Check wireless hardware:
sudo lspci -kv
For hardware Intel Corporation Centrino Wireless-N 2230, a non-free package is needed so, add to /etc/apt/sources.list
deb http://httpredir.debian.org/debian/ stretch main contrib non-free
$ sudo apt update
$ sudo apt upgrade
$ sudo apt install firmware-iwlwifiRestart your computer, after doint that, the wireless interface will be listed after running ip address.
$ sudo ip link set wlp4s0 up
If the last command returns "RTNETLINK answers: Operation not possible due to RF-kill".
$ sudo apt install rfkill
$ sudo rfkill list
Unblock soft block
$ sudo rfkill unblock wifi
Once wifi is unblocked try to set the wireless interface up again.
Scan wifi networks.
$ sudo iwlist scan
$ wpa_passphrase myssid my_very_secret_passphrase
Copy the standard output of the previous command in /etc/wpa_supplicant/wpa_supplicant.conf
Copy the hash from field "psk" and use it in the file /etc/network/interfaces
allow-hotplug wlp4s0
iface wlp4s0 inet dhcp
wpa-ssid myssid
wpa-psk my_hash_from_wpa_passphrase_command
Bring the interface up.
$ sudo ifup wlp4s0
Your wireless interface should now be configured and running, it will also run after reboots due to the allow-hotplug from interfaces file.
Resources: