尝试使用apt-get更新您的Debian发行版时遇到以下问题？

# apt-get update
Ign:1 http://deb.debian.org/debian stretch InRelease
Hit:2 http://deb.debian.org/debian stretch Release
Ign:3 http://repo.r1soft.com/apt stable InRelease
Hit:4 http://repo.r1soft.com/apt stable Release
Hit:5 http://security.debian.org/debian-security stretch/updates InRelease
Ign:8 https://download.webmin.com/download/repository sarge InRelease
Hit:9 https://download.webmin.com/download/repository sarge Release
Err:11 https://packages.sury.org/php stretch InRelease
FailReason: ConnectionRefused
Reading package lists… Done
W: Failed to fetch https://packages.sury.org/php/dists/stretch/InRelease FailReason: ConnectionRefused
W: Some index files failed to download. They have been ignored, or old ones used instead.

在这种情况下，该apt仓库(packages.sury.org)上的pgp密钥被吊销/更改。
要解决此问题，您需要下载新密钥并按如下所示导入它：

wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg

这应该可以解决问题，您可以再次发出" apt-get update"命令进行测试。