Booting a Headless Raspberry Pi Using an Ubuntu Image
Setting SSH on a raspberry
In this simplified guide, we will see how to run Ubuntu on raspberry pi. What you need to follow in this guide are is a Raspberry Pi Kit composed of:

i) A raspberry pi (obviously)
ii) An SD card (Ideally 32 GB)
iii) An SD card reader/writer
iv) The power supply
v) An Ethernet cable (not in the kit)
You can buy a kit from Banggood at: https://www.banggood.com/fr/Catda-4GB-RAM-Raspberry-Pi-4B-+-Black-Cover-Box-+-Power-Supply-+-32-or-64GB-Memory-Card-+Micro-HDMI-DIY-Kit-p-1770449.html?rmmds=myorder&cur_warehouse=CN&ID=56726447184
You will also need a Linux-based system that is connected to the same router as the Ethernet cable.
STEP 1
Download an Ubuntu Raspberry pi image from https://ubuntu.com/download/raspberry-pi
$ wget https://ubuntu.com/download/raspberry-pi/thank-you?version=20.04.2&architecture=server-arm64+raspi
STEP 2
Decompress the “xz” file using this command:
$ xz -d [name of image].img.xz
STEP 3
Plug the SD card (using the reader/writer) and find its device name. To find the name of the latest plugged USB device you can you the dmesg command:
$ dmesg | tail -10
“tail -10” shows the 10 last lines of dmesg
[ WARNING: Be sure that you have the right device name. Otherwise, you may break your system.]
STEP 4
Copy the image into the SD card:
$ sudo dd bs=4M if=[image name].img of=/dev/sda conv=fsync
STEP 5
Plug the raspberry pi: the SD card, the power supply, and the ethernet cable. Then power it on.
STEP 6
Find the IP address of the Raspberry Pi. You can use the “$nmap” for this:
$ nmap -sP [IP address, example: 192.168.1.4]/[subnet mask, example: 24]
More details here: https://vitux.com/find-devices-connected-to-your-network-with-nmap/
STEP 7
Ssh into the raspberry pi:
$ ssh ubuntu@[IP address]
The password is: ubuntu
Conclusion
That is it. You now have access to a Raspberry PI system. Congratulation.