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Manual Pages  — YPBIND


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 network 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 domain.

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 messages 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:
  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.
  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).
  domainname , server1 , server2 , server3 , ...Allow the system administrator to lock ypbind to a particular domain and group of NIS servers. Up to ten servers can be specified. There must not be any spaces between the commas in the domain/server specification. This option is used to ensure that the system binds only to one domain and only to one of the specified 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 cannot make sense out of the arguments, 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.

  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 subnets where no local NIS servers are available. The -m flag can only be used in conjunction with the -S flag above (if used without 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 not.


  the files used to hold binding information for each NIS domain
  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 <Mt deraadt@fsa.ca>

YPBIND (8) April 9, 1995

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