sudo apt update

错误如下

Ign:1 http://security.ubuntu.com/ubuntu focal-security InRelease
Ign:2 http://us.archive.ubuntu.com/ubuntu focal InRelease          
Err:3 http://security.ubuntu.com/ubuntu focal-security Release     SECURITY: URL redirect target contains control characters, rejecting. [IP: 91.189.91.81 80]
Ign:4 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease  
Ign:5 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease
Err:6 http://us.archive.ubuntu.com/ubuntu focal ReleaseSECURITY: URL redirect target contains control characters, rejecting. [IP: 91.189.91.81 80]
Err:7 http://us.archive.ubuntu.com/ubuntu focal-updates ReleaseSECURITY: URL redirect target contains control characters, rejecting. [IP: 91.189.91.83 80]
Err:8 http://us.archive.ubuntu.com/ubuntu focal-backports ReleaseSECURITY: URL redirect target contains control characters, rejecting. [IP: 91.189.91.83 80]
Reading package lists... Done
E: The repository 'http://security.ubuntu.com/ubuntu focal-security Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu focal Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu focal-updates Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu focal-backports Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

--- > 换源后解决

换源方法如后面。

就换源就解决了，很简单

1，更换网络，改用手机连接

2，更换https软件软件源，比如清华的。

打开链接：https://mirror.tuna.tsinghua.edu.cn/help/ubuntu/

选择合适的ubuntu版本，更新仓库配置文件/etc/apt/sources.list。

mv /etc/apt/sources.list /etc/apt/sources.list_bak
vim /etc/apt/sources.list
 

refer https://blog.csdn.net/shangyexin/article/details/102657776