give a
395 comma-separated list of the add-ons to enable:
397 configure --enable-add-ons=linuxthreads
401 Add-ons can add features (including entirely new shared libraries), override
402 files, provide support for additional architectures, and just about anything
403 else. The existing makefiles do most of the work; only some few stub rules
404 must be written to get everything running.
406 Most add-ons are tightly coupled to a specific GNU libc version. Please
407 check that the add-ons work with the GNU libc. For example the linuxthreads
408 add-on has the same numbering scheme as the libc and will in general only
409 work with the corresponding libc.
411 {AJ} With glibc 2.2 the crypt add-on and with glibc 2.1 the localedata
412 add-on have been integrated into the normal glibc distribution, crypt and
413 localedata are therefore not anymore add-ons.
416 1.12. My XXX kernel emulates a floating-point coprocessor for me.
417 Should I enable --with-fp?
419 {ZW} An emulated FPU is just as good as a real one, as far as the C library
420 is concerned. You only need to say --without-fp if your machine has no way
421 to execute floating-point instructions.
423 People who are interested in squeezing the last drop of performance
424 out of their machine may wish to avoid the trap overhead, but this is
425 far more trouble than it's worth: you then have to compile
426 *everything* this way, including the compiler's internal libraries
427 (libgcc.a for GNU C), because the calling conventions change.
430 1.13. When compiling GNU libc I get lots of errors saying functions
431 in glibc are duplicated in libgcc.
433 {EY} This is *exactly* the same problem that I was having. The problem was
434 due to the fact that configure didn't correctly detect that the linker flag
435 --no-whole-archive was supported in my linker. In my case it was because I
436 had run ./configure with bogus CFLAGS, and the test failed.
438 One thing that is particularly annoying about this problem is that once this
439 is misdetected, running configure again won't fix it unless you first delete
442 {UD} Starting with glibc-2.0.3 there should be a better test to avoid some
443 problems of this kind. The setting of CFLAGS is checked at the very
444 beginning and if it is not usable `configure' will bark.
447 1.14. Why do I get messages about missing thread functions when I use
448 librt? I don't even use threads.
450 {UD} In this case you probably mixed up your installation. librt uses
451 threads internally and has implicit references to the thread library.
452 Normally these references are satisfied automatically but if the thread
453 library is not in the expected place you must tell the linker where it is.
454 When using GNU ld it works like this:
456 gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt
458 The `/some/other/dir' should contain the thread library. `ld' will use the
459 given path to find the implicitly referenced library while not disturbing
463 1.15. What's the problem with configure --enable-omitfp?
465 {AJ} When --enable-omitfp is set the libraries are built without frame
466 pointers. Some compilers produce buggy code for this model and therefore we
467 don't advise using it at the moment.
469 If you use --enable-omitfp, you're on your own. If you encounter problems
470 with a library that was build this way, we advise you to rebuild the library
471 without --enable-omitfp. If the problem vanishes consider tracking the
472 problem down and report it as compiler failure.
474 Since a library built with --enable-omitfp is undebuggable on most systems,
475 debuggable libraries are also built - you can use them by appending "_g" to
478 The compilation of these extra libraries and the compiler optimizations slow
479 down the build process and need more disk space.
482 1.16. I get failures during `make check'. What should I do?
484 {AJ} The testsuite should compile and run cleanly on your system; every
485 failure should be looked into. Depending on the failures, you probably
486 should not install the library at all.
488 You should consider using the `glibcbug' script to report the failure,
489 providing as much detail as possible. If you run a test directly, please
490 remember to set up the environment correctly. You want to test the compiled
491 library - and not your installed one. The best way is to copy the exact
492 command line which failed and run the test from the subdirectory for this
495 There are some failures which are not directly related to the GNU libc:
496 - Some compilers produce buggy code. No compiler gets single precision
497 complex numbers correct on Alpha. Otherwise, the egcs 1.1 release should be
498 ok; gcc 2.8.1 might cause some failures; gcc 2.7.2.x is so buggy that
499 explicit checks have been used so that you can't build with it.
500 - The kernel might have bugs. For example on Linux/Alpha 2.0.34 the
501 floating point handling has quite a number of bugs and therefore most of
502 the test cases in the math subdirectory will fail. Linux 2.2 has
503 fixes for the floating point support on Alpha. The Linux/SPARC kernel has
504 also some bugs in the FPU emulation code (as of Linux 2.2.0).
505 - Other tools might have problems. For example bash 2.03 gives a
506 segmentation fault running the tst-rpmatch.sh test script.
509 1.17. What is symbol versioning good for? Do I need it?
511 {AJ} Symbol versioning solves problems that are related to interface
512 changes. One version of an interface might have been introduced in a
513 previous version of the GNU C library but the interface or the semantics of
514 the function has been changed in the meantime. For binary compatibility
515 with the old library, a newer library needs to still have the old interface
516 for old programs. On the other hand, new programs should use the new
517 interface. Symbol versioning is the solution for this problem. The GNU
518 libc version 2.1 uses symbol versioning by default if the installed binutils
521 We don't advise building without symbol versioning, since you lose binary
522 compatibility - forever! The binary compatibility you lose is not only
523 against the previous version of the GNU libc (version 2.0) but also against
527 1.18. How can I compile on my fast ix86 machine a working libc for my slow
528 i386? After installing libc, programs abort with "Illegal
531 {AJ} glibc and gcc might generate some instructions on your machine that
532 aren't available on i386. You've got to tell glibc that you're configuring
533 for i386 with adding i386 as your machine, for example:
535 ../configure --prefix=/usr i386-pc-linux-gnu
537 And you need to tell gcc to only generate i386 code, just add `-mcpu=i386'
538 (just -m386 doesn't work) to your CFLAGS.
540 {UD} This applies not only to the i386. Compiling on a i686 for any older
541 model will also fail if the above methods are not used.
544 1.19. `make' complains about a missing dlfcn/libdl.so when building
545 malloc/libmemprof.so. How can I fix this?
547 {AJ} Older make version (<= 3.78.90) have a bug which was hidden by a bug in
548 glibc (<= 2.1.2). You need to upgrade make to a newer or fixed version.
550 After upgrading make, you should remove the file sysd-sorted in your build
551 directory. The problem is that the broken make creates a wrong order for
552 one list in that file. The list has to be recreated with the new make -
553 which happens if you remove the file.
555 You might encounter this bug also in other situations where make scans
556 directories. I strongly advise to upgrade your make version to 3.79 or
560 1.20. Which tools should I use for MIPS?
562 {AJ} You should use the current development version of gcc 2.97 from CVS.
563 gcc 2.95.x does not work correctly on mips-linux.
565 You need also recent binutils, anything before and including 2.10 will not
566 work correctly. Either try the Linux binutils 2.10.0.33 from HJ Lu or the
567 current development version of binutils from CVS.
