Marcos Placona Blog

Programming, technology and the taming of the web.

Month: September 2009

IPTABLES – Opening server ports to specific IP addresses

Reading time: 1 – 2 minutes

Iptables shell script
(Photo: Jordan W)

I have been doing some housekeeping on my VPS, and decided there’s a few ports that should only be accessed by certain IP addresses for security purposes.
My VPS uses Linux, so I had to find a way to somehow changing my iptables settings to block the specific ports to every IP address, except for the ones I specified.
It’s pretty straight forward, and here  how you can block a specific port to everyone except for some IP addresses (the instructions are for Centos 5.5, but should work for other distros without problems):
Open our iptables settings file:

sudo nano /etc/sysconfig/iptables

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Updating Java on Centos

Reading time: 3 – 5 minutes

Java on Centos
(Photo: tutchiio)

I’m only writing this blog post because I usually try to keep my VPS up to date, and usually one of the things I have to do to accomplish such thing is updating the Java version.
I always need to do a little bit of “googling” in order to find my way around this, as there’s a few steps that need to be taken, so you can make sure that your classpath is correct, and that the newly installed Java is running as your default installation.
I start by going to the Java website and downloading the most recent version.
It can be a bit tricky to download Java using wget, as Java’s wesbite uses your session in order to download the file, so if you try something like:

wget http://link_to_new_java_update

You will end up with a file called something like:

I’ve just downloaded the file to my downloads folder.
It’s got everything you need, but a big name you don’t need, so let’s simply rename it, and move it to where we want it to be installed.
If you want to find out where your java installation is, simply execute the following command:

which java

In my case I normally install things in “/opt/soft”, so I simply issue the following command:

sudo mv *.bin /opt/soft/jdk-6u16-linux-i586.bin

This will move everything with a .bin extension to the place where I like to install my software. Notice that as I’m moving it to a protected folder “/opt”, I need to use sudo in front, so I have the necessary permissions to create files.
The file should now be called “jdk-6u16-linux-i586.bin” and be located at “/opt/soft” in my case, so:

cd /opt/soft

We then need to give it some permissions, as we are going to have to call this file as an executable:

sudo chmod a+x jdk-6u16-linux-i586.bin

If you execute ls-l on the command line, you should now see that this file has execute permissions.
You can now execute the file by issuing:


It will then ask to read a bunch of terms & conditions, and you are going to have to type “yes” to accept it.
Once you’ve accepted it, you will have to change your classpath, so your system becomes “aware” that a new java version has been installed, and is going to be used.
Create or edit the file /etc/profile.d/

sudo nano /etc/profile.d/

This file must have the following code:

export JAVA_HOME=/opt/soft/jdk1.6.0_16/
export PATH=$JAVA_HOME/bin:$PATH
export PATH=$PATH:$JAVA_HOME/bin

In this case we are updating to JDK 1.6 release 16, but you should replace it with whatever versio you are installing.
By running:

java -version

You should see that the current version is the one you’ve just installed. If it’s not, it means you’ve done something wrong, so just repeat all the steps carefully, and you should be ok.