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Installing the GNU C Library **************************** Before you do anything else, you should read the FAQ at <https://sourceware.org/glibc/wiki/FAQ>. It answers common questions and describes problems you may experience with compilation and installation. You will need recent versions of several GNU tools: definitely GCC and GNU Make, and possibly others. *Note Tools for Compilation::, below. Configuring and compiling the GNU C Library =========================================== The GNU C Library cannot be compiled in the source directory. You must build it in a separate build directory. For example, if you have unpacked the GNU C Library sources in '/src/gnu/glibc-VERSION', create a directory '/src/gnu/glibc-build' to put the object files in. This allows removing the whole build directory in case an error occurs, which is the safest way to get a fresh start and should always be done. From your object directory, run the shell script 'configure' located at the top level of the source tree. In the scenario above, you'd type $ ../glibc-VERSION/configure ARGS... Please note that even though you're building in a separate build directory, the compilation may need to create or modify files and directories in the source directory. 'configure' takes many options, but the only one that is usually mandatory is '--prefix'. This option tells 'configure' where you want the GNU C Library installed. This defaults to '/usr/local', but the normal setting to install as the standard system library is '--prefix=/usr' for GNU/Linux systems and '--prefix=' (an empty prefix) for GNU/Hurd systems. It may also be useful to pass 'CC=COMPILER' and 'CFLAGS=FLAGS' arguments to 'configure'. 'CC' selects the C compiler that will be used, and 'CFLAGS' sets optimization options for the compiler. Any compiler options required for all compilations, such as options selecting an ABI or a processor for which to generate code, should be included in 'CC'. Options that may be overridden by the GNU C Library build system for particular files, such as for optimization and debugging, should go in 'CFLAGS'. The default value of 'CFLAGS' is '-g -O2', and the GNU C Library cannot be compiled without optimization, so if 'CFLAGS' is specified it must enable optimization. For example: $ ../glibc-VERSION/configure CC="gcc -m32" CFLAGS="-O3" The following list describes all of the available options for 'configure': '--prefix=DIRECTORY' Install machine-independent data files in subdirectories of 'DIRECTORY'. The default is to install in '/usr/local'. '--exec-prefix=DIRECTORY' Install the library and other machine-dependent files in subdirectories of 'DIRECTORY'. The default is to the '--prefix' directory if that option is specified, or '/usr/local' otherwise. '--with-headers=DIRECTORY' Look for kernel header files in DIRECTORY, not '/usr/include'. The GNU C Library needs information from the kernel's header files describing the interface to the kernel. The GNU C Library will normally look in '/usr/include' for them, but if you specify this option, it will look in DIRECTORY instead. This option is primarily of use on a system where the headers in '/usr/include' come from an older version of the GNU C Library. Conflicts can occasionally happen in this case. You can also use this option if you want to compile the GNU C Library with a newer set of kernel headers than the ones found in '/usr/include'. '--enable-kernel=VERSION' This option is currently only useful on GNU/Linux systems. The VERSION parameter should have the form X.Y.Z and describes the smallest version of the Linux kernel the generated library is expected to support. The higher the VERSION number is, the less compatibility code is added, and the faster the code gets. '--with-binutils=DIRECTORY' Use the binutils (assembler and linker) in 'DIRECTORY', not the ones the C compiler would default to. You can use this option if the default binutils on your system cannot deal with all the constructs in the GNU C Library. In that case, 'configure' will detect the problem and suppress these constructs, so that the library will still be usable, but functionality may be lost--for example, you can't build a shared libc with old binutils. '--with-nonshared-cflags=CFLAGS' Use additional compiler flags CFLAGS to build the parts of the library which are always statically linked into applications and libraries even with shared linking (that is, the object files contained in 'lib*_nonshared.a' libraries). The build process will automatically use the appropriate flags, but this option can be used to set additional flags required for building applications and libraries, to match local policy. '--disable-shared' Don't build shared libraries even if it is possible. Not all systems support shared libraries; you need ELF support and (currently) the GNU linker. '--enable-static-pie' Enable static position independent executable (static PIE) support. Static