NSCA README

Purpose

The purpose of this addon is to allow you to send service check results to a central monitoring server running Nagios in a secure manner.

Contents

There are two pieces to this addon:

1) nsca - This program runs as a daemon on the central server that runs Nagios. It listens for host and service check results from remote machines (sent using the send_nsca program described below). Upon receiving data from a remote client, the daemon will make a very basic attempt at validating the data it has received from the client. This is done by decrypting the data with the password stored in the nsca.cfg file. If the decrypted data looks okay (i.e. it was originally encrypted by the send_ncsa program using the same password), the daemon will make entries in the Nagios external command file telling Nagios to process the host or service check result.

      Notes: The nsca daemon must have sufficient rights
              to open the Nagios command file for writing.  Also,
      Nagios will only process passive service check
              results that it finds in the external command file
              if the service has been defined in the host config
              file (i.e. hosts.cfg) and it is being monitored.

2) send_nsca - This is the client program that is used to send service check information from a remote machine to the nsca daemon on the central machine that runs Nagios. Service check information is read from the standard input in tab-delimited format as follows:

        <host_name>[tab]<svc_description>[tab]<return_code>[tab]<plugin_output>[newline]

          where:

        <host_name>=short name of host that the
                                service is associated with
        <svc_description>=description of the service
        <return_code>=numeric return code
        <plugin_output>=output from service check

      Host check information is submitted in a similiar
      fashion - just leave out the service description:

        <host_name>[tab]<return_code>[tab]<plugin_output>[newline]

Compiling

The code is very basic and may not work on your particular system without some tweaking. I just haven't put a lot of effort into this addon. Most users should be able to compile the daemon and client piece with the following commands...

./configure make all

The binaries will be located in the src/ directory after you run 'make all' and will have to be installed manually.

Installing

The send_nsca program and associate config file (nsca.cfg) should be placed on remote machines that you want to have communicate with the nsca daemon. This means that you may have to compile the send_nsca program on the remote machine, if its not the same OS/architecture as that of the central server.

The nsca daemon and the configuration file (nsca.cfg) should be placed somewhere on the central server running Nagios.

NOTES: Make sure that you specify and use the same password in both the nsca.cfg and send_nsca.cfg files! If you use a different password to encrypt the data than you do to decrypt it, the nsca daemon will reject the data you send it.

Security

There are some security implications with allowing remote clients to provide service check results to Nagios. Because of this, you have the option of encrypting the packets that the NSCA client sends to the NSCA daemon. Read the SECURITY file for more information on the security risks of running NSCA, along with an explanation of what kind of protection the encryption provides you.

Running Under INETD or XINETD

If you plan on running nsca under inetd or xinetd and making use of TCP wrappers, you need to do the following things:

1) Add a line to your /etc/services file as follows (modify the port number as you see fit)

nsca            5667/tcp    # NSCA

2) Add entries for the NSCA daemon to either your inetd or xinetd configuration files. Which one your use will depend on which superserver is installed on your system. Both methods are described below. NOTE: If you run nsca under inetd or xinetd, the server_port and allowed_hosts variables in the nrpe configuration file are ignored.

INETD If your system uses the inetd superserver WITH tcpwrappers, add an entry to /etc/inetd.conf as follows:

nsca    stream  tcp     nowait  <user> /usr/sbin/tcpd <nscabin> -c <nscacfg> --inetd

If your system uses the inetd superserver WITHOUT tcpwrappers, add an entry to /etc/inetd.conf as follows:

nsca    stream  tcp     nowait  <user> <nscabin> -c <nscacfg> --inetd

• Replace with the name of the user that nsca server should run as. Example: nagios

• Replace with the path to the nsca binary on your system. Example: /usr/local/nagios/nsca

• Replace with the path to the nsca config file on your system. Example: /usr/local/nagios/nsca.cfg

  XINETD If your system uses xinetd instead of inetd, you'll probably want to create a file called 'nsca' in your /etc/xinetd.d directory that contains the following entries (a sample config file called nsca.xinetd should be created in the root folder of the distribution after you run the configure script):

  default: on

  description: NSCA

  service nsca { flags = REUSE socket_type = stream
  wait = no user = group = server = server_args = -c --inetd log_on_failure += USERID disable = no only_from = ... }

• Replace with the name of the user that the nsca server should run as.

• Replace with the name of the group that the nsca server should run as.

• Replace with the path to the nsca binary on your system.

• Replace with the path to the nsca config file on your system.

• Replace the fields with the IP addresses of hosts which are allowed to connect to the NSCA daemon. This only works if xinetd was compiled with support for tcpwrappers.

3) Restart inetd or xinetd will the following command (pick the one that is appropriate for your system:

/etc/rc.d/init.d/inet restart

/etc/rc.d/init.d/xinetd restart

4) Add entries to your /etc/hosts.allow and /etc/hosts.deny file to enable TCP wrapper protection for the nsca service. This is optional, although highly recommended.

Questions?

If you have questions about this addon, or problems getting things working, send me email.

-- Ethan Galstad ([email protected])