下準備
sudo apt update
sudo apt upgrade
※ お好みで
sudo apt autoremove
updaterのインストール
sudo apt install ubuntu-release-upgrader-core
アップデートの設定
cat /etc/update-manager/release-upgrades
実行すると下記が表示されると思います．
僕の場合はPrompt=nerverと設定されていたので一番下の行をPrompt=normalまたはPrompt=ltsに変えてあげます．
# Default behavior for the release upgrader.
[DEFAULT]
# Default prompting behavior, valid options:
#
# never - Never check for, or allow upgrading to, a new release.
# normal - Check to see if a new release is available. If more than one new
# release is found, the release upgrader will attempt to upgrade to
# the supported release that immediately succeeds the
# currently-running release.
# lts - Check to see if a new LTS release is available. The upgrader
# will attempt to upgrade to the first LTS release available after
# the currently-running one. Note that if this option is used and
# the currently-running release is not itself an LTS release the
# upgrader will assume prompt was meant to be normal.
Prompt=never
アップデートの実行
do-release-upgrade
※ 心配なら下で確認することができます．
do-release-upgrade -c