5 This document describes installation on all supported operating
6 systems (the Linux/Unix family, OpenVMS and Windows)
8 To install OpenSSL, you will need:
10 * A make implementation
11 * Perl 5 with core modules (please read NOTES.PERL)
12 * The perl module Text::Template (please read NOTES.PERL)
14 * a development environment in the form of development libraries and C
16 * a supported operating system
18 For additional platform specific requirements, solutions to specific
19 issues and other details, please read one of these:
22 * NOTES.WIN (any supported Windows)
23 * NOTES.DJGPP (DOS platform with DJGPP)
25 Notational conventions in this document
26 ---------------------------------------
28 Throughout this document, we use the following conventions in command
31 $ command Any line starting with a dollar sign
32 ($) is a command line.
34 { word1 | word2 | word3 } This denotes a mandatory choice, to be
35 replaced with one of the given words.
36 A simple example would be this:
38 $ echo { FOO | BAR | COOKIE }
40 which is to be understood as one of
49 [ word1 | word2 | word3 ] Similar to { word1 | word2 | word3 }
50 except it's optional to give any of
51 those. In addition to the examples
52 above, this would also be valid:
56 {{ target }} This denotes a mandatory word or
57 sequence of words of some sort. A
58 simple example would be this:
62 which is to be understood to use the
63 command 'type' on some file name
64 determined by the user.
66 [[ options ]] Similar to {{ target }}, but is
69 Note that the notation assumes spaces around {, }, [, ], {{, }} and
70 [[, ]]. This is to differentiate from OpenVMS directory
71 specifications, which also use [ and ], but without spaces.
76 If you want to just get on with it, do:
92 on Windows (only pick one of the targets for configuration):
94 $ perl Configure { VC-WIN32 | VC-WIN64A | VC-WIN64I | VC-CE }
99 If any of these steps fails, see section Installation in Detail below.
101 This will build and install OpenSSL in the default location, which is:
103 Unix: normal installation directories under /usr/local
104 OpenVMS: SYS$COMMON:[OPENSSL-'version'...], where 'version' is the
105 OpenSSL version number with underscores instead of periods.
106 Windows: C:\Program Files\OpenSSL or C:\Program Files (x86)\OpenSSL
108 If you want to install it anywhere else, run config like this:
112 $ ./config --prefix=/opt/openssl --openssldir=/usr/local/ssl
116 $ @config --prefix=PROGRAM:[INSTALLS] --openssldir=SYS$MANAGER:[OPENSSL]
119 Configuration Options
120 ---------------------
122 There are several options to ./config (or ./Configure) to customize
123 the build (note that for Windows, the defaults for --prefix and
124 --openssldir depend in what configuration is used and what Windows
125 implementation OpenSSL is built on. More notes on this in NOTES.WIN):
128 Don't build with support for deprecated APIs below the
129 specified version number. For example "--api=1.1.0" will
130 remove support for all APIS that were deprecated in OpenSSL
131 version 1.1.0 or below.
133 --cross-compile-prefix=PREFIX
134 The PREFIX to include in front of commands for your
135 toolchain. It's likely to have to end with dash, e.g.
136 a-b-c- would invoke GNU compiler as a-b-c-gcc, etc.
137 Unfortunately cross-compiling is too case-specific to
138 put together one-size-fits-all instructions. You might
139 have to pass more flags or set up environment variables
140 to actually make it work. Android and iOS cases are
141 discussed in corresponding Configurations/10-main.cf
142 sections. But there are cases when this option alone is
143 sufficient. For example to build the mingw64 target on
144 Linux "--cross-compile-prefix=x86_64-w64-mingw32-"
145 works. Naturally provided that mingw packages are
146 installed. Today Debian and Ubuntu users have option to
147 install a number of prepackaged cross-compilers along
148 with corresponding run-time and development packages for
149 "alien" hardware. To give another example
150 "--cross-compile-prefix=mipsel-linux-gnu-" suffices
151 in such case. Needless to mention that you have to
152 invoke ./Configure, not ./config, and pass your target
156 Build OpenSSL with debugging symbols.
159 The name of the directory under the top of the installation
160 directory tree (see the --prefix option) where libraries will
161 be installed. By default this is "lib". Note that on Windows
162 only ".lib" files will be stored in this location. dll files
163 will always be installed to the "bin" directory.
