UPSCLI_INIT(3)

NAME

upscli_init - Initialize upsclient module specifying security properties.

SYNOPSIS

        #include <upsclient.h>

        int upscli_init(
                int certverify,
                const char *certpath,
                const char *certname,
                const char *certpasswd);

DESCRIPTION

The upscli_init() function initializes upsclient module and sets many TLS/SSL-related properties: certverify to 1 makes certificate verification required for all SSL connections and certpath is the location of certificate database.

certverify

Specify a non-zero value to require that server certificate is valid, and abort the STARTTLS attempt if it is not.

Specify a zero value to ignore any results of such a check (e.g. only log the situation), or not do it at all.

certpath

If compiled with OpenSSL, certpath refers to directory containing certificates where the certificates must be named according to their hash values ending in a ".0" extension. If two certificates result in the same hash value (thus file name), the ".0" can be incremented to ".1" and so on, as needed. The shell command for creating links in this manner would be:
```
:; ln -s ca.pem ./$(openssl x509 -hash -noout -in ca.pem).0
```
Alternatively, the c_rehash utility (provided by e.g. openssl-perl package) can take a directory and iterate it to link all certificates found in that directory, in the manner described above.
If compiled with NSS, the certpath refers to a directory containing its database files.

certname and certpasswd

If using SSL, you can specify certname with the subject name of the certificate to send to upsd, and certpasswd with the password used to decrypt certificate private key.

If compiled with NSS, this allows to choose one of many certificates that may be stored in the database.

Notably, the certname (if not empty) can be used to verify that the specified file provides a certificate with expected subject name, or possibly matches the expected host name or IP address.

Other nuances

If compiled with NSS, the client library would normally log either the infamous message "Init SSL without certificate database" if no certpath was provided, or "Init SSL with certificate database located at %s" otherwise. Since some programmatic consumers become confused by such extra text on the stderr of tools they call (such as monitoring systems doing upsc queries), you can export an environment variable NUT_QUIET_INIT_SSL with string values "true", "TRUE" or "1", to avoid logging these messages and only emit them as debug stream (seen at verbosity 1 or higher).

As part of general initialization, upscli_init() function can call the upscli_init_default_connect_timeout(3) method (if it was never used before): this allows unmodified (legacy) NUT clients to consistently benefit from presence of the NUT_DEFAULT_CONNECT_TIMEOUT environment variable for upscli_connect(3) attempts to be not blocking (as per default).

You can call upscli_add_host_cert(3) to register specific host security policy before initializing connections to them.

You must call upscli_cleanup(3) when exiting application.

Starting with NUT v2.8.5, you can use upscli_ssl_caps(3) from consumer code to query the library about its build circumstances (whether it supports SSL, and which backend(s)).

RETURN VALUE

The upscli_init() function returns 1 on success, or -1 if an error occurs.