11.18 "apt-get update -u"时遭遇"There is no public key available for the following key IDs"

https://scz.617.cn/unix/200904201931.txt

Q:

# apt-get update -u
... ...
Reading package lists... Done
W: There is no public key available for the following key IDs:
4D270D06F42584E6
W: You may want to run apt-get update to correct these problems

A:

apt-get install debian-keyring debian-archive-keyring
apt-key update
apt-get update -u