166 Directory for OpenSSL configuration files, and also the
167 default certificate and key store. Defaults are:
170 Windows: C:\Program Files\Common Files\SSL
171 or C:\Program Files (x86)\Common Files\SSL
172 OpenVMS: SYS$COMMON:[OPENSSL-COMMON]
175 The top of the installation directory tree. Defaults are:
178 Windows: C:\Program Files\OpenSSL
179 or C:\Program Files (x86)\OpenSSL
180 OpenVMS: SYS$COMMON:[OPENSSL-'version']
183 Build OpenSSL without debugging symbols. This is the default.
186 This is a developer flag that switches on various compiler
187 options recommended for OpenSSL development. It only works
188 when using gcc or clang as the compiler. If you are
189 developing a patch for OpenSSL then it is recommended that
190 you use this option where possible.
192 --with-zlib-include=DIR
193 The directory for the location of the zlib include file. This
194 option is only necessary if enable-zlib (see below) is used
195 and the include file is not already on the system include
199 On Unix: this is the directory containing the zlib library.
200 If not provided the system library path will be used.
201 On Windows: this is the filename of the zlib library (with or
202 without a path). This flag must be provided if the
203 zlib-dynamic option is not also used. If zlib-dynamic is used
204 then this flag is optional and a default value ("ZLIB1") is
205 used if not provided.
206 On VMS: this is the filename of the zlib library (with or
207 without a path). This flag is optional and if not provided
208 then "GNV$LIBZSHR", "GNV$LIBZSHR32" or "GNV$LIBZSHR64" is
209 used by default depending on the pointer size chosen.
212 Don't build the AFALG engine. This option will be forced if
213 on a platform that does not support AFALG.
216 Build with the Address sanitiser. This is a developer option
217 only. It may not work on all platforms and should never be
218 used in production environments. It will only work when used
219 with gcc or clang and should be used in conjunction with the
223 Do not use assembler code. On some platforms a small amount
224 of assembler code may still be used.
227 Do not build support for async operations.
230 Don't automatically load all supported ciphers and digests.
231 Typically OpenSSL will make available all of its supported
232 ciphers and digests. For a statically linked application this
233 may be undesirable if small executable size is an objective.
234 This only affects libcrypto. Ciphers and digests will have to
235 be loaded manually using EVP_add_cipher() and
236 EVP_add_digest() if this option is used. This option will
237 force a non-shared build.
240 Don't automatically load all libcrypto/libssl error strings.
241 Typically OpenSSL will automatically load human readable
242 error strings. For a statically linked application this may
243 be undesirable if small executable size is an objective.
247 Don't build the CAPI engine. This option will be forced if
248 on a platform that does not support CAPI.
251 Don't build support for CMS features
254 Don't build support for SSL/TLS compression. If this option
255 is left enabled (the default), then compression will only
256 work if the zlib or zlib-dynamic options are also chosen.
259 Build support for debugging memory allocated via
260 OPENSSL_malloc() or OPENSSL_zalloc().
262 enable-crypto-mdebug-backtrace
263 As for crypto-mdebug, but additionally provide backtrace
264 information for allocated memory.
265 TO BE USED WITH CARE: this uses GNU C functionality, and
266 is therefore not usable for non-GNU config targets. If
267 your build complains about the use of '-rdynamic' or the
268 lack of header file execinfo.h, this option is not for you.
269 ALSO NOTE that even though execinfo.h is available on your
270 system (through Gnulib), the functions might just be stubs
274 Don't build support for Certificate Transparency.
277 Don't build with support for any deprecated APIs. This is the
278 same as using "--api" and supplying the latest version
282 Don't build support for datagram based BIOs. Selecting this
283 option will also force the disabling of DTLS.
286 Don't build support for loading Dynamic Shared Objects.
289 Don't build the dynamically loaded engines. This only has an
290 effect in a "shared" build
293 Don't build support for Elliptic Curves.
296 Don't build support for binary Elliptic Curves
298 enable-ec_nistp_64_gcc_128
299 Enable support for optimised implementations of some commonly
300 used NIST elliptic curves. This is only supported on some
304 Build support for gathering entropy from EGD (Entropy
308 Don't build support for loading engines.
311 Don't compile in any error strings.
314 Don't compile in filename and line number information (e.g.
315 for errors and memory allocation).
317 enable-fuzz-libfuzzer, enable-fuzz-afl
318 Build with support for fuzzing using either libfuzzer or AFL.
319 These are developer options only. They may not work on all
320 platforms and should never be used in production environments.
321 See the file fuzz/README.md for further details.
324 Don't runt the fuzz test suite when testing. Use with
325 caution, as those tests may be important. However, that
326 suite is particularly slow, and is therefore skippable.
329 Don't build support for GOST based ciphersuites. Note that
330 if this feature is enabled then GOST ciphersuites are only
331 available if the GOST algorithms are also available through
332 loading an externally supplied engine.
335 Build support for DTLS heartbeats.
338 Don't build the padlock engine.
341 Don't generate dependencies.
344 Don't build support for writing multiple records in one
345 go in libssl (Note: this is a different capability to the
346 pipelining functionality).
349 Don't build support for the NPN TLS extension.
352 Don't build support for OCSP.
355 Don't build with support for Position Independent Code.
358 Don't use POSIX IO capabilities.
361 Don't build support for Pre-Shared Key based ciphersuites.
364 Don't use hardware RDRAND capabilities.
367 Don't build support for RFC3779 ("X.509 Extensions for IP
368 Addresses and AS Identifiers")
371 Build support for SCTP
374 Do not create shared libraries, only static ones. See "Note
375 on shared libraries" below.
378 Don't build support for socket BIOs
381 Don't build support for SRP or SRP based ciphersuites.
384 Don't build SRTP support
387 Exclude SSE2 code paths. Normally SSE2 extension is
388 detected at run-time, but the decision whether or not the
389 machine code will be executed is taken solely on CPU
390 capability vector. This means that if you happen to run OS
391 kernel which does not support SSE2 extension on Intel P4
392 processor, then your application might be exposed to
393 "illegal instruction" exception. There might be a way
394 to enable support in kernel, e.g. FreeBSD kernel can be
395 compiled with CPU_ENABLE_SSE, and there is a way to
396 disengage SSE2 code paths upon application start-up,
397 but if you aim for wider "audience" running such kernel,
398 consider no-sse2. Both the 386 and no-asm options imply
402 Build with the SSL Trace capabilities (adds the "-trace"
403 option to s_client and s_server).
406 Don't build the statically linked engines. This only
407 has an impact when not built "shared".
410 Don't use any C "stdio" features. Only libcrypto and libssl
411 can be built in this way. Using this option will suppress
412 building the command line applications. Additionally since
413 the OpenSSL tests also use the command line applications the
414 tests will also be skipped.
417 Don't try to build with support for multi-threaded
421 Build with support for multi-threaded applications. Most
422 platforms will enable this by default. However if on a
423 platform where this is not the case then this will usually
424 require additional system-dependent options! See "Note on
425 multi-threading" below.
428 Don't build Time Stamping Authority support.
431 Build with the Undefined Behaviour sanitiser. This is a
432 developer option only. It may not work on all platforms and
433 should never be used in production environments. It will only
434 work when used with gcc or clang and should be used in
435 conjunction with the "-DPEDANTIC" option (or the
436 --strict-warnings option).
439 Don't build with the "UI" capability (i.e. the set of
440 features enabling text based prompts).
