ok

CMD:entrainement(playerid, params[])
{
    static
        n_string[50];

    format(n_string, sizeof(n_string), "hostname %s", params);

    return SendRconCommand(n_string);
}

------------------

CMD:entrainement(playerid, params[])
{
    new
        str[9+50 char] = !"hostname ";

    strcat(str, params, sizeof(str));

    return SendRconCommand(str);
}