Some wifi adapter manufacturers do not have Linux wifi drivers available in the Linux installation distribution. In such cases you need to manually install a suitable driver on the laptop after installing the Linux OS.
I used this method for an Asus D515 Laptop running Linux Ubuntu Version 20 which did not recognize the wifi adapter and with no direct internet connection via ethernet available.
There are two potential ways of doing this: installation via internet connection created using mobile phone tethering, or offline installation using previously downloaded wifi installation package.
Check your current network configuration with:
ip a
If the output from “ip a” does not list a wifi adapter in your network configuration then you will need to manually install a wifi driver.
Next check the specification of your wifi adapter:
lspci | grep Network
If you have an RTL8821CE you will see something like this:
Network controller: Realtek Semiconductor Co., Ltd. RTL8821CE 802.11ac PCIe
If this is the case, then follow the instructions below to manually install the wifi driver on your system.
Install With Internet Connection Via Mobile Tethering
The steps involved are simple:
1. Use mobile phone tethering to create a temporary internet connection to the laptop.
For this you require the USB Cable to connect between mobile and laptop.
Then activate USB tethering on the mobile (under Android Settings)
2. Install mokutil:
apt-get install mokutil && mokutil –sb-state
Note: if it reports Secure Boot is enabled then shutdown, disable Secure Boot in BIOS and then restart.
(Secure Boot is primarily a mechanism for Microsoft to enforce its vendor lock-in)
3. Install the driver:
apt-get install rtl8821ce-dkms
4. Remove the mobile tethering and reboot the laptop.
The wifi adapter should now be recognized by Ubuntu.
Check with:
ip a
or
ifconfig
You can now configure a wifi internet connection on the laptop.
Install With No Internet Connection (Offline)
If you have no internet connection available, an offline install can be carried out as follows:
On a computer with Internet connection, first download the driver installation file using wget:
wget http://archive.ubuntu.com/ubuntu/pool/universe/r/rtl8821ce/rtl8821ce-dkms_5.5.2.1-0ubuntu4_all.deb
Should the above link no longer be available or current, check at pkgs.org for the current link:
https://pkgs.org/search/?q=rtl8821ce-dkms
Copy the file onto a USB stick and then use this to copy the file onto the computer where you want to install the driver.
Switch to the directory that contains the driver file you copied across and start the installation:
apt install ./rtl8821ce-dkms_5.5.2.1-0ubuntu4_all.deb