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OPENSSL_CONFIG(3) Library Functions Manual OPENSSL_CONFIG(3)

OPENSSL_config, OPENSSL_no_config
simple crypto and ssl library configuration

#include <openssl/conf.h>
void
OPENSSL_config(const char *appname);
void
OPENSSL_no_config(void);

OPENSSL_config() initializes the crypto library with OPENSSL_init_crypto(3) and then calls OPENSSL_load_builtin_modules(3), ENGINE_load_builtin_engines(3), and CONF_modules_load_file(3) with the standard configuration file and the given appname. If appname is NULL, then the default name openssl_conf is used. Any errors are ignored. Further calls to OPENSSL_config() have no effect.
OPENSSL_no_config() suppresses the loading of any configuration file, so that any future calls to OPENSSL_config() or to OPENSSL_init_crypto(3) will ensure the library is initialized but no configuration file will be loaded.
Calling these functions is optional. All required initialization of the crypto libraries happens automatically when needed.
If an application is compiled with the preprocessor symbol OPENSSL_LOAD_CONF #define'd, OpenSSL_add_all_algorithms(3) automatically calls OPENSSL_config().
Applications should free up configuration at application closedown by calling CONF_modules_free(3).

/etc/ssl/openssl.cnf
standard configuration file

CONF_modules_free(3), CONF_modules_load_file(3), OPENSSL_init_crypto(3), OPENSSL_load_builtin_modules(3), openssl.cnf(5)

OPENSSL_config() and OPENSSL_no_config() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.
April 7, 2018 OpenBSD-current