569 Please note that `make check' might fail for a number of the math tests
570 because of problems of the FPU emulation in the Linux kernel (the MIPS FPU
571 doesn't handle all cases and needs help from the kernel).
573 For details check also my page <http://www.suse.de/~aj/glibc-mips.html>.
576 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
578 2. Installation and configuration issues
580 2.1. Can I replace the libc on my Linux system with GNU libc?
582 {UD} You cannot replace any existing libc for Linux with GNU libc. It is
583 binary incompatible and therefore has a different major version. You can,
584 however, install it alongside your existing libc.
586 For Linux there are three major libc versions:
588 libc-5 original ELF libc
591 You can have any combination of these three installed. For more information
592 consult documentation for shared library handling. The Makefiles of GNU
593 libc will automatically generate the needed symbolic links which the linker
597 2.2. How do I configure GNU libc so that the essential libraries
598 like libc.so go into /lib and the other into /usr/lib?
600 {UD,AJ} Like all other GNU packages GNU libc is designed to use a base
601 directory and install all files relative to this. The default is
602 /usr/local, because this is safe (it will not damage the system if installed
603 there). If you wish to install GNU libc as the primary C library on your
604 system, set the base directory to /usr (i.e. run configure --prefix=/usr
605 <other_options>). Note that this can damage your system; see question 2.3 for
608 Some systems like Linux have a filesystem standard which makes a difference
609 between essential libraries and others. Essential libraries are placed in
610 /lib because this directory is required to be located on the same disk
611 partition as /. The /usr subtree might be found on another
612 partition/disk. If you configure for Linux with --prefix=/usr, then this
613 will be done automatically.
615 To install the essential libraries which come with GNU libc in /lib on
616 systems other than Linux one must explicitly request it. Autoconf has no
617 option for this so you have to use a `configparms' file (see the `INSTALL'
618 file for details). It should contain:
623 The first line specifies the directory for the essential libraries, the
624 second line the directory for system configuration files.
627 2.3. How should I avoid damaging my system when I install GNU libc?
629 {ZW} If you wish to be cautious, do not configure with --prefix=/usr. If
630 you don't specify a prefix, glibc will be installed in /usr/local, where it
631 will probably not break anything. (If you wish to be certain, set the
632 prefix to something like /usr/local/glibc2 which is not used for anything.)
634 The dangers when installing glibc in /usr are twofold:
636 * glibc will overwrite the headers in /usr/include. Other C libraries
637 install a different but overlapping set of headers there, so the effect
638 will probably be that you can't compile anything. You need to rename
639 /usr/include out of the way before running `make install'. (Do not throw
640 it away; you will then lose the ability to compile programs against your
643 * None of your old libraries, static or shared, can be used with a
644 different C library major version. For shared libraries this is not a
645 problem, because the filenames are different and the dynamic linker
646 will enforce the restriction. But static libraries have no version
647 information. You have to evacuate all the static libraries in
648 /usr/lib to a safe location.
650 The situation is rather similar to the move from a.out to ELF which
651 long-time Linux users will remember.
654 2.4. Do I need to use GNU CC to compile programs that will use the
657 {ZW} In theory, no; the linker does not care, and the headers are supposed
658 to check for GNU CC before using its extensions to the C language.
660 However, there are currently no ports of glibc to systems where another
661 compiler is the default, so no one has tested the headers extensively
662 against another compiler. You may therefore encounter difficulties. If you
663 do, please report them as bugs.
665 Also, in several places GNU extensions provide large benefits in code
666 quality. For example, the library has hand-optimized, inline assembly
667 versions of some string functions. These can only be used with GCC. See
668 question 3.8 for details.
671 2.5. When linking with the new libc I get unresolved symbols
672 `crypt' and `setkey'. Why aren't these functions in the
675 {} Removed. Does not apply anymore.
678 2.6. When I use GNU libc on my Linux system by linking against
679 the libc.so which comes with glibc all I get is a core dump.
681 {UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the
682 user specifies a --dynamic-linker argument. This is the name of the libc5
683 dynamic linker, which does not work with glibc.
685 For casual use of GNU libc you can just specify to the linker
686 --dynamic-linker=/lib/ld-linux.so.2
688 which is the glibc dynamic linker, on Linux systems. On other systems the
689 name is /lib/ld.so.1. When linking via gcc, you've got to add
690 -Wl,--dynamic-linker=/lib/ld-linux.so.2
692 to the gcc command line.
694 To change your environment to use GNU libc for compiling you need to change
695 the `specs' file of your gcc. This file is normally found at
697 /usr/lib/gcc-lib/<arch>/<version>/specs
699 In this file you have to change a few things:
701 - change `ld-linux.so.1' to `ld-linux.so.2'
703 - remove all expression `%{...:-lgmon}'; there is no libgmon in glibc
705 - fix a minor bug by changing %{pipe:-} to %|
707 Here is what the gcc-2.7.2 specs file should look like when GNU libc is
710 -----------------------------------------------------------------------
712 %{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*}
718 %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}
727 %{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s
730 -m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}}
733 %{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}}
739 %{!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}
741 *switches_need_spaces:
745 %{funsigned-char:-D__CHAR_UNSIGNED__}
748 -D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386)
756 -----------------------------------------------------------------------
758 Things get a bit more complicated if you have GNU libc installed in some
759 other place than /usr, i.e., if you do not want to use it instead of the old
760 libc. In this case the needed startup files and libraries are not found in
761 the regular places. So the specs file must tell the compiler and linker
764 Version 2.7.2.3 does and future versions of GCC will automatically
765 provide the correct specs.
768 2.7. Looking through the shared libc file I haven't found the
769 functions `stat', `lstat', `fstat', and `mknod' and while
770 linking on my Linux system I get error messages. How is
771 this supposed to work?
773 {RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed
774 to be undefined references in libc.so.6! Your problem is probably a missing
775 or incorrect /usr/lib/libc.so file; note that this is a small text file now,
776 not a symlink to libc.so.6. It should look something like this:
778 GROUP ( libc.so.6 libc_nonshared.a )
781 2.8. When I run an executable on one system which I compiled on
782 another, I get dynamic linker errors. Both systems have the same
783 version of glibc installed. What's wrong?
785 {ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the
786 other with egcs (any version). Egcs has functions in its internal
787 `libgcc.a' to support exception handling with C++. They are linked into
788 any program or dynamic library compiled with egcs, whether it needs them or
789 not. Dynamic libraries then turn around and export those functions again
790 unless special steps are taken to prevent them.
792 When you link your program, it resolves its references to the exception
793 functions to the ones exported accidentally by libc.so. That works fine as
794 long as libc has those functions. On the other system, libc doesn't have
795 those functions because it was compiled by gcc 2.8, and you get undefined
796 symbol errors. The symbols in question are named things like
797 `__register_frame_info'.
799 For glibc 2.0, the workaround is to not compile libc with egcs. We've also
800 incorporated a patch which should prevent the EH functions sneaking into
801 libc. It doesn't matter what compiler you use to compile your program.
