The Jargon File (version 4.4.7, 29 Dec 2003):

casting the runes
 n.

    What a guru does when you ask him or her to run a particular program and
    type at it because it never works for anyone else; esp. used when nobody
    can ever see what the guru is doing different from what J. Random Luser
    does. Compare incantation, runes, examining the entrails; also see
    the AI koan about Tom Knight in Some AI Koans (in Appendix A).

    A correspondent from England tells us that one of ICL's most talented
    systems designers used to be called out occasionally to service machines
    which the field circus had given up on. Since he knew the design inside
    out, he could often find faults simply by listening to a quick outline of
    the symptoms. He used to play on this by going to some site where the field
    circus had just spent the last two weeks solid trying to find a fault, and
    spreading a diagram of the system out on a table top. He'd then shake some
    chicken bones and cast them over the diagram, peer at the bones intently
    for a minute, and then tell them that a certain module needed replacing.
    The system would start working again immediately upon the replacement.


The Free On-line Dictionary of Computing (30 December 2018):

casting the runes

    What a guru does when you ask him or her to run a
   particular program because it never works for anyone else;
   especially used when nobody can ever see what the guru is
   doing different from what J. Random Luser does.

   Compare incantation, runes, examining the entrails; also
   see the AI koan about Tom Knight.

   (1997-12-26)