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FAQ.in
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Frequently Asked Questions about the GNU C Library
This document tries to answer questions a user might have when installing
and using glibc. Please make sure you read this before sending questions or
bug reports to the maintainers.
The GNU C library is very complex. The installation process has not been
completely automated; there are too many variables. You can do substantial
damage to your system by installing the library incorrectly. Make sure you
understand what you are undertaking before you begin.
If you have any questions you think should be answered in this document,
please let me know.
--drepper@cygnus.com
? Compiling glibc
?? What systems does the GNU C Library run on?
{UD} This is difficult to answer. The file `README' lists the architectures
GNU libc was known to run on *at some time*. This does not mean that it
still can be compiled and run on them now.
The systems glibc is known to work on as of this release, and most probably
in the future, are:
*-*-gnu GNU Hurd
i[3456]86-*-linux-gnu Linux-2.x on Intel
m68k-*-linux-gnu Linux-2.x on Motorola 680x0
alpha-*-linux-gnu Linux-2.x on DEC Alpha
powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems
sparc-*-linux-gnu Linux-2.x on SPARC
sparc64-*-linux-gnu Linux-2.x on UltraSPARC
arm-*-none ARM standalone systems
arm-*-linux Linux-2.x on ARM
arm-*-linuxaout Linux-2.x on ARM using a.out binaries
Ports to other Linux platforms are in development, and may in fact work
already, but no one has sent us success reports for them. Currently no
ports to other operating systems are underway, although a few people have
expressed interest.
If you have a system not listed above (or in the `README' file) and you are
really interested in porting it, contact
<bug-glibc@gnu.org>
??binsize What compiler do I need to build GNU libc?
{UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC
are used to increase portability and speed.
GNU CC is found, like all other GNU packages, on
ftp://ftp.gnu.org/pub/gnu
and the many mirror sites. ftp.gnu.org is always overloaded, so try to find
a local mirror first.
You should always try to use the latest official release. Older versions
may not have all the features GNU libc requires. The current releases of
egcs (1.0.3 and 1.1.1) should work with the GNU C library (for powerpc see
?powerpc; for ARM see ?arm).
While the GNU CC should be able to compile glibc it is nevertheless adviced
to use EGCS. Comparing the sizes of glibc on Intel compiled with a recent
EGCS and gcc 2.8.1 shows this:
text data bss dec hex filename
egcs-2.93.10 862897 15944 12824 891665 d9b11 libc.so
gcc-2.8.1 959965 16468 12152 988585 f15a9 libc.so
Make up your own decision.
GNU CC versions 2.95 and above are derived from egcs, and they may do even
better.
Please note that gcc 2.95 and 2.95.x cannot compile glibc on Alpha due to
problems in the complex float support.
?? When I try to compile glibc I get only error messages.
What's wrong?
{UD} You definitely need GNU make to build GNU libc. No other make
program has the needed functionality.
We recommend version GNU make version 3.75 or 3.77. Versions before 3.75
have bugs and/or are missing features. Version 3.76 has bugs which
appear when building big projects like GNU libc. 3.76.1 appears to work but
some people have reported problems. If you build GNU make 3.77 from source,
please read ?make first.
?? Do I need a special linker or assembler?
{ZW} If you want a shared library, you need a linker and assembler that
understand all the features of ELF, including weak and versioned symbols.
The static library can be compiled with less featureful tools, but lacks key
features such as NSS.
For Linux or Hurd, you want binutils 2.8.1.0.23, 2.9.1, or 2.9.1.0.15 or
higher. These are the only versions we've tested and found reliable. Other
versions after 2.8.1.0.23 may work but we don't recommend them, especially
not when C++ is involved. Earlier versions do not work at all.
Other operating systems may come with system tools that have all the
necessary features, but this is moot because glibc hasn't been ported to
them.
??powerpc Which compiler should I use for powerpc?
{GK} You want to use at least gcc 2.95 (together with the right versions
of all the other tools, of course). See also question ?excpt.
??arm Which tools should I use for ARM?
{PB} You should use egcs 1.1 or a later version. For ELF systems some
changes are needed to the compiler; a patch against egcs-1.1.x can be found
at:
<ftp://ftp.netwinder.org/users/p/philb/egcs-1.1.1pre2-diff-981126>
Binutils 2.9.1.0.16 or later is also required.
?? Do I need some more things to compile the GNU C Library?
{UD} Yes, there are some more :-).
