Ubuntu新手执行sudo apt-get update时出现503服务不可用错误求助

问题重现 #

执行命令：

sudo apt-get update

出现以下错误输出：

Err:118 http://archive.ubuntu.com/ubuntu focal-backports/universe DEP-11 48x48 Icons  503  Service Unavailable [IP: 185.125.190.36 80]
Err:119 http://archive.ubuntu.com/ubuntu focal-backports/universe DEP-11 64x64 Icons  503  Service Unavailable [IP: 185.125.190.36 80]
Fetched 1213 kB in 13s (90.4 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-backports/universe/dep11/icons-48x48.tar  503  Service Unavailable [IP: 185.125.190.36 80]
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-backports/universe/dep11/icons-64x64.tar  503  Service Unavailable [IP: 185.125.190.36 80]
W: Some index files failed to download. They have been ignored, or old ones used instead.

此前多次执行apt-get update均出现类似503错误。

解决方案 #

1. 等待官方源恢复 #

503错误多为Ubuntu官方源的临时故障，间隔一段时间后重新执行更新命令即可：

sudo apt-get update

2. 更换国内镜像源 #

国内镜像源稳定性更强，以Ubuntu 20.04（focal）为例，操作步骤如下：

• 备份原源列表：

sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak

• 编辑源列表文件：

sudo nano /etc/apt/sources.list

• 将文件内容替换为阿里云镜像源（也可替换为清华、中科大等其他国内源）：

deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

• 保存退出（按Ctrl+O回车确认，再按Ctrl+X退出），重新执行更新：

sudo apt-get update

3. 临时禁用backports源（若无需使用） #

如果暂时不需要backports源的内容，可通过注释相关条目避免错误：

• 编辑源列表：

sudo nano /etc/apt/sources.list

• 找到所有包含focal-backports的行，在行首添加#注释掉，保存后执行更新：

sudo apt-get update

后续需要启用时，删除对应行首的#即可。

4. 清理APT缓存后重试 #

清理本地缓存，重新获取索引文件：

sudo apt-get clean
sudo apt-get update

内容的提问来源于stack exchange，提问作者Mmm Mmmm