在 Ubuntu 系统中执行 sudo apt update 时，经常会遇到 Hash Sum mismatch（哈希值不匹配）错误，导致软件源索引下载失败。本文以 Ubuntu 22.04（jammy）为例，分享解决方案，核心是切换稳定的清华镜像源彻底解决该问题。
一、问题现象
执行 apt update 时出现如下报错，核心特征是 Hash Sum mismatch，提示下载的文件哈希值与服务器声明的不一致：
E: Failed to fetch
http://mirrors.aliyun.com/ubuntu/dists/jammy/universe/source/by-hash/SHA256/8f73d18065a4f05ee7362c50553ea4b26ca2b4b3786472676b6b1ee58b4cff72
Hash Sum mismatch Hashes expected file:
- SHA256:f73d18065a4f05ee7362c50553ea4b26ca2b4b3786472676b6b1ee58b4cff72
Hashes received file:
- SHA256:d071b2b37ce6c225da79f73684b8c56ddff86539e89f2c519208bcc2b9f1e59
Some index files failed download. They have been ignored, old ones used instead.
