Install Squid: Use sudo apt install squid on Ubuntu/Debian, use sudo dnf install squid on CentOS/RHEL, and start the service. 2. Configure basic settings: Edit /etc/squid/squid.conf, optionally change http_port, add acl definitions to allow networks such as 192.168.1.0/24, and ensure that the http_access allow rule is before deny all. 3. Restart Squid and verify: Use sudo systemctl restart squid and check port monitoring through ss or netstat. 4. Configure the firewall: Use ufw allow 3128 on Ubuntu, and firewall-cmd --add-port=3128/tcp on CentOS/RHEL. 5. Client settings: Configure the proxy IP and port 3128 on the client, or set the http_proxy environment variable. 6. Enable authentication (optional): Install apache2-utils or httpd-tools, create a password file, add authentication parameters to the configuration, and restart Squid. 7. Monitoring and Troubleshooting: Check /var/log/squid/access.log and cache.log, check the ACL order, configuration syntax, and firewall to solve common problems. After completing these steps, you will successfully deploy a basic Squid proxy server and can further enhance functionality as needed.

Setting up a proxy server on Linux using Squid is a practical way to control and monitor web traffic, improve performance through caching, or restrict access in a network. Squid is one of the most widely used open-source proxy servers, especially for HTTP, HTTPS, and FTP. Here's how to configure a basic proxy server with Squid on a Linux system.

1. Install Squid on Your Linux System

Squid is available in the default repositories of most Linux distributions.

On Ubuntu/Debian:

 sudo apt update
sudo apt install squid -y

On CentOS/RHEL/Rocky Linux:

 sudo dnf install squid -y

After installation, start and enable the service:

 sudo systemctl enable squid
sudo systemctl start squid

Check status:

 sudo systemctl status squid

2. Configure Basic Proxy Settings

The main configuration file for Squid is /etc/squid/squid.conf . Before making changes, back it up:

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

Open the config file:

 sudo nano /etc/squid/squid.conf

Key Configuration Options:

• Change the default port (optional):
  By default, Squid listens on port 3128. To change it:

   http_port 3128

  Replace 3128 with your desired port.

• Allow access from your network:
  By default, Squid only allows localhost. To allow a local network (eg, 192.168.1.0/24), add:

   acl localnet src 192.168.1.0/24
  http_access allows localnet

  You can add multiple acl lines for different subnets.

• Set visible hostname (optional but recommended):

   visible_hostname proxy.yourdomain.com

?? Always place http_access allow rules before the final http_access deny all line, or clients will be blocked.

Save and exit the file.

3. Restart and Test Squid

After making changes, restart Squid:

 sudo systemctl restart squid

Ensure the port is listening:

 sudo netstat -tulnp | grep :3128

If netstat is not installed:

 sudo apt install net-tools # Debian/Ubuntu
sudo dnf install net-tools # RHEL/CentOS

Or use:

 ss -tuln | grep 3128

4. Configure Firewall (if enabled)

Allow the Squid port through the firewall.

Using ufw (Ubuntu):

 sudo ufw allows 3128

Using firewalld (CentOS/RHEL):

 sudo firewall-cmd --permanent --add-port=3128/tcp
sudo firewall-cmd --reload

5. Client-Side Proxy Configuration

On client machines, configure the browser or system proxy settings:

• IP Address: Your Squid server's IP
• Port: 3128 (or your custom port)

For command-line tools like curl or wget , set environment variables:

 export http_proxy=http://squid-server-ip:3128
export https_proxy=http://squid-server-ip:3128

To make it permanent, add to ~/.bashrc or /etc/environment .

6. Enable Authentication (Optional)

To restrict access with username/password:

1. Install htpasswd (if not present):

    sudo apt install apache2-utils # Debian/Ubuntu
   sudo dnf install httpd-tools # RHEL/CentOS

2. Create a password file and user:

    sudo htpasswd -c /etc/squid/passwd username

3. In squid.conf , add:

    auth_param basic program /usr/lib/squid/basic_ncsa_auth /etc/squid/passwd
   auth_param basic children 5
   auth_param basic realm Squid Basic Authentication
   auth_param basic credentialsttl 2 hours
   
   acl authenticated_users proxy_auth REQUIRED
   http_access allows authenticated_users

Restart Squid afterward.

7. Monitor and Troubleshoot

• Check logs:

   sudo tail -f /var/log/squid/access.log
  sudo tail -f /var/log/squid/cache.log

• Common issues:

  • Clients getting "Access Denied": Check ACL order and subnet definitions.
  • Squid not starting: Validate config with sudo squid -k parse .
  • Connection timeouts: Verify firewall and network settings.

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That's it. You now have a working proxy server with Squid. From here, you can enhance it with SSL interference, bandwidth limits, or content filtering based on your needs. Just remember to keep security in mind—especially if exposing the proxy beyond your internal network.

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