The Linux NIS(YP)/NYS/NIS+ HOWTO
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# 5. The RPC Portmapper

To run any of the software mentioned below you will need to run the program /sbin/portmap. Some Linux distributions already have the code in the /sbin/init.d/ or /etc/rc.d/ files to start up this daemon. All you have to do is to activate it and reboot your Linux machine. Read your Linux Distribution Documentation how to do this.

The RPC portmapper (portmap(8)) is a server that converts RPC program numbers into TCP/IP (or UDP/IP) protocol port numbers. It must be running in order to make RPC calls (which is what the NIS/NIS+ client software does) to RPC servers (like a NIS or NIS+ server) on that machine. When an RPC server is started, it will tell portmap what port number it is listening to, and what RPC program numbers it is prepared to serve. When a client wishes to make an RPC call to a given program number, it will first contact portmap on the server machine to determine the port number where RPC packets should be sent.

Since RPC servers could be started by inetd(8), portmap should be running before inetd is started.

For secure RPC, the portmapper needs the Time service. Make sure, that the Time service is enabled in /etc/inetd.conf on all hosts:

    #
    # Time service is used for clock syncronization.
    #
    time    stream  tcp     nowait  root    internal
    time    dgram   udp     wait    root    internal

IMPORTANT: Don't forget to restart inetd after changes on its configuration file !

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