Hi George,
This actually depends on what you have defined in your vid map. In general, using the unix authentication is not a recommended setup unless you control the client machine.
Once you enable the vid mapping for unix (or even without this), you can allow unix connection from a certain hosts to use the local identity when connecting to the MGM by defining a tident mapping. For example the truncated output of eos vid ls could look like this:
tident:"unix@iota":gid => root
tident:"unix@iota":uid => root
Anyone connecting from the iota machine with unix auth will be mapped to the id advertised by the client. You can add such entries with the usual eos vid map -tident ..... You can also enable this for every unix authentication by modifying the initial rule introduced when enabling unix mapping to point to root rather than nobody - but this is definitely not recommended.
Cheers,
Elvin