PIE is similar to static executable, but can be loaded at any address without help from a dynamic linker. All static programs as well as static tests are built as static PIE, except for those marked with no-pie. The resulting glibc can be used with the GCC option, -static-pie, which is available with GCC 8 or above, to create static PIE. This option also implies that glibc programs and tests are created as dynamic position independent executables (PIE) by default. '--enable-cet' '--enable-cet=permissive' Enable Intel Control-flow Enforcement Technology (CET) support. When the GNU C Library is built with '--enable-cet' or '--enable-cet=permissive', the resulting library is protected with indirect branch tracking (IBT) and shadow stack (SHSTK). When CET is enabled, the GNU C Library is compatible with all existing executables and shared libraries. This feature is currently supported on i386, x86_64 and x32 with GCC 8 and binutils 2.29 or later. Note that when CET is enabled, the GNU C Library requires CPUs capable of multi-byte NOPs, like x86-64 processors as well as Intel Pentium Pro or newer. With '--enable-cet', it is an error to dlopen a non CET enabled shared library in CET enabled application. With '--enable-cet=permissive', CET is disabled when dlopening a non CET enabled shared library in CET enabled application. NOTE: '--enable-cet' has been tested for i686, x86_64 and x32 on non-CET processors. '--enable-cet' has been tested for i686, x86_64 and x32 on CET processors. '--disable-profile' Don't build libraries with profiling information. You may want to use this option if you don't plan to do profiling. '--enable-static-nss' Compile static versions of the NSS (Name Service Switch) libraries. This is not recommended because it defeats the purpose of NSS; a program linked statically with the NSS libraries cannot be dynamically reconfigured to use a different name database. '--enable-hardcoded-path-in-tests' By default, dynamic tests are linked to run with the installed C library. This option hardcodes the newly built C library path in dynamic tests so that they can be invoked directly. '--disable-timezone-tools' By default, timezone related utilities ('zic', 'zdump', and 'tzselect') are installed with the GNU C Library. If you are building these independently (e.g. by using the 'tzcode' package), then this option will allow disabling the install of these. Note that you need to make sure the external tools are kept in sync with the versions that the GNU C Library expects as the data formats may change over time. Consult the 'timezone' subdirectory for more details. '--enable-stack-protector' '--enable-stack-protector=strong' '--enable-stack-protector=all' Compile the C library and all other parts of the glibc package (including the threading and math libraries, NSS modules, and transliteration modules) using the GCC '-fstack-protector', '-fstack-protector-strong' or '-fstack-protector-all' options to detect stack overruns. Only the dynamic linker and a small number of routines called directly from assembler are excluded from this protection. '--enable-bind-now' Disable lazy binding for installed shared objects and programs. This provides additional security hardening because it enables full RELRO and a read-only global offset table (GOT), at the cost of slightly increased program load times. '--enable-pt_chown' The file 'pt_chown' is a helper binary for 'grantpt' (*note Pseudo-Terminals: Allocation.) that is installed setuid root to fix up pseudo-terminal ownership. It is not built by default because systems using the Linux kernel are commonly built with the 'devpts' filesystem enabled and mounted at '/dev/pts', which manages pseudo-terminal ownership automatically. By using '--enable-pt_chown', you may build 'pt_chown' and install it setuid and owned by 'root'. The use of 'pt_chown' introduces additional security risks to the system and you should enable it only if you understand and accept those risks. '--disable-werror' By default, the GNU C Library is built with '-Werror'. If you wish to build without this option (for example, if building with a newer version of GCC than this version of the GNU C Library was tested with, so new warnings cause the build with '-Werror' to fail), you can configure with '--disable-werror'. '--disable-mathvec' By default for x86_64, the GNU C Library is built with the vector math library. Use this option to disable the vector math library. '--enable-tunables' Tunables support allows additional library parameters to be customized at runtime. This feature is enabled by default. This option can take the following values: 'yes' This is the default if no option is passed to configure. This enables tunables and selects the default frontend (currently 'valstring'). 'no' This option disables tunables. 