How to use proprietary wireless drivers during Debian USB install?

Question

I downloaded the Debian amd64 netinstall ISO and put it onto a USB stick. The installer runs fine, but my laptop requires proprietary wireless drivers (iwlwifi) to get internet during the install. During the "Detect Network Hardware" stage the installer asks me for removable media with the drivers on it.

The install USB isn't writable (because it was created using dd and an ISO image). I tried placing the iwlwifi files on a separate USB, but the Debian installer couldn't find/detect them (and unfortunately, the installer doesn't give any info on why it failed - it just pauses for a moment and then goes back to the screen asking for removable media with the drivers on them).

How do I make a USB disk with the iwlwifi drivers that the installer can recognize, or put them onto the installer disk?

Answer 1

The easiest way imho, is to use one of the ”unofficial” images that contain non-free firmware.

They can be found here:
https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/

And the direct link to the netinstall with non-free firmware is:
https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/9.3.0+nonfree/amd64/bt-cd/

Just do as you normally do and write your image to USB, you then have access to the iwlwifi drivers ”out-of-the-box” when installing.

Answer 2

try to use this image it already contains the firmware needed for your wifi device

Unofficial Debian Stretch 9.30 cd including firmware-nonfree

there is netinstall image as you asked

and here all the official information about the firmware and how to install it by hand https://wiki.debian.org/Firmware
there is no updated informations on stretch but i think it'd be the same as jessie, see that both distributions shares the same tree of directories on both the netinstall images.

Answer 3

See 6.4. Loading Missing Firmware from the Debian GNU/Linux Installation Guide.

If a device driver requests firmware that is not available, debian-installer will display a dialog offering to load the missing firmware. If this option is selected, debian-installer will scan available devices for either loose firmware files or packages containing firmware.

Which devices are scanned and which file systems are supported depends on the architecture, the installation method and the stage of the installation. Especially during the early stages of the installation, loading the firmware is most likely to succeed from a FAT-formatted floppy disk or USB stick. On i386 and amd64 firmware can also be loaded from an MMC or SD card.

Official CD images do not include non-free firmware. The most common method to load such firmware is from some removable medium such as a USB stick. Alternatively, unofficial CD builds containing non-free firmware can be found at https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/. To prepare a USB stick (or other medium like a hard drive partition, or floppy disk), the firmware files or packages must be placed in either the root directory or a directory named /firmware of the file system on the medium. The recommended file system to use is FAT as that is most certain to be supported during the early stages of the installation.

Have a good look at that section of the manual as it contains more information about installing packages and making sure they are updated correctly after install.

(Also, part 5.4. Troubleshooting the Installation Process suggests to switch to Virtual console 4 (VT4) to check for any specific error messages, and part 6.1.1. Using the graphical installer explains that Ctrl+Alt+Fx can be used to switch to VTx. But it does not help much in this case.)