* GNU gettext. This package contains the tools needed to construct
`message catalog' files containing translated versions of system
messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror
site. (We distribute compiled message catalogs, but they may not be
updated in patches.) Please note that the required minimal version
(0.10.35) of gettext is alpha software and available from
ftp://alpha.gnu.org/gnu .
* Some files are built with special tools. E.g., files ending in .gperf
need a `gperf' program. The GNU version (now available in a separate
package, formerly only as part of libg++) is known to work while some
vendor versions do not.
You should not need these tools unless you change the source files.
* Perl 5 is needed if you wish to test an installation of GNU libc
as the primary C library.
* When compiling for Linux, the header files of the Linux kernel must
be available to the compiler as <linux/*.h> and <asm/*.h>.
* lots of disk space (~400MB for i?86-linux; more for RISC platforms).
* plenty of time. Compiling just the shared and static libraries for
i?86-linux takes approximately 1h on an AMD-K6@225MHz w/ 96MB of RAM,
45mins on a Celeron@400MHz w/ 128MB, and 55mins on a Alpha@533MHz w/ 256MB.
Multiply this by 1.5 or 2.0 if you build profiling and/or the highly
optimized version as well. For Hurd systems times are much higher.
You should avoid compiling in a NFS mounted filesystem. This is
very slow.
James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time of
45h34m for a full build (shared, static, and profiled) on Atari
Falcon (Motorola 68030 @ 16 Mhz, 14 Mb memory) and Jan Barte
<yann@plato.uni-paderborn.de> reports 22h48m on Atari TT030
(Motorola 68030 @ 32 Mhz, 34 Mb memory)
A full build of the PowerPC library took 1h on a PowerPC 750@400Mhz w/
64MB of RAM, and about 9h on a 601@60Mhz w/ 72Mb.
If you have some more measurements let me know.
?? What version of the Linux kernel headers should be used?
{AJ,UD} The headers from the most recent Linux kernel should be used. The
headers used while compiling the GNU C library and the kernel binary used
when using the library do not need to match. The GNU C library runs without
problems on kernels that are older than the kernel headers used. The other
way round (compiling the GNU C library with old kernel headers and running
on a recent kernel) does not necessarily work. For example you can't use
new kernel features if you used old kernel headers to compile the GNU C
library.
{ZW} Even if you are using a 2.0 kernel on your machine, we recommend you
compile GNU libc with 2.2 kernel headers. That way you won't have to
recompile libc if you ever upgrade to kernel 2.2. To tell libc which
headers to use, give configure the --with-headers switch
(e.g. --with-headers=/usr/src/linux-2.2.0/include).
Note that you must configure the 2.2 kernel if you do this, otherwise libc
will be unable to find <linux/version.h>. Just change the current directory
to the root of the 2.2 tree and do `make include/linux/version.h'.
?? The compiler hangs while building iconvdata modules. What's
wrong?
{ZW} This is a problem with old versions of GCC. Initialization of large
static arrays is very slow. The compiler will eventually finish; give it
time.
The problem is fixed in egcs 1.1.
?? When I run `nm -u libc.so' on the produced library I still
find unresolved symbols. Can this be ok?
{UD} Yes, this is ok. There can be several kinds of unresolved symbols:
* magic symbols automatically generated by the linker. These have names
like __start_* and __stop_*
* symbols starting with _dl_* come from the dynamic linker
* weak symbols, which need not be resolved at all (fabs for example)
Generally, you should make sure you find a real program which produces
errors while linking before deciding there is a problem.
??addon What are these `add-ons'?
{UD} To avoid complications with export rules or external source code some
optional parts of the libc are distributed as separate packages (e.g., the
crypt package, see ?crypt).
To use these packages as part of GNU libc, just unpack the tarfiles in the
libc source directory and tell the configuration script about them using the
--enable-add-ons option. If you give just --enable-add-ons configure tries
to find all the add-on packages in your source tree. This may not work. If
it doesn't, or if you want to select only a subset of the add-ons, give a
comma-separated list of the add-ons to enable:
configure --enable-add-ons=crypt,linuxthreads
for example.
Add-ons can add features (including entirely new shared libraries), override
files, provide support for additional architectures, and just about anything
else. The existing makefiles do most of the work; only some few stub rules
must be written to get everything running.
Most add-ons are tightly coupled to a specific GNU libc version. Please
check that the add-ons work with the GNU libc. For example the crypt and
linuxthreads add-ons have the same numbering scheme as the libc and will in
general only work with the corresponding libc.