803 For glibc 2.1, we've chosen to do it the other way around: libc.so
804 explicitly provides the EH functions. This is to prevent other shared
805 libraries from doing it.
807 {UD} Starting with glibc 2.1.1 you can compile glibc with gcc 2.8.1 or
808 newer since we have explicitly add references to the functions causing the
809 problem. But you nevertheless should use EGCS for other reasons
812 {GK} On some Linux distributions for PowerPC, you can see this when you have
813 built gcc or egcs from the Web sources (gcc versions 2.95 or earlier), then
814 re-built glibc. This happens because in these versions of gcc, exception
815 handling is implemented using an older method; the people making the
816 distributions are a little ahead of their time.
818 A quick solution to this is to find the libgcc.a file that came with the
819 distribution (it would have been installed under /usr/lib/gcc-lib), do
820 `ar x libgcc.a frame.o' to get the frame.o file out, and add a line saying
821 `LDLIBS-c.so += frame.o' to the file `configparms' in the directory you're
822 building in. You can check you've got the right `frame.o' file by running
823 `nm frame.o' and checking that it has the symbols defined that you're
826 This will let you build glibc with the C compiler. The C++ compiler
827 will still be binary incompatible with any C++ shared libraries that
828 you got with your distribution.
831 2.9. How can I compile gcc 2.7.2.1 from the gcc source code using
834 {AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later.
835 But you should get at least gcc 2.95.2.1 (or later versions) instead.
838 2.10. The `gencat' utility cannot process the catalog sources which
839 were used on my Linux libc5 based system. Why?
841 {UD} The `gencat' utility provided with glibc complies to the XPG standard.
842 The older Linux version did not obey the standard, so they are not
845 To ease the transition from the Linux version some of the non-standard
846 features are also present in the `gencat' program of GNU libc. This mainly
847 includes the use of symbols for the message number and the automatic
848 generation of header files which contain the needed #defines to map the
851 Here is a simple SED script to convert at least some Linux specific catalog
852 files to the XPG4 form:
854 -----------------------------------------------------------------------
855 # Change catalog source in Linux specific format to standard XPG format.
856 # Ulrich Drepper <drepper@cygnus.com>, 1996.
860 s/\$ #\([^ ]*\).*/\1/
862 s/\$ #[^ ]* *\(.*\)/\$ \1/
868 s/\(.*\)\n\(.*\)/\2 \1/
870 -----------------------------------------------------------------------
873 2.11. Programs using libc have their messages translated, but other
874 behavior is not localized (e.g. collating order); why?
876 {ZW} Translated messages are automatically installed, but the locale
877 database that controls other behaviors is not. You need to run localedef to
878 install this database, after you have run `make install'. For example, to
879 set up the French Canadian locale, simply issue the command
881 localedef -i fr_CA -f ISO-8859-1 fr_CA
883 Please see localedata/README in the source tree for further details.
886 2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS
887 works great. But the glibc NIS+ doesn't seem to work.
889 {TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for
890 storing information about the NIS+ server and their public keys, because the
891 nis.conf file does not contain all the necessary information. You have to
892 copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is
893 byte order independent) or generate it with nisinit from the nis-tools
894 package; available at
896 http://www.suse.de/~kukuk/linux/nisplus.html
899 2.13. I have killed ypbind to stop using NIS, but glibc
902 {TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from
903 ypbind. ypbind 3.3 and older versions don't always remove these files, so
904 glibc will continue to use them. Other BSD versions seem to work correctly.
905 Until ypbind 3.4 is released, you can find a patch at
907 <ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz>
910 2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call:
911 RPC: Unable to receive; errno = Connection refused" when using NIS.
913 {TK} You need a ypbind version which is 64bit clean. Some versions are not
914 64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3,
915 you need the patch from ftp.kernel.org (See the previous question). I don't
916 know about other versions.
919 2.15. After installing glibc name resolving doesn't work properly.
921 {AJ} You probably should read the manual section describing nsswitch.conf
922 (just type `info libc "NSS Configuration File"'). The NSS configuration
923 file is usually the culprit.
926 2.16. How do I create the databases for NSS?
928 {AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create
929 the database files. The glibc sources contain a Makefile which does the
930 necessary conversion and calls to create those files. The file is
931 `db-Makefile' in the subdirectory `nss' and you can call it with `make -f
932 db-Makefile'. Please note that not all services are capable of using a
933 database. Currently passwd, group, ethers, protocol, rpc, services shadow
934 and netgroup are implemented. See also question 2.31.
937 2.17. I have /usr/include/net and /usr/include/scsi as symlinks
938 into my Linux source tree. Is that wrong?
940 {PB} This was necessary for libc5, but is not correct when using glibc.
941 Including the kernel header files directly in user programs usually does not
942 work (see question 3.5). glibc provides its own <net/*> and <scsi/*> header
943 files to replace them, and you may have to remove any symlink that you have
944 in place before you install glibc. However, /usr/include/asm and
945 /usr/include/linux should remain as they were.
948 2.18. Programs like `logname', `top', `uptime' `users', `w' and
949 `who', show incorrect information about the (number of)
950 users on my system. Why?
952 {MK} See question 3.2.
955 2.19. After upgrading to glibc 2.1 with symbol versioning I get
956 errors about undefined symbols. What went wrong?
958 {AJ} The problem is caused either by wrong program code or tools. In the
959 versioned libc a lot of symbols are now local that were global symbols in
960 previous versions. It seems that programs linked against older versions
961 often accidentally used libc global variables -- something that should not
964 The only way to fix this is to recompile your program. Sorry, that's the
965 price you might have to pay once for quite a number of advantages with
969 2.20. When I start the program XXX after upgrading the library
971 XXX: Symbol `_sys_errlist' has different size in shared
972 object, consider re-linking
973 Why? What should I do?
975 {UD} As the message says, relink the binary. The problem is that a few
976 symbols from the library can change in size and there is no way to avoid
977 this. _sys_errlist is a good example. Occasionally there are new error
978 numbers added to the kernel and this must be reflected at user level,
979 breaking programs that refer to them directly.
981 Such symbols should normally not be used at all. There are mechanisms to
982 avoid using them. In the case of _sys_errlist, there is the strerror()
983 function which should _always_ be used instead. So the correct fix is to
984 rewrite that part of the application.
986 In some situations (especially when testing a new library release) it might
987 be possible that a symbol changed size when that should not have happened.
988 So in case of doubt report such a warning message as a problem.
991 2.21. What do I need for C++ development?
993 {HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or
994 gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++
995 support and works directly with glibc 2.1. If you use gcc-2.8.1 with
996 libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available
998 <ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz>
1000 Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work
1001 very well with the GNU C library due to vtable thunks. If you're upgrading
1002 from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library
1003 compiled for 2.0 is not compatible due to the new Large File Support (LFS)
1006 {UD} But since in the case of a shared libstdc++ the version numbers should
1007 be different existing programs will continue to work.
