apt-get update failed. "Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake:
Debian apt 源更新， https 错误。
apt-get install ca-certificates
Ign:1 https://mirrors.tuna.tsinghua.edu.cn/debian stretch InRelease
Ign:2 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-updates InRelease
Hit:4 http://cdn-fastly.deb.debian.org/debian buster InRelease
Hit:5 http://cdn-fastly.deb.debian.org/debian buster-updates InRelease
Hit:3 http://security-cdn.debian.org/debian-security buster/updates InRelease
Ign:6 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports InRelease
Ign:7 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates InRelease
Err:8 https://mirrors.tuna.tsinghua.edu.cn/debian stretch Release
Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification. [IP: 101.6.8.193 443]
Err:9 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-updates Release
Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification. [IP: 101.6.8.193 443]
Err:10 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports Release
Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification. [IP: 101.6.8.193 443]
Err:11 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates Release
Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification. [IP: 101.6.8.193 443]
You can add [trusted=yes] in the sources.list. For example:
deb [trusted=yes] http://ppa.launchpad.net/repo_name/pkg/ubuntu vivid main
deb-src [trusted=yes] http://ppa.launchpad.net/repo_name/pkg/ubuntu vivid main
deb [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free
# deb-src [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free
deb [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free
# deb-src [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free
deb [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free
# deb-src [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free
deb [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates main contrib non-free
# deb-src [trusted=yes] https://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates main contrib non-free