These options allow you to create a pair of local files, with
username:uid/groupname:gid pairs, one per line. Alternatively, files can
be in standard /etc/passwd / /etc/group format.
The uid/gids are for the remote server, their local counterparts are
looked up with a local getpwnam/getgrnam call. Any stat() calls will
show with the remapped local uid/gid, and any chown() calls will be
remapped back to the remote uid/gid.