1010 2.22. Even statically linked programs need some shared libraries
1011 which is not acceptable for me. What can I do?
1013 {AJ} NSS (for details just type `info libc "Name Service Switch"') won't
1014 work properly without shared libraries. NSS allows using different services
1015 (e.g. NIS, files, db, hesiod) by just changing one configuration file
1016 (/etc/nsswitch.conf) without relinking any programs. The only disadvantage
1017 is that now static libraries need to access shared libraries. This is
1018 handled transparently by the GNU C library.
1020 A solution is to configure glibc with --enable-static-nss. In this case you
1021 can create a static binary that will use only the services dns and files
1022 (change /etc/nsswitch.conf for this). You need to link explicitly against
1023 all these services. For example:
1025 gcc -static test-netdb.c -o test-netdb \
1026 -Wl,--start-group -lc -lnss_files -lnss_dns -lresolv -Wl,--end-group
1028 The problem with this approach is that you've got to link every static
1029 program that uses NSS routines with all those libraries.
1031 {UD} In fact, one cannot say anymore that a libc compiled with this
1032 option is using NSS. There is no switch anymore. Therefore it is
1033 *highly* recommended *not* to use --enable-static-nss since this makes
1034 the behaviour of the programs on the system inconsistent.
1037 2.23. I just upgraded my Linux system to glibc and now I get
1038 errors whenever I try to link any program.
1040 {ZW} This happens when you have installed glibc as the primary C library but
1041 have stray symbolic links pointing at your old C library. If the first
1042 `libc.so' the linker finds is libc 5, it will use that. Your program
1043 expects to be linked with glibc, so the link fails.
1045 The most common case is that glibc put its `libc.so' in /usr/lib, but there
1046 was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the
1047 problem, just delete /lib/libc.so. You may also need to delete other
1048 symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5.
1050 {AJ} The perl script test-installation.pl which is run as last step during
1051 an installation of glibc that is configured with --prefix=/usr should help
1052 detect these situations. If the script reports problems, something is
1056 2.24. When I use nscd the machine freezes.
1058 {UD} You cannot use nscd with Linux 2.0.*. There is functionality missing
1059 in the kernel and work-arounds are not suitable. Besides, some parts of the
1060 kernel are too buggy when it comes to using threads.
1062 If you need nscd, you have to use at least a 2.1 kernel.
1064 Note that I have at this point no information about any other platform.
1067 2.25. I need lots of open files. What do I have to do?
1069 {AJ} This is at first a kernel issue. The kernel defines limits with
1070 OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the
1071 number of used file descriptors. You need to change these values in your
1072 kernel and recompile the kernel so that the kernel allows more open
1073 files. You don't necessarily need to recompile the GNU C library since the
1074 only place where OPEN_MAX and FD_SETSIZE is really needed in the library
1075 itself is the size of fd_set which is used by select.
1077 The GNU C library is now select free. This means it internally has no
1078 limits imposed by the `fd_set' type. Instead all places where the
1079 functionality is needed the `poll' function is used.
1081 If you increase the number of file descriptors in the kernel you don't need
1082 to recompile the C library.
1084 {UD} You can always get the maximum number of file descriptors a process is
1085 allowed to have open at any time using
1087 number = sysconf (_SC_OPEN_MAX);
1089 This will work even if the kernel limits change.
1092 2.26. How do I get the same behavior on parsing /etc/passwd and
1093 /etc/group as I have with libc5 ?
1095 {TK} The name switch setup in /etc/nsswitch.conf selected by most Linux
1096 distributions does not support +/- and netgroup entries in the files like
1097 /etc/passwd. Though this is the preferred setup some people might have
1098 setups coming over from the libc5 days where it was the default to recognize
1099 lines like this. To get back to the old behaviour one simply has to change
1100 the rules for passwd, group, and shadow in the nsswitch.conf file as
1112 2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc
1115 {AJ,CG} If you just upgrade the glibc from 2.0.x (x <= 7) to 2.1, binaries
1116 that have been linked against glibc 2.0 will continue to work.
1118 If you compile your own binaries against glibc 2.1, you also need to
1119 recompile some other libraries. The problem is that libio had to be changed
1120 and therefore libraries that are based or depend on the libio of glibc,
1121 e.g. ncurses, slang and most C++ libraries, need to be recompiled. If you
1122 experience strange segmentation faults in your programs linked against glibc
1123 2.1, you might need to recompile your libraries.
1125 Another problem is that older binaries that were linked statically against
1126 glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of
1127 libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled
1128 static libraries (libfoo.a) which happen to depend on the older libio
1129 behavior will be broken by the glibc 2.1 upgrade. We plan to produce a
1130 compatibility library that people will be able to link in if they want
1131 to compile a static library generated against glibc 2.0 into a program
1132 on a glibc 2.1 system. You just add -lcompat and you should be fine.
1134 The glibc-compat add-on will provide the libcompat.a library, the older
1135 nss modules, and a few other files. Together, they should make it
1136 possible to do development with old static libraries on a glibc 2.1
1137 system. This add-on is still in development. You can get it from
1138 <ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz>
1139 but please keep in mind that it is experimental.
1142 2.28. Why is extracting files via tar so slow?
1144 {AJ} Extracting of tar archives might be quite slow since tar has to look up
1145 userid and groupids and doesn't cache negative results. If you have nis or
1146 nisplus in your /etc/nsswitch.conf for the passwd and/or group database,
1147 each file extractions needs a network connection. There are two possible
1150 - do you really need NIS/NIS+ (some Linux distributions add by default
1151 nis/nisplus even if it's not needed)? If not, just remove the entries.
1153 - if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes
1157 2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error
1158 before `_IO_seekoff'"). How should I fix this?
1160 {AJ} You might get the following errors when upgrading to glibc 2.1:
1162 In file included from /usr/include/stdio.h:57,
1164 /usr/include/libio.h:335: parse error before `_IO_seekoff'
1165 /usr/include/libio.h:335: parse error before `_G_off64_t'
1166 /usr/include/libio.h:336: parse error before `_IO_seekpos'
1167 /usr/include/libio.h:336: parse error before `_G_fpos64_t'
1169 The problem is a wrong _G_config.h file in your include path. The
1170 _G_config.h file that comes with glibc 2.1 should be used and not one from
1171 libc5 or from a compiler directory. To check which _G_config.h file the
1172 compiler uses, compile your program with `gcc -E ...|grep G_config.h' and
1173 remove that file. Your compiler should pick up the file that has been
1174 installed by glibc 2.1 in your include directory.
1177 2.30. After upgrading to glibc 2.1, libraries that were compiled against
1178 glibc 2.0.x don't work anymore.
1180 {AJ} See question 2.27.
1183 2.31. What happened to the Berkeley DB libraries? Can I still use db
1184 in /etc/nsswitch.conf?
