我从 Jessie 升级到 Debian Stretch：
cat /etc/issue
Debian GNU/Linux 9 \n \l
当我运行时，apt-get update
它仍然检查 jessie 来源：示例：
Ign:5 http://ftp.debian.org/debian jessie-backports/main Translation-de_DE
Ign:7 http://ftp.debian.org/debian jessie-backports/main Translation-de
Ign:10 http://ftp.debian.org/debian jessie-backports/main Translation-en
Ign:11 http://ftp.debian.org/debian jessie-backports/main all DEP-11 Metadata
Ign:13 http://ftp.debian.org/debian jessie-backports/main amd64 DEP-11 Metadata
Ign:14 http://ftp.debian.org/debian jessie-backports/main DEP-11 64x64 Icons
Ign:15 http://ftp.debian.org/debian jessie-backports/main DEP-11 128x128 Icons
我的 /etc/apt/sources.list 仅包含：
deb http://deb.debian.org/debian/ stretch main contrib non-free
deb http://deb.debian.org/debian/ stretch-updates main contrib non-free
deb http://deb.debian.org/debian-security/ stretch/updates main contrib non-free
我不明白为什么。
答案1
按照 AB 的建议，替换了 /etc/apt/sources.list.d/ 上所有文件的 debian 版本，它也解决了我的问题。