YPFILES(NF) System V NFS (12/3/90) YPFILES(NF)
NAME
ypfiles - the network information service database and
directory structure
DESCRIPTION
The network information service (NIS) lookup service uses a
database of dbm files in the directory hierarchy, /etc/yp.
A dbm database consists of two files which are created by
calls to the dbm(NS) library package. One has the filename
extension, .pag, and the other has the filename extension,
.dir. For instance, the database named hosts.nam, is
implemented by the pair of files hosts.nam.pag and
hosts.nam.dir. A dbm database served by NIS is called a NIS
map. A NIS domain is a named set of NIS maps. Each NIS
domain is implemented as a subdirectory of /etc/yp
containing the map. Any number of NIS domains can exist;
each such domain may contain any number of NIS maps.
No maps are required by the NIS lookup service itself,
although they may be required for the normal operation of
other parts of the system. There is no list of maps which
NIS serves: if the map exists in a given domain and if a
client asks about it, the NIS will serve it. For a map to
be accessible consistently, it must exist on all NIS servers
serving the domain. To provide data consistency among the
replicated maps, an entry to run ypxfr(NADM) periodically
should be made in /usr/lib/crontab on each server. More
information on this topic is in ypxfr.
NIS maps should contain two distinguished key-value pairs.
The first is the key, YP_LAST_MODIFIED, which contains a
ten-character ASCII order number. This order number should
be the UNIX time in seconds when the map was built. The
second key is YP_MASTER_NAME, with the name of the NIS
master server as a value. makedbm(NADM) generates both
key-value pairs automatically. A map that does not contain
both key-value pairs can be served by the NIS, but the
ypserv(NADM) process will be unable to return values for Get
order number or Get master name requests. In addition, the
values of these two keys are used by ypxfr when it transfers
a map from a master NIS server to a slave. If ypxfr cannot
figure out where to get the map or if it is unable to
determine whether the local copy is more recent than the
copy at the master, you must set extra command line switches
when you run it.
NIS maps must be generated and modified only at the master
server. They are copied to the slaves using ypxfr to avoid
potential byte-ordering problems among NIS servers running
on machines with different architectures and to minimize the
amount of disk space required for the dbm files. The NIS
database can be initially set up for both masters and slaves
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YPFILES(NF) System V NFS (12/3/90) YPFILES(NF)
by using ypinit(NADM).
After the server databases are set up, it is probable that
the contents of some maps will change. In general, some
ASCII source version of the database exists on the master;
it can be changed with a standard text editor. The update
is incorporated into the NIS map and is propagated from the
master to the slaves by running /etc/yp/Makefile. All
initially supplied maps have corresponding entries in
/etc/yp/Makefile; if you add a NIS map, you should edit this
file to support the new map. The makefile uses makedbm to
generate the NIS map on the master and yppush(NADM) to
propagate the changed map to the slaves. yppush is a client
of the map, ypservers, which lists all the NIS servers.
SEE ALSO
makedbm(NADM), ypinit(NADM), ypmake(NADM), ypxfr(NADM),
yppush(NADM), yppoll(NADM), ypserv(NADM), rpcinfo(NADM)
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