R.I. Gen. Laws § 15-5-20: Service on or notice to defendant.

No person shall be entitled to a divorce from the bond of marriage unless the defendant, in accordance with rules adopted by the court, has been personally served with process if within the state, or with personal notice duly authenticated if out of the state, or unless the defendant has entered an appearance in the cause; or unless it appears to the satisfaction of the court that the petitioner does not know the address nor the residence of the defendant and has not been able to ascertain either after reasonable and due inquiry and search for six (6) months, in which case the court, or in vacation a judge of the court, may authorize notice by publication of the pendency of the petition for divorce to be given in a manner provided by law; provided, that in cases where indigence has been established, the court may, as an alternative to publication and upon motion and in appropriate circumstance, authorize an alternate means of service of process in the manner provided by Rule 4 of the Family Court Rules of Procedure for Domestic Relations.