Network Monitoring with Linux

During the installation here, I found an old ICL DRS-10 serial terminal hiding in a cupboard. This terminal, or an equivalent, can be attached to a Linux box and used as a dedicated monitoring screen.

The exact settings required in /etc/gettydefs depend on the specifications of your terminal. For the DRS-10, we used the following entry for Red Hat:

# 9600 baud Dumb Terminal entry
DT9600# B9600 CS8 CLOCAL # B9600 SANE -ISTRIP \
CLOCAL #@S login: #DT9600

Now we need to edit the /etc/inittab file to present a login screen on the terminal. Be careful when playing with this file: it is possible to render your Linux system unbootable. Add the entry:

S1:3456:respawn:/sbin/getty ttyS0 DT9600 vt220

Finally, force init to re-examine its configuration file by typing:

/sbin/telinit q

If all is well, your terminal should bring up a login prompt. From there, you can bring up netconsole in the usual fashion.

Setting up such a serial terminal is described in more detail in the Text-Terminal HOWTO (www.linuxhq.com/HOWTO/Text-Terminal-HOWTO.html).

NOCOL has a web interface, included in the archive, and instructions for setting it up are found in the INSTALL file. In essence, this is a web version of netconsole which can be customized to look a bit more flashy (see Figure 1).

Figure 1. Web Version of Netconsole

The hostmon part of NOCOL is also very powerful. It allows you to install a Perl-based client on machines on your network in order to monitor aspects such as available disk space, mail queues, etc. The scripts can be extended to monitor any custom software you may be running. (We added an extension to monitor queues on our X.400/SMTP mail gateway software.)

An API to the system is provided that allows you to script your own monitors in Perl. Because of this, NOCOL has the power to monitor anything.

As an example of NOCOL's flexibility, I coded an extension to the notifier tool, which utilized our internal SMS messaging system. This allowed text messages describing CRITICAL problems to be sent to my mobile phone. This was done by coding an e-mail front-end to the SMS gateway, so all notifer had to do was fire off an e-mail in the correct format.

In essence, NOCOL has proven itself to be an extremely useful tool. It has alerted us to network problems as soon as they occurred, and the fact that it is freeware (it comes under a “not-quite-GPL” agreement) is just another example of great software under Linux being available for no cost.

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