在 Ubuntu 22.04 上面常常會遇到跑 apt upgrade 時系統跟你說有些 package 不打算升級：
$ sudo apt upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
python3-distupgrade ubuntu-release-upgrader-core ubuntu-release-upgrader-gtk
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
以往遇到這種情況，如果確定要裝就是開 dist-upgrade 下去，但會發現也還是不為所動：
$ sudo apt full-upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
python3-distupgrade ubuntu-release-upgrader-core ubuntu-release-upgrader-gtk
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
這個可能是遇到 PhasedUpdates，這個設計是在最後一關推出去的階段，一次不要更新 100% 的機器。
可以從 apt policy 看到現在的比率是 20%：(這是我已經升級上去的樣子)
$ apt policy python3-distupgrade
python3-distupgrade:
Installed: 1:22.04.18
Candidate: 1:22.04.18
Version table:
*** 1:22.04.18 500 (phased 20%)
500 http://tw.archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages
500 http://tw.archive.ubuntu.com/ubuntu jammy-updates/main i386 Packages
100 /var/lib/dpkg/status
1:22.04.10 500
500 http://tw.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
500 http://tw.archive.ubuntu.com/ubuntu jammy/main i386 Packages
而對於 LTS 的使用者，這個功能在 APT 的支援是從 Ubuntu 22.04 開始，以前只有桌面的 Update Manager 才有支援，所以不太會遇到：
Up to Focal (20.04), Update Manager is the only package manager that supports phased updates (reference). Any other update mechanism installs all updates regardless of the Phased-Update-Percentage.
(話說 wiki 頁上面可以看到有「User stories」這段，用 User story 的格式把這個功能的目的描述出來了)
所以一般人可以忽略掉，而對於有意願想要幫忙測試的人，也可以透過設定蓋過 Phased Updates 的比例設定...
