May 292014

Today I want to repost for my readers a really interesting article by Gionatan Danti first posted on his blog, I hope you enjoy it as much as I do

File compression is an old trick: one of the first (if not the first) program capable of compressing files was “SQ”, in the early 1980s, but the first widespread, mass-know compressor probably was ZIP (released in 1989).

In other word, compressing a file to save space is nothing new and, while current TB-sized, low costs disks provide plenty of space, sometime compression is desirable because it not only reduces the space needed to store data, but it can even increase I/O performance due to the lower amount of bits to be written or read to/from the storage subsystem. This is especially true when comparing the ever-increasing CPU speed to the more-or-less stagnant mechanical disk performance (SSDs are another matter, of course).

While compression algorithms and programs varies, basically we can distinguish to main categories: generic lossless compressors and specialized, lossy compressors.

If the last categories include compressors with quite spectacular compression factor, they can typically be used only when you want to preserve the general information as a whole, and you are not interested in a true bit-wise precise representation of the original data. In other word, you can use a lossy compressor for storing an high-resolution photo or a song, but not for storing a compressed executable on your disk (executable need to be perfectly stored, bit per bit) or text log files (we don’t want to lose information on text files, right?).

So, for the general use case, lossless compressors are the way to go. But what compressor to use from the many available? Sometime different programs use the same underlying algorithm or even the same library implementation, so using one or another is a relatively low-important choice. However, when comparing compressors using different compression algorithms, the choice must be a weighted one: you want to privilege high compression ratio or speed? In other word, you need a fast and low-compression algorithm or a slow but more effective one?

In this article, we are going to examine many different compressors based on few different compressing libraries:

  • lz4, a new, high speed compression program and algorithm
  • lzop, based on the fast lzo library, implementing the LZO algorithm
  • gzip and pigz (multithreaded gzip), based on the zip library which implements the ZIP alg
  • bzip2 and pbzip2 (multithreaded bzip2), based on the libbzip2 library implementing the Burrows–Wheeler compressing scheme
  • 7-zip, based mainly (but not only) on the LZMA algorithm
  • xz, another LZMA-based program

Continue reading »

flattr this!

Dec 282013

Article by Alessio bash, first published on his blog

Many security policies require you to change the port number of the SSH service to ensure greater security in a Linux system. Situation now used throughout the IT world and used mostly by users who have their own private server. Today I want to show you how to add another security layer without having to change the SSH port. To do this we’ll incorporate the famous Google Authenticator to our ssh service, in this way we’ll have a safe, two steps security, by entering our password and the combination given from the GA application. Let’s see how to do this… Continue reading »

flattr this!

Nov 102012

In a previous post we’ve seen how to Enable automatic security update in Debian/Ubuntu, I use it on my Debian VPS and I must say that I’ve forgot to be worried about security updates thanks to this, but perhaps you have a Red Hat 6 or Centos 6 and you want to sleep well as well ?

There is no problem, today we’ll see how to achieve the same result on a Centos 6 machine.
Continue reading »

flattr this!

Supercharge WordPress, Part 1

This article of mine has been original published on Wazi WordPress, the popular content managing system (CMS), is easy to set up and use, and well supported by both its community and professional consultants. WordPress depends upon a complete stack that comprises an operating system, database, web server, and PHP. If you can optimize this [...]

2 Useful plugins for Yum

In these days i’ve worked a lot on Red Hat Enterprise and Centos machines, and so i’ve used yum to install, upgrade, remove and download packages. I’m more used to .deb packages (or the portage system), and so for me these plugins are both new and really useful to extend the basic functions of yum. [...]