?? My XXX kernel emulates a floating-point coprocessor for me.
Should I enable --with-fp?
{ZW} An emulated FPU is just as good as a real one, as far as the C library
is concerned. You only need to say --without-fp if your machine has no way
to execute floating-point instructions.
People who are interested in squeezing the last drop of performance
out of their machine may wish to avoid the trap overhead, but this is
far more trouble than it's worth: you then have to compile
*everything* this way, including the compiler's internal libraries
(libgcc.a for GNU C), because the calling conventions change.
?? When compiling GNU libc I get lots of errors saying functions
in glibc are duplicated in libgcc.
{EY} This is *exactly* the same problem that I was having. The problem was
due to the fact that configure didn't correctly detect that the linker flag
--no-whole-archive was supported in my linker. In my case it was because I
had run ./configure with bogus CFLAGS, and the test failed.
One thing that is particularly annoying about this problem is that once this
is misdetected, running configure again won't fix it unless you first delete
config.cache.
{UD} Starting with glibc-2.0.3 there should be a better test to avoid some
problems of this kind. The setting of CFLAGS is checked at the very
beginning and if it is not usable `configure' will bark.
?? Why do I get messages about missing thread functions when I use
librt? I don't even use threads.
{UD} In this case you probably mixed up your installation. librt uses
threads internally and has implicit references to the thread library.
Normally these references are satisfied automatically but if the thread
library is not in the expected place you must tell the linker where it is.
When using GNU ld it works like this:
gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt
The `/some/other/dir' should contain the thread library. `ld' will use the
given path to find the implicitly referenced library while not disturbing
any other link path.
?? What's the problem with configure --enable-omitfp?
{AJ} When --enable-omitfp is set the libraries are built without frame
pointers. Some compilers produce buggy code for this model and therefore we
don't advise using it at the moment.
If you use --enable-omitfp, you're on your own. If you encounter problems
with a library that was build this way, we advise you to rebuild the library
without --enable-omitfp. If the problem vanishes consider tracking the
problem down and report it as compiler failure.
Since a library built with --enable-omitfp is undebuggable on most systems,
debuggable libraries are also built - you can use them by appending "_g" to
the library names.
The compilation of these extra libraries and the compiler optimizations slow
down the build process and need more disk space.
?? I get failures during `make check'. What should I do?
{AJ} The testsuite should compile and run cleanly on your system; every
failure should be looked into. Depending on the failures, you probably
should not install the library at all.
You should consider using the `glibcbug' script to report the failure,
providing as much detail as possible. If you run a test directly, please
remember to set up the environment correctly. You want to test the compiled
library - and not your installed one. The best way is to copy the exact
command line which failed and run the test from the subdirectory for this
test in the sources.
There are some failures which are not directly related to the GNU libc:
- Some compilers produce buggy code. No compiler gets single precision
complex numbers correct on Alpha. Otherwise, the egcs 1.1 release should be
ok; gcc 2.8.1 might cause some failures; gcc 2.7.2.x is so buggy that
explicit checks have been used so that you can't build with it.
- The kernel might have bugs. For example on Linux/Alpha 2.0.34 the
floating point handling has quite a number of bugs and therefore most of
the test cases in the math subdirectory will fail. Linux 2.2 has
fixes for the floating point support on Alpha. The Linux/SPARC kernel has
also some bugs in the FPU emulation code (as of Linux 2.2.0).
- Other tools might have problems. For example bash 2.03 gives a
segmentation fault running the tst-rpmatch.sh test script.
?? What is symbol versioning good for? Do I need it?
{AJ} Symbol versioning solves problems that are related to interface
changes. One version of an interface might have been introduced in a
previous version of the GNU C library but the interface or the semantics of
the function has been changed in the meantime. For binary compatibility
with the old library, a newer library needs to still have the old interface
for old programs. On the other hand, new programs should use the new
interface. Symbol versioning is the solution for this problem. The GNU
libc version 2.1 uses symbol versioning by default if the installed binutils
supports it.
We don't advise building without symbol versioning, since you lose binary
compatibility - forever! The binary compatibility you lose is not only
against the previous version of the GNU libc (version 2.0) but also against
all future versions.
?? How can I compile on my fast ix86 machine a working libc for my slow
i386? After installing libc, programs abort with "Illegal
Instruction".