443 Enable additional unit test APIs. This should not typically
444 be used in production deployments.
446 enable-weak-ssl-ciphers
447 Build support for SSL/TLS ciphers that are considered "weak"
448 (e.g. RC4 based ciphersuites).
451 Build with support for zlib compression/decompression.
454 Like "zlib", but has OpenSSL load the zlib library
455 dynamically when needed. This is only supported on systems
456 where loading of shared libraries is supported.
459 On Intel hardware, use the 80386 instruction set only
460 (the default x86 code is more efficient, but requires at
461 least a 486). Note: Use compiler flags for any other CPU
462 specific configuration, e.g. "-m32" to build x86 code on
466 Don't build support for negotiating the specified SSL/TLS
467 protocol (one of ssl, ssl3, tls, tls1, tls1_1, tls1_2, dtls,
468 dtls1 or dtls1_2). If "no-tls" is selected then all of tls1,
469 tls1_1 and tls1_2 are disabled. Similarly "no-dtls" will
470 disable dtls1 and dtls1_2. The "no-ssl" option is synonymous
471 with "no-ssl3". Note this only affects version negotiation.
472 OpenSSL will still provide the methods for applications to
473 explicitly select the individual protocol versions.
476 As for no-<prot> but in addition do not build the methods for
477 applications to explicitly select individual protocol
481 Build with support for the specified algorithm, where <alg>
482 is one of: md2 or rc5.
485 Build without support for the specified algorithm, where
486 <alg> is one of: bf, blake2, camellia, cast, chacha, cmac,
487 des, dh, dsa, ecdh, ecdsa, idea, md4, md5, mdc2, ocb,
488 ploy1305, rc2, rc4, rmd160, scrypt, seed or whirlpool. The
489 "ripemd" algorithm is deprecated and if used is synonymous
492 -Dxxx, -lxxx, -Lxxx, -fxxx, -mXXX, -Kxxx
493 These system specific options will be passed through to the
494 compiler to allow you to define preprocessor symbols, specify
495 additional libraries, library directories or other compiler
499 Installation in Detail
500 ----------------------
502 1a. Configure OpenSSL for your operation system automatically:
504 NOTE: This is not available on Windows.
506 $ ./config [[ options ]] # Unix
510 $ @config [[ options ]] ! OpenVMS
512 For the remainder of this text, the Unix form will be used in all
513 examples, please use the appropriate form for your platform.
515 This guesses at your operating system (and compiler, if necessary) and
516 configures OpenSSL based on this guess. Run ./config -t to see
517 if it guessed correctly. If you want to use a different compiler, you
518 are cross-compiling for another platform, or the ./config guess was
519 wrong for other reasons, go to step 1b. Otherwise go to step 2.
521 On some systems, you can include debugging information as follows:
523 $ ./config -d [[ options ]]
525 1b. Configure OpenSSL for your operating system manually
527 OpenSSL knows about a range of different operating system, hardware and
528 compiler combinations. To see the ones it knows about, run
534 $ perl Configure # All other platforms
536 For the remainder of this text, the Unix form will be used in all
537 examples, please use the appropriate form for your platform.
539 Pick a suitable name from the list that matches your system. For most
540 operating systems there is a choice between using "cc" or "gcc". When
541 you have identified your system (and if necessary compiler) use this name
542 as the argument to Configure. For example, a "linux-elf" user would
545 $ ./Configure linux-elf [[ options ]]
547 If your system isn't listed, you will have to create a configuration
548 file named Configurations/{{ something }}.conf and add the correct
549 configuration for your system. See the available configs as examples
550 and read Configurations/README and Configurations/README.design for
553 The generic configurations "cc" or "gcc" should usually work on 32 bit
556 Configure creates a build file ("Makefile" on Unix, "makefile" on Windows
557 and "descrip.mms" on OpenVMS) from a suitable template in Configurations,
558 and defines various macros in include/openssl/opensslconf.h (generated from
559 include/openssl/opensslconf.h.in).
