How To Block Specific Keywords Using Squid Proxy Server

The Squid proxy server is an open-source, high-performance proxy caching server for web clients that supports FTP, HTTPS, and HTTP data objects. It is mainly designed to accelerate content delivery by caching frequently requested data and freeing bandwidth. A lesser-known feature of Squid, however, is the ability to restrict access to certain websites or to block specific keywords. This article will guide you through the steps needed to block specific keywords using Squid proxy server.

Before we proceed, please note that you should have root or sudo user access to the Squid server to configure these settings.

Step 1: Install Squid

If you haven’t already installed Squid, you can do so by executing the following commands. The example commands given below are suitable for a Ubuntu or Debian-based Linux distribution.

sudo apt-get update 
sudo apt-get install squid 

For CentOS, RHEL and Fedora, use:

sudo yum update 
sudo yum install squid 

Step 2: Backup Squid Configuration File

Before making any changes to the Squid configuration file, it’s a good practice to make a backup. This can be done with the following command:

sudo cp /etc/squid/squid.conf /etc/squid/squid.conf.bak 

Step 3: Create a Keywords List File

Next, you will need to create a new file containing all the keywords you wish to block. For example, if you want to block the words “example” and “test”, you can create a file named “blocked_keywords.txt”. Use a text editor, such as nano or vim, to create and edit the file.

sudo nano /etc/squid/blocked_keywords.txt 

Add the keywords you want to block, each on a new line:

Save and close the file.

Step 4: Configure Squid to Block Keywords

Now you need to configure Squid to block the keywords listed in the file you just created. Open the Squid configuration file in a text editor:

sudo nano /etc/squid/squid.conf 

You will need to define an Access Control List (ACL) for your blocked keywords and then deny access based on that list. In the configuration file, scroll down to the ACL section and add the following lines:

The first line creates an ACL named “blocked_keywords” that matches URLs against the regular expressions listed in the “blocked_keywords.txt” file. The second line denies HTTP access to any URLs that match the “blocked_keywords” ACL.

Remember to save and close the file.

Step 5: Restart Squid Service

For the changes to take effect, you need to restart the Squid service. Use the following command:

sudo systemctl restart squid 

Conclusion

By following these steps, you have now successfully set up a Squid proxy server to block specific keywords. This is a powerful tool for network administrators looking to enforce certain browsing policies. However, it should be used responsibly, and users should be informed about any keyword restrictions in place.

Remember to regularly update your blocked keywords list based on your requirements. Each time you make changes to the list, you must restart the Squid service for the changes to take effect. Happy networking!