ypfiles(NF)                     19 June 1992                     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 an NIS map.  An 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 con-
    tain 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(NADM)

    NIS maps should contain two distinguished key-value pairs.  The first is
    the key, YPLASTMODIFIED, 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 YPMASTERNAME, 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 addi-
    tion, 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 cannot 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 architec-
    tures 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 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
    an 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), rpcinfo(NADM), ypinit(NADM), ypmake(NADM), yppoll(NADM),
    yppush(NADM), ypserv(NADM), ypxfr(NADM)