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rtl8821CU/README.md

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# 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:
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:
```bash
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"
```
Make sure to set your `ATTR{idVendor}` and the `-v` argument to the left portion of the output of lsusb device ID, and your `ATTR{idProduct}` and `-p` argument to the right portion of the lsusb device ID. For example (for the Cudy AC600 usb wifi adapter) the output from `lsusb` command looks like this:
```
Bus 001 Device 016: ID 0bda:c811 Realtek Semiconductor Corp. 802.11ac NIC
```
then your configuration in `/lib/udev/rules.d/40-usb_modeswitch.rules` should be
```
# Realtek 8211CU Wifi AC USB
ATTR{idVendor}=="0bda", ATTR{idProduct}=="c811", RUN+="/usr/sbin/usb_modeswitch -K -v 0bda -p c811"
```
## 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
``
### Monitor mode
Use the tool 'iw', please don't use other tools like 'airmon-ng'
```
iw dev wlan0 set monitor none
```