1 Installing the GNU C Library
2 ****************************
4 Before you do anything else, you should read the FAQ at
5 <https://sourceware.org/glibc/wiki/FAQ>. It answers common questions
6 and describes problems you may experience with compilation and
9 You will need recent versions of several GNU tools: definitely GCC
10 and GNU Make, and possibly others. *Note Tools for Compilation::,
13 Configuring and compiling the GNU C Library
14 ===========================================
16 The GNU C Library cannot be compiled in the source directory. You must
17 build it in a separate build directory. For example, if you have
18 unpacked the GNU C Library sources in '/src/gnu/glibc-VERSION', create a
19 directory '/src/gnu/glibc-build' to put the object files in. This
20 allows removing the whole build directory in case an error occurs, which
21 is the safest way to get a fresh start and should always be done.
23 From your object directory, run the shell script 'configure' located
24 at the top level of the source tree. In the scenario above, you'd type
26 $ ../glibc-VERSION/configure ARGS...
28 Please note that even though you're building in a separate build
29 directory, the compilation may need to create or modify files and
30 directories in the source directory.
32 'configure' takes many options, but the only one that is usually
33 mandatory is '--prefix'. This option tells 'configure' where you want
34 the GNU C Library installed. This defaults to '/usr/local', but the
35 normal setting to install as the standard system library is
36 '--prefix=/usr' for GNU/Linux systems and '--prefix=' (an empty prefix)
39 It may also be useful to set the CC and CFLAGS variables in the
40 environment when running 'configure'. CC selects the C compiler that
41 will be used, and CFLAGS sets optimization options for the compiler.
43 The following list describes all of the available options for
47 Install machine-independent data files in subdirectories of
48 'DIRECTORY'. The default is to install in '/usr/local'.
50 '--exec-prefix=DIRECTORY'
51 Install the library and other machine-dependent files in
52 subdirectories of 'DIRECTORY'. The default is to the '--prefix'
53 directory if that option is specified, or '/usr/local' otherwise.
55 '--with-headers=DIRECTORY'
56 Look for kernel header files in DIRECTORY, not '/usr/include'. The
57 GNU C Library needs information from the kernel's header files
58 describing the interface to the kernel. The GNU C Library will
59 normally look in '/usr/include' for them, but if you specify this
60 option, it will look in DIRECTORY instead.
62 This option is primarily of use on a system where the headers in
63 '/usr/include' come from an older version of the GNU C Library.
64 Conflicts can occasionally happen in this case. You can also use
65 this option if you want to compile the GNU C Library with a newer
66 set of kernel headers than the ones found in '/usr/include'.
68 '--enable-kernel=VERSION'
69 This option is currently only useful on GNU/Linux systems. The
70 VERSION parameter should have the form X.Y.Z and describes the
71 smallest version of the Linux kernel the generated library is
72 expected to support. The higher the VERSION number is, the less
73 compatibility code is added, and the faster the code gets.
75 '--with-binutils=DIRECTORY'
76 Use the binutils (assembler and linker) in 'DIRECTORY', not the
77 ones the C compiler would default to. You can use this option if
78 the default binutils on your system cannot deal with all the
79 constructs in the GNU C Library. In that case, 'configure' will
80 detect the problem and suppress these constructs, so that the
81 library will still be usable, but functionality may be lost--for
82 example, you can't build a shared libc with old binutils.
85 Don't build shared libraries even if it is possible. Not all
86 systems support shared libraries; you need ELF support and
87 (currently) the GNU linker.
90 Don't build libraries with profiling information. You may want to
91 use this option if you don't plan to do profiling.
94 Compile static versions of the NSS (Name Service Switch) libraries.
95 This is not recommended because it defeats the purpose of NSS; a
96 program linked statically with the NSS libraries cannot be
97 dynamically reconfigured to use a different name database.
99 '--enable-hardcoded-path-in-tests'
100 By default, dynamic tests are linked to run with the installed C
101 library. This option hardcodes the newly built C library path in
102 dynamic tests so that they can be invoked directly.
