Scenario / Question:

How do I setup freeNX on a remote server system and connect to it.

Solution / Answer:

Installing the freeNX server software on the remote server machine and using the NoMachine freenx client to connect to it from you local machine.

Installing freeNX Server:

On the server you want to control with freeNX

Install freenx using yum:

# yum install nx freenx

Copy minimal configuration file:

# cp /etc/nxserver/node.conf.sample /etc/nxserver/node.conf

Enable PASSDB for NX Database User Authentication pass-through:

Uncomment and change the following line in /etc/nxserver/node.conf

Installing Nagios server and network monitoring on Centos 5 server

The official documentation can be found at http://support.nagios.com/knowledge-base/official-documentation

Install necessary packages

yum install httpd gcc glibc glibc-common gd gd-devel php

Create Nagios User account and group

useradd -m nagios

Create nagcmd group for allowing external commands to be submitted through the web interface. Add both the nagios user and the apache user

groupadd nagcmd
usermod -a -G nagcmd nagios
usermod -a -G nagcmd apache

Create Directory to store Nagios installation files

mkdir /opt/Nagios

Download Nagios and Plugins

Save file to directory /opt/Nagios

The following are simple wrapper scripts for the Xymon server and client that will allow you to automatically start them during boot-up, just as you would any other standard unix service:

cd /etc/rc.d/init.d/xymon
nano xymon


Xymon Server Code

#!/bin/bash
##
# chkconfig: 345 55 25
# description: Xymon Server Monitor
#
# source function library
. /etc/rc.d/init.d/functions

How do I get my VirtualBox Guest VM’s to start and stop when the host system reboots, shutdown, or starts.

Solution / Answer:

Create an init.d script so that VirtualBox Guest VM are controlled as a system service.

Install VirtualBox VM Service script

The original script was for Ubuntu systems found here . Modified for Centos by Kevin Swanson found here .

Create Config File for vboxcontrol service script

# mkdir /etc/virtualbox
# touch /etc/virtualbox/machines_enabled

The file “machines_enabled” located in “/etc/virtualbox” is where we list the names of the Guest VM’s that we want vboxcontrol to control.

Casual VirtualBox users might not know about the awesome power that lurks just beneath the surface in the Command Line Interface (CLI).

netstat command and shell pipe feature can be used to dig out more information about particular IP address connection. You can find out total established connections, closing connection, SYN and FIN bits and much more. You can also display summary statistics for each protocol using netstat.

This is useful to find out if your server is under attack or not. You can also list abusive IP address using this method.
# netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n
Output:

      1 CLOSE_WAIT
      1 established)
      1 Foreign
      3 FIN_WAIT1
      3 LAST_ACK
     13 ESTABLISHED
     17 LISTEN
    154 FIN_WAIT2
    327 TIME_WAIT

Dig out more information about a specific ip address:
# netstat -nat |grep {IP-address} | awk '{print $6}' | sort | uniq -c | sort -n

Background:

Securing your Linux server is important to protect your data, intellectual property, and time, from the hands of crackers (hackers). The system administrator is responsible for security Linux box. In this first part of a Linux server security series, I will provide 20 hardening tips for default installation of Linux system.

#1: Encrypt Data Communication

All data transmitted over a network is open to monitoring. Encrypt transmitted data whenever possible with password or using keys / certificates.

Introduction

Network security is a primary consideration in any decision to host a website as the threats are becoming more widespread and persistent every day. One means of providing additional protection is to invest in a firewall. Though prices are always falling, in some cases you may be able to create a comparable unit using the Linux iptables package on an existing server for little or no additional expenditure.

This chapter shows how to convert a Linux server into: