Apt update Fail public key is not available

General Discussions
1

I tried to download ubuntu on docker and got the following error.
What is the solution?

Err:1 Index of /ubuntu jammy-security InRelease
The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 871920D1991BC93C

2

How did you try to download? What commands did you use?

3

Download the “Docker Quickstart Terminal” and start docker.
After that, I pulled and ran ubuntu.
The command is “apt update”.
I also typed “apt install gnupg” and got the following output

root@7ab3dedb2562:~# apt install gnupg
Reading package lists… Done
Building dependency tree… Done
Reading state information… Done
Package gnupg is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

4

(it’s) inexcusable
I retried the ubuntu version from 22.04 to 18.04 and the above error disappeared.