所以我从镜像下载了apache spark，文件是：

spark-2.4.6-bin-hadoop2.7.tgz

我下载了密钥、.asc和.sha512文件。
我跑了：

gpg --import KEYS

然后我证实：

>gpg --verify spark-2.4.6-bin-hadoop2.7.tgz.asc spark-2.4.6-bin-hadoop2.7.tgz
gpg: Signature made Fri 29 May 20:02:32 2020 EDT
gpg:                using RSA key C41AB674424FC3FB
gpg: Good signature from "Holden Karau (CODE SIGNING KEY) <holden@apache.org>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: CA19 E2CC 201B 6522 D3A2  A05D C41A B674 424F C3FB

那么这个警告是关于什么的呢？那我该怎么做才对呢？