Comment (by Roland Haas):

This is rather strange. The optioin list looks ok to me to be honest. Adding -lcocalmrns to LDFLAGS is ok.

The error message about missing main is strange since main is provided by the Cactus flesh. Is it possible that the COCAL library defines its own main and that that one interferes? It would be good to see all the error messages and not just the last couple. Would you mind taking a look at http://einsteintoolkit.org/support.html#general-guidelines-for-questions and provide the files described in there, please?

Since COCAL is not part of the Einstein Toolkit (and, at least until the recent past, had an unusual build system), have you contacted the COCAL author (Antonios Toskaros), who may be able to provide advise as well?

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2679/how-to-link-an-externally-compiled-library