Ubuntu 公式サイトに手順が書かれているのでその通りにやるだけ

How to install Ubuntu Server on your Raspberry Pi


Raspberry Pi Imager をダウンロード

Wi-Fi接続する場合は system-boot の network-config の編集が必要


% ssh ubuntu@
ubuntu@'s password:
You are required to change your password immediately (administrator enforced)
Welcome to Ubuntu 20.10 (GNU/Linux 5.8.0-1006-raspi aarch64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Tue Dec  1 09:45:39 UTC 2020

  System load:  0.42              Temperature:           47.7 C
  Usage of /:   3.4% of 58.24GB   Processes:             144
  Memory usage: 7%                Users logged in:       0
  Swap usage:   0%                IPv4 address for eth0:

0 updates can be installed immediately.
0 of these updates are security updates.

The list of available updates is more than a week old.
To check for new updates run: sudo apt update

The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

WARNING: Your password has expired.
You must change your password now and login again!
Changing password for ubuntu.
Current password:
New password:
Retype new password:
passwd: password updated successfully
Connection to closed.