1186 {AJ} Due to too many incompatible changes in disk layout and API of Berkeley
1187 DB and a too tight coupling of libc and libdb, the db library has been
1188 removed completely from glibc 2.2. The only place that really used the
1189 Berkeley DB was the NSS db module.
1191 The NSS db module has been rewritten to support a number of different
1192 versions of Berkeley DB for the NSS db module. Currently the releases 2.x
1193 and 3.x of Berkeley DB are supported. The older db 1.85 library is not
1194 supported. You can use the version from glibc 2.1.x or download a version
1195 from Sleepycat Software (http://www.sleepycat.com). The library has to be
1196 compiled as shared library and installed in the system lib directory
1197 (normally /lib). The library needs to have a special soname to be found by
1200 If public structures change in a new Berkeley db release, this needs to be
1203 Currently the code searches for libraries with a soname of "libdb.so.3"
1204 (that's the name from db 2.4.14 which comes with glibc 2.1.x) and
1205 "libdb-3.0.so" (the name used by db 3.0.55 as default).
1207 The nss_db module is now in a separate package since it requires a database
1208 library being available.
1211 2.32. What has do be done when upgrading to glibc 2.2?
1213 {AJ} The upgrade to glibc 2.2 should run smoothly, there's in general no
1214 need to recompile programs or libraries. Nevertheless, some changes might
1215 be needed after upgrading:
1216 - The utmp daemon has been removed and is not supported by glibc anymore.
1217 If it has been in use, it should be switched off.
1218 - Programs using IPv6 have to be recompiled due to incompatible changes in
1219 sockaddr_in6 by the IPv6 working group.
1220 - The Berkeley db libraries have been removed (for details see question 2.31).
1221 - The format of the locale files has changed, all locales should be
1222 regenerated with localedef. All statically linked applications which use
1223 i18n should be recompiled, otherwise they'll not be localized.
1224 - glibc comes with a number of new applications. For example ldconfig has
1225 been implemented for glibc, the libc5 version of ldconfig is not needed
1227 - There's no more K&R compatibility in the glibc headers. The GNU C library
1228 requires a C compiler that handles especially prototypes correctly.
1229 Especially gcc -traditional will not work with glibc headers.
1231 Please read also the NEWS file which is the authoritative source for this
1232 and gives more details for some topics.
1235 2.33. The makefiles want to do a CVS commit.
1237 {UD} Only if you are not specifying the --without-cvs flag at configure
1238 time. This is what you always have to use if you are checking sources
1239 directly out of the public CVS repository or you have your own private
1243 2.34. When compiling C++ programs, I get a compilation error in streambuf.h.
1245 {BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to
1246 apply a patch to the include files in /usr/include/g++, because the fpos_t
1247 type has changed in glibc 2.2. The patch is at
1248 http://clisp.cons.org/~haible/gccinclude-glibc-2.2-compat.diff
1251 2.35. When recompiling GCC, I get compilation errors in libio.
1253 {BH} You are trying to recompile gcc 2.95.2? Use gcc 2.95.3 instead.
1254 This version is needed because the fpos_t type and a few libio internals
1255 have changed in glibc 2.2, and gcc 2.95.3 contains a corresponding patch.
1258 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1260 3. Source and binary incompatibilities, and what to do about them
1262 3.1. I expect GNU libc to be 100% source code compatible with
1263 the old Linux based GNU libc. Why isn't it like this?
1265 {DMT,UD} Not every extension in Linux libc's history was well thought-out.
1266 In fact it had a lot of problems with standards compliance and with
1267 cleanliness. With the introduction of a new version number these errors can
1268 now be corrected. Here is a list of the known source code
1271 * _GNU_SOURCE: glibc does not make the GNU extensions available
1272 automatically. If a program depends on GNU extensions or some
1273 other non-standard functionality, it is necessary to compile it
1274 with the C compiler option -D_GNU_SOURCE, or better, to put
1275 `#define _GNU_SOURCE' at the beginning of your source files, before
1276 any C library header files are included. This difference normally
1277 manifests itself in the form of missing prototypes and/or data type
1278 definitions. Thus, if you get such errors, the first thing you
1279 should do is try defining _GNU_SOURCE and see if that makes the
1282 For more information consult the file `NOTES' in the GNU C library
1285 * reboot(): GNU libc sanitizes the interface of reboot() to be more
1286 compatible with the interface used on other OSes. reboot() as
1287 implemented in glibc takes just one argument. This argument
1288 corresponds to the third argument of the Linux reboot system call.
1289 That is, a call of the form reboot(a, b, c) needs to be changed into
1290 reboot(c). Beside this the header <sys/reboot.h> defines the needed
1291 constants for the argument. These RB_* constants should be used
1292 instead of the cryptic magic numbers.
1294 * swapon(): the interface of this function didn't change, but the
1295 prototype is in a separate header file <sys/swap.h>. This header
1296 file also provides the SWAP_* constants defined by <linux/swap.h>;
1297 you should use them for the second argument to swapon().
1299 * errno: If a program uses the variable "errno", then it _must_
1300 include <errno.h>. The old libc often (erroneously) declared this
1301 variable implicitly as a side-effect of including other libc header
1302 files. glibc is careful to avoid such namespace pollution, which,
1303 in turn, means that you really need to include the header files that
1304 you depend on. This difference normally manifests itself in the
1305 form of the compiler complaining about references to an undeclared
1308 * Linux-specific syscalls: All Linux system calls now have appropriate
1309 library wrappers and corresponding declarations in various header files.
1310 This is because the syscall() macro that was traditionally used to
1311 work around missing syscall wrappers are inherently non-portable and
1312 error-prone. The following table lists all the new syscall stubs,
1313 the header-file declaring their interface and the system call name.
1315 syscall name: wrapper name: declaring header file:
1316 ------------- ------------- ----------------------
1317 bdflush bdflush <sys/kdaemon.h>
1318 syslog ksyslog_ctl <sys/klog.h>
1320 * lpd: Older versions of lpd depend on a routine called _validuser().
1321 The library does not provide this function, but instead provides
1322 __ivaliduser() which has a slightly different interface. Simply
1323 upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD
1324 lpd is known to be working).
1326 * resolver functions/BIND: like on many other systems the functions of
1327 the resolver library are not included in libc itself. There is a
1328 separate library libresolv. If you get undefined symbol errors for
1329 symbols starting with `res_*' simply add -lresolv to your linker
1332 * the `signal' function's behavior corresponds to the BSD semantic and
1333 not the SysV semantic as it was in libc-5. The interface on all GNU
1334 systems shall be the same and BSD is the semantic of choice. To use
1335 the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE.
1336 See question 3.7 for details.
1339 3.2. Why does getlogin() always return NULL on my Linux box?
