You can use rbash (restricted bash shell).

If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the following are disallowed or not performed:

* changing directories with cd
* setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
* specifying command names containing /
* specifying a file name containing a / as an argument to the . builtin command
* Specifying a filename containing a slash as an argument to the -p option to the hash builtin command
* importing function definitions from the shell environment at startup
* parsing the value of SHELLOPTS from the shell environment at startup
* redirecting output using the >, >|, <>, >&, &>, and >> redirection operators
* using the exec builtin command to replace the shell with another command
* adding or deleting builtin commands with the -f and -d options to the enable builtin command
* Using the enable builtin command to enable disabled shell builtins
* specifying the -p option to the command builtin command
* turning off restricted mode with set +r or set +o restricted.

How to restrict user ? Continue Reading…

Linux machines are known to be pretty secure.

Studies have shown that Linux has been designed in a secure manner. Yet, despite all the security features that come bundled with a Linux installation, you need to configure these features correctly to make them work for you. I’ll guide you through the process of setting up of one of the tools that help secure your machine – the firewall. We will use the iptables firewall for this exercise. I am assuming that you are using a server running Red Hat Enterprise Linux 4 or similar. However, most of the steps should work fine on other Linux distributions as well. In this article we will setup a firewall on a Linux server running the Apache Web Server, FTP, and SSH.

Let us first see what ports these applications use and which of them need to have a port open on the firewall.

The Apache web server runs on port 80 by default. Apache is going to server all our web content on this port, therefore we need to keep this port open on the firewall. The SSH service runs on port 22. We need to be able to remotely connect to our server to work, so we keep it open. FTP runs on port 21 and it too needs the port to be open to communication.

Next, make sure you have iptables installed. Run this command as the root user:

apt-cache search iptables Continue Reading…

You probably heard before of the term Denial of Service. What does this mean? How can you stop DOS?

Taking advantage of a known problem with the Operating System or any running services on the target, a good programmer can build an application that sends some data that causes the targeted system to crash.

The worst case scenario is not when a hacker crashes a service, but when it finds a way to maximize the CPU usage causing a total malfunction on the system.

Of course most of the attacks are not initiated by these kind of programmers, but by “script kiddies” who only read about it, find the program’s source over the web and just use it without knowing the mechanisms it uses.

Usually, DoS attacks are closely related to brute force attacks. The brute force attack uses all combinations of possible characters or dictionary word lists to try find out any passwords on the system (eg root accounts). When a root account in a network is found out, any DoS attacks can be done easily over the specific network.

Here are some of the most known DoS attacks:

1. SYN Floods Continue Reading…

First, don’t panic! This is usually a simple matter so long as you have physical access to the console.

Simply follow the steps below to boot the system bypassing login, and then set a new password:

Step 1. Reboot the system. Make sure your physically present.

Step 2. When the Grub menu comes up, press “e” to edit the menu selections.

Step 3. Select the kernel you would usually boot and press “e” to edit the settings.

Continue Reading…

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