Yet another web log

Version control systems like CVS or Subversion are designed for keeping track of the changes of a project and for having the possibility to revert to old revisions if something goes wrong. In contrast to regular relational databases, these systems are made only for adding new content to a repository, and not for removing data from it. In fact, deleting old content is not a built-in functionality in SVN, and mostly requires removing entire revisions from the repository or even creating a new one.

But what happens if you accidentally commit a password or other sensitive information to a repository? This post explains how to remove this confidential data permanently from the repository by simply overwriting it in old revisions, i.e. without having to remove revisions or create a new repository.

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WordPress is a very popular open-source blog software and is used widely throughout the Internet. However, with great success comes great attack potential: like any other wide spread open-source software, WordPress is target for frequent hacking attacks and spam-bots. All the more important is it to always update the distribution to the latest release.

As Debian/Ubuntu user, I am spoiled when it comes to update management: apt-get updates most of my software, and apticron notifies me when updates are available. For WordPress however, the packaged versions of Debian/Ubuntu are really old and less adjustable which unfortunately makes a manual installation inevitable. While there are several automated WordPress update mechanisms out there, I couldn’t find a simple notify-on-update tool.

This post introduces the WordPress Update Notifier (WP-UN), a simple script that frequently compares the installed WordPress version with the latest available one. If a new version is available, it sends an e-mail to a given address.

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Greylisting is a very efficient technique for fighting spam and can reduce the spam messages in your mailbox by more than 90%. It uses the fact that most spammers only try delivering their spam-mails once, whereas real mail transfer agents (such as the ones regular e-mail service providers are using) try delivering each message up to 4-5 days before they give up.

I have always wondered why most ESPs don’t offer greylisting for their mailboxes, but only rely on less effective and resource-hungry post-retrieval filter methods. Unfortunately, my e-mail provider is one of them so that I get at least a couple of spam mails a day …

Luckily, it is very easy to set up your own mail relay with greylisting support, i.e. a mail server that simply forwards the mail to your real provider once it passes the greylist-filter.

This little tutorial describes how to set up Postfix and SQLgrey as mail relay.

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