1341 {UD} The GNU C library has a format for the UTMP and WTMP file which differs
1342 from what your system currently has. It was extended to fulfill the needs
1343 of the next years when IPv6 is introduced. The record size is different and
1344 some fields have different positions. The files written by functions from
1345 the one library cannot be read by functions from the other library. Sorry,
1346 but this is what a major release is for. It's better to have a cut now than
1347 having no means to support the new techniques later.
1350 3.3. Where are the DST_* constants found in <sys/time.h> on many
1353 {UD} These constants come from the old BSD days and are not used anymore
1354 (libc5 does not actually implement the handling although the constants are
1357 Instead GNU libc contains zone database support and compatibility code for
1358 POSIX TZ environment variable handling. For former is very much preferred
1362 3.4. The prototypes for `connect', `accept', `getsockopt',
1363 `setsockopt', `getsockname', `getpeername', `send',
1364 `sendto', and `recvfrom' are different in GNU libc from
1365 any other system I saw. This is a bug, isn't it?
1367 {UD} No, this is no bug. This version of GNU libc already follows the new
1368 Single Unix specifications (and I think the POSIX.1g draft which adopted the
1369 solution). The type for a parameter describing a size is now `socklen_t', a
1373 3.5. On Linux I've got problems with the declarations in Linux
1376 {UD,AJ} On Linux, the use of kernel headers is reduced to the minimum. This
1377 gives Linus the ability to change the headers more freely. Also, user
1378 programs are now insulated from changes in the size of kernel data
1381 For example, the sigset_t type is 32 or 64 bits wide in the kernel. In
1382 glibc it is 1024 bits wide. This guarantees that when the kernel gets a
1383 bigger sigset_t (for POSIX.1e realtime support, say) user programs will not
1384 have to be recompiled. Consult the header files for more information about
1387 Therefore you shouldn't include Linux kernel header files directly if glibc
1388 has defined a replacement. Otherwise you might get undefined results because
1392 3.6. I don't include any kernel headers myself but the compiler
1393 still complains about redeclarations of types in the kernel
1396 {UD} The kernel headers before Linux 2.1.61 and 2.0.32 don't work correctly
1397 with glibc. Compiling C programs is possible in most cases but C++ programs
1398 have (due to the change of the name lookups for `struct's) problems. One
1399 prominent example is `struct fd_set'.
1401 There might be some problems left but 2.1.61/2.0.32 fix most of the known
1402 ones. See the BUGS file for other known problems.
1405 3.7. Why don't signals interrupt system calls anymore?
1407 {ZW} By default GNU libc uses the BSD semantics for signal(), unlike Linux
1408 libc 5 which used System V semantics. This is partially for compatibility
1409 with other systems and partially because the BSD semantics tend to make
1410 programming with signals easier.
1412 There are three differences:
1414 * BSD-style signals that occur in the middle of a system call do not
1415 affect the system call; System V signals cause the system call to
1416 fail and set errno to EINTR.
1418 * BSD signal handlers remain installed once triggered. System V signal
1419 handlers work only once, so one must reinstall them each time.
1421 * A BSD signal is blocked during the execution of its handler. In other
1422 words, a handler for SIGCHLD (for example) does not need to worry about
1423 being interrupted by another SIGCHLD. It may, however, be interrupted
1426 There is general consensus that for `casual' programming with signals, the
1427 BSD semantics are preferable. You don't need to worry about system calls
1428 returning EINTR, and you don't need to worry about the race conditions
1429 associated with one-shot signal handlers.
1431 If you are porting an old program that relies on the old semantics, you can
1432 quickly fix the problem by changing signal() to sysv_signal() throughout.
1433 Alternatively, define _XOPEN_SOURCE before including <signal.h>.
1435 For new programs, the sigaction() function allows you to specify precisely
1436 how you want your signals to behave. All three differences listed above are
1437 individually switchable on a per-signal basis with this function.
1439 If all you want is for one specific signal to cause system calls to fail and
1440 return EINTR (for example, to implement a timeout) you can do this with
1444 3.8. I've got errors compiling code that uses certain string
1447 {AJ} glibc 2.1 has special string functions that are faster than the normal
1448 library functions. Some of the functions are additionally implemented as
1449 inline functions and others as macros. This might lead to problems with
1450 existing codes but it is explicitly allowed by ISO C.
1452 The optimized string functions are only used when compiling with
1453 optimizations (-O1 or higher). The behavior can be changed with two feature
1456 * __NO_STRING_INLINES: Don't do any string optimizations.
1457 * __USE_STRING_INLINES: Use assembly language inline functions (might
1458 increase code size dramatically).
1460 Since some of these string functions are now additionally defined as macros,
1461 code like "char *strncpy();" doesn't work anymore (and is unnecessary, since
1462 <string.h> has the necessary declarations). Either change your code or
1463 define __NO_STRING_INLINES.
1465 {UD} Another problem in this area is that gcc still has problems on machines
1466 with very few registers (e.g., ix86). The inline assembler code can require
1467 almost all the registers and the register allocator cannot always handle
1470 One can disable the string optimizations selectively. Instead of writing
1472 cp = strcpy (foo, "lkj");
1476 cp = (strcpy) (foo, "lkj");
1478 This disables the optimization for that specific call.
1481 3.9. I get compiler messages "Initializer element not constant" with
1482 stdin/stdout/stderr. Why?
1484 {RM,AJ} Constructs like:
1485 static FILE *InPtr = stdin;
1487 lead to this message. This is correct behaviour with glibc since stdin is
1488 not a constant expression. Please note that a strict reading of ISO C does
1489 not allow above constructs.
1491 One of the advantages of this is that you can assign to stdin, stdout, and
1492 stderr just like any other global variable (e.g. `stdout = my_stream;'),
1493 which can be very useful with custom streams that you can write with libio
1494 (but beware this is not necessarily portable). The reason to implement it
1495 this way were versioning problems with the size of the FILE structure.
1497 To fix those programs you've got to initialize the variable at run time.
1498 This can be done, e.g. in main, like:
1506 or by constructors (beware this is gcc specific):
1509 static void inPtr_construct (void) __attribute__((constructor));
1510 static void inPtr_construct (void) { InPtr = stdin; }
1513 3.10. I can't compile with gcc -traditional (or
1514 -traditional-cpp). Why?
1516 {AJ} glibc2 does break -traditional and -traditonal-cpp - and will continue
1517 to do so. For example constructs of the form:
1523 are useful for debugging purposes (you can use foo with your debugger that's
1524 why we need the enum) and for compatibility (other systems use defines and
1528 3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible?
1530 {AJ} The GNU C library is compatible with the ANSI/ISO C standard. If
1531 you're using `gcc -ansi', the glibc includes which are specified in the
1532 standard follow the standard. The ANSI/ISO C standard defines what has to be
1533 in the include files - and also states that nothing else should be in the
1534 include files (btw. you can still enable additional standards with feature
1537 The GNU C library is conforming to ANSI/ISO C - if and only if you're only
1538 using the headers and library functions defined in the standard.
