When any changes occur to the maps, the master needs to distribute the new copies to the slaves. It actually transfers the files using the NIS transport itself, as we saw earlier when we built the slaves (these were the “Transferring <map name>” messages).
There are two commands used to propagate the maps around the servers: ypxfr and yppush.
This runs on the slave and communicates with the ypxfrd running on the master to request the download of an individual map. For example, to update the hosts file from the master we could run the following command:
fluorine# /usr/lib/netsvc/yp/ypxfr hosts.byname flourine#
It's possible that sometimes the slave maps may not get updated for some reason; maybe the slave server was down ...