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/kernel-devel, bc and git have been installed.

First, clone this repository

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

Check the name of the interface

Check the interface name of your wifi adapter using ifconfig. Usually, it will be wlan0 by default, but it may vary depends on the kernel and your device. On Ubuntu, for example, it may be named as wlx + MAC address. (https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/)

If this is the case, you can either disable the feature following the link above, or replace the name used in the driver by

grep -lr . | xargs sed -i '' -e '/ifcfg-wlan0/!s/wlan0/<name of the device>/g'

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:

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

lsusb

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):

Edit usb_modeswitch rules:

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

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

Build with Raspberry Pi 4

To build this driver for Raspberry Pi 4, you need to follow the steps below.

#Follow the build step until just before ./dkms-install.sh

# Update and upgrade apt
sudo apt update -y
sudo apt upgrade -y

# Install bc
sudo apt-get install bc

# Reboot the system
sudo reboot

Next, edit the MakeFire to change these two lines

CONFIG_PLATFORM_I386_PC = y
CONFIG_PLATFORM_ARM_RPI = n

CONFIG_PLATFORM_I386_PC = n
CONFIG_PLATFORM_ARM_RPI = y

Then, run these lines to fix Make error on ARM processor

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

Finally, continue the steps above to install via dkms

# Run dkms install with sudo
sudo ./dkms-install.sh

and you should see wlan1 pop up on your Pi 4.

tobychui/rtl8821CU