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I am new to Ubuntu and I am trying to get a Mercusys AC650 usb wifi to work in Ubuntu 20.04. I was very happy to see a solution already listed here in Ask Ubuntu and I followed some commands which had the AC650 connecting to my wifi. The commands from the question 'Realtek RTL8811CU Wifi Dongle' that I used to have the wifi working initially were;

sudo apt install build-essential -y
mkdir -p ~/build
cd ~/build
sudo apt install git
git clone https://github.com/brektrou/rtl8821CU.git
cd rtl8821CU
make
sudo make install

However the wifi stopped functioning and I had to get a wired connection up to get the internet once more. Once back on the internet I moved the folder ~/build/rtl8821CU to the recycling folder and completed the commands listed above to once again have the wifi working once more. I think the first time the wifi stopped working was due to a ubuntu software update having been completed and then a reboot of the machine. When the software update initialised once again after the wifi was once more working for a second time the wifi stopped working after I rebooted.

Please could you advise how I get this Mercusys AC650 wifi working once more in Ubuntu 20.04 as I believe the automatic software updates cause the code I used previously to good effect to now no longer function?

Peter
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2 Answers2

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You can use dkms to install the driver for a new kernel version, in terminal do

cd rtl8821CU
make clean
sudo ./dkms-install.sh
Jeremy31
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  • Many thanks for the prompt reply! I tried using terminal with these recommended steps but no joy. The wifi is not operating. The dkms install went through the steps in terminal and seemed to have gone through okay but no overall change to the problem. I am unsure what steps might be required to shine more light on this issue? – Peter Dec 02 '20 at 22:21
  • Check in terminal dkms status you might need a reboot – Jeremy31 Dec 02 '20 at 22:38
  • I rebooted and no wifi yet. I have entered in terminal dkms status and I got two entries - I installed rtl8192eu earlier in efforts to get the AC650 wifi working: 'first line' rtl8192eu, 1.0: added 'second line' rtl8821CU, 5.4.1, 5.4.0-56-generic, x86_64: installed (WARNING! Diff between built and installed module!) – Peter Dec 02 '20 at 23:06
  • I will have to look into this as I got similar results with a different module with the same kernel – Jeremy31 Dec 02 '20 at 23:10
  • Hello Jeremy31. Checking in to see if you have had an opportunity to resolve this wifi connection issue? I could try moving the folder ~/build/rtl8821CU to the recycling folder and completing the commands listed originally to once again have the wifi working; through the use of a wire connection? Then see if a software update works this time? – Peter Dec 10 '20 at 19:54
  • Not sure as that kernel was recently removed because of issues – Jeremy31 Dec 11 '20 at 22:50
  • Many thanks for your assistance. As you pointed out that the kernal had been removed/replaced I re-plugged the wire connection back in to see if there was a new software update. There was a new 200 odd Mb software update so I ran that to install and then restarted. Once the system was rebooted both the wire connection and wifi connection were connected so I removed the wire connection and left the wifi running by itself! This seems to have resolved this problem for now as the wifi is back working thanks again. – Peter Dec 12 '20 at 18:51
  • I just saw the same when I installed the .58 today and there isn't anything different in the dkms make log for the module that would cause a failure on 56 – Jeremy31 Dec 12 '20 at 20:02
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Try installing this: https://github.com/morrownr/8821cu-20210118

First update and upgrade system packages:

sudo apt update && sudo apt upgrade

Then install all the required packages:

sudo apt install -y build-essential dkms git

Then download te driver in a folder and remove all the previous drivers.

mkdir ~/build
cd ~/build
git clone https://github.com/morrownr/8821cu-20210118
cd 8821cu-20210118
git pull
sudo ./remove-driver.sh

At this point you will need to reboot. Afetr rebooting:

cd ~/build/8821cu-20210118
sudo ./install-driver.sh

And accept to reboot when offered.

Hope it helps, I've been trying different drivers for a week now and this was the only one that worked.

Best regards.

P.M.
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