Realtek RTL8811CU/RTL8821CU USB wifi adapter driver version 5.4.1 for Linux 4.4.x up to 5.x

Before build this driver make sure make, gcc, linux-header and git have been installed.

First, clone this repository

mkdir -p ~/build
cd ~/build
git clone https://github.com/brektrou/rtl8821CU.git

Build and install with DKMS

DKMS is a system which will automatically recompile and install a kernel module when a new kernel gets installed or updated. To make use of DKMS, install the dkms package.

Debian/Ubuntu:

sudo apt-get install dkms

Arch Linux/Manjaro:

sudo pacman -S dkms

To make use of the DKMS feature with this project, just run:

./dkms-install.sh

If you later on want to remove it, run:

./dkms-remove.sh

Plug your USB-wifi-adapter into your PC

If wifi can be detected, congratulations. If not, maybe you need to switch your device usb mode by the following steps in terminal:

1. find your usb-wifi-adapter device ID, like "0bda:1a2b", by type:

lsusb

2. switch the mode by type: (the device ID must be yours.)

Need install usb_modeswitch (Archlinux: sudo pacman -S usb_modeswitch)

sudo usb_modeswitch -KW -v 0bda -p 1a2b
systemctl start bluetooth.service - starting Bluetooth service if it's in inactive state

It should work.

Make it permanent

If steps above worked fine and in order to avoid periodically having to make usb_modeswitch you can make it permanent (Working in Ubuntu 18.04 LTS):

1. Edit usb_modeswitch rules:

   sudo nano /lib/udev/rules.d/40-usb_modeswitch.rules

2. Append before the end line LABEL="modeswitch_rules_end" the following:

   # Realtek 8211CU Wifi AC USB
   ATTR{idVendor}=="0bda", ATTR{idProduct}=="1a2b", RUN+="/usr/sbin/usb_modeswitch -K -v 0bda -p 1a2b"
   

Build and install without DKMS

Use following commands:

cd ~/build/rtl8821CU
make
sudo make install

If you later on want to remove it, do the following:

cd ~/build/rtl8821CU
sudo make uninstall

Checking installed driver

If you successfully install the driver, the driver is installed on /lib/modules/<linux version>/kernel/drivers/net/wireless/realtek/rtl8821cu. Check the driver with the ls command:

ls /lib/modules/$(uname -r)/kernel/drivers/net/wireless/realtek/rtl8821cu

Make sure 8821cu.ko file present on that directory

Check with DKMS (if installing via DKMS):

sudo dkms status

ARM architecture tweak for this driver (this solves compilation problem of this driver):

# For AArch32
sudo cp /lib/modules/$(uname -r)/build/arch/arm/Makefile /lib/modules/$(uname -r)/build/arch/arm/Makefile.$(date +%Y%m%d%H%M)
sudo sed -i 's/-msoft-float//' /lib/modules/$(uname -r)/build/arch/arm/Makefile
sudo ln -s /lib/modules/$(uname -r)/build/arch/arm /lib/modules/$(uname -r)/build/arch/armv7l

# For AArch64
sudo cp /lib/modules/$(uname -r)/build/arch/arm64/Makefile /lib/modules/$(uname -r)/build/arch/arm64/Makefile.$(date +%Y%m%d%H%M)
sudo sed -i 's/-mgeneral-regs-only//' /lib/modules/$(uname -r)/build/arch/arm64/Makefile

Monitor mode

Use the tool 'iw', please don't use other tools like 'airmon-ng'

iw dev wlan0 set monitor none