我正在使用python37作為基礎映象製作專案映象，但構建過程中執行apt-get update時出現GPG簽名錯誤

本地作業系統為Mac OS，docker 環境為desktop for docker ：

Docker version 20.10.7, build f0df350

錯誤詳情：

Err:1 http://ports.ubuntu.com/ubuntu-ports focal InRelease
  At least one invalid signature was encountered.
Get:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease [107 kB]
 

Err:2 http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease
  At least one invalid signature was encountered.
Err:3 http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease
  At least one invalid signature was encountered.
Err:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease
  At least one invalid signature was encountered.
Reading package lists... Done
W: GPG error: http:
 
//ports.ubuntu.com/ubuntu-ports focal InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for
 
 repository creation and user configuration details.
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

解決方案：

docker image prune -a

會清理一些映象，然後再進行構建，就沒有報錯了

參考文章：stackoverflow