After a good bit of trial and error I have managed to cluster together two OS X machines. The master is running Mathematica 9.0 and the secondary 11.0. All was well and good, the remote command being
ssh -x -f -l nwalton treebeard.local "/Applications/Mathematica\ \
11.app/Contents/MacOS/WolframKernel" -mathlink -linkmode Connect `4` \
-linkname '`2`' -subkernel -noinit
To get some short term extra performance I grabbed a trial version of 11.3 on to a third machine with the same remote command save for host and login names
ssh -x -f -l install install.local "/Applications/Mathematica\ \
11.app/Contents/MacOS/WolframKernel" -mathlink -linkmode Connect `4` \
-linkname '`2`' -subkernel -noinit
The third machine runs Mathematica standalone fine, but when I add it to the cluster the master running 9.0 reports
LaunchKernels::forw: Kernel version 9 is newer than master kernel. >>
The previous remote kernel still fires up as before.
What is going on? I'm perplexed.