path file - issues in the configuration

hello dear experts

meanwhile i have tried to install wp on a rootserver that is administrated by my friend i have got issues while trying to establish a db connection.

then i tried to run a test-teh connection script which gives back the following results

    Warning: mysqli_connect(): (HY000/2002): No such file or directory in 
    /sites/www.mysite.de/testconnection.php on line 2
    Warning: mysqli_error() expects exactly 1 parameter,
    0 given in /sites/www.mysite.de/testconnection.php on line 4
    Could not connect:

well - what does this script-results say - do i have issues and errors in the path of the pipe!?do i have to do corrections here

     * For information on other constants that can be used for debugging,
     * visit the Codex.
     *
     * @link https://codex.wordpress.org/Debugging_in_WordPress
     */
    define( 'WP_DEBUG', false );
    
    /* That's all, stop editing! Happy publishing. */
    
    /** Absolute path to the WordPress directory. */
    if ( ! defined( 'ABSPATH' ) ) {
        define( 'ABSPATH', dirname( __FILE__ ) . '/' );
    }
    
    /** Sets up WordPress vars and included files. */
    require_once( ABSPATH . 'wp-settings.php' );

well - i am musing what is going on here