17:37UTC:root@bard:~# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.5 LTS
Release: 18.04
Codename: bionic
17:38UTC:root@bard:~# do-release-upgrade
Checking for a new Ubuntu release
There is no development version of an LTS available.
To upgrade to the latest non-LTS develoment release
set Prompt=normal in /etc/update-manager/release-upgrades.`
アップグレード マネージャーに、LTS の「開発」バージョンは利用できないと表示されるのはなぜですか?
17:41UTC:root@bard:~# cat /etc/update-manager/release-upgrades
# 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=lts
このシステムには、汎用ファイル（のように見えます）があります/etc/apt/sources.list。さまざまなubuntu.comBionic リポジトリを指します。
??
答え1
ああ! 特別な状況: Canonical が Focal を保留している重大なバグ。「ポイント」リリース (20.04.01) はリリースされていますが、18.04LTS からのアップグレード用にはまだ「リリース」されていません。
https://discourse.ubuntu.com/t/focal-fossa-20-04-1-lts-point-release-status-tracking/17604