Manual:OPENSSL config(3)

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OPENSSL_config, OPENSSL_no_config - simple OpenSSL configuration functions


 #include <openssl/conf.h>

 void OPENSSL_config(const char *config_name);
 void OPENSSL_no_config(void);


OPENSSL_config() configures OpenSSL using the standard openssl.cnf configuration file name using config_name. If config_name is NULL then the file specified in the environment variable OPENSSL_CONF will be used, and if that is not set then a system default location is used. Errors are silently ignored. Multiple calls have no effect.

OPENSSL_no_config() disables configuration. If called before OPENSSL_config() no configuration takes place.

Applications should free up configuration at application closedown by calling CONF_modules_free().

If the application is built with OPENSSL_LOAD_CONF defined, then a call to OpenSSL_add_all_algorithms() will implicitly call OPENSSL_config() first.


The OPENSSL_config() function is designed to be a very simple "call it and forget it" function. It is however much better than nothing. Applications which need finer control over their configuration functionality should use the configuration functions such as CONF_modules_load() directly. This function is deprecated and its use should be avoided. Applications should instead call CONF_modules_load() during initialization (that is before starting any threads).

There are several reasons why calling the OpenSSL configuration routines is advisable. For example new ENGINE functionality was added to OpenSSL 0.9.7. In OpenSSL 0.9.7 control functions can be supported by ENGINEs, this can be used (among other things) to load dynamic ENGINEs from shared libraries (DSOs). However very few applications currently support the control interface and so very few can load and use dynamic ENGINEs. Equally in future more sophisticated ENGINEs will require certain control operations to customize them. If an application calls OPENSSL_config() it doesn't need to know or care about ENGINE control operations because they can be performed by editing a configuration file.


Neither OPENSSL_config() nor OPENSSL_no_config() return a value.


conf(5), CONF_modules_load_file(3), CONF_modules_free(3)


OPENSSL_config() and OPENSSL_no_config() first appeared in OpenSSL 0.9.7