If the user specifies a queue name and does not specify nodes(nodes=NULL) when creating the LSF cluster context with RxLSFCluster(), it will use all the hosts available in that queue(assuming that they are valid). If both the queue and nodes are specified, it uses the intersection of them. If queue = "all" and nodes = NULL, we use the system command 'ls_gethostinfo' to get the host names and then check their validity.