Source list
vim /etc/apt/sources.list
deb http://ftp.fi.debian.org/debian/ stretch main non-free contrib deb-src http://ftp.fi.debian.org/debian/ stretch main non-free contrib deb http://security.debian.org/debian-security stretch/updates main contrib non-free deb-src http://security.debian.org/debian-security stretch/updates main contrib non-free # stretch-updates, previously known as 'volatile' deb http://ftp.fi.debian.org/debian/ stretch-updates main contrib non-free deb-src http://ftp.fi.debian.org/debian/ stretch-updates main contrib non-free # stretch-backports, previously on backports.debian.org deb http://ftp.fi.debian.org/debian/ stretch-backports main contrib non-free deb-src http://ftp.fi.debian.org/debian/ stretch-backports main contrib non-free
Install Intel 9260 wireless
apt-get update apt-get -t stretch-backports install firmware-iwlwifi modprobe -r iwlwifi ; modprobe iwlwifi