在ubuntu更新时，出现错误E: Some index files Failed to download.They have been ignored,or old ones used instead.
在sudo apt-get update的时候出现了下列问题：
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.
所以在docker里面装Nginx的时候也出现问题：
root@0cc8c10d217a:~# apt-get install Nginx
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
Suggested packages:
fcgiwrap Nginx-doc
The following NEW packages will be installed:
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!
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?
因为刚刚换过apt-get源，所以百度了一下知道大概的做法是DNS出现了问题
应着重查看以下方面：
cat /etc/resolv.conf查看里面的domain,search和nameserver配置是否正确。
然后一看是DNS出现了问题，所以将nameserver修改成8.8.8.8后，问题得到了解决。
