Go back to fronty page View most popular entries View latest additions Submit tutorials to UnixTutorials.info
UnixTutorials logo

Search results for IPTABLES Explained Part 4: IPTables and Portsentry, the dynamic duo


Taking advantage of SELinux in Red Hat Enterprise Linux

Post date: April 15, 2005, 21:04 Category: Security Views: 4516 Comments
Tutorial quote: The release of Red Hat Enterprise Linux 4 debuts the first commercially supported inclusion of Security-Enhanced Linux (SELinux). An installation of Red Hat's latest enterprise operating system has SELinux installed and enabled by default. In the past SELinux has been criticized for a lack of commercial support, many big sites were unable to use it due to the lack of support (Fedora Core 3 doesn't have the support that they require). Now in Red Hat Enterprise Linux 4, SELinux is a supported part of the OS, and such objections to the use of SELinux have gone away. SELinux is now widely regarded as being suitable for the largest sites.

Building a Linux Cluster, Part 1

Post date: April 18, 2005, 03:04 Category: Network Views: 2931 Comments
Tutorial quote: Linux clusters have escaped. As the general popularity of the Linux operating system increases, more complex solutions built with it are becoming increasingly common in the "traditional" (more conservative) IT world. Linux computer clusters, whose provenance was originally universities and research institutions such as the U.S. National Laboratories, are showing up in increasing numbers as high-performance computing solutions within such areas as oil and gas exploration, computer-aided engineering, visualization, and software development. Linux clusters providing highly-available web, mail, and other infrastructure services are also increasingly common. If past computing history is any indicator of future trends, widespread use of Linux clusters in the mainstream IT world cannot be far behind.

OpenOffice 2.0: Creating database forms

Post date: December 13, 2005, 12:12 Category: Software Views: 3504 Comments
Tutorial quote: ather than having a shallow affair with OpenOffice 2.0, we can use it to get a little more intimate with the data. We can even badger it into forming relations. Why force your database tables into a marriage with OpenOffice? Because, as with human relations, life -- and data -- are pretty meaningless without tight connections.

This tip on creating forms is part of a series I'm writing on OpenOffice.org 2.0 Base. So far, I've discussed making a plain database from scratch, creating tables, entering data using the table editor and a simple form and creating a view of a table or tables.

Let's start off with a description of what table relations are anyway, then discuss how to create a data entry form like this one, which has data from two related tables.

Hardening Linux: a 10 step approach to a secure server

Post date: June 22, 2005, 10:06 Category: Security Views: 4180 Comments
Tutorial quote: The Internet has become a far more dangerous place than it was 20 years ago. Nowadays, Operating System and application security is an integral part of a server configuration and, while firewalls are very important, they are not the panacea.

This list of steps is intended as a guideline with a practical approach. We’ll try to provide a complete picture without getting into unnecesary details. This list won’t replace a good book on secure systems administration, but it will be useful as a quick guide.

Before we get started it’s worth to mention that security is not a status: it’s just a process. The correct initial setup of the server only provides a good start and helps you get half the way through. But you actually need to walk the other half of the road, by providing proper security vigilance, monitoring and updating.

Xen Virtualization and Linux Clustering, Part 1

Post date: January 21, 2006, 06:01 Category: System Views: 4309 Comments
Tutorial quote: Have you heard about Xen virtualization and want to get some hands-on experience? Do you want to experiment with Linux clustering but only have a single computer to devote to the cause? If you answered yes to either of these questions, keep reading.

In this article, I briefly introduce the concepts of Xen virtualization and Linux clustering. From there, I show you how to set up multiple operating systems on a single computer using Xen and how to configure them for use with clustering. I should point out that a cluster implemented in this manner does not provide the computational power of multiple physical computers. It does, however, offer a way to prototype a cluster as well as provide a cost-effective development environment for cluster-based software. Even if you're not interested in clustering, this article gives you hands-on experience using Xen virtualization.

Execute Commands on Multiple Linux or UNIX Servers part II

Post date: December 28, 2005, 10:12 Category: System Views: 3957 Comments
Tutorial quote: I have already covered how to execute commands on multiple Linux or UNIX servers via shell script. The disadvantage of script is commands do not run in parallel on all servers. However, several tools exist to automate this procedure in parallel. With the help of tool called tentakel, you run distributed command execution. It is a program for executing the same command on many hosts in parallel using ssh (it supports other methods too). Main advantage is you can create several sets of servers according requirements. For example webserver group, mail server group, home servers group etc. The command is executed in parallel on all servers in this group (time saving). By default, every result is printed to stdout (screen). The output format can be defined for each group.