'valstring' This enables tunables and selects the 'valstring' frontend for tunables. This frontend allows users to specify tunables as a colon-separated list in a single environment variable 'GLIBC_TUNABLES'. '--enable-obsolete-nsl' By default, libnsl is only built as shared library for backward compatibility and the NSS modules libnss_compat, libnss_nis and libnss_nisplus are not built at all. Use this option to enable libnsl with all depending NSS modules and header files. '--disable-crypt' Do not install the passphrase-hashing library 'libcrypt' or the header file 'crypt.h'. 'unistd.h' will still declare the function 'crypt'. Using this option does not change the set of programs that may need to be linked with '-lcrypt'; it only means that the GNU C Library will not provide that library. This option is for hackers and distributions experimenting with independently-maintained implementations of libcrypt. It may become the default in a future release. '--disable-experimental-malloc' By default, a per-thread cache is enabled in 'malloc'. While this cache can be disabled on a per-application basis using tunables (set glibc.malloc.tcache_count to zero), this option can be used to remove it from the build completely. '--build=BUILD-SYSTEM' '--host=HOST-SYSTEM' These options are for cross-compiling. If you specify both options and BUILD-SYSTEM is different from HOST-SYSTEM, 'configure' will prepare to cross-compile the GNU C Library from BUILD-SYSTEM to be used on HOST-SYSTEM. You'll probably need the '--with-headers' option too, and you may have to override CONFIGURE's selection of the compiler and/or binutils. If you only specify '--host', 'configure' will prepare for a native compile but use what you specify instead of guessing what your system is. This is most useful to change the CPU submodel. For example, if 'configure' guesses your machine as 'i686-pc-linux-gnu' but you want to compile a library for 586es, give '--host=i586-pc-linux-gnu' or just '--host=i586-linux' and add the appropriate compiler flags ('-mcpu=i586' will do the trick) to 'CC'. If you specify just '--build', 'configure' will get confused. '--with-pkgversion=VERSION' Specify a description, possibly including a build number or build date, of the binaries being built, to be included in '--version' output from programs installed with the GNU C Library. For example, '--with-pkgversion='FooBar GNU/Linux glibc build 123''. The default value is 'GNU libc'. '--with-bugurl=URL' Specify the URL that users should visit if they wish to report a bug, to be included in '--help' output from programs installed with the GNU C Library. The default value refers to the main bug-reporting information for the GNU C Library. To build the library and related programs, type 'make'. This will produce a lot of output, some of which may look like errors from 'make' but aren't. Look for error messages from 'make' containing '***'. Those indicate that something is seriously wrong. The compilation process can take a long time, depending on the configuration and the speed of your machine. Some complex modules may take a very long time to compile, as much as several minutes on slower machines. Do not panic if the compiler appears to hang. If you want to run a parallel make, simply pass the '-j' option with an appropriate numeric parameter to 'make'. You need a recent GNU 'make' version, though. To build and run test programs which exercise some of the library facilities, type 'make check'. If it does not complete successfully, do not use the built library, and report a bug after verifying that the problem is not already known. *Note Reporting Bugs::, for instructions on reporting bugs. Note that some of the tests assume they are not being run by 'root'. We recommend you compile and test the GNU C Library as an unprivileged user. Before reporting bugs make sure there is no problem with your system. The tests (and later installation) use some pre-existing files of the system such as '/etc/passwd', '/etc/nsswitch.conf' and others. These files must all contain correct and sensible content. Normally, 'make check' will run all the tests before reporting all problems found and exiting with error status if any problems occurred. You can specify 'stop-on-test-failure=y' when running 'make check' to make the test run stop and exit with an error status immediately when a failure occurs. The GNU C Library pretty printers come with their own set of scripts for testing, which run together with the rest of the testsuite through 'make check'. These scripts require the following tools to run successfully: * Python 2.7/3.4 or later Python is required for running the printers' test scripts. As of release time, Python 3.6 is the newest verified to work to test the pretty printers. * PExpect 4.0 The printer tests drive GDB through test programs and compare its output to the printers'. PExpect is used to capture the output of GDB, and should be compatible with the Python version in your system. As of release time PExpect 4.3 is the newest verified to work to test the pretty printers. * GDB 7.8 or later with support for Python 2.7/3.4 or