104 '--disable-timezone-tools'
105 By default, timezone related utilities ('zic', 'zdump', and
106 'tzselect') are installed with the GNU C Library. If you are
107 building these independently (e.g. by using the 'tzcode' package),
108 then this option will allow disabling the install of these.
110 Note that you need to make sure the external tools are kept in sync
111 with the versions that the GNU C Library expects as the data
112 formats may change over time. Consult the 'timezone' subdirectory
115 '--enable-stack-protector'
116 '--enable-stack-protector=strong'
117 '--enable-stack-protector=all'
118 Compile the C library and all other parts of the glibc package
119 (including the threading and math libraries, NSS modules, and
120 transliteration modules) using the GCC '-fstack-protector',
121 '-fstack-protector-strong' or '-fstack-protector-all' options to
122 detect stack overruns. Only the dynamic linker and a small number
123 of routines called directly from assembler are excluded from this
127 Disable lazy binding for installed shared objects. This provides
128 additional security hardening because it enables full RELRO and a
129 read-only global offset table (GOT), at the cost of slightly
130 increased program load times.
133 The file 'pt_chown' is a helper binary for 'grantpt' (*note
134 Pseudo-Terminals: Allocation.) that is installed setuid root to fix
135 up pseudo-terminal ownership. It is not built by default because
136 systems using the Linux kernel are commonly built with the 'devpts'
137 filesystem enabled and mounted at '/dev/pts', which manages
138 pseudo-terminal ownership automatically. By using
139 '--enable-pt_chown', you may build 'pt_chown' and install it setuid
140 and owned by 'root'. The use of 'pt_chown' introduces additional
141 security risks to the system and you should enable it only if you
142 understand and accept those risks.
145 By default, the GNU C Library is built with '-Werror'. If you wish
146 to build without this option (for example, if building with a newer
147 version of GCC than this version of the GNU C Library was tested
148 with, so new warnings cause the build with '-Werror' to fail), you
149 can configure with '--disable-werror'.
152 By default for x86_64, the GNU C Library is built with the vector
153 math library. Use this option to disable the vector math library.
156 Tunables support allows additional library parameters to be
157 customized at runtime. This feature is enabled by default. This
158 option can take the following values:
161 This is the default if no option is passed to configure. This
162 enables tunables and selects the default frontend (currently
166 This option disables tunables.
169 This enables tunables and selects the 'valstring' frontend for
170 tunables. This frontend allows users to specify tunables as a
171 colon-separated list in a single environment variable
174 '--enable-obsolete-nsl'
175 By default, libnsl is only built as shared library for backward
176 compatibility and the NSS modules libnss_compat, libnss_nis and
177 libnss_nisplus are not built at all. Use this option to enable
178 libnsl with all depending NSS modules and header files.
180 '--disable-experimental-malloc'
181 By default, a per-thread cache is enabled in 'malloc'. While this
182 cache can be disabled on a per-application basis using tunables
183 (set glibc.malloc.tcache_count to zero), this option can be used to
184 remove it from the build completely.
186 '--build=BUILD-SYSTEM'
188 These options are for cross-compiling. If you specify both options
189 and BUILD-SYSTEM is different from HOST-SYSTEM, 'configure' will
190 prepare to cross-compile the GNU C Library from BUILD-SYSTEM to be
191 used on HOST-SYSTEM. You'll probably need the '--with-headers'
192 option too, and you may have to override CONFIGURE's selection of
193 the compiler and/or binutils.
195 If you only specify '--host', 'configure' will prepare for a native
196 compile but use what you specify instead of guessing what your
197 system is. This is most useful to change the CPU submodel. For
198 example, if 'configure' guesses your machine as 'i686-pc-linux-gnu'
199 but you want to compile a library for 586es, give
200 '--host=i586-pc-linux-gnu' or just '--host=i586-linux' and add the
201 appropriate compiler flags ('-mcpu=i586' will do the trick) to
204 If you specify just '--build', 'configure' will get confused.
206 '--with-pkgversion=VERSION'
207 Specify a description, possibly including a build number or build
208 date, of the binaries being built, to be included in '--version'
209 output from programs installed with the GNU C Library. For
210 example, '--with-pkgversion='FooBar GNU/Linux glibc build 123''.
