What Is the Difference between the Internal IP Address of a Server and the External IP Address?

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Problem scenario
You want to find the external and internal IP addresses of your servers.  You are not sure which is which.  

Solution
The internal IP address is found by issuing one of these commands on Linux:

ip addr show
ifconfig

For Windows, open a command prompt and run this command:

ipconfig

For Linux servers the external IP address is found by running this command (assuming your server has access to the internet):

curl http://icanhazip.com

For Windows open a web browser and go to http://ipchicken.com

If you are using AWS and your server does not have access to the internet,

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How Do You Install and Configure the NRPE Agent (to Have Nagios Monitor) on a RHEL Server in AWS?

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Problem scenario
You have Nagios core installed on a server in AWS.  You want a new AWS RedHat Enterprise Linux server to have the NRPE agent.  You want thorough directions for this process to potentially automate it.  How do you install and configure the NRPE agent on a RHEL server and configure a Nagios core server to monitor it?

Solution
Prerequisites

  1. You need to know the internal IP address of 1) the Nagios core server;

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How Do You Install Nagios on RedHat Linux Step-By-Step?

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Problem scenario
You have a small AWS server (e.g., t2.micro with 1 GB of RAM) running RedHat Enterprise Linux.  How do you install Nagios on it?  You want thorough directions to install and configure the Nagios monitoring server on RHEL.

Solution
As root or a sudoer user, run a script with the following content:

# Written by continualintegration.com
​# This script installs Nagios.

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How Do You Install and Configure the NRPE Agent on Ubuntu?

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Problem scenario
You want the Nagios Core server to monitor another AWS server.  How do you install and configure the NRPE agent on Ubuntu?

Solution
Follow these step-by-step directions if you are using AWS.  If the servers are not in AWS, the directions below may still work. These directions assume that the Nagios core server is running on Ubuntu in AWS. (If you want to know how to set up Nagios core on Ubuntu,

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How Do You Install Nagios on Ubuntu Step-By-Step?

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Problem scenario
You have a small AWS server (e.g., t2.nano with 0.5 GB of RAM) running Ubuntu.  How do you install Nagios on it?

Solution
1. As root or a sudoer user, run a script with the following content (sudo bash /tmp/install.sh):

# Written by continualintegration.com
​#This script installs Nagios.  There is some interactive portion at the beginning.  
# But it should be easy to install Nagios using the following.

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How Do You Troubleshoot This Error “javac: command not found”?

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Problem scenario
You have Java installed. The “java -version” command returns data showing that Java was been installed correctly.  You try to use the javac command to compile a .java file.  You get this error:

-bash: javac: command not found

How do you compile your Java code when javac is not recognized?

Solution
As root,

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How Do You Change the MAC Address of Your Wireless Network Adapter on a Windows 7 Machine?

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Problem scenario
You want to change the MAC address of your wireless network adapter (e.g., you want a WiFi network to see your laptop as a different or new machine).  How do you do this?

Solution
1.  Go to Control Panel -Network and Internet

2.  Go to “Network and Sharing Center”

3.  Click on “Change adapter settings”

4.

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How Do You Troubleshoot This Error with a PostgreSQL Front End Application “Connection refused … Is the server running on host “x.x.x.x” and accepting TCP/IP connections on port 5432″?

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Problem scenario
With a SQL front end (e.g., pgAdmin or HeidiSQL) you get this error “could not connect to server: Connection refused 0x0000274D/10061) Is the server running on host “x.x.x.x” and accepting TCP/IP connections on port 5432?

You double checked you are trying to connect to the correct IP address (x.x.x.x).  You know port 5432 is not blocked.  You know the postgres service is listening on port 5432 on the destination server.

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Comprehending Being Sued for Online Postings (e.g., Frivolous Libel Lawsuits)

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Worried about being sued for something you posted online?  You may need to educate yourself about the risks.

American citizens may want to understand the context of online defamation by buying Be Careful Who You SLAPP by Delfino and Day.  To learn about strategic lawsuits designed to silence people in the USA, there is no better book than SLAPPs: Being Sued for Speaking Out by Rock Pring.  

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Where Do You Find the IP Address from Most Recent Login on a Linux Server?

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Problem scenario
You want to know where the Linux users are logging on from (e.g., for security and configuration reasons).  You want to know the IP addresses of their desktops.  Where do you find the IP address from most recent login on a Linux server?

Solution
To see the most recent login session details (including IP address), run this command:

last

After you press enter you’ll see the most recent logins.

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