561 1c. Configure OpenSSL for building outside of the source tree.
563 OpenSSL can be configured to build in a build directory separate from
564 the directory with the source code. It's done by placing yourself in
565 some other directory and invoking the configuration commands from
570 $ mkdir /var/tmp/openssl-build
571 $ cd /var/tmp/openssl-build
572 $ /PATH/TO/OPENSSL/SOURCE/config [[ options ]]
576 $ /PATH/TO/OPENSSL/SOURCE/Configure {{ target }} [[ options ]]
580 $ set default sys$login:
581 $ create/dir [.tmp.openssl-build]
582 $ set default [.tmp.openssl-build]
583 $ @[PATH.TO.OPENSSL.SOURCE]config [[ options ]]
587 $ @[PATH.TO.OPENSSL.SOURCE]Configure {{ target }} [[ options ]]
592 $ mkdir \temp-openssl
594 $ perl d:\PATH\TO\OPENSSL\SOURCE\Configure {{ target }} [[ options ]]
596 Paths can be relative just as well as absolute. Configure will
597 do its best to translate them to relative paths whenever possible.
599 2. Build OpenSSL by running:
602 $ mms ! (or mmk) OpenVMS
605 This will build the OpenSSL libraries (libcrypto.a and libssl.a on
606 Unix, corresponding on other platforms) and the OpenSSL binary
607 ("openssl"). The libraries will be built in the top-level directory,
608 and the binary will be in the "apps" subdirectory.
610 If the build fails, look at the output. There may be reasons for
611 the failure that aren't problems in OpenSSL itself (like missing
612 standard headers). If you are having problems you can get help by
613 sending an email to the openssl-users email list (see
614 https://www.openssl.org/community/mailinglists.html for details). If it
615 is a bug with OpenSSL itself, please report the problem to
616 <rt@openssl.org> (note that your message will be recorded in the request
617 tracker publicly readable at
618 https://www.openssl.org/community/index.html#bugs and will be
619 forwarded to a public mailing list). Please check out the request
620 tracker. Maybe the bug was already reported or has already been
623 (If you encounter assembler error messages, try the "no-asm"
624 configuration option as an immediate fix.)
626 Compiling parts of OpenSSL with gcc and others with the system
627 compiler will result in unresolved symbols on some systems.
629 3. After a successful build, the libraries should be tested. Run:
633 $ nmake test # Windows
635 NOTE: you MUST run the tests from an unprivileged account (or
636 disable your privileges temporarily if your platform allows it).
638 If some tests fail, look at the output. There may be reasons for
639 the failure that isn't a problem in OpenSSL itself (like a
640 malfunction with Perl). You may want increased verbosity, that
641 can be accomplished like this:
643 $ make VERBOSE=1 test # Unix
645 $ mms /macro=(VERBOSE=1) test ! OpenVMS
647 $ nmake VERBOSE=1 test # Windows
649 If you want to run just one or a few specific tests, you can use
650 the make variable TESTS to specify them, like this:
652 $ make TESTS='test_rsa test_dsa' test # Unix
653 $ mms/macro="TESTS=test_rsa test_dsa" test ! OpenVMS
654 $ nmake TESTS='test_rsa test_dsa' test # Windows
656 And of course, you can combine (Unix example shown):
658 $ make VERBOSE=1 TESTS='test_rsa test_dsa' test
660 You can find the list of available tests like this:
662 $ make list-tests # Unix
663 $ mms list-tests ! OpenVMS
664 $ nmake list-tests # Windows
666 Have a look at the manual for the perl module Test::Harness to
667 see what other HARNESS_* variables there are.
669 If you find a problem with OpenSSL itself, try removing any
670 compiler optimization flags from the CFLAGS line in Makefile and
671 run "make clean; make" or corresponding.