211 The default value is 'GNU libc'.
214 Specify the URL that users should visit if they wish to report a
215 bug, to be included in '--help' output from programs installed with
216 the GNU C Library. The default value refers to the main
217 bug-reporting information for the GNU C Library.
219 To build the library and related programs, type 'make'. This will
220 produce a lot of output, some of which may look like errors from 'make'
221 but aren't. Look for error messages from 'make' containing '***'.
222 Those indicate that something is seriously wrong.
224 The compilation process can take a long time, depending on the
225 configuration and the speed of your machine. Some complex modules may
226 take a very long time to compile, as much as several minutes on slower
227 machines. Do not panic if the compiler appears to hang.
229 If you want to run a parallel make, simply pass the '-j' option with
230 an appropriate numeric parameter to 'make'. You need a recent GNU
231 'make' version, though.
233 To build and run test programs which exercise some of the library
234 facilities, type 'make check'. If it does not complete successfully, do
235 not use the built library, and report a bug after verifying that the
236 problem is not already known. *Note Reporting Bugs::, for instructions
237 on reporting bugs. Note that some of the tests assume they are not
238 being run by 'root'. We recommend you compile and test the GNU C
239 Library as an unprivileged user.
241 Before reporting bugs make sure there is no problem with your system.
242 The tests (and later installation) use some pre-existing files of the
243 system such as '/etc/passwd', '/etc/nsswitch.conf' and others. These
244 files must all contain correct and sensible content.
246 Normally, 'make check' will run all the tests before reporting all
247 problems found and exiting with error status if any problems occurred.
248 You can specify 'stop-on-test-failure=y' when running 'make check' to
249 make the test run stop and exit with an error status immediately when a
252 The GNU C Library pretty printers come with their own set of scripts
253 for testing, which run together with the rest of the testsuite through
254 'make check'. These scripts require the following tools to run
257 * Python 2.7.6/3.4.3 or later
259 Python is required for running the printers' test scripts.
263 The printer tests drive GDB through test programs and compare its
264 output to the printers'. PExpect is used to capture the output of
265 GDB, and should be compatible with the Python version in your
268 * GDB 7.8 or later with support for Python 2.7.6/3.4.3 or later
270 GDB itself needs to be configured with Python support in order to
271 use the pretty printers. Notice that your system having Python
272 available doesn't imply that GDB supports it, nor that your
273 system's Python and GDB's have the same version.
275 If these tools are absent, the printer tests will report themselves as
276 'UNSUPPORTED'. Notice that some of the printer tests require the GNU C
277 Library to be compiled with debugging symbols.
279 To format the 'GNU C Library Reference Manual' for printing, type
280 'make dvi'. You need a working TeX installation to do this. The
281 distribution builds the on-line formatted version of the manual, as Info
282 files, as part of the build process. You can build them manually with
285 The library has a number of special-purpose configuration parameters
286 which you can find in 'Makeconfig'. These can be overwritten with the
287 file 'configparms'. To change them, create a 'configparms' in your
288 build directory and add values as appropriate for your system. The file
289 is included and parsed by 'make' and has to follow the conventions for
292 It is easy to configure the GNU C Library for cross-compilation by
293 setting a few variables in 'configparms'. Set 'CC' to the
294 cross-compiler for the target you configured the library for; it is
295 important to use this same 'CC' value when running 'configure', like
296 this: 'CC=TARGET-gcc configure TARGET'. Set 'BUILD_CC' to the compiler
297 to use for programs run on the build system as part of compiling the
298 library. You may need to set 'AR' to cross-compiling versions of 'ar'
299 if the native tools are not configured to work with object files for the
300 target you configured for. When cross-compiling the GNU C Library, it
301 may be tested using 'make check
302 test-wrapper="SRCDIR/scripts/cross-test-ssh.sh HOSTNAME"', where SRCDIR
303 is the absolute directory name for the main source directory and
304 HOSTNAME is the host name of a system that can run the newly built
305 binaries of the GNU C Library. The source and build directories must be
306 visible at the same locations on both the build system and HOSTNAME.