{AJ} glibc and gcc might generate some instructions on your machine that
aren't available on i386. You've got to tell glibc that you're configuring
for i386 with adding i386 as your machine, for example:
../configure --prefix=/usr i386-pc-linux-gnu
And you need to tell gcc to only generate i386 code, just add `-mcpu=i386'
(just -m386 doesn't work) to your CFLAGS.
{UD} This applies not only to the i386. Compiling on a i686 for any older
model will also fail if the above methods are not used.
? Installation and configuration issues
?? Can I replace the libc on my Linux system with GNU libc?
{UD} You cannot replace any existing libc for Linux with GNU libc. It is
binary incompatible and therefore has a different major version. You can,
however, install it alongside your existing libc.
For Linux there are three major libc versions:
libc-4 a.out libc
libc-5 original ELF libc
libc-6 GNU libc
You can have any combination of these three installed. For more information
consult documentation for shared library handling. The Makefiles of GNU
libc will automatically generate the needed symbolic links which the linker
will use.
?? How do I configure GNU libc so that the essential libraries
like libc.so go into /lib and the other into /usr/lib?
{UD,AJ} Like all other GNU packages GNU libc is designed to use a base
directory and install all files relative to this. The default is
/usr/local, because this is safe (it will not damage the system if installed
there). If you wish to install GNU libc as the primary C library on your
system, set the base directory to /usr (i.e. run configure --prefix=/usr
<other_options>). Note that this can damage your system; see ?safety for
details.
Some systems like Linux have a filesystem standard which makes a difference
between essential libraries and others. Essential libraries are placed in
/lib because this directory is required to be located on the same disk
partition as /. The /usr subtree might be found on another
partition/disk. If you configure for Linux with --prefix=/usr, then this
will be done automatically.
To install the essential libraries which come with GNU libc in /lib on
systems other than Linux one must explicitly request it. Autoconf has no
option for this so you have to use a `configparms' file (see the `INSTALL'
file for details). It should contain:
slibdir=/lib
sysconfdir=/etc
The first line specifies the directory for the essential libraries, the
second line the directory for system configuration files.
??safety How should I avoid damaging my system when I install GNU libc?
{ZW} If you wish to be cautious, do not configure with --prefix=/usr. If
you don't specify a prefix, glibc will be installed in /usr/local, where it
will probably not break anything. (If you wish to be certain, set the
prefix to something like /usr/local/glibc2 which is not used for anything.)
The dangers when installing glibc in /usr are twofold:
* glibc will overwrite the headers in /usr/include. Other C libraries
install a different but overlapping set of headers there, so the effect
will probably be that you can't compile anything. You need to rename
/usr/include out of the way before running `make install'. (Do not throw
it away; you will then lose the ability to compile programs against your
old libc.)
* None of your old libraries, static or shared, can be used with a
different C library major version. For shared libraries this is not a
problem, because the filenames are different and the dynamic linker
will enforce the restriction. But static libraries have no version
information. You have to evacuate all the static libraries in
/usr/lib to a safe location.
The situation is rather similar to the move from a.out to ELF which
long-time Linux users will remember.
?? Do I need to use GNU CC to compile programs that will use the
GNU C Library?
{ZW} In theory, no; the linker does not care, and the headers are supposed
to check for GNU CC before using its extensions to the C language.
However, there are currently no ports of glibc to systems where another
compiler is the default, so no one has tested the headers extensively
against another compiler. You may therefore encounter difficulties. If you
do, please report them as bugs.
Also, in several places GNU extensions provide large benefits in code
quality. For example, the library has hand-optimized, inline assembly
versions of some string functions. These can only be used with GCC. See
?string for details.
??crypt When linking with the new libc I get unresolved symbols
`crypt' and `setkey'. Why aren't these functions in the
libc anymore?
{UD} The US places restrictions on exporting cryptographic programs and
source code. Until this law gets abolished we cannot ship the cryptographic
functions together with glibc.
The functions are available, as an add-on (see ?addon). People in the US
may get it from the same place they got GNU libc from. People outside the
US should get the code from ftp.gwdg.de [134.76.11.100] in the directory
pub/linux/glibc, or another archive site outside the USA. The README explains
how to install the sources.
If you already have the crypt code on your system the reason for the failure
is probably that you did not link with -lcrypt. The crypto functions are in
a separate library to make it possible to export GNU libc binaries from the
US.
?? When I use GNU libc on my Linux system by linking against
the libc.so which comes with glibc all I get is a core dump.
{UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the
user specifies a --dynamic-linker argument. This is the name of the libc5
dynamic linker, which does not work with glibc.
