（問題解決篇）ubuntu更新時，出現錯誤E: Some index files failed to download。。。

在ubuntu更新時，出現錯誤E: Some index files failed to download.They have been ignored, or old ones used instead.
在sudo apt-get update的時候出現了下列問題：

root@0cc8c10d217a:~# sudo apt-get update

sudo: unable to resolve host 0cc8c10d217a

Err http://archive.ubuntu.com trusty InRelease

  

Err http://archive.ubuntu.com trusty-security InRelease

  

Err http://archive.ubuntu.com trusty-updates InRelease

  

Err http://archive.ubuntu.com trusty-proposed InRelease

  

Err http://archive.ubuntu.com trusty-backports InRelease

  

Err http://archive.ubuntu.com trusty Release.gpg

  Could not resolve 'archive.ubuntu.com'

Err http://archive.ubuntu.com trusty-security Release.gpg

  Could not resolve 'archive.ubuntu.com'

Err http://archive.ubuntu.com trusty-updates Release.gpg

  Could not resolve 'archive.ubuntu.com'

Err http://archive.ubuntu.com trusty-proposed Release.gpg

  Could not resolve 'archive.ubuntu.com'

Err http://archive.ubuntu.com trusty-backports Release.gpg

  Could not resolve 'archive.ubuntu.com'

Reading package lists... Done

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty/InRelease  

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

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

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-proposed/InRelease  

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

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty/Release.gpg  Could not resolve 'archive.ubuntu.com'

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-security/Release.gpg  Could not resolve 'archive.ubuntu.com'

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-updates/Release.gpg  Could not resolve 'archive.ubuntu.com'

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-proposed/Release.gpg  Could not resolve 'archive.ubuntu.com'

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-backports/Release.gpg  Could not resolve 'archive.ubuntu.com'

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

因此在docker裏面裝nginx的時候也出現問題：

root@0cc8c10d217a:~# apt-get install  nginx

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following extra packages will be installed:

  nginx-common nginx-core

Suggested packages:

  fcgiwrap nginx-doc

The following NEW packages will be installed:

  nginx nginx-common nginx-core

0 upgraded, 3 newly installed, 0 to remove and 241 not upgraded.

Need to get 349 kB of archives.

After this operation, 1,300 kB of additional disk space will be used.

Do you want to continue? [Y/n] Y

WARNING: The following packages cannot be authenticated!

  nginx-common nginx-core nginx

Install these packages without verification? [y/N] Y

Err http://archive.ubuntu.com/ubuntu/ trusty-updates/main nginx-common all 1.4.6-1ubuntu3.7

  Could not resolve 'archive.ubuntu.com'

Err http://archive.ubuntu.com/ubuntu/ trusty-updates/main nginx-core amd64 1.4.6-1ubuntu3.7

  Could not resolve 'archive.ubuntu.com'

Err http://archive.ubuntu.com/ubuntu/ trusty-updates/main nginx all 1.4.6-1ubuntu3.7

  Could not resolve 'archive.ubuntu.com'

E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/n/nginx/nginx-common_1.4.6-1ubuntu3.7_all.deb  Could not resolve 'archive.ubuntu.com'

E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/n/nginx/nginx-core_1.4.6-1ubuntu3.7_amd64.deb  Could not resolve 'archive.ubuntu.com'

E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/n/nginx/nginx_1.4.6-1ubuntu3.7_all.deb  Could not resolve 'archive.ubuntu.com'

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

由於剛剛換過apt-get源 ，因此百度了一下知道大概的作法是DNS出現了問題

應着重查看如下方面：
cat /etc/resolv.conf查看裏面的domain, search和nameserver配置是否正確。
而後一看是DNS出現了問題，因此將nameserver修改爲8.8.8.8後，問題獲得瞭解決。