308 In general, when testing the GNU C Library, 'test-wrapper' may be set
309 to the name and arguments of any program to run newly built binaries.
310 This program must preserve the arguments to the binary being run, its
311 working directory and the standard input, output and error file
312 descriptors. If 'TEST-WRAPPER env' will not work to run a program with
313 environment variables set, then 'test-wrapper-env' must be set to a
314 program that runs a newly built program with environment variable
315 assignments in effect, those assignments being specified as 'VAR=VALUE'
316 before the name of the program to be run. If multiple assignments to
317 the same variable are specified, the last assignment specified must take
318 precedence. Similarly, if 'TEST-WRAPPER env -i' will not work to run a
319 program with an environment completely empty of variables except those
320 directly assigned, then 'test-wrapper-env-only' must be set; its use has
321 the same syntax as 'test-wrapper-env', the only difference in its
322 semantics being starting with an empty set of environment variables
323 rather than the ambient set.
325 Installing the C Library
326 ========================
328 To install the library and its header files, and the Info files of the
329 manual, type 'make install'. This will build things, if necessary,
330 before installing them; however, you should still compile everything
331 first. If you are installing the GNU C Library as your primary C
332 library, we recommend that you shut the system down to single-user mode
333 first, and reboot afterward. This minimizes the risk of breaking things
334 when the library changes out from underneath.
336 'make install' will do the entire job of upgrading from a previous
337 installation of the GNU C Library version 2.x. There may sometimes be
338 headers left behind from the previous installation, but those are
339 generally harmless. If you want to avoid leaving headers behind you can
340 do things in the following order.
342 You must first build the library ('make'), optionally check it ('make
343 check'), switch the include directories and then install ('make
344 install'). The steps must be done in this order. Not moving the
345 directory before install will result in an unusable mixture of header
346 files from both libraries, but configuring, building, and checking the
347 library requires the ability to compile and run programs against the old
348 library. The new '/usr/include', after switching the include
349 directories and before installing the library should contain the Linux
350 headers, but nothing else. If you do this, you will need to restore any
351 headers from libraries other than the GNU C Library yourself after
352 installing the library.
354 You can install the GNU C Library somewhere other than where you
355 configured it to go by setting the 'DESTDIR' GNU standard make variable
356 on the command line for 'make install'. The value of this variable is
357 prepended to all the paths for installation. This is useful when
358 setting up a chroot environment or preparing a binary distribution. The
359 directory should be specified with an absolute file name. Installing
360 with the 'prefix' and 'exec_prefix' GNU standard make variables set is
363 The GNU C Library includes a daemon called 'nscd', which you may or
364 may not want to run. 'nscd' caches name service lookups; it can
365 dramatically improve performance with NIS+, and may help with DNS as
368 One auxiliary program, '/usr/libexec/pt_chown', is installed setuid
369 'root' if the '--enable-pt_chown' configuration option is used. This
370 program is invoked by the 'grantpt' function; it sets the permissions on
371 a pseudoterminal so it can be used by the calling process. If you are
372 using a Linux kernel with the 'devpts' filesystem enabled and mounted at
373 '/dev/pts', you don't need this program.
375 After installation you might want to configure the timezone and
376 locale installation of your system. The GNU C Library comes with a
377 locale database which gets configured with 'localedef'. For example, to
378 set up a German locale with name 'de_DE', simply issue the command
379 'localedef -i de_DE -f ISO-8859-1 de_DE'. To configure all locales that
380 are supported by the GNU C Library, you can issue from your build
381 directory the command 'make localedata/install-locales'.
