さくらVPSでUbuntu 18.04から20.04へのアップグレード

% sudo apt update && sudo apt upgrade   # ひとまず最新に更新
% sudo apt dist-upgrade                 # 現リリースで可能なパッケージのアップグレード
% sudo apt autoremove                   # 不要パッケージの削除
% sudo apt install update-manager-core  # まだ未インストールなら
% sudo do-release-upgrade               # いよいよ20.04へのアップグレード開始

  * Contniue [yN] Details [d] -> Y
  * Configuring libc6
    - Restart services during package upgrades without asking? -> Yes
  * Configuration file '/etc/ntp.conf'
    -> Y: install the package maintainer's version
  * Configuration file '/etc/crontab'
    -> Y: install the package maintainer's version
  * Configuration file '/etc/sysctl.conf'
    -> Y: install the package maintainer's version
  * Configuration openssh-server
    -> keep the local version currently installed
  * Remove obsolete packages?
    -> y
  * To finish the upgrade, a restart is required.
    -> y

% cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.5 LTS"