Many distributions of Linux prefer to include only free software and drivers by default, and Debian falls into that category. The reason for this can be due to moral decisions or licensing restrictions, but the result may be that a specific network card or hardware device ceases to function out of the box. Commonly, this is very typical with wireless cards. One example of this is Intel wireless cards. While these typically work without any tinkering needed when it comes to end-user distributions (Ubuntu, Linux Mint, and so on), Enterprise distributions such as Debian often don't include these and force you to jump through additional hoops. The reason for this is because the software required for these cards to function isn't open-source, so the decision was made to not include it in the default repositories. Thankfully, this usually isn't too difficult to rectify providing you know the steps.

On Debian systems, there is a non-free parameter that can be added to your APT sources that tells the distribution that you would like such packages included when you search for and install software. But before you do this, make sure that you actually do need additional firmware. One dead giveaway is if Debian complains about missing firmware while booting. Without rebooting, you may see errors in the logs complaining about a lack of firmware for a hardware device. To view any output on your system that may be complaining about missing firmware, try the following command:

dmesg |grep firmware

To add the non-free component of your APT sources in Debian, first make a backup of your original sources.list file:

# cp /etc/apt/sources.list /etc/apt/sources.list.bak

Then, add the non-free parameter to the main repository. On my Debian Jessie system, the line looks like this:

deb http://ftp.us.debian.org/debian/ jessie main contrib non-free

Once that's done, refresh your sources with the following command:

# apt-get update

From this point forward, the non-free binary packages should be available to you. You can confirm this by searching for and listing available firmware packages on your system. The output should contain several nonfree packages. To perform this search, try the following command:

aptitude search firmware

For example, if firmware-linux-nonfree shows up in your list of available packages, then you've performed these steps correctly.

Unfortunately, detailing a full list of hardware compatibility for Debian and the required firmware for each would be beyond the scope of this book. However, the logs should give you a general idea of what firmware is missing, allowing you to search your package database for specific packages. Typically, copying a line of output from dmesg regarding failure to load firmware and doing a Google search will take you right to what package is needed to resolve the situation. In my case, the most commonly needed firmware package I run into is firmware-iwlwifi. Additionally, firmware-atheros and firmware-b43-installer are also common.