383 To configure the locally used timezone, set the 'TZ' environment
384 variable. The script 'tzselect' helps you to select the right value.
385 As an example, for Germany, 'tzselect' would tell you to use
386 'TZ='Europe/Berlin''. For a system wide installation (the given paths
387 are for an installation with '--prefix=/usr'), link the timezone file
388 which is in '/usr/share/zoneinfo' to the file '/etc/localtime'. For
389 Germany, you might execute 'ln -s /usr/share/zoneinfo/Europe/Berlin
392 Recommended Tools for Compilation
393 =================================
395 We recommend installing the following GNU tools before attempting to
396 build the GNU C Library:
398 * GNU 'make' 3.79 or newer
400 You need the latest version of GNU 'make'. Modifying the GNU C
401 Library to work with other 'make' programs would be so difficult
402 that we recommend you port GNU 'make' instead. *Really.* We
403 recommend GNU 'make' version 3.79. All earlier versions have
404 severe bugs or lack features.
408 GCC 4.9 or higher is required. In general it is recommended to use
409 the newest version of the compiler that is known to work for
410 building the GNU C Library, as newer compilers usually produce
411 better code. As of release time, GCC 7.1 is the newest compiler
412 verified to work to build the GNU C Library.
414 For PowerPC 64-bits little-endian (powerpc64le), GCC 6.2 or higher
415 is required. This compiler version is the first to provide the
416 features required for building the GNU C Library with support for
419 For multi-arch support it is recommended to use a GCC which has
420 been built with support for GNU indirect functions. This ensures
421 that correct debugging information is generated for functions
422 selected by IFUNC resolvers. This support can either be enabled by
423 configuring GCC with '--enable-gnu-indirect-function', or by
424 enabling it by default by setting 'default_gnu_indirect_function'
425 variable for a particular architecture in the GCC source file
428 You can use whatever compiler you like to compile programs that use
431 Check the FAQ for any special compiler issues on particular
434 * GNU 'binutils' 2.25 or later
436 You must use GNU 'binutils' (as and ld) to build the GNU C Library.
437 No other assembler or linker has the necessary functionality at the
438 moment. As of release time, GNU 'binutils' 2.27 is the newest
439 verified to work to build the GNU C Library.
441 * GNU 'texinfo' 4.7 or later
443 To correctly translate and install the Texinfo documentation you
444 need this version of the 'texinfo' package. Earlier versions do
445 not understand all the tags used in the document, and the
446 installation mechanism for the info files is not present or works
447 differently. As of release time, 'texinfo' 6.0 is the newest
448 verified to work to build the GNU C Library.
450 * GNU 'awk' 3.1.2, or higher
452 'awk' is used in several places to generate files. Some 'gawk'
453 extensions are used, including the 'asorti' function, which was
454 introduced in version 3.1.2 of 'gawk'. As of release time, 'gawk'
455 version 4.1.3 is the newest verified to work to build the GNU C
458 * GNU 'bison' 2.7 or later
460 'bison' is used to generate the 'yacc' parser code in the 'intl'
465 Perl is not required, but it is used if present to test the
466 installation. We may decide to use it elsewhere in the future.
468 * GNU 'sed' 3.02 or newer
470 'Sed' is used in several places to generate files. Most scripts
471 work with any version of 'sed'. As of release time, 'sed' version
472 4.2.2 is the newest verified to work to build the GNU C Library.
474 If you change any of the 'configure.ac' files you will also need
476 * GNU 'autoconf' 2.69 (exactly)
478 and if you change any of the message translation files you will need
480 * GNU 'gettext' 0.10.36 or later
482 You may also need these packages if you upgrade your source tree using
483 patches, although we try to avoid this.