Arcane Linux Commands: dc

Post date: December 31, 2007, 01:12 Category: Miscellaneous Views: 4159 Comments
Tutorial quote: If anybody within earshot of you is struggling to learn sed and ever remarks "This is like learning Klingon! Could they make it any more cryptic?", you can always point them to dc.

dc is the command-line Unix "Reverse-Polish Notation"(RPN) calculator. The name stands for "desktop calculator". OK, so what is a Polish calculator and why would you want to reverse one? The math that you do in school uses infix notation, with the operator between the numbers (3 + 5). Prefix notation puts the operator first (+ 3 5) and is what the Lisp language uses. The prefix notation is known as "Polish notation" after the nationality of Jan Łukasiewicz who invented it. Postfix notation, then, has the operator at the rear (3 5 +), and so is also the reverse of Polish notation.

What's the difference? In computer programming, you have to specify what order you want a multi-part calculation to be in. Everybody is familiar with the old problem of A*B-C. For A=5, B=3, C=2, multiplying first and subtracting second gives you 13, while subtracting first and multiplying second gives you 5. To specify which operations you want performed first, you have to either memorize the complex orders of operations (which change from one language to the next) or use a lot of parenthesis ((A*B)-C) or (A*(B-C)). Hey, that's what everybody complains about in all those languages that use parenthesis!

Benchmarking Filesystems Part II

Post date: January 6, 2006, 22:01 Category: Benchmarks Views: 5368 Comments
Tutorial quote: After the last article was published, I have received more than a dozen requests for a second filesystem benchmark using the 2.6 kernel. Since that time, I have converted entirely to XFS for every Linux machine I use, so I may be a bit bias regarding the XFS filesystem. I tried to keep the hardware roughly the same. Instead of a Western Digital 250GB and Promise ATA/100 controller, I am now am using a Seagate 400GB and Maxtor ATA/133 Promise controller. The physical machine remains the same, there is an additional 664MB of swap and I am now running Debian Etch. In the previous article, I was running Slackware 9.1 with custom compiled filesystem utilities. I've added a small section in the beginning that shows the filesystem creation and mount time, I've also added a graph showing these new benchmarks. After the first round of benchmarks, I received a sleuth of e-mails asking for the raw numbers. The numbers are now included in tables at the end of this e-mail for both the last and current set of benchmarks.

My First Linux Server, Part 1

Post date: April 14, 2005, 22:04 Category: Miscellaneous Views: 5130 Comments
Tutorial quote: Many small businesses are turning to Linux as way to swim against the tide of rising software costs. Are you thinking about diving into Linux for your small business? From the outside, Linux can appear to be a deep ocean of strange jargon in unchartered waters. Who has the time to wade through all that to save a few clams? With Linux, it's not a sink or swim proposition.

Linux is now a lot simpler than you may think. We can provide you with the easiest, simplest, no-problem process for installing Linux on a PC. After going through this simple installation process, you will have a basic machine that you can configure into any kind of server, workstation, or office desktop. Future articles in this My First Linux Server series will help you build productive, Linux-based servers and small office workstations.

The best choices for your first Linux machine are probably the popular Red Hat Linux or SUSE Linux, primarily because both are easy to install and configure. Additionally, these companies are sound choices for the home office or small business. Both vendors have specialized in Linux for many years and offer full corporate product lines supporting your expansion.

Creating Really Teensy ELF Executables for Linux

Post date: April 12, 2005, 18:04 Category: Miscellaneous Views: 3290 Comments
Tutorial quote: If you're a programmer who's become fed up with software bloat, then may you find herein the perfect antidote.

This document explores methods for squeezing excess bytes out of simple programs. (Of course, the more practical purpose of this document is to describe a few of the inner workings of the ELF file format and the Linux operating system. But hopefully you can also learn something about how to make really teensy ELF executables in the process.)

Please note that the information and examples given here are, for the most part, specific to ELF executables on a Linux platform running under an Intel-386 architecture. I imagine that a good bit of the information is applicable to other ELF-based Unices, but my experiences with such are too limited for me to say with certainty.

The assembly code that appears in this document is written for use with Nasm. (Besides being more appropriate for our needs, Nasm's syntax beats the hell out of AT&T syntax for anyone who learned x86 assembly language before learning to use Gas.) Nasm is freely available and extremely portable; see http://nasm.sourceforge.net/.

Please also note that if you aren't a little bit familiar with assembly code, you may find parts of this document sort of hard to follow.
Web-based applications and online marketing solutions - LumoLink