There was, unfortunately, an awkward detail — the old-school Unix vendors who had backed the effort were under severe pressure from the new school of open-source Unixes, and were in some cases in the process of abandoning (in favor of Linux) the proprietary Unixes for which they had gone to so much effort to secure conformance.

The conformance testing needed to verify Single Unix Specification conformance is an expensive proposition. It would need to be done on a per-distribution basis, but is well out of the reach of most distributors of open-source operating systems. In any case, Linux changes so fast that any given release of a distribution would probably be obsolete by the time it could get certified.^[145]

Standards like the Single Unix Specification have not entirely lost their relevance. They're still valuable guides for Unix implementers. But how The Open Group and other institutions of the old-school Unix standardization process will adapt to the rapid tempo of open-source releases (and to the low- or zero-budget operation of open-source development groups!) remains to be seen.