YPBIND(8) BSD System Manager's Manual YPBIND(8)
ypbind -- NIS domain binding daemon
ypbind [-ypset] [-ypsetme] [-s] [-m] [-S domainname,server1,server2,...]
The ypbind utility is the process that maintains NIS binding information.
At startup, it searches for an NIS server responsible for serving the
system's default domain (as set by the domainname(1) command) using net-
work broadcasts. Once it receives a reply, it will store the address of
the server and other information in a special file located in
/var/yp/binding. The NIS routines in the standard C library can then use
this file when processing NIS requests. There may be several such files
since it is possible for an NIS client to be bound to more than one
After a binding has been established, ypbind will send DOMAIN_NONACK
requests to the NIS server at one minute intervals. If it fails to
receive a reply to one of these requests, ypbind assumes that the server
is no longer running and resumes its network broadcasts until another
binding is established. The ypbind utility will also log warning mes-
sages using the syslog(3) facility each time it detects that a server has
stopped responding, as well as when it has bound to a new server.
The following options are available:
-ypset It is possible to force ypbind to bind to a particular NIS server
host for a given domain by using the ypset(8) command. However,
ypbind refuses YPBINDPROC_SETDOM requests by default since it has
no way of knowing exactly who is sending them. Using the -ypset
flag causes ypbind to accept YPBINDPROC_SETDOM requests from any
host. This option should only be used for diagnostic purposes
and only for limited periods since allowing arbitrary users to
reset the binding of an NIS client poses a severe security risk.
This is similar to the -ypset flag, except that it only permits
YPBINDPROC_SETDOM requests to be processed if they originated
from the local host.
-s Cause ypbind to run in secure mode: it will refuse to bind to any
NIS server that is not running as root (i.e., that is not using
privileged TCP ports).
Allow the system administrator to lock ypbind to a particular
domain and group of NIS servers. Up to ten servers can be speci-
fied. There must not be any spaces between the commas in the
domain/server specification. This option is used to insure that
the system binds only to one domain and only to one of the speci-
fied servers, which is useful for systems that are both NIS
servers and NIS clients: it provides a way to restrict what
machines the system can bind to without the need for specifying
the -ypset or -ypsetme options, which are often considered to be
security holes. The specified servers must have valid entries in
the local /etc/hosts file. IP addresses may be specified in
place of hostnames. If ypbind can't make sense out of the argu-
ments, it will ignore the -S flag and continue running normally.
Note that ypbind will consider the domainname specified with the
-S flag to be the system default domain.
-m Cause ypbind to use a 'many-cast' rather than a broadcast for
choosing a server from the restricted mode server list. In many-
cast mode, ypbind will transmit directly to the
YPPROC_DOMAIN_NONACK procedure of the servers specified in the
restricted list and bind to the server that responds the fastest.
This mode of operation is useful for NIS clients on remote sub-
nets where no local NIS servers are available. The -m flag can
only be used in conjunction with the -S flag above (if used with-
out the -S flag, it has no effect).
The ypbind utility will not make continuous attempts to keep secondary
domains bound. If a server for a secondary domain fails to respond to a
ping, ypbind will broadcast for a new server only once before giving up.
If a client program attempts to reference the unbound domain, ypbind will
try broadcasting again. By contrast, ypbind will automatically maintain
a binding for the default domain whether client programs reference it ot
the files used to hold binding information for each NIS
/etc/rc.conf system configuration file where the system default domain
and ypbind startup options are specified
domainname(1), syslog(3), yp(8), ypserv(8), ypset(8)
Theo de Raadt <deraadtATfsa.ca>
BSD April 9, 1995 BSD