Where to define command in nagios

I want to define new command in nagios for remote host but i can't find out where should i write this thing

define command   {


}

on remote host i have only this file

 vim /usr/local/nagios/etc/nrpe.cfg

Should i write that in above file or i have to write that on nagios host not on remote computer

There is no commands.cfg file on my remote host

From serverfault Master

• Which Nagios packages do you have installed? On my CentOS 5.4 boxes, the Nagios config is in /etc/nagios. Take a look there. The filename is /etc/nagios/nagios.cfg

  Edit

  On the remote side, you need an entry in the nrpe.cfg that looks like command[something]=/some/path/to/command/binary. Then, on the Nagios host, you do your define service { }. The important part is that the command to run is going to look like check_nrpe!something, where something is the same as the one in nrpe.cfg.

  Master : i have nagios 3.2. and i am talking bout remote machine. the only cfg file i have is /usr/local/nagios/etc/nrpe.cfg I am taking about NRPE plugin

  Master : Actually i have that nagios.cfg but that is on host where nagios monitoring system is installed. i am talking about where nagios plugin and NRPE plugin is installed. where do i have to define command and in which file. EITHER on host or remote computer

  Bill Weiss : Oh, ok. You need to have two parts for NRPE to work. I'll update my answer with it so I can get some formatting.
  From Bill Weiss