WSL Ubuntu 20.04执行sudo apt-get update时出现503 Service Unavailable错误求助

以下是针对该问题的可行解决方案：

• 切换WSL网络模式

  1. 打开PowerShell执行wsl --shutdown关闭所有WSL实例
  2. 在用户目录（C:\Users\<你的用户名>）下新建或编辑.wslconfig文件，添加以下内容：

     [wsl2]
     networkMode=mirrored
     

  3. 重启WSL后再次执行sudo apt-get update

• 重置WSL与Windows网络栈
  在PowerShell中依次执行以下命令，完成后重启电脑：

  netsh winsock reset
  netsh int ip reset all
  netsh winhttp reset proxy
  ipconfig /flushdns
  wsl --shutdown
  

• 改用HTTPS源
  编辑apt源配置文件：

  sudo nano /etc/apt/sources.list
  

  将文件中所有http://开头的源地址替换为https://，例如把http://archive.ubuntu.com/ubuntu改为https://archive.ubuntu.com/ubuntu。保存退出后执行sudo apt-get update。

• 重置apt缓存
  执行以下命令清除旧缓存并重新拉取索引：

  sudo apt-get clean
  sudo rm -rf /var/lib/apt/lists/*
  sudo apt-get update
  

• 排查防火墙/安全软件拦截
  暂时关闭Windows防火墙或第三方安全软件，测试是否能正常更新，确认是否存在网络拦截情况。

错误信息详情 #

Err:1 http://archive.ubuntu.com/ubuntu focal InRelease
      503  Service Unavailable [IP: 91.189.91.81 80]
Err:2 http://archive.ubuntu.com/ubuntu focal-updates InRelease
      503  Service Unavailable [IP: 91.189.91.81 80]
Err:3 http://security.ubuntu.com/ubuntu focal-security InRelease
      503  Service Unavailable [IP: 185.125.190.39 80]
Err:4 http://archive.ubuntu.com/ubuntu focal-backports InRelease
      503  Service Unavailable [IP: 91.189.91.81 80]
Reading package lists... Done
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal/InRelease  503  Service Unavailable [IP: 91.189.91.81 80]
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-updates/InRelease  503  Service Unavailable [IP: 91.189.91.81 80]
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-backports/InRelease  503  Service Unavailable [IP: 91.189.91.81 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/focal-security/InRelease  503  Service Unavailable [IP: 185.125.190.39 80]
W: Some index files failed to download. They have been ignored, or old ones used instead.

内容的提问来源于stack exchange，提问作者sebastian balcero