Spotlight customer reviews:
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Customer Rating:  
Summary: Important book
Comment: A lot of people think Linux is bullet proof, but its not. If not configured correctly, it can be just as insecure as Windows.
Hardening Linux is an important book in that it shows how to harden Linux to be very secure.
Customer Rating:
Summary: antispam descriptions are outdated
Comment: With the onslaught of malware in all its deviant forms, securing your linux machine should be a high priority. Linux now has a plethora of tools and procedures to aid in this. But where can you start? Perhaps here. Turnbull tries to help you make sense of what you can do, where hopefully you already have some linux sysadmin experience.
He goes into considerable detail about many potential weaknesses. Consider, for example, having compilers on your machine. These are usually installed by default and available to any user. But if your users never compile, then it's worth removing the compilers, or restricting their usage to you alone. This is one of the crucial preventive steps recommended in the book.
There are others. Though his description of immutable files is a trifle overstated. They "cannot be written to by any user, even by the root user, regardless of their file permissions". Immediately contradicted by the book showing how to change this attribute on a file. Thence, you as root can certainly alter or even delete it.
The discussion of antispam methods is outdated. The descriptions of some do not go into their limitations. Like for Postfix, it is possible to check the Subject line of an email against a list of regular expressions, and reject any matches. This is a first generation antispam method, circa 1998. It has proved virtually useless against spammers. The problem is that a spammer can craft a Subject line so that the recipient (who is wetware) can recognise the meaning, while making it very hard for software, which has rigid rules, to detect it.
There are two problems with the book mentioning the regexp filter. Firstly, you can waste a lot of your time, writing those regexps to try to detect as much spam as possible. Plus the time to maintain and adding more such rules, when your first tries prove inadequate. Secondly, there is the run time cost. The clock cycles spent on applying this filter are largely wasted. If you get a lot of messages, this can affect the performance of your mail server. Remember that the more rules you have, the longer it takes, because you usually have to apply all of them to each message's header.
The book would better serve you if it explained that Postfix could have the above filter, but why you should refrain from doing so. A more perceptive analysis.
Also, blacklists are discussed as another antispam method, for both sendmail and Postfix. But the application of the blacklists is limited and outdated. More powerful usages of blacklists now exist. And there is no description of using milter filters with sendmail, to fight spam. This has been a recent important enhancement of sendmail.
Customer Rating:
Summary: Much more than I expected
Comment: I thought this might just be a book on iptables and other firewalls, but it's much more. In 400 pages, this covers everything from initial installation right through what to do if you did get breached. It covers email security, ftp,
dns and bind, ssh, file systems, pam authentication, firewalls, penetration testing and more.
The really impressive thing is that everything is covered well - obviously some of these subjects could be hundreds of pages by themselves, but the author manages to succintly present the important concepts.
I'd certainly recommend this to anyone running a Linux box.
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