later GDB itself needs to be configured with Python support in order to use the pretty printers. Notice that your system having Python available doesn't imply that GDB supports it, nor that your system's Python and GDB's have the same version. As of release time GNU 'debugger' 8.0.1 is the newest verified to work to test the pretty printers. If these tools are absent, the printer tests will report themselves as 'UNSUPPORTED'. Notice that some of the printer tests require the GNU C Library to be compiled with debugging symbols. To format the 'GNU C Library Reference Manual' for printing, type 'make dvi'. You need a working TeX installation to do this. The distribution builds the on-line formatted version of the manual, as Info files, as part of the build process. You can build them manually with 'make info'. The library has a number of special-purpose configuration parameters which you can find in 'Makeconfig'. These can be overwritten with the file 'configparms'. To change them, create a 'configparms' in your build directory and add values as appropriate for your system. The file is included and parsed by 'make' and has to follow the conventions for makefiles. It is easy to configure the GNU C Library for cross-compilation by setting a few variables in 'configparms'. Set 'CC' to the cross-compiler for the target you configured the library for; it is important to use this same 'CC' value when running 'configure', like this: 'configure TARGET CC=TARGET-gcc'. Set 'BUILD_CC' to the compiler to use for programs run on the build system as part of compiling the library. You may need to set 'AR' to cross-compiling versions of 'ar' if the native tools are not configured to work with object files for the target you configured for. When cross-compiling the GNU C Library, it may be tested using 'make check test-wrapper="SRCDIR/scripts/cross-test-ssh.sh HOSTNAME"', where SRCDIR is the absolute directory name for the main source directory and HOSTNAME is the host name of a system that can run the newly built binaries of the GNU C Library. The source and build directories must be visible at the same locations on both the build system and HOSTNAME. In general, when testing the GNU C Library, 'test-wrapper' may be set to the name and arguments of any program to run newly built binaries. This program must preserve the arguments to the binary being run, its working directory and the standard input, output and error file descriptors. If 'TEST-WRAPPER env' will not work to run a program with environment variables set, then 'test-wrapper-env' must be set to a program that runs a newly built program with environment variable assignments in effect, those assignments being specified as 'VAR=VALUE' before the name of the program to be run. If multiple assignments to the same variable are specified, the last assignment specified must take precedence. Similarly, if 'TEST-WRAPPER env -i' will not work to run a program with an environment completely empty of variables except those directly assigned, then 'test-wrapper-env-only' must be set; its use has the same syntax as 'test-wrapper-env', the only difference in its semantics being starting with an empty set of environment variables rather than the ambient set. Installing the C Library ======================== To install the library and its header files, and the Info files of the manual, type 'make install'. This will build things, if necessary, before installing them; however, you should still compile everything first. If you are installing the GNU C Library as your primary C library, we recommend that you shut the system down to single-user mode first, and reboot afterward. This minimizes the risk of breaking things when the library changes out from underneath. 'make install' will do the entire job of upgrading from a previous installation of the GNU C Library version 2.x. There may sometimes be headers left behind from the previous installation, but those are generally harmless. If you want to avoid leaving headers behind you can do things in the following order. You must first build the library ('make'), optionally check it ('make check'), switch the include directories and then install ('make install'). The steps must be done in this order. Not moving the directory before install will result in an unusable mixture of header files from both libraries, but configuring, building, and checking the library requires the ability to compile and run programs against the old library. The new '/usr/include', after switching the include directories and before installing the library should contain the Linux headers, but nothing else. If you do this, you will need to restore any headers from libraries other than the GNU C Library yourself after installing the library. You can install the GNU C Library somewhere other than where you configured it to go by setting the 'DESTDIR' GNU standard make variable on the command line for 'make install'. The value of this variable is prepended to all the paths for installation. This is useful when setting up a chroot environment or preparing a binary distribution. The directory should be specified with an absolute file name. Installing with the 'prefix' and 'exec_prefix' GNU standard make variables set is not supported. The GNU C Library includes a daemon called 'nscd', which you may or may not want to run. 