Cause of the Error
This error occurs while trying to connect to a ClickHouse server using clickhouse-client. The cause of the error is either:
- the client configuration file config.xmlis missing the root certificate in the machine CA default store, or
- there is a self-signed or internal CA certificate that is not configured
Solution
If using an internal or self-signed CA, configure the CA root certificate in config.xml in the client directory (e.g. /etc/clickhouse-client) and disable the loading of the default root CA certificates from the default location.
Here is an example configuration:
<openSSL>
    <client>
        <loadDefaultCAFile>false</loadDefaultCAFile>
        <caConfig>/etc/clickhouse-server/certs/marsnet_ca.crt</caConfig>
        <cacheSessions>true</cacheSessions>
        <disableProtocols>sslv2,sslv3</disableProtocols>
        <preferServerCiphers>true</preferServerCiphers>
        <invalidCertificateHandler>
            <name>RejectCertificateHandler</name>
        </invalidCertificateHandler>
    </client>
</openSSL>
Additional resources
View https://clickhouse.com/docs/en/interfaces/cli/#configuration_files