Category Archives: Security

how to firewalld

“Firewalld provides a dynamically managed firewall with support for network/firewall zones that define the trust level of network connections or interfaces. It has support for IPv4, IPv6 firewall settings, ethernet bridges and IP sets. There is a separation of runtime and permanent configuration options. It also provides an interface for services or applications to add firewall rules directly.” –

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Linux ACL Permissions


“Access Control List (ACL) provides an additional, more flexible permission mechanism for file systems.
It is designed to assist with UNIX file permissions.
ACL allows you to give permissions for any user or group to any disc resource.” (Wikipedia)
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chmod suid sgid sticky bit


Linux chmod has a few options that can make your life a lot easier when managing a shared storage.
The most needed are chmod suid sgid sticky bit.
Also the impact of each one is different between files and folders.
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iptables examples on CentOS


“iptables is a user space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall (implemented as different Netfilter modules) and the chains and rules it stores.
Different kernel modules and programs are currently used for different protocols; iptables applies to IPv4, ip6tables to IPv6, arptables to ARP, and ebtables to Ethernet frames.”

In this tutorial I will give a few essential examples of how to use iptables on CentOS
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Copy SSH public key to another server instructions

copy ssh public key


You need to have a public key. If you haven’t generated keys before use:

ssh-keygen -t rsa

copy ssh public key is very simple. there are some ways to achieve this:

Using ssh-copy-id (recommended)

ssh-copy-id user@host

with this very simple command you can copy your public key to any user@host combination

Using scp

scp .ssh/ user@host2:.ssh/authorized_keys

cd ~/ before.

The different is that scp will create a new file called authorized_keys while ssh-copy-id will add to id.

OpenVPN ALS Adito SSL VPN Gateway on CentOS


OpenVPN ALS Adito SSL VPN Gateway is a web-based SSL-VPN server written in Java and it is completely free and open-source.
The installation on CentOS 6 Linux Operating System is fairly simple using the next few steps (we will use CentOS Minimal x86_64).
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How to disable java in all browsers at once


Several major companies have been hacked lately. Security advice for web users last week from the US Department of Homeland Security encouraging to disable java on browsers. Disable java in each browser takes time. You will learn how to disable java for all at once. and also for each browser if needed.

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Filter your visits in Google Analytics (Do not track your IP)


Setting up Google Analytics to not track your visits is a bit tricky. You can filter by IP, but most of us are using dynamic IP so we need another solution. You’ll learn to setup a cookie on your browser and configure settings in google analytics to achieve this.

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Using modern.IE – Testing for Internet Explorer just got a little easier

internet explorer logo

Microsoft to developers: This is the ‘modern.IE’ world

Microsoft announced their new tool called modern.IE.
Using this tool (website) you can scan for common coding problems.

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