For casual use of GNU libc you can just specify to the linker
--dynamic-linker=/lib/ld-linux.so.2
which is the glibc dynamic linker, on Linux systems. On other systems the
name is /lib/ld.so.1. When linking via gcc, you've got to add
-Wl,--dynamic-linker=/lib/ld-linux.so.2
to the gcc command line.
To change your environment to use GNU libc for compiling you need to change
the `specs' file of your gcc. This file is normally found at
/usr/lib/gcc-lib/<arch>/<version>/specs
In this file you have to change a few things:
- change `ld-linux.so.1' to `ld-linux.so.2'
- remove all expression `%{...:-lgmon}'; there is no libgmon in glibc
- fix a minor bug by changing %{pipe:-} to %|
Here is what the gcc-2.7.2 specs file should look like when GNU libc is
installed at /usr:
-----------------------------------------------------------------------
*asm:
%{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*}
*asm_final:
%|
*cpp:
%{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}
*cc1:
%{profile:-p}
*cc1plus:
*endfile:
%{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s
*link:
-m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}}
*lib:
%{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}}
*libgcc:
-lgcc
*startfile:
%{!shared: %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} %{!p:%{profile:gcrt1.o%s} %{!profile:crt1.o%s}}}} crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s}
*switches_need_spaces:
*signed_char:
%{funsigned-char:-D__CHAR_UNSIGNED__}
*predefines:
-D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386)
*cross_compile:
0
*multilib:
. ;
-----------------------------------------------------------------------
Things get a bit more complicated if you have GNU libc installed in some
other place than /usr, i.e., if you do not want to use it instead of the old
libc. In this case the needed startup files and libraries are not found in
the regular places. So the specs file must tell the compiler and linker
exactly what to use.
Version 2.7.2.3 does and future versions of GCC will automatically
provide the correct specs.
?? Looking through the shared libc file I haven't found the
functions `stat', `lstat', `fstat', and `mknod' and while
linking on my Linux system I get error messages. How is
this supposed to work?
{RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed
to be undefined references in libc.so.6! Your problem is probably a missing
or incorrect /usr/lib/libc.so file; note that this is a small text file now,
not a symlink to libc.so.6. It should look something like this:
GROUP ( libc.so.6 libc_nonshared.a )
??excpt When I run an executable on one system which I compiled on
another, I get dynamic linker errors. Both systems have the same
version of glibc installed. What's wrong?
{ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the
other with egcs (any version). Egcs has functions in its internal
`libgcc.a' to support exception handling with C++. They are linked into
any program or dynamic library compiled with egcs, whether it needs them or
not. Dynamic libraries then turn around and export those functions again
unless special steps are taken to prevent them.
When you link your program, it resolves its references to the exception
functions to the ones exported accidentally by libc.so. That works fine as
long as libc has those functions. On the other system, libc doesn't have
those functions because it was compiled by gcc 2.8, and you get undefined
symbol errors. The symbols in question are named things like
`__register_frame_info'.
For glibc 2.0, the workaround is to not compile libc with egcs. We've also
incorporated a patch which should prevent the EH functions sneaking into
libc. It doesn't matter what compiler you use to compile your program.
For glibc 2.1, we've chosen to do it the other way around: libc.so
explicitly provides the EH functions. This is to prevent other shared
libraries from doing it.
{UD} Starting with glibc 2.1.1 you can compile glibc with gcc 2.8.1 or
newer since we have explicitly add references to the functions causing the
problem. But you nevertheless should use EGCS for other reasons
(see ?binsize).
{GK} On some Linux distributions for PowerPC, you can see this when you have
built gcc or egcs from the Web sources (gcc versions 2.95 or earlier), then
re-built glibc. This happens because in these versions of gcc, exception
handling is implemented using an older method; the people making the
distributions are a little ahead of their time.
A quick solution to this is to find the libgcc.a file that came with the
distribution (it would have been installed under /usr/lib/gcc-lib), do
`ar x libgcc.a frame.o' to get the frame.o file out, and add a line saying
`LDLIBS-c.so += frame.o' to the file `configparms' in the directory you're
building in. You can check you've got the right `frame.o' file by running
`nm frame.o' and checking that it has the symbols defined that you're
missing.
This will let you build glibc with the C compiler. The C++ compiler
will still be binary incompatible with any C++ shared libraries that
you got with your distribution.
?? How can I compile gcc 2.7.2.1 from the gcc source code using
glibc 2.x?
{AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later.
But you should get at least gcc 2.8.1 or egcs 1.1 (or later versions)
instead.
?? The `gencat' utility cannot process the catalog sources which
were used on my Linux libc5 based system. Why?
{UD} The `gencat' utility provided with glibc complies to the XPG standard.
The older Linux version did not obey the standard, so they are not
compatible.
To ease the transition from the Linux version some of the non-standard
features are also present in the `gencat' program of GNU libc. This mainly
includes the use of symbols for the message number and the automatic
generation of header files which contain the needed #defines to map the
symbols to integers.
Here is a simple SED script to convert at least some Linux specific catalog
files to the XPG4 form:
-----------------------------------------------------------------------
# Change catalog source in Linux specific format to standard XPG format.
# Ulrich Drepper <drepper@cygnus.com>, 1996.
#
/^\$ #/ {
h
s/\$ #\([^ ]*\).*/\1/
x
s/\$ #[^ ]* *\(.*\)/\$ \1/
}
/^# / {
s/^# \(.*\)/\1/
G
s/\(.*\)\n\(.*\)/\2 \1/
}
-----------------------------------------------------------------------
?? Programs using libc have their messages translated, but other
behavior is not localized (e.g. collating order); why?
{ZW} Translated messages are automatically installed, but the locale
database that controls other behaviors is not. You need to run localedef to
install this database, after you have run `make install'. For example, to
set up the French Canadian locale, simply issue the command
localedef -i fr_CA -f ISO-8859-1 fr_CA
Please see localedata/README in the source tree for further details.
?? I have set up /etc/nis.conf, and the Linux libc 5 with NYS
works great. But the glibc NIS+ doesn't seem to work.
{TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for
storing information about the NIS+ server and their public keys, because the
nis.conf file does not contain all the necessary information. You have to
copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is
byte order independent) or generate it with nisinit from the nis-tools
package; available at
http://www.suse.de/~kukuk/linux/nisplus.html
?? I have killed ypbind to stop using NIS, but glibc
continues using NIS.
{TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from
ypbind. ypbind 3.3 and older versions don't always remove these files, so
glibc will continue to use them. Other BSD versions seem to work correctly.
Until ypbind 3.4 is released, you can find a patch at
<ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz>
?? Under Linux/Alpha, I always get "do_ypcall: clnt_call:
RPC: Unable to receive; errno = Connection refused" when using NIS.
{TK} You need a ypbind version which is 64bit clean. Some versions are not
64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3,
you need the patch from ftp.kernel.org (See the previous question). I don't
know about other versions.
?? After installing glibc name resolving doesn't work properly.
{AJ} You probably should read the manual section describing nsswitch.conf
(just type `info libc "NSS Configuration File"'). The NSS configuration
file is usually the culprit.
?? How do I create the databases for NSS?
{AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create
the database files. The glibc sources contain a Makefile which does the
necessary conversion and calls to create those files. The file is
`db-Makefile' in the subdirectory `nss' and you can call it with `make -f
db-Makefile'. Please note that not all services are capable of using a
database. Currently passwd, group, ethers, protocol, rpc, services shadow
and netgroup are implemented.
?? I have /usr/include/net and /usr/include/scsi as symlinks
into my Linux source tree. Is that wrong?
{PB} This was necessary for libc5, but is not correct when using glibc.
Including the kernel header files directly in user programs usually does not
work (see ?kerhdr). glibc provides its own <net/*> and <scsi/*> header
files to replace them, and you may have to remove any symlink that you have
in place before you install glibc. However, /usr/include/asm and
/usr/include/linux should remain as they were.
?? Programs like `logname', `top', `uptime' `users', `w' and
`who', show incorrect information about the (number of)
users on my system. Why?
{MK} See ?getlog.
?? After upgrading to glibc 2.1 with symbol versioning I get
errors about undefined symbols. What went wrong?
{AJ} The problem is caused either by wrong program code or tools. In the
versioned libc a lot of symbols are now local that were global symbols in
previous versions. It seems that programs linked against older versions
often accidentally used libc global variables -- something that should not
happen.
The only way to fix this is to recompile your program. Sorry, that's the
price you might have to pay once for quite a number of advantages with
symbol versioning.
?? When I start the program XXX after upgrading the library
I get
XXX: Symbol `_sys_errlist' has different size in shared
object, consider re-linking
Why? What should I do?