485 Specific advice for GNU/Linux systems
486 =====================================
488 If you are installing the GNU C Library on GNU/Linux systems, you need
489 to have the header files from a 3.2 or newer kernel around for
490 reference. (For the ia64 architecture, you need version 3.2.18 or newer
491 because this is the first version with support for the 'accept4' system
492 call.) These headers must be installed using 'make headers_install';
493 the headers present in the kernel source directory are not suitable for
494 direct use by the GNU C Library. You do not need to use that kernel,
495 just have its headers installed where the GNU C Library can access them,
496 referred to here as INSTALL-DIRECTORY. The easiest way to do this is to
497 unpack it in a directory such as '/usr/src/linux-VERSION'. In that
498 directory, run 'make headers_install
499 INSTALL_HDR_PATH=INSTALL-DIRECTORY'. Finally, configure the GNU C
500 Library with the option '--with-headers=INSTALL-DIRECTORY/include'. Use
501 the most recent kernel you can get your hands on. (If you are
502 cross-compiling the GNU C Library, you need to specify
503 'ARCH=ARCHITECTURE' in the 'make headers_install' command, where
504 ARCHITECTURE is the architecture name used by the Linux kernel, such as
507 After installing the GNU C Library, you may need to remove or rename
508 directories such as '/usr/include/linux' and '/usr/include/asm', and
509 replace them with copies of directories such as 'linux' and 'asm' from
510 'INSTALL-DIRECTORY/include'. All directories present in
511 'INSTALL-DIRECTORY/include' should be copied, except that the GNU C
512 Library provides its own version of '/usr/include/scsi'; the files
513 provided by the kernel should be copied without replacing those provided
514 by the GNU C Library. The 'linux', 'asm' and 'asm-generic' directories
515 are required to compile programs using the GNU C Library; the other
516 directories describe interfaces to the kernel but are not required if
517 not compiling programs using those interfaces. You do not need to copy
518 kernel headers if you did not specify an alternate kernel header source
519 using '--with-headers'.
521 The Filesystem Hierarchy Standard for GNU/Linux systems expects some
522 components of the GNU C Library installation to be in '/lib' and some in
523 '/usr/lib'. This is handled automatically if you configure the GNU C
524 Library with '--prefix=/usr'. If you set some other prefix or allow it
525 to default to '/usr/local', then all the components are installed there.
530 There are probably bugs in the GNU C Library. There are certainly
531 errors and omissions in this manual. If you report them, they will get
532 fixed. If you don't, no one will ever know about them and they will
533 remain unfixed for all eternity, if not longer.
535 It is a good idea to verify that the problem has not already been
536 reported. Bugs are documented in two places: The file 'BUGS' describes
537 a number of well known bugs and the central GNU C Library bug tracking
538 system has a WWW interface at <https://sourceware.org/bugzilla/>. The
539 WWW interface gives you access to open and closed reports. A closed
540 report normally includes a patch or a hint on solving the problem.
542 To report a bug, first you must find it. With any luck, this will be
543 the hard part. Once you've found a bug, make sure it's really a bug. A
544 good way to do this is to see if the GNU C Library behaves the same way
545 some other C library does. If so, probably you are wrong and the
546 libraries are right (but not necessarily). If not, one of the libraries
547 is probably wrong. It might not be the GNU C Library. Many historical
548 Unix C libraries permit things that we don't, such as closing a file
551 If you think you have found some way in which the GNU C Library does
552 not conform to the ISO and POSIX standards (*note Standards and
553 Portability::), that is definitely a bug. Report it!
555 Once you're sure you've found a bug, try to narrow it down to the
556 smallest test case that reproduces the problem. In the case of a C
557 library, you really only need to narrow it down to one library function
558 call, if possible. This should not be too difficult.
560 The final step when you have a simple test case is to report the bug.
561 Do this at <http://www.gnu.org/software/libc/bugs.html>.
563 If you are not sure how a function should behave, and this manual
564 doesn't tell you, that's a bug in the manual. Report that too! If the
565 function's behavior disagrees with the manual, then either the library
566 or the manual has a bug, so report the disagreement. If you find any
567 errors or omissions in this manual, please report them to the bug
568 database. If you refer to specific sections of the manual, please
569 include the section names for easier identification.