6 of the best content filters for Linux

With more and more countries implementing varying degrees of restrictions on content access, internet censorship has become a hotly debated topic.

When implemented by ISPs on behalf of the government's, without offering end users any option in the matter, internet censorship is a curb on your freedoms, but in the hands of a home user or system administrator, the same web content filters become a powerful tool to protect your children and even machines from harm.

Web filters use various tricks to restrict access to content. While some use whitelists and blacklists to govern what websites users can browse to, others are designed to block content based on keywords, while others still can be configured to weed out various scripts and file formats.

There are commercial solutions on offer, but most tools offer free licences to home users and the thriving communities provide an excellent support system via mailing lists, forums and wikis.

While we prefer tools that can do more than just block a list of websites, we really want applications that aren't too complicated to setup and would satisfy the needs of most home users. This is why DansGuardian makes the list: even though it's perfectly at home on a large network, it's just as comfortable on a standalone machine and can handle your daily gripes using its default settings.

FoxFilter

The first tool on our list is also perhaps the easiest to install and setup and fall in love with. This Firefox add on supports every Firefox variant from 3.0.0 up, and should satisfy the needs of cautious parents. All you need to do to get a functioning content filter is to click on the shiny green install button.

While FoxFilter is free to use, and all filtering features are available at no cost, there are some Premium features that can be enabled by paying a small support fee. You can click on the small green icon at the bottom-right of the Firefox window to launch the FoxFilter settings.

The configuration options are split across a series of tabs at the top of the FoxFilter Settings page. There are two filtering options under the General tab: one that only allows access to the websites you specify in the Allowed list, and the other to filter the content-based blocked sites list, keywords and sensitivity settings.

Additionally, there are four sensitivity options to choose from. You can make FoxFilter examine the metadata of the title, the URL and even the content of the page. These are important options, because FoxFilter will look for each of the listed keywords in each of these, and weed out all objectionable content.

The default keyword list accessible from the Blocked tab is not large, and it's up to you to fill it out with terms you want to block. You should be careful though, because some words, such as 'lust' can become completely innocent when part of 'illustration', for example, and the onus is on you to add such words to the ignore list to prevent false positives.

There isn't a separate list of blocked sites, but you can add either a word such as 'YouTube', or the exact URL into the keyword list itself.

FoxFilter 7.6.1
Price: Free
Website: https://addons.mozilla.org/en-US/firefox/addon/4351

Rejecting content based on a superficial inspection, which can be painfully slow at times.

Rating: 5/10

WebCleaner

For those of you who want a very precise tool that will remove all offensive advertisements from the moment it's installed, with a default setting for just about all manners of inappropriate content, WebCleaner is the tool to use.

Installing WebCleaner, if you follow the instructions on the official website, may not always go smoothly, so we suggest that after downloading the source tarball, you follow these steps: decompress the tarball, run ./configure, run make, and then run the python setup.py build command. Finally, run the command python setup.py install --home $HOME.

You'll need to start the WebCleaner service from the terminal with webcleaner start. The next step is to configure your browser to use the proxy at localhost and port 8080. Point your browser then to http://localhost:8080 to start configuring WebCleaner.

The odd thing about most of WebCleaner's enabled-by-default filters is that you're recommended not to edit them. However, the filters can be updated by clicking on the Update Filter Configuration button from the Filter Update page.

While the browser interface for WebCleaner is easy to navigate, it's difficult to add custom rules and create your own filters. Some rules, such as bad words in the URL, can be easily modified. Click on 'Erotic' on the left pane under Filter configuration, choose Bad words in the URL in the middle pane and scroll down to the bottom of the left-hand pane until you see the Attributes field. You can now add keywords to the existing list.

Webcleaner 2.41
Price: Free under GPL
Website: http://sourceforge.net/projects/webcleaner

Difficult to create custom rules, but most will be satisfied with the defaults.

Rating: 8/10