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     The irs(3) functions are a set of routines in the C library which provide
     access to various system maps.  The maps that irs currently controls are
     the following: passwd, group, services, protocols, hosts, networks and
     netgroup.  When a program first calls a function that accesses one of
     these maps, the irs configuration file is read, and the source of each
     map is determined for the life of the process.

     If this file does not exist, the irs routines default to using local
     sources for all information, with the exception of the host and networks
     maps, which use the Domain Name System (DNS).

     Each record in the file consists of one line.  A record consists of a
     map-name, an access-method and possibly a (comma delimited) set of op­
     tions, separated by tabs or spaces.  Blank lines, and text between a #
     and a newline are ignored.

     Available maps:

           Map name        Information in map
           =========       ==================================
           passwd          User authentication information
           group           User group membership information
           services        Network services directory
           protocols       Network protocols directory
           hosts           Network hosts directory
           networks        Network "network names" directory
           netgroup        Network "host groups" directory

     Available access methods:

           Access method   Description
           =============   =================================================
           local           Use a local file, usually in /etc
           dns             Use the domain name service (includes hesiod)
           nis             Use the Sun-compatible Network Information Service
           irp             Use the IRP daemon on the localhost.

     Available options:

           Option          Description
           ========        ================================================
           continue        don't stop searching if you can't find something
           merge           don't stop searching if you CAN find something

     The continue option creates ``union namespaces'' whereby subsequent ac­
     cess methods of the same map type can be tried if a name cannot be found
     using earlier access methods.  This can be quite confusing in the case of
     host names, since the name to address and address to name mappings can be
     visibly asymmetric even though the data used by any given access method
     is entirely consistent.  This behavior is, therefore, not the default.
           group           nis

           # Services comes from just the local file.
           services        local

           protocols       local

           # Hosts comes first from DNS, failing that, the local file
           hosts           dns     continue
           hosts           local

           # Networks comes first from the local file, and failing
           # that the, irp daemon
           networks        local   continue
           networks        irp

           netgroup        local


     If a local user needs to be in the local host's ``wheel'' group but not
     in every host's ``wheel'' group, put them in the local host's /etc/group
     ``wheel'' entry and set up the ``groups'' portion of your /etc/irs.conf
     file as:

           group   local   continue,merge
           group   nis

     NIS takes a long time to time out.  Especially for hosts if you use the
     -d option to your server's ``ypserv'' daemon.

     It is important that the irs.conf file contain an entry for each map.  If
     a map is not mentioned in the irs.conf file, all queries to that map will

     The classic NIS mechanism for specifying union namespaces is to add an
     entry to a local map file whose name is ``+''.  In IRS, this is done via
     ``continue'' and/or ``merge'' map options.  While this results in a small
     incompatibility when local map files are imported from non-IRS systems to
     IRS systems, there are compensating advantages in security and configura­


     /etc/irs.conf      The file irs.conf resides in /etc.


     groups(5),  hosts(5),  netgroup(5),  networks(5),  passwd(5),
     protocols(5),  services(5)

 BIND                          November 16, 1997                             2

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