after upgrade of 20.04 wifi stops working (ultimate-N 6300)

[dieter-erich]

Hi,
upon upgrading my ubuntu-20.04 to the latest stage the wifi stopped working (network manager does not even show the icon but ethernet works). Wifi of the older ubuntu-16.04 installed on the same PC works normally. I have scanned the net for hours and tried various of the described solutions but none worked for me. The hardware tool described here https://linux-hardware.org shows that the Intel driver 'Centrion Ultimate-N 6300' is missing. No idea why it disappeared! Can anybody please give me a point per point instruction of how to install this driver correctly!
Thanks, a lot, D.

[jeremy31]

Try

sudo modprobe iwlwifi

[chili555]

Jeremy and I would also like to see:

dmesg | grep iwl

[dieter-erich]

Thank you!

sudo modprobe iwlwifi:
modprobe: ERROR: ../libkmod/libkmod-module.c:838 kmod_module_insert_module() could not find module by name='iwlwifi'
modprobe: ERROR: could not insert 'iwlwifi': Unknown symbol in module, or unknown parameter (see dmesg)

dmesg | grep iwl:
no output

[jeremy31]

What results for

dpkg -l | grep linux-modules-extra-$(uname -r); dkms status; modinfo iwlwifi

[dieter-erich]

I get:
"modinfo: ERROR: Module iwlwifi not found."

[jeremy31]

Do

sudo apt install --reinstall linux-modules-extra-$(uname -r)

Reboot

[dieter-erich]

Hi, some more info:
not being able to find this driver I did: sudo apt-get install backport-iwlwifi-dkms
but "ls /usr/lib/firmware|grep wifi" shows me a lot of .ucode files but none containing "6300"
Could it be that I have to fetch this file from somewhere else?

[dieter-erich]

sudo apt install --reinstall linux-modules-extra-$(uname -r) gives me:
.............................
Unpacking linux-modules-extra-5.8.0-38-generic (5.8.0-38.43~20.04.1) ...
Setting up linux-modules-extra-5.8.0-38-generic (5.8.0-38.43~20.04.1) ...
Processing triggers for linux-image-5.8.0-38-generic (5.8.0-38.43~20.04.1) ...
/etc/kernel/postinst.d/dkms:
* dkms: running auto installation service for kernel 5.8.0-38-generic
Error! Your kernel headers for kernel 5.8.0-38-generic cannot be found.
Please install the linux-headers-5.8.0-38-generic package,
or use the --kernelsourcedir option to tell DKMS where it's located
Error! Your kernel headers for kernel 5.8.0-38-generic cannot be found.
Please install the linux-headers-5.8.0-38-generic package,
or use the --kernelsourcedir option to tell DKMS where it's located
.................................................. ...........................................
So I must have screwed up also the linux-headers. How do I reinstall them?

[jeremy31]

Do

sudo apt purge backport-iwlwifi-dkms
sudo apt install --reinstall linux-headers-5.8.0-38-generic linux-modules-extra-5.8.0-38-generic

Reboot if no errors