Setup SNMP On A Linux Host

This article will cover the basic setup of SNMP on a Linux host. Typically I enable this service to monitor the performance of a Linux host using Cacti.

Problems Booting Centos Guest In A Virtual Machine

Problem

Booting into a fresh Centos installation inside a virtual machine results in a black screen. The Centos login screen does not appear. This problem has been replicated in VMWare Workstation 9, VMWare ESX 4.0, and Virtual Box.

Resolution

This problem occurs when the Centos ISO is still attached to the virtual guest. Disconnect the Centos ISO and reboot the virtual machine.

Linux Error Message: inter-device move failed, unable to remove target: Is a directory

 Trying to move some files from a network share to a USB drive on the Linux terminal and came up with the following unexpected error message:

inter-device move failed, unable to remove target: Is a directory 

In my case it turned out to be that the destination folder already existed. By changing the destination folder to a folder that didn't exist and the move worked straight away. It's weird because I would've assumed that the default behaviour would've been to merge the contents of the two folders and delete the source folder. I'll do some more research on this one when I get the chance.

Mounting A Local Linux Folder

OK so I've probably got myself into a unique situation here. I thought I would be smart and try setting up transmission to download torrents directly to my wdtvlivehub. It was a good idea at the time but it's really not working out too well. Firstly, I mounted the wdtvlivehub to a mount point on my Raspberry Pi. Works perfect.

The problem comes us with the way bit torrent works. It's doing massive amounts of really small network IOs writing and reading blocks from the disk. In my case this happens across a 100 Mbps network. I don't think the Pi is handling it that well. The other side affect appears to be on the wdtvlivehub side of things. It looks like it's detecting the file changes and is always trying to recompile the media library. Side affect - the wdtvlivehub is not usable (but I'm sure fixable :) )

I've already added a powered USB disk to the Pi and the performance is much, much better. The next step is to relocate the existing torrents without upsetting transmission. To do this I'm going to setup a folder on the new external disk, move across my partially downloaded torrents, then mount this folder back to the original mount point.

To start with I'll create the new folders to match my existing structure

mkdir /media/usbdrive2/wdtvlivehubmkdir /media/usbdrive2/wdtvlivehub/temp

Next I'll copy the partially completed torrents across

mv /media/wdtvlivehub/temp/*.part /media/usbdrive2/wdtvlivehub/temp

Next I'll add the following lines to my /etc/fstab:

/media/usbdrive2/wdtvlivehub /media/wdtvlivehub auto bind,gid=46,defaults 0 0

To finish up I re-mount all the mount points specified by fstab

sudo mount -a 

Problems Mounting Drives Formatted With ExFAT In Ubuntu

Plugging in one of my external hard drives into a fresh Ubuntu 12.10 install today and it's failed with the following error message:

mount: unknown filesystem type 'exfat'

Luckily following the instructions on this blog resolved the problem quickly. In short it takes 3 short commands to add exFAT support to your Ubuntu desktop:

sudo apt-add-repository ppa:relan/exfat 

sudo apt-get update 

sudo apt-get install fuse-exfat

Enable Remote Connections to MySQL

By default MySQL is configured in such a way that it won't accept remote connections. I'm guessing the is by design and a security feature. This makes sense because a lot of programs use a local MySQL database which should be secured from remote connections. Fortunately if you need to open up your MySQL database server it's an easy thing to do!

Ubuntu–Adding An Extra Disk To The Server

Note – these instructions don’t cover the physical side of adding a disk to your server. They assume that the disk has already been added and that we’re back at the command line.

# confirm details of second disk

sudo lshw -C disk

# open fdisk partitioning tool (assuming new disk is /dev/sdb)

sudo fdisk /dev/sdb

# at the menu press "n" and "enter" to create a new partition

# press "p" to create a primary partition

# press "1" to create 1 partition

# press enter to accept the default start position of the partition

# press enter to accept the default end position of the partition

# press "w" to write the partition

# create the filesystem

sudo mkfs -t ext4 /dev/sdb1

# create the mount point

sudo mkdir /srv

# automount the partition on startup - edit the fstab

sudo nano /etc/fstab

# add the following line

/dev/sdb1 /srv ext4 defaults 0 1

# remount the filesystems

sudo mount -a

To finish reboot the server and confirm the changes have taken affect and remain intact after the reboot.

How To Install A LAMP Server On Ubuntu

Open up a terminal session (or SSH onto the Ubuntu server) and run the following command:

sudo apt-get install apache2 php5 libapache2-mod-php5 mysql-server libapache2-mod-auth-mysql php5-mysql phpmyadmin 

This will download approximately 40MB and use 105MB of disk space. During the install you will be prompted a couple of times:

• mysql admin password – enter a password of your choosing



• The next screen will ask you if you would like your webserver reconfigured automatically. Select apache2 and click ok.