'nscd' caches name service lookups; it can dramatically improve performance with NIS+, and may help with DNS as well. One auxiliary program, '/usr/libexec/pt_chown', is installed setuid 'root' if the '--enable-pt_chown' configuration option is used. This program is invoked by the 'grantpt' function; it sets the permissions on a pseudoterminal so it can be used by the calling process. If you are using a Linux kernel with the 'devpts' filesystem enabled and mounted at '/dev/pts', you don't need this program. After installation you might want to configure the timezone and locale installation of your system. The GNU C Library comes with a locale database which gets configured with 'localedef'. For example, to set up a German locale with name 'de_DE', simply issue the command 'localedef -i de_DE -f ISO-8859-1 de_DE'. To configure all locales that are supported by the GNU C Library, you can issue from your build directory the command 'make localedata/install-locales'. To configure the locally used timezone, set the 'TZ' environment variable. The script 'tzselect' helps you to select the right value. As an example, for Germany, 'tzselect' would tell you to use 'TZ='Europe/Berlin''. For a system wide installation (the given paths are for an installation with '--prefix=/usr'), link the timezone file which is in '/usr/share/zoneinfo' to the file '/etc/localtime'. For Germany, you might execute 'ln -s /usr/share/zoneinfo/Europe/Berlin /etc/localtime'. Recommended Tools for Compilation ================================= We recommend installing the following GNU tools before attempting to build the GNU C Library: * GNU 'make' 4.0 or newer As of relase time, GNU 'make' 4.2.1 is the newest verified to work to build the GNU C Library. * GCC 4.9 or newer GCC 4.9 or higher is required. In general it is recommended to use the newest version of the compiler that is known to work for building the GNU C Library, as newer compilers usually produce better code. As of release time, GCC 8.1.1 is the newest compiler verified to work to build the GNU C Library. For PowerPC 64-bits little-endian (powerpc64le), GCC 6.2 or higher is required. This compiler version is the first to provide the features required for building the GNU C Library with support for '_Float128'. For multi-arch support it is recommended to use a GCC which has been built with support for GNU indirect functions. This ensures that correct debugging information is generated for functions selected by IFUNC resolvers. This support can either be enabled by configuring GCC with '--enable-gnu-indirect-function', or by enabling it by default by setting 'default_gnu_indirect_function' variable for a particular architecture in the GCC source file 'gcc/config.gcc'. You can use whatever compiler you like to compile programs that use the GNU C Library. Check the FAQ for any special compiler issues on particular platforms. * GNU 'binutils' 2.25 or later You must use GNU 'binutils' (as and ld) to build the GNU C Library. No other assembler or linker has the necessary functionality at the moment. As of release time, GNU 'binutils' 2.31.1 is the newest verified to work to build the GNU C Library. * GNU 'texinfo' 4.7 or later To correctly translate and install the Texinfo documentation you need this version of the 'texinfo' package. Earlier versions do not understand all the tags used in the document, and the installation mechanism for the info files is not present or works differently. As of release time, 'texinfo' 6.5 is the newest verified to work to build the GNU C Library. * GNU 'awk' 3.1.2, or higher 'awk' is used in several places to generate files. Some 'gawk' extensions are used, including the 'asorti' function, which was introduced in version 3.1.2 of 'gawk'. As of release time, 'gawk' version 4.2.1 is the newest verified to work to build the GNU C Library. * GNU 'bison' 2.7 or later 'bison' is used to generate the 'yacc' parser code in the 'intl' subdirectory. As of release time, 'bison' version 3.0.4 is the newest verified to work to build the GNU C Library. * Perl 5 Perl is not required, but it is used if present to test the installation. We may decide to use it elsewhere in the future. As of release time 'perl' version 5.28.0 is the newest verified to work to build the GNU C Library. * GNU 'sed' 3.02 or newer 'Sed' is used in several places to generate files. Most scripts work with any version of 'sed'. As of release time, 'sed' version 4.5 is the newest verified to work to build the GNU C Library. If you change any of the 'configure.ac' files you will also need * GNU 'autoconf' 2.69 (exactly) and