After a map is changed, the Makefile uses yppush to propagate a new map to the slave servers (unless
NOPUSH is set in the Makefile).
It does this by informing the ypserv daemon and sending
a map transfer request. The ypserv daemon on the slave
then starts a ypxfr process, which in turn contacts the ypxfrd daemon on the master server. Some basic checks are made (for
example did the map really change?) and then the map is transferred. ypxfr on the slave then sends a response to the yppush process
indicating whether the transfer succeeded.
Occasionally, maps fail to propagate and you must to use ypxfr manually to send new map information. You can choose to use ypxfr in two different ways: periodically through the root crontab file, or interactively on the command line. These approaches are discussed in the following sections.