{UD} As the message says, relink the binary. The problem is that a few
symbols from the library can change in size and there is no way to avoid
this. _sys_errlist is a good example. Occasionally there are new error
numbers added to the kernel and this must be reflected at user level,
breaking programs that refer to them directly.
Such symbols should normally not be used at all. There are mechanisms to
avoid using them. In the case of _sys_errlist, there is the strerror()
function which should _always_ be used instead. So the correct fix is to
rewrite that part of the application.
In some situations (especially when testing a new library release) it might
be possible that a symbol changed size when that should not have happened.
So in case of doubt report such a warning message as a problem.
?? What do I need for C++ development?
{HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or
gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++
support and works directly with glibc 2.1. If you use gcc-2.8.1 with
libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available
as:
<ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz>
Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work
very well with the GNU C library due to vtable thunks. If you're upgrading
from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library
compiled for 2.0 is not compatible due to the new Large File Support (LFS)
in version 2.1.
{UD} But since in the case of a shared libstdc++ the version numbers should
be different existing programs will continue to work.
?? Even statically linked programs need some shared libraries
which is not acceptable for me. What can I do?
{AJ} NSS (for details just type `info libc "Name Service Switch"') won't
work properly without shared libraries. NSS allows using different services
(e.g. NIS, files, db, hesiod) by just changing one configuration file
(/etc/nsswitch.conf) without relinking any programs. The only disadvantage
is that now static libraries need to access shared libraries. This is
handled transparently by the GNU C library.
A solution is to configure glibc with --enable-static-nss. In this case you
can create a static binary that will use only the services dns and files
(change /etc/nsswitch.conf for this). You need to link explicitly against
all these services. For example:
gcc -static test-netdb.c -o test-netdb.c \
-lc -lnss_files -lnss_dns -lresolv
The problem with this approach is that you've got to link every static
program that uses NSS routines with all those libraries.
{UD} In fact, one cannot say anymore that a libc compiled with this
option is using NSS. There is no switch anymore. Therefore it is
*highly* recommended *not* to use --enable-static-nss since this makes
the behaviour of the programs on the system inconsistent.
?? I just upgraded my Linux system to glibc and now I get
errors whenever I try to link any program.
{ZW} This happens when you have installed glibc as the primary C library but
have stray symbolic links pointing at your old C library. If the first
`libc.so' the linker finds is libc 5, it will use that. Your program
expects to be linked with glibc, so the link fails.
The most common case is that glibc put its `libc.so' in /usr/lib, but there
was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the
problem, just delete /lib/libc.so. You may also need to delete other
symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5.
{AJ} The perl script test-installation.pl which is run as last step during
an installation of glibc that is configured with --prefix=/usr should help
detect these situations. If the script reports problems, something is
really screwed up.
?? When I use nscd the machine freezes.
{UD} You cannot use nscd with Linux 2.0.*. There is functionality missing
in the kernel and work-arounds are not suitable. Besides, some parts of the
kernel are too buggy when it comes to using threads.
If you need nscd, you have to use at least a 2.1 kernel.
Note that I have at this point no information about any other platform.
?? I need lots of open files. What do I have to do?
{AJ} This is at first a kernel issue. The kernel defines limits with
OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the
number of used file descriptors. You need to change these values in your
kernel and recompile the kernel so that the kernel allows to use more open
files. You don't necessarily need to recompile the GNU C library since the
only place where OPEN_MAX and FD_SETSIZE is really needed in the library
itself is the size of fd_set which is used by select.
The GNU C library is now select free. This means it internally has no
limits imposed by the `fd_set' type. Instead all places where the
functionality is needed the `poll' function is used.
If you increase the number of file descriptors in the kernel you don't need
to recompile the C library.
{UD} You can always get the maximum number of file descriptors a process is
allowed to have open at any time using
number = sysconf (_SC_OPEN_MAX);
This will work even if the kernel limits change.
?? How do I get the same behavior on parsing /etc/passwd and
/etc/group as I have with libc5 ?
{TK} The name switch setup in /etc/nsswitch.conf selected by most Linux
distributions does not support +/- and netgroup entries in the files like
/etc/passwd. Though this is the preferred setup some people might have
setups coming over from the libc5 days where it was the default to recognize
lines like this. To get back to the old behaviour one simply has to change
the rules for passwd, group, and shadow in the nsswitch.conf file as
follows:
passwd: compat
group: compat
shadow: compat
passwd_compat: nis
group_compat: nis
shadow_compat: nis
??libs What needs to be recompiled when upgrading from glibc 2.0 to glibc
2.1?
