Besides the availability of a device driver, some hardware also requires so-called firmware or microcode to be loaded into the device before it can become operational. This is most common for network interface cards (especially wireless NICs), but for example some USB devices and even some hard disk controllers also require firmware.

With many graphics cards, basic functionality is available without additional firmware, but the use of advanced features requires an appropriate firmware file to be installed in the system.

Számos régebbi eszköz, amely a működéséhez firmware-t igényel, ezt a firmware állományt a gyártó magán az eszközön helyezte el, egy EEPROM/Flash chipen. Manapság az új eszközök már nem tartalmazzák a firmware-t ily módon, ezért a firmware állományt az operációs rendszernek minden rendszer indulásnál fel kell töltenie az eszközre.

In most cases firmware is non-free according to the criteria used by the Debian GNU/Linux project and thus cannot be included in the main distribution. If the device driver itself is included in the distribution and if Debian GNU/Linux legally can distribute the firmware, it will often be available as a separate package from the non-free-firmware section of the archive (prior to Debian GNU/Linux 12.0: from the non-free section).

However, this does not mean that such hardware cannot be used during installation. Starting with Debian GNU/Linux 12.0, following the 2022 General Resolution about non-free firmware, official installation images can include non-free firmware packages. By default, debian-installer will detect required firmware (based on kernel logs and modalias information), and install the relevant packages if they are found on an installation medium (e.g. on the netinst). The package manager gets automatically configured with the matching components so that those packages get security updates. This usually means that the non-free-firmware component gets enabled, in addition to main.

Users who wish to disable firmware lookup entirely can do so by setting the firmware=never boot parameter. It's an alias for the longer hw-detect/firmware-lookup=never form.

Unless firmware lookup is disabled entirely, debian-installer still supports loading firmware files or packages containing firmware from a removable medium, such as a USB stick. See 6.4. szakasz - Hiányzó firmware betöltése for detailed information on how to load firmware files or packages during the installation. Note that debian-installer is less likely to prompt for firmware files now that non-free firmware packages can be included on installation images.

Ha debian-installer felszólít firmware állomány betöltésére, de nincs ilyen firmware-ed, vagy nem akarsz nem ingyenes firmware-t telepíteni a rendszeredre, megpróbálhatod firmware betöltése nélkül folytatni. Nemegyszer előfordul, hogy a meghajtó azért kér további firmware-t, mert bizonyos körülmények között szüksége lehet rá, de enélkül is jól működik az eszköz a legtöbb rendszeren (ez a helyzet pl. bizonyos hálózati kártyáknál, amik tg3 meghajtót használnak).