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NSCA - Nagios Service Check Acceptor

TL;DR? You can jump straight to Compiling and Installing.

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.

Explanation

There are two pieces to this addon:

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.
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> is the short name of host that the service is associated with
- <svc_description> is the description of the service
- <return_code> is the numeric return code
- <plugin_output> is the 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. 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:

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

nsca 5667/tcp # NSCA
Add entries for the NSCA daemon to either your inetd or xinetd configuration files. Which one you use will depend on which superserver is installed on your system. Both methods are described below.

Notes:

If you run nsca under inetd or xinetd, the server_port variable in the nsca configuration file is 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 <user> with the name of the user that nsca server should run as (example: nagios).
  - Replace <nscabin> with the path to the nsca binary on your system (example: /usr/local/nagios/nsca).
  - Replace <nscacfg> 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            = <user>
  group           = <group>
  server          = <nscabin>
  server_args     = -c <nscacfg> --inetd
  log_on_failure  += USERID
  disable         = no
  only_from       = <ipaddress1> <ipaddress2> ...
}
```
  - Replace <user> with the name of the user that the nsca server should run as (example: nagios).
  - Replace <group> with the name of the group that the nsca server should run as (example: nagios).
  - Replace <nscabin> with the path to the nsca binary on your system (example: /usr/local/nagios/nsca).
  - Replace <nscacfg> with the path to the nsca config file on your system (example: /usr/local/nagios/nsca.cfg).
  - Replace the <ipaddress> 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.

Restart inetd or xinetd. You know your system best, but some examples are:

service inetd restart
service xinetd restart

systemctl restart inetd.service
systemctl restart xinetd.service

Add entries to your /etc/hosts.allow and /etc/hosts.deny files to enable TCP wrapper protection for the nsca service. Alternatively, you can adjust your firewall settings as needed. This is an optional step, although highly recommended.

Changes

Changes can be seen at the CHANGELOG file.

Contributors

See the file at CONTRIBUTORS for a full list of authors, contributors, and maintainers.

Current Version

The current version of this program can be found at:

https://github.com/NagiosEnterprises/nsca/

Other open-source Nagios software can be found at:

https://github.com/NagiosEnterprises/

License Notice

This software is released under GPLv2. See the full license at the LICENSE file.

Questions?

If you have any questions, comments, or suggestions, feel free to contact us via the support forum or through our Github page.