Tag Archives: Xymon

Installing CentOS 6.4 from a Net Install Image on a Virtual Host

An Opportunity To Play Around with CentOS

One of the personal projects that I’ve always had itching away at the back of my mind was the urge to revamp my home network monitoring and security.  One of the tools that I love using for network monitoring is Xymon.  However, this gives me an opportunity to do things slightly different.  I have decided to give CentOS a go instead of my typical choice of Debian for a Linux distro in a server environment.  I am curious to see what advancements have been made in the RPM world, and I’d like to keep my Red Hat skills up to date.  What better way to do so than to set up a CentOS server with some production tools and services on it :)

Pre-installation Setup

So here we are, I have the CentOS Netinst (Net Install) image loaded into a VM, and I boot up the guest.

Since this is a fresh install on a 20GB virtual disk, I’m going to select “Install or upgrade an existing system” here.

I press “enter” and lots of console logging and scrolling action takes place.

Eventually I am prompted to “test the media”.  Usually this is referring to a physical CD typically used to install the OS on a physical server.  To me the phrasing feels a bit antiquated in this day of cloud services.

In any case, I still say yes, hoping that it will catch any errors in the ISO image file before I run into a bug during the installation process.  Better safe than sorry.

After the virtual disk is “successfully verified” to be OK, I try to move forward with the installation.

Be sure to note that after your virtual disk is verified OK, that the installer may decide to eject your CD media, in order to give you an opportunity to test other media.

Since I have no other media to test, this is actually kind of annoying. In order to continue with the installation, I have to go into the VM settings and re-connect the CDROM to the VM.

Select your language and keyboard options if the defaults are not suitable.  Otherwise, just  move past these dialogues by selecting “OK”, or hitting enter.


When you are asked “What type of media contains the installation image?”, select “URL”.
Continue reading Installing CentOS 6.4 from a Net Install Image on a Virtual Host

Syncronizing Xymon’s ‘bb-hosts’ Configurations

I’ve been using Xymon (formerly known as “Hobbit”) for a long time.  In most situations, I have Xymon running in a redundant configuration, with two or more instances of Xymon working together to monitor a network.

Even though Xymon works very well, a single change to the primary server’s configuration file (the “bb-hosts” file) means that you have to make the same change to all other ‘bb-hosts’ files in all other Xymon instances.

There are some creative ways to eliminate the drudgery of updating all these files any time a change to the primary file is necessary.  One method, for example would be to have the master file exported via NFS to all the other Xymon server instances, and each of those instances would sym-link to that primary ‘bb-hosts’ file from their local mount of that NFS export.

I don’t like the NFS export idea, because if the primary server has a problem, and the NFS export is no longer available, all instances of Xymon would break – badly.

Instead, I’ve opted for automatically synchronizing the ‘bb-hosts’ file across all Xymon instances via the use of apache, cron, a sym-link, and a simple bash script.

Here’s  how it works:

  • On the primary Xymon instance, sym-link ‘/home/xymon/server/etc/bb-hosts’ to ‘/var/www/bb-hosts’.
  • On the other instances of Xymon, run a bash script which grabs the primary server’s ‘bb-hosts’ via HTTP, which does some simple comparisons, and over-writes the local Xymon ‘bb-hosts’ if changes are detected.
  • Automat this script with cron.

Perhaps the trickiest part of doing this is the actual script used to grab, compare, and over-write the ‘bb-hosts’ file for the other instances of Xymon.  The script I’ve written below grabs the primary ‘bb-hosts’ file, and does a simple MD5 comparison with md5sum, and if it detects a change in the ‘bb-hosts’ file, it will send an e-mail to notify me that this change has occurred, along with details on what has changed.

Here’s the script:

wget http://somewebhost.domain.com/bb-hosts -qO "$REMOTE_BB_HOSTS"
LOCAL_MD5=`md5sum $LOCAL_BB_HOSTS  | cut -d " " -f 1`
REMOTE_MD5=`md5sum  $REMOTE_BB_HOSTS  | cut -d " " -f 1`
#echo "$LOCAL_MD5"
#echo "$REMOTE_MD5"
if [ "$LOCAL_MD5" != "$REMOTE_MD5" ]; then
        echo "Generated by $0" > $BB_HOSTS_DIFFS;
        mail -s "Xymon: monitor-02 bb-hosts updated" alertme@email.com < $BB_HOSTS_DIFFS;

If you need a way to keep your Xymon ‘bb-hosts’ files in sync, something along the lines of the above script just may be what you’re looking for. If you’re currently accomplishing the same thing in an interesting way, please post a comment and let me know!