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                                            在ubuntu下执行sudo apt-get update时，经常会遇到报错：

Err http://security.ubuntu.com precise-security InRelease

Err http://security.ubuntu.com precise-security Release.gpg
  Temporary failure resolving 'security.ubuntu.com'
Err http://cn.archive.ubuntu.com precise InRelease

Err http://cn.archive.ubuntu.com precise-updates InRelease

Err http://cn.archive.ubuntu.com precise-backports InRelease

Err http://cn.archive.ubuntu.com precise Release.gpg
  Temporary failure resolving 'cn.archive.ubuntu.com'
Err http://cn.archive.ubuntu.com precise-updates Release.gpg
  Temporary failure resolving 'cn.archive.ubuntu.com'
Err http://cn.archive.ubuntu.com precise-backports Release.gpg
  Temporary failure resolving 'cn.archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/precise/InRelease  

W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/precise-updates/InRelease  

W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/precise-backports/InRelease  

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/precise-security/InRelease  

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/precise-security/Release.gpg  Temporary failure resolving 'security.ubuntu.com'

W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/precise/Release.gpg  Temporary failure resolving 'cn.archive.ubuntu.com'

W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/precise-updates/Release.gpg  Temporary failure resolving 'cn.archive.ubuntu.com'

W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/precise-backports/Release.gpg  Temporary failure resolving 'cn.archive.ubuntu.com'

W: Some index files failed to download. They have been ignored, or old ones used instead.12345678910111213141516171819202122232425262728293031323334

一般都会推荐使用国内的镜像源，比如163或者阿里云的镜像服务器 
将下列文本添加到/etc/apt/sources.list文件里

deb http://mirrors.aliyun.com/ubuntu/ raring main restricted universe multiverse  
deb http://mirrors.aliyun.com/ubuntu/ raring-security main restricted universe multiverse  
deb http://mirrors.aliyun.com/ubuntu/ raring-updates main restricted universe multiverse  
deb http://mirrors.aliyun.com/ubuntu/ raring-proposed main restricted universe multiverse  
deb http://mirrors.aliyun.com/ubuntu/ raring-backports main restricted universe multiverse  
deb-src http://mirrors.aliyun.com/ubuntu/ raring main restricted universe multiverse  
deb-src http://mirrors.aliyun.com/ubuntu/ raring-security main restricted universe multiverse  
deb-src http://mirrors.aliyun.com/ubuntu/ raring-updates main restricted universe multiverse  
deb-src http://mirrors.aliyun.com/ubuntu/ raring-proposed main restricted universe multiverse  
deb-src http://mirrors.aliyun.com/ubuntu/ raring-backports main restricted universe multiverse  12345678910

但是执行sudo apt-get update仍然报错，问题在于DNS没有配置好。 
解决方法：

sudo vi /etc/resolv.conf1

添加

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1
#这里用的是阿里云的DNS服务器
nameserver 223.5.5.5  
nameserver 223.6.6.6

之后执行sudo apt-get update就正常了。

参考： 
ubuntu apt-get update 失败解决。 
Ubuntu操作系统“Failed to fetch”错误的解决方法 
docker ubuntu容器更换阿里源
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原文链接：https://blog.csdn.net/feiniao8651/article/details/60332535