1541 3.12. I can't access some functions anymore. nm shows that they do
1542 exist but linking fails nevertheless.
1544 {AJ} With the introduction of versioning in glibc 2.1 it is possible to
1545 export only those identifiers (functions, variables) that are really needed
1546 by application programs and by other parts of glibc. This way a lot of
1547 internal interfaces are now hidden. nm will still show those identifiers
1548 but marking them as internal. ISO C states that identifiers beginning with
1549 an underscore are internal to the libc. An application program normally
1550 shouldn't use those internal interfaces (there are exceptions,
1551 e.g. __ivaliduser). If a program uses these interfaces, it's broken. These
1552 internal interfaces might change between glibc releases or dropped
1556 3.13. When using the db-2 library which comes with glibc is used in
1557 the Perl db modules the testsuite is not passed. This did not
1558 happen with db-1, gdbm, or ndbm.
1560 {} Removed. Does not apply anymore.
1563 3.14. The pow() inline function I get when including <math.h> is broken.
1564 I get segmentation faults when I run the program.
1566 {UD} Nope, the implementation is correct. The problem is with egcs version
1567 prior to 1.1. I.e., egcs 1.0 to 1.0.3 are all broken (at least on Intel).
1568 If you have to use this compiler you must define __NO_MATH_INLINES before
1569 including <math.h> to prevent the inline functions from being used. egcs 1.1
1570 fixes the problem. I don't know about gcc 2.8 and 2.8.1.
1573 3.15. The sys/sem.h file lacks the definition of `union semun'.
1575 {UD} Nope. This union has to be provided by the user program. Former glibc
1576 versions defined this but it was an error since it does not make much sense
1577 when thinking about it. The standards describing the System V IPC functions
1578 define it this way and therefore programs must be adopted.
1581 3.16. Why has <netinet/ip_fw.h> disappeared?
1583 {AJ} The corresponding Linux kernel data structures and constants are
1584 totally different in Linux 2.0 and Linux 2.2. This situation has to be
1585 taken care in user programs using the firewall structures and therefore
1586 those programs (ipfw is AFAIK the only one) should deal with this problem
1590 3.17. I get floods of warnings when I use -Wconversion and include
1591 <string.h> or <math.h>.
1593 {ZW} <string.h> and <math.h> intentionally use prototypes to override
1594 argument promotion. -Wconversion warns about all these. You can safely
1595 ignore the warnings.
1597 -Wconversion isn't really intended for production use, only for shakedown
1598 compiles after converting an old program to standard C.
1601 3.18. After upgrading to glibc 2.1, I receive errors about
1602 unresolved symbols, like `_dl_initial_searchlist' and can not
1603 execute any binaries. What went wrong?
1605 {AJ} This normally happens if your libc and ld (dynamic linker) are from
1606 different releases of glibc. For example, the dynamic linker
1607 /lib/ld-linux.so.2 comes from glibc 2.0.x, but the version of libc.so.6 is
1610 The path /lib/ld-linux.so.2 is hardcoded in every glibc2 binary but
1611 libc.so.6 is searched via /etc/ld.so.cache and in some special directories
1612 like /lib and /usr/lib. If you run configure with another prefix than /usr
1613 and put this prefix before /lib in /etc/ld.so.conf, your system will break.
1615 So what can you do? Either of the following should work:
1617 * Run `configure' with the same prefix argument you've used for glibc 2.0.x
1618 so that the same paths are used.
1619 * Replace /lib/ld-linux.so.2 with a link to the dynamic linker from glibc
1622 You can even call the dynamic linker by hand if everything fails. You've
1623 got to set LD_LIBRARY_PATH so that the corresponding libc is found and also
1624 need to provide an absolute path to your binary:
1626 LD_LIBRARY_PATH=<path-where-libc.so.6-lives> \
1627 <path-where-corresponding-dynamic-linker-lives>/ld-linux.so.2 \
1628 <path-to-binary>/binary
1630 For example `LD_LIBRARY_PATH=/libold /libold/ld-linux.so.2 /bin/mv ...'
1631 might be useful in fixing a broken system (if /libold contains dynamic
1632 linker and corresponding libc).
1634 With that command line no path is used. To further debug problems with the
1635 dynamic linker, use the LD_DEBUG environment variable, e.g.
1636 `LD_DEBUG=help echo' for the help text.
1638 If you just want to test this release, don't put the lib directory in
1639 /etc/ld.so.conf. You can call programs directly with full paths (as above).
1640 When compiling new programs against glibc 2.1, you've got to specify the
1641 correct paths to the compiler (option -I with gcc) and linker (options
1642 --dynamic-linker, -L and --rpath).
1645 3.19. bonnie reports that char i/o with glibc 2 is much slower than with
1646 libc5. What can be done?
1648 {AJ} The GNU C library uses thread safe functions by default and libc5 used
1649 non thread safe versions. The non thread safe functions have in glibc the
1650 suffix `_unlocked', for details check <stdio.h>. Using `putc_unlocked' etc.
1651 instead of `putc' should give nearly the same speed with bonnie (bonnie is a
1652 benchmark program for measuring disk access).
1655 3.20. Programs compiled with glibc 2.1 can't read db files made with glibc
1656 2.0. What has changed that programs like rpm break?
1658 {} Removed. Does not apply anymore.
1661 3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but
1662 when I try to use it, it always returns -1 and sets errno to ENOSYS.
1664 {ZW} You are using a 2.0 Linux kernel, and the function you are trying to
1665 use is only implemented in 2.1/2.2. Libc considers this to be a function
1666 which exists, because if you upgrade to a 2.2 kernel, it will work. One
1667 such function is sigaltstack.
1669 Your program should check at runtime whether the function works, and
1670 implement a fallback. Note that Autoconf cannot detect unimplemented
1671 functions in other systems' C libraries, so you need to do this anyway.
1674 3.22. My program segfaults when I call fclose() on the FILE* returned
1675 from setmntent(). Is this a glibc bug?
1677 {GK} No. Don't do this. Use endmntent(), that's what it's for.
1679 In general, you should use the correct deallocation routine. For instance,
1680 if you open a file using fopen(), you should deallocate the FILE * using
1681 fclose(), not free(), even though the FILE * is also a pointer.
1683 In the case of setmntent(), it may appear to work in most cases, but it
1684 won't always work. Unfortunately, for compatibility reasons, we can't
1685 change the return type of setmntent() to something other than FILE *.
1688 3.23. I get "undefined reference to `atexit'"
1690 {UD} This means that your installation is somehow broken. The situation is
1691 the same as for 'stat', 'fstat', etc (see question 2.7). Investigate why the
1692 linker does not pick up libc_nonshared.a.
1694 If a similar message is issued at runtime this means that the application or
1695 DSO is not linked against libc. This can cause problems since 'atexit' is
1696 not exported anymore.
1699 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1703 4.1. After I changed configure.in I get `Autoconf version X.Y.
1704 or higher is required for this script'. What can I do?
