It says: If versnum is not specified, rpcinfo tries to ping all available version numbers for that program number. This option avoids calls to remote rpcbind to find the address of the service. The serv_address is specified in universal address format of the given transport. However, "universal address format" is not defined anywhere. It's not even easily googlable. I ended up reading an implementation (in the Linux kernel, oddly enough) to find out what it actually is: it appends the port number to the numeric form of the address, *as big-endian octets separated by dots*. Thus, for example, port 2049 is represented as ".8.1". I think this is a consequence of the incomplete assimilation of TI-RPC from 20 years ago, but it's long past time to at least document what this syntax is.