将服务器从 18.04 升级到 20.04 后，我得到了以下列表没有候选版本软件包。我该如何处理这份清单？是否应该移除并清理它们？
例如，我知道我不需要旧版本的 PHP 包，但是如果我遇到一些systemd-services我不知道的东西，我该如何检查这些是否是必需的，并在必要时安全地删除它们？
忽略此警告不会阻止升级完成。
No candidate ver: libxcb-util0
No candidate ver: libxmlada4.1
No candidate ver: libxmlada4.4.0
No candidate ver: libxp6
No candidate ver: libxtables10
No candidate ver: libyahoo2-11
No candidate ver: libzeroc-ice35
No candidate ver: linux-image-3.13.0-123-generic
No candidate ver: linux-image-3.13.0-48-generic
No candidate ver: linux-image-3.13.0-68-generic
No candidate ver: linux-image-4.4.0-121-generic
No candidate ver: linux-image-4.4.0-140-generic
No candidate ver: linux-image-4.4.0-178-generic
No candidate ver: linux-image-4.4.0-185-generic
No candidate ver: linux-image-4.4.0-83-generic
No candidate ver: linux-image-extra-4.4.0-121-generic
No candidate ver: linux-image-extra-4.4.0-140-generic
No candidate ver: linux-image-extra-4.4.0-83-generic
No candidate ver: linux-modules-4.4.0-178-generic
No candidate ver: linux-modules-4.4.0-185-generic
No candidate ver: linux-modules-extra-4.4.0-178-generic
No candidate ver: linux-modules-extra-4.4.0-185-generic
No candidate ver: lxc-common
No candidate ver: mountall
No candidate ver: mysql-server-5.5
No candidate ver: perl-modules
No candidate ver: php5-cli
No candidate ver: php5-common
No candidate ver: php5-curl
No candidate ver: php5-gd
No candidate ver: php5-intl
No candidate ver: php5-json
No candidate ver: php5-mcrypt
No candidate ver: php5-mysql
No candidate ver: php5-readline
No candidate ver: php7.0-bz2
No candidate ver: php7.0-cli
No candidate ver: php7.0-common
No candidate ver: php7.0-curl
No candidate ver: php7.0-gd
No candidate ver: php7.0-intl
No candidate ver: php7.0-json
No candidate ver: php7.0-mbstring
No candidate ver: php7.0-mcrypt
No candidate ver: php7.0-mysql
No candidate ver: php7.0-opcache
No candidate ver: php7.0-readline
No candidate ver: php7.0-xml
No candidate ver: php7.0-zip
No candidate ver: python3-aptdaemon.pkcompat
No candidate ver: python3.4
No candidate ver: python3.4-minimal
No candidate ver: python3.5-minimal
No candidate ver: ruby1.9.1
No candidate ver: systemd-services
No candidate ver: systemd-shim
No candidate ver: sysv-rc
No candidate ver: upstart
No candidate ver: webmin
正如评论中提到的，据我所知，这最初是一个 Ubuntu 14.04 服务器，并且已经升级到 16.04。
答案1
看起来这些是可以清除的旧的未使用的包：
sudo apt purge `dpkg --list | grep ^rc | awk '{ print $2; }'`
（我在这里找到了这个信息：https://butwt.wordpress.com/2020/06/29/problems-upgrading-ubuntu-server-lts/）
答案2
由于固定包裹，我遇到了这种情况。
在看/etc/apt/preferences.d/
Package: *该目录中的文件中类似行可能会导致 do-release-upgrade 出现问题