How to check if a proxy is set in Linux

Introduction

In this lab, you will learn how to check for configured proxy settings in a Linux environment. We will explore different methods to identify if a proxy server is being used for network connections.

You will begin by examining common environment variables like http_proxy, https_proxy, and ftp_proxy using the echo command. Following this, you will investigate system-wide proxy configurations by inspecting the /etc/environment file and checking for proxy settings specifically configured for the apt package manager within the /etc/apt/apt.conf.d directory. This hands-on approach will equip you with the skills to diagnose potential network connectivity issues related to proxy configurations in Linux.

Skills Graph

Check proxy variable with echo $http_proxy

In this step, we will start exploring network configurations in Linux by checking proxy environment variables. Environment variables are dynamic values that affect the processes running on a computer. They can store information like paths, user names, and in this case, network proxy settings.

A proxy server acts as an intermediary for requests from clients seeking resources from other servers. In some network environments, you might need to configure proxy settings for applications to access the internet. These settings are often stored in environment variables like http_proxy, https_proxy, and ftp_proxy.

We can use the echo command, which you learned in the previous lab, to display the value of an environment variable. To access the value of a variable, you prefix its name with a dollar sign ($).

Open your terminal if it's not already open. Remember, you can find the Xfce Terminal icon on the left side of your desktop.

Type the following command and press Enter:

echo $http_proxy

This command will print the current value of the http_proxy environment variable. If no HTTP proxy is configured through this variable, the command will likely output an empty line.

Next, let's check the https_proxy variable, which is used for secure HTTPS connections:

echo $https_proxy

And finally, the ftp_proxy variable for FTP connections:

echo $ftp_proxy

The output of these commands will show you if any proxy settings are configured via these specific environment variables in your current terminal session. Understanding how to check these variables is a fundamental step in troubleshooting network connectivity issues in a Linux environment.

Click Continue to proceed to the next step and verify your actions.

Verify proxy settings in /etc/environment

In the previous step, you checked proxy settings stored in environment variables for your current terminal session. However, system-wide environment variables are often configured in files like /etc/environment. This file is read by the system at startup and sets environment variables for all users and processes.

Let's inspect the contents of the /etc/environment file to see if any proxy settings are defined there. We will use the cat command, which is used to display the content of files. Since /etc/environment is a system file, you might need administrator privileges to read it, although in this Lab environment, you can read it as the labex user.

Type the following command in your terminal and press Enter:

cat /etc/environment

You will see the contents of the file printed to your terminal. The output might look something like this:

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"
## http_proxy="http://your_proxy_server:port/"
## https_proxy="http://your_proxy_server:port/"
## ftp_proxy="http://your_proxy_server:port/"

In this example output, you can see the PATH variable is set, which tells the system where to look for executable programs. You might also see lines for http_proxy, https_proxy, and ftp_proxy. Notice that these lines start with a #. In configuration files, the # symbol usually indicates a comment, meaning the line is ignored by the system. So, in this example, the proxy settings are commented out and not active.

If you see lines like http_proxy="http://your_proxy_server:port/" without the # at the beginning, it means a system-wide proxy is configured. The actual proxy server address and port will be different depending on the network setup.

Examining /etc/environment is a crucial step in understanding how system-wide settings are applied and can help diagnose why applications might or might not be using a proxy.

Click Continue to move on to the next step.

Inspect apt proxy with cat /etc/apt/apt.conf.d

In the previous steps, you checked environment variables and the /etc/environment file for proxy settings. Another important place where proxy configurations can be set, especially for package managers like apt, is within the /etc/apt/apt.conf.d/ directory.

This directory contains configuration files for the apt package manager. These files often end with .conf and are read by apt when it runs commands like sudo apt update or sudo apt install. Proxy settings specifically for apt are frequently placed in a file within this directory.

To see the contents of this directory, we can use the ls command, which lists files and directories.

Type the following command and press Enter:

ls /etc/apt/apt.conf.d/

The output will show a list of files in that directory. It might look something like this:

00CDMountPoint  01autoremove  10periodic  15update-apt-xapian-index  20archive  20auto-upgrades  50unattended-upgrades  70debconf  99synaptic

You are looking for files that might contain proxy configurations. Common filenames for proxy settings in this directory include proxy.conf, 10proxy, or similar names.

To inspect the content of a specific file, you can use the cat command followed by the full path to the file. For example, if you saw a file named 10proxy in the output of ls, you would use:

cat /etc/apt/apt.conf.d/10proxy

If a proxy is configured for apt, the file content might look like this:

Acquire::http::Proxy "http://your_apt_proxy_server:port/";
Acquire::https::Proxy "http://your_apt_proxy_server:port/";

This configuration tells apt to use the specified proxy server for HTTP and HTTPS connections when downloading packages.

Even if you don't see a file explicitly named proxy.conf or similar, proxy settings could be included in other configuration files within this directory. However, checking for files with "proxy" in their name is a good starting point.

Understanding where apt looks for proxy settings is essential for troubleshooting issues when trying to install or update software in a proxied network environment.

Click Continue to complete this lab.

Summary

In this lab, we learned how to check for proxy settings in a Linux environment. We began by using the echo command to inspect the values of common proxy environment variables such as http_proxy, https_proxy, and ftp_proxy, which can indicate proxy configurations for the current terminal session.

Following this, we explored how to verify system-wide proxy settings by examining the contents of the /etc/environment file, a common location for defining environment variables that affect all users and processes. Finally, we learned how to inspect application-specific proxy configurations, specifically for the apt package manager, by viewing relevant files within the /etc/apt/apt.conf.d directory. These steps provide a comprehensive approach to identifying where proxy settings might be configured in a Linux system.