更新
sudo apt update && sudo apt upgrade
更新之后可能需要重启：
sudo reboot
升级
默认升级时会禁用第三方源，如果设置了第三方源可以使用RELEASE_UPGRADER_ALLOW_THIRD_PARTY保留：
RELEASE_UPGRADER_ALLOW_THIRD_PARTY=1 do-release-upgrade -d
修复APT更新问题
如果遇到提示“Missing Signed-By in the sources.list(5) entry for …”
先删除原本的源：
sudo rm /etc/apt/sources.list
sudo rm /etc/apt/sources.list.d/third-party.sources
新建DEB822格式的源（Ubuntu 的软件源配置文件变更为 DEB822 格式）：
sudo nano /etc/apt/sources.list.d/ubuntu.sources
可以使用清华TUNA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
# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
# Types: deb-src
# 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
# 以下安全更新软件源包含了官方源与镜像站配置，如有需要可自行修改注释切换
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
# Types: deb-src
# URIs: http://security.ubuntu.com/ubuntu/
# Suites: noble-security
# Components: main restricted universe multiverse
# Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
# 预发布软件源，不建议启用
# Types: deb
# URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu
# Suites: noble-proposed
# Components: main restricted universe multiverse
# Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
# # Types: deb-src
# # URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu
# # Suites: noble-proposed
# # Components: main restricted universe multiverse
# # Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
如果是Ubuntu Ports源（ARM (arm64, armhf)、PowerPC (ppc64el)、RISC-V (riscv64)和S390x等架构）：
Types: deb
URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports
Suites: noble noble-updates noble-backports
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
Types: deb-src
URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports
Suites: noble noble-updates noble-backports
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
# 以下安全更新软件源包含了官方源与镜像站配置，如有需要可自行修改注释切换
Types: deb
URIs: http://ports.ubuntu.com/ubuntu-ports/
Suites: noble-security
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Types: deb-src
URIs: http://ports.ubuntu.com/ubuntu-ports/
Suites: noble-security
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
# 预发布软件源，不建议启用
# Types: deb
# URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports
# Suites: noble-proposed
# Components: main restricted universe multiverse
# Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
# Types: deb-src
# URIs: https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports
# Suites: noble-proposed
# Components: main restricted universe multiverse
# Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg