ubuntu 1804.1 升级失败：Hash Sum mismatch

20191224 本地虚拟机 ubuntu 1804.1 很久没用，先升级一下 ubuntu ，结果遇到问题，升不上去！

$ cat /etc/issue
Ubuntu 18.04.1 LTS \n \l

照例，sudo apt update & sudo apt upgrade ，但是 update 就出错了！

sudo apt update
错误如下

…
Reading package lists… Done
E: Failed to fetch http://mirrors.aliyun.com/ubuntu/dists/bionic-updates/main/binary-amd64/by-hash/SHA256/1fc26aa9068c94f64aaf27415e896356f170c8f2c2b9d952a7354773f82d389c Hash Sum mismatch
Hashes of expected file:
- Filesize:816660 [weak]
- SHA256:1fc26aa9068c94f64aaf27415e896356f170c8f2c2b9d952a7354773f82d389c
- SHA1:b790e96ef8a8c656bd539b8d7072efeb91d53275 [weak]
- MD5Sum:d59679d8b7bda2355df95e51adce4e09 [weak]
Hashes of received file:
- SHA256:a2b9d89caf25fb7a3ae8267edac104b495790a43b86d98971d123d7f3f11b582
- SHA1:ca06617424e81168a43d285f7509aba8eeb31b46 [weak]
- MD5Sum:86fbe9596b0466ec6919576f0290a6eb [weak]
- Filesize:816660 [weak]
Last modification reported: Sat, 21 Dec 2019 18:59:02 +0000
Release file created at: Tue, 24 Dec 2019 17:14:40 +0000
E: Some index files failed to download. They have been ignored, or old ones used instead.

2、按照建议，尝试修复

sudo apt clean
sudo apt update --fix-missing
之后，还是一样的错误

3、换个源试试

目前一直使用的是阿里云的源，换成清华的试试！
找到一个很全的国内源
https://blog.csdn.net/xiefeisd/article/details/86663243

sudo vim sources.list
删除原来的阿里云源，复制清华的源

再来
sudo apt update
ok！不报错误了！

其中，中途有个提示
 The default action is to keep your current version.
*** cloud.cfg (Y/I/N/O/D/Z) [default=N] ? 

*** 直接回车使用缺省，也就是保持当前的 cloud.cfg 版本

sudo apt upgrade
完成！

$ cat /etc/issue
Ubuntu 18.04.3 LTS \n \l

** 升级之后，无需重启（reboot）！