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Man pages are written by sys-admin and developers for IT techs, and are intended more as a reference than as a how to. Man pages are very useful for people who are already familiar with Linux, Unix, and BSD operating systems. Use man pages when you just need to know the syntax for particular commands or configuration file, but they are not helpful for new Linux users. Man pages are not good for learning something new for the first time. Here are thirty best documentation sites on the web for learning Linux and Unix like operating systems.
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My 10 UNIX Command Line Mistakes

Anyone who has never made a mistake has never tried anything new. -- Albert Einstein.

Here are a few mistakes that I made while working at UNIX prompt. Some mistakes caused me a good amount of downtime. Most of these mistakes are from my early days as a UNIX admin.
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Poll: Your Favorite Scripting Language?

Like most sys admin, I'm lazy. I try to automate almost all things in order to save time. Inexperienced sys admin and help desk staff working under me finds all these tools useful. It saves their time and avoids security issues. Automation allows help desk staff to do things that they don't have enough direct system knowledge to do themselves. However, selecting correct tool and applying correct methodology is very important.
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Misunderstandings of the GPL Licensing is a common issue. It can create problem for both developers and sys admins. Most developers and admin think that they understood all legal mumbo jumbo associated with GPL. You can take the Free Software licensing quiz and test your knowledge of the GPL and LGPL.

Since y'day I noticed one of our article related to ORDB.org spam blocker receiving lots of traffic. I received couple of calls from our clients because most emails was getting bounced via Exchange or Postfix mail server.

ORDB is now configured to return each IP as spam source

ORDB was a database of open relay email servers, provided until 2006 as a voluntary service to block spam. Now ORDB.org service has been re-activated and it is returning every IP address queried as being on its blacklist. I guess this was done to punish lazy sys admin / mail administrators ;)

If you or your mail server / gateway / firewall querying relays.ordb.org; please stop it immediately. If you query relays.ordb.org - mail server will rejecting all incoming mails from that server.

Symantec Mail Security for MS-Exchange Server - Spam Filter

Symantec Mail Security for Microsoft Exchange configuration in the list of Anti-spam blacklist servers including relays.ordb.org. Immediately remove the entry.

Remove ORDB.ORG from MS-Exchange Server Spam Filter

In Exchange Server 2003 you can find the feature for blacklist support within the global settings of your organization. Visit MS-Exchange System Manager > Global Settings > Message Delivery Properties -> Connection Filtering tab > Remove relays.ordb.org

Remove Linux / UNIX - Postfix Mail Server - Spam Filter

Open postfix configuration file and remove the following line:
reject_rbl_client relays.ordb.org,
Restart postfix mail server:
# service postfix restart

Happy 20th Birthday Perl!

Perl is a dynamic programming language created by Larry Wall and first released in 1987. Perl is used in many sys admin and web related projects. Perl 1 was released to the public by Larry Wall 20 years ago today. Perl 5.10 isn’t just a bug fix version: it’s full of new features that I’m eager to use: named captures in regular expressions, state variables for subroutines, the defined-or operator, a switch statement (called given-when, though), a faster regex engine, and more. You can read more here and here.

Quick tip: Perl One Liners

Practical Extraction and Report Language is hackers and sys admin's # 1 choice language :)

This site offers examples - perl one liners for command line use, a summary of important perl command line arguments, and how to convert between 1-liners and full Perl scripts. This page assumes the reader has a reasonable amount of Perl experience.

Perl One Liners