If rpc.yppasswdd is invoked with the -i flag, password changes will
be made to the master.passwd template file and the hash map files
in-place, which means it won't have to run a complete map update.
Instead, it calls /var/yp/Makefile with the 'pushpw' target, which
just pushes the maps to the slaves and runs yp_mkdb -c to tell the
local ypserv to flush its database cache.
The server will check the passwd.byname and passwd.byuid maps to see
if they were built in 'insecure' or 'secure' mode (i.e. with real
encrypted passwords in them or without) and update them accordingly.
This combined with rpc.ypxfrd greatly reduces the amount of time it
takes to complete an NIS password change, especially with very large
passwd databases.
