• 备份原有的源列表文件（/etc/apt/sources.list.d/ubuntu.sources 备份为 /etc/apt/sources.list.d/ubuntu.sources.bak）

$ sudo cp /etc/apt/sources.list.d/ubuntu.sources /etc/apt/sources.list.d/ubuntu.sources.bak

• 编辑源列表文件（/etc/apt/sources.list.d/ubuntu.sources）

$ sudo nano /etc/apt/sources.list.d/ubuntu.sources

• 修改前（修改第二行 URIs:...）

Types: deb
URIs: http://archive.ubuntu.com/ubuntu/
Suites: noble noble-updates noble-backports
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

Types: deb
URIs: http://security.ubuntu.com/ubuntu/
Suites: noble-security
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

• 修改后（把 URIs: 后面的替换为：https://mirrors.tuna.tsinghua.edu.cn/ubuntu/  清华的源）

Types: deb
URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu/
Suites: noble noble-updates noble-backports
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

Types: deb
URIs: http://security.ubuntu.com/ubuntu/
Suites: noble-security
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

• 保存退出后，运行

$ sudo apt update -y && sudo apt upgrade -y

完成