if you change any of the message translation files you will need * GNU 'gettext' 0.10.36 or later As of release time, GNU 'gettext' version 0.19.8.1 is the newest version verified to work to build the GNU C Library. You may also need these packages if you upgrade your source tree using patches, although we try to avoid this. Specific advice for GNU/Linux systems ===================================== If you are installing the GNU C Library on GNU/Linux systems, you need to have the header files from a 3.2 or newer kernel around for reference. (For the ia64 architecture, you need version 3.2.18 or newer because this is the first version with support for the 'accept4' system call.) These headers must be installed using 'make headers_install'; the headers present in the kernel source directory are not suitable for direct use by the GNU C Library. You do not need to use that kernel, just have its headers installed where the GNU C Library can access them, referred to here as INSTALL-DIRECTORY. The easiest way to do this is to unpack it in a directory such as '/usr/src/linux-VERSION'. In that directory, run 'make headers_install INSTALL_HDR_PATH=INSTALL-DIRECTORY'. Finally, configure the GNU C Library with the option '--with-headers=INSTALL-DIRECTORY/include'. Use the most recent kernel you can get your hands on. (If you are cross-compiling the GNU C Library, you need to specify 'ARCH=ARCHITECTURE' in the 'make headers_install' command, where ARCHITECTURE is the architecture name used by the Linux kernel, such as 'x86' or 'powerpc'.) After installing the GNU C Library, you may need to remove or rename directories such as '/usr/include/linux' and '/usr/include/asm', and replace them with copies of directories such as 'linux' and 'asm' from 'INSTALL-DIRECTORY/include'. All directories present in 'INSTALL-DIRECTORY/include' should be copied, except that the GNU C Library provides its own version of '/usr/include/scsi'; the files provided by the kernel should be copied without replacing those provided by the GNU C Library. The 'linux', 'asm' and 'asm-generic' directories are required to compile programs using the GNU C Library; the other directories describe interfaces to the kernel but are not required if not compiling programs using those interfaces. You do not need to copy kernel headers if you did not specify an alternate kernel header source using '--with-headers'. The Filesystem Hierarchy Standard for GNU/Linux systems expects some components of the GNU C Library installation to be in '/lib' and some in '/usr/lib'. This is handled automatically if you configure the GNU C Library with '--prefix=/usr'. If you set some other prefix or allow it to default to '/usr/local', then all the components are installed there. Reporting Bugs ============== There are probably bugs in the GNU C Library. There are certainly errors and omissions in this manual. If you report them, they will get fixed. If you don't, no one will ever know about them and they will remain unfixed for all eternity, if not longer. It is a good idea to verify that the problem has not already been reported. Bugs are documented in two places: The file 'BUGS' describes a number of well known bugs and the central GNU C Library bug tracking system has a WWW interface at <https://sourceware.org/bugzilla/>. The WWW interface gives you access to open and closed reports. A closed report normally includes a patch or a hint on solving the problem. To report a bug, first you must find it. With any luck, this will be the hard part. Once you've found a bug, make sure it's really a bug. A good way to do this is to see if the GNU C Library behaves the same way some other C library does. If so, probably you are wrong and the libraries are right (but not necessarily). If not, one of the libraries is probably wrong. It might not be the GNU C Library. Many historical Unix C libraries permit things that we don't, such as closing a file twice. If you think you have found some way in which the GNU C Library does not conform to the ISO and POSIX standards (*note Standards and Portability::), that is definitely a bug. Report it! Once you're sure you've found a bug, try to narrow it down to the smallest test case that reproduces the problem. In the case of a C library, you really only need to narrow it down to one library function call, if possible. This should not be too difficult. The final step when you have a simple test case is to report the bug. Do this at <http://www.gnu.org/software/libc/bugs.html>. If you are not sure how a function should behave, and this manual doesn't tell you, that's a bug in the manual. Report that too! If the function's behavior disagrees with the manual, then either the library or the manual has a bug, so report the disagreement. If you find any errors or omissions in this manual, please report them to the bug database. If you refer to specific sections of the manual, please include the section names for easier identification.