673 Please send bug reports to <rt@openssl.org>.
675 4. If everything tests ok, install OpenSSL with
677 $ make install # Unix
678 $ mms install ! OpenVMS
679 $ nmake install # Windows
681 This will install all the software components in this directory
682 tree under PREFIX (the directory given with --prefix or its
687 bin/ Contains the openssl binary and a few other
690 Contains the header files needed if you want
691 to build your own programs that use libcrypto
693 lib Contains the OpenSSL library files.
694 lib/engines Contains the OpenSSL dynamically loadable engines.
696 share/man/man1 Contains the OpenSSL command line man-pages.
697 share/man/man3 Contains the OpenSSL library calls man-pages.
698 share/man/man5 Contains the OpenSSL configuration format man-pages.
699 share/man/man7 Contains the OpenSSL other misc man-pages.
701 share/doc/openssl/html/man1
702 share/doc/openssl/html/man3
703 share/doc/openssl/html/man5
704 share/doc/openssl/html/man7
705 Contains the HTML rendition of the man-pages.
707 OpenVMS ('arch' is replaced with the architecture name, "Alpha"
708 or "ia64", 'sover' is replaced with the shared library version
709 (0101 for 1.1), and 'pz' is replaced with the pointer size
710 OpenSSL was built with):
712 [.EXE.'arch'] Contains the openssl binary.
713 [.EXE] Contains a few utility scripts.
715 Contains the header files needed if you want
716 to build your own programs that use libcrypto
718 [.LIB.'arch'] Contains the OpenSSL library files.
719 [.ENGINES'sover''pz'.'arch']
720 Contains the OpenSSL dynamically loadable engines.
721 [.SYS$STARTUP] Contains startup, login and shutdown scripts.
722 These define appropriate logical names and
724 [.SYSTEST] Contains the installation verification procedure.
725 [.HTML] Contains the HTML rendition of the manual pages.
728 Additionally, install will add the following directories under
729 OPENSSLDIR (the directory given with --openssldir or its default)
732 certs Initially empty, this is the default location
733 for certificate files.
734 private Initially empty, this is the default location
735 for private key files.
736 misc Various scripts.
738 Package builders who want to configure the library for standard
739 locations, but have the package installed somewhere else so that
740 it can easily be packaged, can use
742 $ make DESTDIR=/tmp/package-root install # Unix
743 $ mms/macro="DESTDIR=TMP:[PACKAGE-ROOT]" install ! OpenVMS
745 The specified destination directory will be prepended to all
746 installation target paths.
748 Compatibility issues with previous OpenSSL versions:
750 * COMPILING existing applications
752 OpenSSL 1.1.0 hides a number of structures that were previously
753 open. This includes all internal libssl structures and a number
754 of EVP types. Accessor functions have been added to allow
755 controlled access to the structures' data.
757 This means that some software needs to be rewritten to adapt to
758 the new ways of doing things. This often amounts to allocating
759 an instance of a structure explicitly where you could previously
760 allocate them on the stack as automatic variables, and using the
761 provided accessor functions where you would previously access a
762 structure's field directly.
764 Some APIs have changed as well. However, older APIs have been
765 preserved when possible.
767 Environment Variables
768 ---------------------
770 A number of environment variables can be used to provide additional control
771 over the build process. Typically these should be defined prior to running
772 config or Configure. Not all environment variables are relevant to all
776 The name of the ar executable to use.
779 Use a different build file name than the platform default
780 ("Makefile" on Unixly platforms, "makefile" on native Windows,
781 "descrip.mms" on OpenVMS). This requires that there is a
782 corresponding build file template. See Configurations/README
783 for further information.
786 The compiler to use. Configure will attempt to pick a default
787 compiler for your platform but this choice can be overridden
788 using this variable. Set it to the compiler executable you wish
789 to use, e.g. "gcc" or "clang".
792 This environment variable has the same meaning as for the
793 "--cross-compile-prefix" Configure flag described above. If both
794 are set then the Configure flag takes precedence.