• Congigure database for phpmyadmin with dbconfig-common? Select Yes



• Enter the mysql password you entered before for the phpmyadmin mysql configuration



• Enter a new administrator password for phpmyadmin

And voila – we done! To test that it’s worked point your browser to http://< server IP>. If everything’s worked you should have a page saying “It Works!”. To use the phpmyadmin tool to administer your site point your browser to /phpmyadmin">http://<serverIP>/phpmyadmin.

And finally the default web root is located at /var/www.

Setup Nagios Monitoring – The Easy Way Part 3

In the first two parts of this guide we’ve installed Nagios 3 onto an Ubuntu server. We’ve restructured the layout of the configuration files so that they are more manageable. In this step we will look at time periods and how to configure them.

Time periods are used just that, a schedule that defines when things should or should not happen. Typical time periods defined in Nagios include:

• 24x7 – All the time, from 00:00 to 23:59 Monday to Sunday.
• Work Hours – 09:00 to 17:00 Monday to Friday.
• After Hours – All the time outside of the work hours.
• Never – Empty schedule with no times defined.

These time periods are used in a few places. Firstly they can be used to determine when host and service checks occur. For example we may want critical production servers to be monitored 24x7 but only want non critical servers monitored during business hours.

The second major place they are used is to determine when contacts should be alerted that problems have occurred. For example we may send alerts to an administrators email group during business hours but send an alert via SMS after work hours.

In the /etc/nagios3/timeperiods folder we’ll create four different time periods:

• /etc/nagios3/timeperiods/24x7.cfg
• /etc/nagios3/timeperiods/never.cfg
• /etc/nagios3/timeperiods/afterhours.cfg
• /etc/nagios3/timeperiods/workhours.cfg

First we’ll start by defining the 24x7 time period. Create the file /etc/nagios3/timeperiods/24x7.cfg as shown below:

# This defines a timeperiod where all times are valid for checks,
# notifications, etc.  The classic "24x7" support nightmare. :-)

define timeperiod{
        timeperiod_name 24x7
        alias           24 Hours A Day, 7 Days A Week
        sunday          00:00-24:00
        monday          00:00-24:00
        tuesday         00:00-24:00
        wednesday       00:00-24:00
        thursday        00:00-24:00
        friday          00:00-24:00
        saturday        00:00-24:00
        }

Next we’ll create the never time period as shown below:

# Here is a slightly friendlier period during work hours
define timeperiod{
        timeperiod_name never
        alias           Never

        }

 

Now we’ll create the afterhours definition:

# The complement of workhours
define timeperiod{
        timeperiod_name nonworkhours
        alias           Non-Work Hours
        sunday          00:00-24:00
        monday          00:00-09:00,17:00-24:00
        tuesday         00:00-09:00,17:00-24:00
        wednesday       00:00-09:00,17:00-24:00
        thursday        00:00-09:00,17:00-24:00
        friday          00:00-09:00,17:00-24:00
        saturday        00:00-24:00
        }

And finally we’ll create the workhours definition:

# Here is a slightly friendlier period during work hours
define timeperiod{
        timeperiod_name workhours
        alias           Standard Work Hours
        monday          09:00-17:00
        tuesday         09:00-17:00
        wednesday       09:00-17:00
        thursday        09:00-17:00
        friday          09:00-17:00
        }

 

These four time period definitions should cover most smaller IT shops. If you need another time period definition it’s as simple as creating a new text file in the /etc/nagios3/timeperiods folder and define the time periods accordingly.

So we’ve finished defining the time periods, in the next blog post we’ll look at defining contacts in Nagios which will make use of the time periods we’ve defined here.

 

 

 

Using Arping To Scan An IP Range For Duplicate IP Addresses

This script will scan an IP range for duplicate IP addresses using the arping command (Linux). Firstly you will need to install arping – in Ubuntu this can be done using the command:

sudo apt-get install arping

Then we need to create the bash script below. Make sure you customise the IP range to suit the range you want to scan. In the below example the script just appends the last number in the IP address sequence so you can only do 254 addresses in a single hit.

for i in $(seq 1 254);
do
echo "Checking 192.168.196.${i}";
sudo arping -q -d -i eth0 -c 2 192.168.196.${i}; [ $? -ne 0 ] && echo "192.168.196.${i} duplicate";
done

Now run this script from the command line to scan the IP range.