{AJ,CG} If you just upgrade the glibc from 2.0.x (x <= 7) to 2.1, binaries
that have been linked against glibc 2.0 will continue to work.
If you compile your own binaries against glibc 2.1, you also need to
recompile some other libraries. The problem is that libio had to be changed
and therefore libraries that are based or depend on the libio of glibc,
e.g. ncurses, slang and most C++ libraries, need to be recompiled. If you
experience strange segmentation faults in your programs linked against glibc
2.1, you might need to recompile your libraries.
Another problem is that older binaries that were linked statically against
glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of
libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled
static libraries (libfoo.a) which happen to depend on the older libio
behavior will be broken by the glibc 2.1 upgrade. We plan to produce a
compatibility library that people will be able to link in if they want
to compile a static library generated against glibc 2.0 into a program
on a glibc 2.1 system. You just add -lcompat and you should be fine.
The glibc-compat add-on will provide the libcompat.a library, the older
nss modules, and a few other files. Together, they should make it
possible to do development with old static libraries on a glibc 2.1
system. This add-on is still in development. You can get it from
<ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz>
but please keep in mind that it is experimental.
?? Why is extracting files via tar so slow?
{AJ} Extracting of tar archives might be quite slow since tar has to look up
userid and groupids and doesn't cache negative results. If you have nis or
nisplus in your /etc/nsswitch.conf for the passwd and/or group database,
each file extractions needs a network connection. There are two possible
solutions:
- do you really need NIS/NIS+ (some Linux distributions add by default
nis/nisplus even if it's not needed)? If not, just remove the entries.
- if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes
with glibc 2.1.
?? Compiling programs I get parse errors in libio.h (e.g. "parse error
before `_IO_seekoff'"). How should I fix this?
{AJ} You might get the following errors when upgrading to glibc 2.1:
In file included from /usr/include/stdio.h:57,
from ...
/usr/include/libio.h:335: parse error before `_IO_seekoff'
/usr/include/libio.h:335: parse error before `_G_off64_t'
/usr/include/libio.h:336: parse error before `_IO_seekpos'
/usr/include/libio.h:336: parse error before `_G_fpos64_t'
The problem is a wrong _G_config.h file in your include path. The
_G_config.h file that comes with glibc 2.1 should be used and not one from
libc5 or from a compiler directory. To check which _G_config.h file the
compiler uses, compile your program with `gcc -E ...|grep G_config.h' and
remove that file. Your compiler should pick up the file that has been
installed by glibc 2.1 in your include directory.
?? After upgrading to glibc 2.1, libraries that were compiled against
glibc 2.0.x don't work anymore.
{AJ} See ?libs.
? Source and binary incompatibilities, and what to do about them
?? I expect GNU libc to be 100% source code compatible with
the old Linux based GNU libc. Why isn't it like this?
{DMT,UD} Not every extension in Linux libc's history was well thought-out.
In fact it had a lot of problems with standards compliance and with
cleanliness. With the introduction of a new version number these errors can
now be corrected. Here is a list of the known source code
incompatibilities:
* _GNU_SOURCE: glibc does not make the GNU extensions available
automatically. If a program depends on GNU extensions or some
other non-standard functionality, it is necessary to compile it
with the C compiler option -D_GNU_SOURCE, or better, to put
`#define _GNU_SOURCE' at the beginning of your source files, before
any C library header files are included. This difference normally
manifests itself in the form of missing prototypes and/or data type
definitions. Thus, if you get such errors, the first thing you
should do is try defining _GNU_SOURCE and see if that makes the
problem go away.
For more information consult the file `NOTES' in the GNU C library
sources.
* reboot(): GNU libc sanitizes the interface of reboot() to be more
compatible with the interface used on other OSes. reboot() as
implemented in glibc takes just one argument. This argument
corresponds to the third argument of the Linux reboot system call.
That is, a call of the form reboot(a, b, c) needs to be changed into
reboot(c). Beside this the header <sys/reboot.h> defines the needed
constants for the argument. These RB_* constants should be used
instead of the cryptic magic numbers.
* swapon(): the interface of this function didn't change, but the
prototype is in a separate header file <sys/swap.h>. This header
file also provides the SWAP_* constants defined by <linux/swap.h>;
you should use them for the second argument to swapon().
* errno: If a program uses the variable "errno", then it _must_
include <errno.h>. The old libc often (erroneously) declared this
variable implicitly as a side-effect of including other libc header