ypserv(1M) ypserv(1M)
NAME
ypserv, ypbind - Yellow Pages server and binder processes
SYNOPSIS
/usr/etc/ypserv
/etc/ypbind
DESCRIPTION
The Yellow Pages (YP) provides a simple network lookup ser-
vice consisting of databases and processes. The databases
are dbm(3X) files in a directory tree rooted at /etc/yp.
These files are described in ypfiles(4). The processes are
/usr/etc/ypserv, the YP database lookup server, and
/etc/ypbind, the YP binder. The programmatic interface to
YP is described in ypclnt(3N). Administrative tools are
described in yppush(1M), ypxfr(1M), yppoll(1M), ypwhich(1M),
and ypset(1M). Tools to see the contents of YP maps are
described in ypcat(1), and ypmatch(1). Database generation
and maintenance tools are described in ypinit(1M),
ypmake(1M), and makedbm(1M).
Both ypserv and ypbind are daemon processes typically
activated at system startup time from /etc/rc. ypserv runs
only on YP server machines with a complete YP database.
ypbind runs on all machines using YP services, both YP
servers and clients.
The ypserv daemon's primary function is to look up informa-
tion in its local database of YP maps. The operations per-
formed by ypserv are defined for the implementor by the YP
Protocol Specification, and for the programmer by the header
file <rpcsvc/ypprot.h>. Communication to and from ypserv
is by means of RPC calls. Lookup functions are described in
ypclnt(3N), and are supplied as C-callable functions in the
C library. There are four lookup functions, all of which
are performed on a specified map within some YP domain:
Match, Get_first, Get_next, and Get_all. The Match opera-
tion takes a key, and returns the associated value. The
Get_first operation returns the first key-value pair from
the map, and Get_next can be used to enumerate the
remainder. Get_all ships the entire map to the requester as
the response to a single RPC request.
Two other functions supply information about the map, rather
than map entries: Get_order_number, and Get_master_name.
In fact, both order number and master name exist in the map
as key-value pairs, but the server will not return either
through the normal lookup functions. (If you examine the
map with makedbm(1M), however, they will be visible.) Other
functions are used within the YP subsystem itself, and are
not of general interest to YP clients. They include
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Do_you_serve_this_domain?, Transfer_map, and
Reinitialize_internal_state.
The function of ypbind is to remember information that lets
client processes on a single node communicate with some
ypserv process. ypbind must run on every machine which has
YP client processes; ypserv may or may not be running on the
same node, but must be running somewhere on the network.
The information ypbind remembers is called a binding - the
association of a domain name with the internet address of
the YP server, and the port on that host at which the ypserv
process is listening for service requests. This information
is cached in the directory /etc/yp/binding using a filename
of domainname.version.
The process of binding is driven by client requests. As a
request for an unbound domain comes in, the ypbind process
broadcasts on the net trying to find a ypserv process that
serves maps within that domain. Since the binding is esta-
blished by broadcasting, there must be at least one ypserv
process on every net. Once a domain is bound by a particu-
lar ypbind, that same binding is given to every client pro-
cess on the node. The ypbind process on the local node or a
remote node may be queried for the binding of a particular
domain by using the ypwhich(1) command.
Bindings and rebindings are handled transparently by the C
library routines. If ypbind is unable to speak to the ypserv
process it's bound to, it marks the domain as unbound, tells
the client process that the domain is unbound, and tries to
bind the domain once again. Requests received for an
unbound domain will wait until the domain requested is
bound. In general, a bound domain is marked as unbound when
the node running ypserv crashes or gets overloaded. In such
a case, ypbind will bind to any YP server (typically one
that is less-heavily loaded) available on the net.
ypbind also accepts requests to set its binding for a par-
ticular domain. The request is usually generated by the YP
subsystem itself. ypset(1M) is a command to access the
Set_domain facility. It is for unsnarling messes. Note that
the Set Domain procedure only accepts requests from
processes running as root.
FILES
If the file /etc/yp/ypserv.log exists when ypserv starts up,
log information will be written to this file when error con-
ditions arise.
The file(s) /etc/yp/binding/domainname.version will be
created to speed up the binding process. These files cache
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the last successful binding created for the given domain,
when a binding is requested these files are checked for
validity and then used.
/etc/yp
/etc/ypbind
SEE ALSO
domainname(1), ypcat(1), ypmatch(1), dbm(3X), ypclnt(3N),
ypfiles(4), makedbm(1M), ypmake(1M), ypinit(1M), yppoll(1M),
yppush(1M), ypset(1M), ypwhich(1M), ypxfr(1M)
YP Protocol Specification, in the CX/UX Network File System
(NFS) manual.
NOTES
Both ypbind and ypserv support multiple domains. The ypserv
process determines the domains it serves by looking for
directories of the same name in the directory /etc/yp. It
will reply to all broadcasts requesting yp service for that
domain. Additionally, the ypbind process can maintain bind-
ings to several domains and their servers, the default
domain is however the one specified by the domainname(1)
command at startup time.
ypserv treats the hosts.byname and hosts.byaddr maps spe-
cially. If a ypmatch to either of these these maps fail,
ypserv will (on option) attempt to resolve the request by
contacting named(1M). This extra functionality is enabled
by originally creating the hosts.byname and hosts.byaddr
maps using the -b option to makedbm(1M). CX/UX typically
contacts named prior to contacting ypserv when resolving
host names and addresses using gethostbyname(3N); however,
other systems may contact only ypserv to determine this
information. This extra functionality allows those systems
to use host information which is only available through the
name server.
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