OPENSSL_config(3) OpenSSL OPENSSL_config(3)
OPENSSL_config, OPENSSL_no_config - simple OpenSSL configuration func-
void OPENSSL_config(const char *config_name);
OPENSSL_config() configures OpenSSL using the standard openssl.cnf con-
figuration file name using config_name. If config_name is NULL then the
default name openssl_conf will be used. Any errors are ignored. Further
calls to OPENSSL_config() will have no effect. The configuration file
format is documented in the conf(5) manual page.
OPENSSL_no_config() disables configuration. If called before
OPENSSL_config() no configuration takes place.
It is strongly recommended that all new applications call OPENSSL_con-
fig() or the more sophisticated functions such as CONF_modules_load()
during initialization (that is before starting any threads). By doing
this an application does not need to keep track of all configuration
options and some new functionality can be supported automatically.
It is also possible to automatically call OPENSSL_config() when an
application calls OPENSSL_add_all_algorithms() by compiling an applica-
tion with the preprocessor symbol OPENSSL_LOAD_CONF #define'd. In this
way configuration can be added without source changes.
The environment variable OPENSSL_CONFIG can be set to specify the loca-
tion of the configuration file.
Currently ASN1 OBJECTs and ENGINE configuration can be performed future
versions of OpenSSL will add new configuration options.
There are several reasons why calling the OpenSSL configuration rou-
tines 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 cer-
tain 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
Applications should free up configuration at application closedown by
The OPENSSL_config() function is designed to be a very simple "call it
and forget it" function. As a result its behaviour is somewhat limited.
It ignores all errors silently and it can only load from the standard
configuration file location for example.
It is however much better than nothing. Applications which need finer
control over their configuration functionality should use the configu-
ration functions such as CONF_load_modules() directly.
Neither OPENSSL_config() nor OPENSSL_no_config() return a value.
conf(5), CONF_load_modules_file(3), CONF_modules_free(3),CONF_mod-
OPENSSL_config() and OPENSSL_no_config() first appeared in OpenSSL
3rd Berkeley Distribution 0.9.7d OPENSSL_config(3)