797 The name of the nm executable to use.
799 OPENSSL_LOCAL_CONFIG_DIR
800 OpenSSL comes with a database of information about how it
801 should be built on different platforms as well as build file
802 templates for those platforms. The database is comprised of
803 ".conf" files in the Configurations directory. The build
804 file templates reside there as well as ".tmpl" files. See the
805 file Configurations/README for further information about the
806 format of ".conf" files as well as information on the ".tmpl"
808 In addition to the standard ".conf" and ".tmpl" files, it is
809 possible to create your own ".conf" and ".tmpl" files and store
810 them locally, outside the OpenSSL source tree. This environment
811 variable can be set to the directory where these files are held
812 and will have Configure to consider them in addition to the
816 The name of the Perl executable to use when building OpenSSL.
819 The command string for the Perl executable to insert in the
820 #! line of perl scripts that will be publically installed.
821 Default: /usr/bin/env perl
822 Note: the value of this variable is added to the same scripts
823 on all platforms, but it's only relevant on Unix-like platforms.
826 The name of the rc executable to use. The default will be as
827 defined for the target platform in the ".conf" file. If not
828 defined then "windres" will be used. The WINDRES environment
829 variable is synonymous to this. If both are defined then RC
833 The name of the ranlib executable to use.
841 The Configure script generates a Makefile in a format relevant to the specific
842 platform. The Makefiles provide a number of targets that can be used. Not all
843 targets may be available on all platforms. Only the most common targets are
844 described here. Examine the Makefiles themselves for the full list.
847 The default target to build all the software components.
850 Remove all build artefacts and return the directory to a "clean"
854 Rebuild the dependencies in the Makefiles. This is a legacy
855 option that no longer needs to be used in OpenSSL 1.1.0.
858 Install all OpenSSL components.
861 Only install the OpenSSL software components.
864 Only install the OpenSSL documentation components.
867 Only install the OpenSSL man pages (Unix only).
870 Only install the OpenSSL html documentation.
873 Prints a list of all the self test names.
876 Build and run the OpenSSL self tests.
879 Uninstall all OpenSSL components.
882 This is a developer option. If you are developing a patch for
883 OpenSSL you may need to use this if you want to update
884 automatically generated files; add new error codes or add new
885 (or change the visibility of) public API functions. (Unix only).
887 Note on multi-threading
888 -----------------------
890 For some systems, the OpenSSL Configure script knows what compiler options
891 are needed to generate a library that is suitable for multi-threaded
892 applications. On these systems, support for multi-threading is enabled
893 by default; use the "no-threads" option to disable (this should never be
896 On other systems, to enable support for multi-threading, you will have
897 to specify at least two options: "threads", and a system-dependent option.
898 (The latter is "-D_REENTRANT" on various systems.) The default in this
899 case, obviously, is not to include support for multi-threading (but
900 you can still use "no-threads" to suppress an annoying warning message
901 from the Configure script.)
903 OpenSSL provides built-in support for two threading models: pthreads (found on
904 most UNIX/Linux systems), and Windows threads. No other threading models are
905 supported. If your platform does not provide pthreads or Windows threads then
906 you should Configure with the "no-threads" option.
908 Note on shared libraries
909 ------------------------
911 For most systems the OpenSSL Configure script knows what is needed to
912 build shared libraries for libcrypto and libssl. On these systems
913 the shared libraries will be created by default. This can be suppressed and
914 only static libraries created by using the "no-shared" option. On systems
915 where OpenSSL does not know how to build shared libraries the "no-shared"
916 option will be forced and only static libraries will be created.
918 Note on random number generation
919 --------------------------------
921 Availability of cryptographically secure random numbers is required for
922 secret key generation. OpenSSL provides several options to seed the
923 internal PRNG. If not properly seeded, the internal PRNG will refuse
924 to deliver random bytes and a "PRNG not seeded error" will occur.
925 On systems without /dev/urandom (or similar) device, it may be necessary
926 to install additional support software to obtain a random seed.
927 Please check out the manual pages for RAND_add(), RAND_bytes(), RAND_egd(),
928 and the FAQ for more information.
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