1706 {UD} You have to get the specified autoconf version (or a later one)
1707 from your favorite mirror of ftp.gnu.org.
1710 4.2. When I try to compile code which uses IPv6 headers and
1711 definitions on my Linux 2.x.y system I am in trouble.
1712 Nothing seems to work.
1714 {UD} The problem is that IPv6 development still has not reached a point
1715 where the headers are stable. There are still lots of incompatible changes
1716 made and the libc headers have to follow.
1718 {PB} The 2.1 release of GNU libc aims to comply with the current versions of
1719 all the relevant standards. The IPv6 support libraries for older Linux
1720 systems used a different naming convention and so code written to work with
1721 them may need to be modified. If the standards make incompatible changes in
1722 the future then the libc may need to change again.
1724 IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it
1725 should contain all the necessary support; until then you should use the
1726 latest 2.1.x release you can find. As of 98/11/26 the currently recommended
1727 kernel for IPv6 is 2.1.129.
1729 Also, as of the 2.1 release the IPv6 API provided by GNU libc is not
1733 4.3. When I set the timezone by setting the TZ environment variable
1734 to EST5EDT things go wrong since glibc computes the wrong time
1735 from this information.
1737 {UD} The problem is that people still use the braindamaged POSIX method to
1738 select the timezone using the TZ environment variable with a format EST5EDT
1739 or whatever. People, if you insist on using TZ instead of the timezone
1740 database (see below), read the POSIX standard, the implemented behaviour is
1741 correct! What you see is in fact the result of the decisions made while
1742 POSIX.1 was created. We've only implemented the handling of TZ this way to
1743 be POSIX compliant. It is not really meant to be used.
1745 The alternative approach to handle timezones which is implemented is the
1746 correct one to use: use the timezone database. This avoids all the problems
1747 the POSIX method has plus it is much easier to use. Simply run the tzselect
1748 shell script, answer the question and use the name printed in the end by
1749 making a symlink /etc/localtime pointing to /usr/share/zoneinfo/NAME (NAME
1750 is the returned value from tzselect). That's all. You never again have to
1753 So, please avoid sending bug reports about time related problems if you use
1754 the POSIX method and you have not verified something is really broken by
1755 reading the POSIX standards.
1758 4.4. What other sources of documentation about glibc are available?
1760 {AJ} The FSF has a page about the GNU C library at
1761 <http://www.gnu.org/software/libc/>. The problem data base of open and
1762 solved bugs in GNU libc is available at
1763 <http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl>. Eric Green has written
1764 a HowTo for converting from Linux libc5 to glibc2. The HowTo is accessible
1765 via the FSF page and at <http://www.imaxx.net/~thrytis/glibc>. Frodo
1766 Looijaard describes a different way installing glibc2 as secondary libc at
1767 <http://huizen.dds.nl/~frodol/glibc>.
1769 Please note that this is not a complete list.
1772 4.5. The timezone string for Sydney/Australia is wrong since even when
1773 daylight saving time is in effect the timezone string is EST.
1775 {UD} The problem for some timezones is that the local authorities decided
1776 to use the term "summer time" instead of "daylight saving time". In this
1777 case the abbreviation character `S' is the same as the standard one. So,
1780 Eastern Standard Time = EST
1781 Eastern Summer Time = EST
1783 Great! To get this bug fixed convince the authorities to change the laws
1784 and regulations of the country this effects. glibc behaves correctly.
1787 4.6. I've build make 3.77 against glibc 2.1 and now make gets
1788 segmentation faults.
1790 {} Removed. Does not apply anymore, use make 3.79 or newer.
1793 4.7. Why do so many programs using math functions fail on my AlphaStation?
1795 {AO} The functions floor() and floorf() use an instruction that is not
1796 implemented in some old PALcodes of AlphaStations. This may cause
1797 `Illegal Instruction' core dumps or endless loops in programs that
1798 catch these signals. Updating the firmware to a 1999 release has
1799 fixed the problem on an AlphaStation 200 4/166.
1802 4.8. The conversion table for character set XX does not match with
1805 {UD} I don't doubt for a minute that some of the conversion tables contain
1806 errors. We tried the best we can and relied on automatic generation of the
1807 data to prevent human-introduced errors but this still is no guarantee. If
1808 you think you found a problem please send a bug report describing it and
1809 give an authoritive reference. The latter is important since otherwise
1810 the current behaviour is as good as the proposed one.
1812 Before doing this look through the list of known problem first:
1814 - the GBK (simplified Chinese) encoding is based on Unicode tables. This
1815 is good. These tables, however, differ slightly from the tables used
1816 by the M$ people. The differences are these [+ Unicode, - M$]:
1823 In addition the Unicode tables contain mappings for the GBK characters
1824 0xA8BC, 0xA8BF, 0xA989 to 0xA995, and 0xFE50 to 0xFEA0.
1826 - when mapping from EUC-CN to GBK and vice versa we ignore the fact that
1827 the coded character at position 0xA1A4 maps to different Unicode
1828 characters. Since the iconv() implementation can do whatever it wants
1829 if it cannot directly map a character this is a perfectly good solution
1830 since the semantics and appearance of the character does not change.
1833 4.9. How can I find out which version of glibc I am using in the moment?
1835 {UD} If you want to find out about the version from the command line simply
1836 run the libc binary. This is probably not possible on all platforms but
1837 where it is simply locate the libc DSO and start it as an application. On
1842 This will produce all the information you need.
1844 What always will work is to use the API glibc provides. Compile and run the
1845 following little program to get the version information:
1847 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1849 #include <gnu/libc-version.h>
1850 int main (void) { puts (gnu_get_libc_version ()); return 0; }
1851 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1853 This interface can also obviously be used to perform tests at runtime if
1854 this should be necessary.
1857 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
1859 Answers were given by:
1860 {UD} Ulrich Drepper, <drepper@cygnus.com>
1861 {DMT} David Mosberger-Tang, <davidm@AZStarNet.com>
1862 {RM} Roland McGrath, <roland@gnu.org>
1863 {AJ} Andreas Jaeger, <aj@suse.de>
1864 {EY} Eric Youngdale, <eric@andante.jic.com>
1865 {PB} Phil Blundell, <Philip.Blundell@pobox.com>
1866 {MK} Mark Kettenis, <kettenis@phys.uva.nl>
1867 {ZW} Zack Weinberg, <zack@rabi.phys.columbia.edu>
1868 {TK} Thorsten Kukuk, <kukuk@suse.de>
1869 {GK} Geoffrey Keating, <geoffk@ozemail.com.au>
1870 {HJ} H.J. Lu, <hjl@gnu.org>
1871 {CG} Cristian Gafton, <gafton@redhat.com>
1872 {AO} Alexandre Oliva, <oliva@lsd.ic.unicamp.br>
1873 {BH} Bruno Haible, <haible@clisp.cons.org>
1877 outline-regexp:"\\?"