公司的一台电脑，操作系统为Ubuntu 14.04 LTS，默认的语言为英语。
通过远程连接到终端，执行更新命令：
admin@lnxServer:~$ sudo apt update
[sudo] password for admin:
Err http://us.archive.ubuntu.com trusty InRelease
Err http://us.archive.ubuntu.com trusty-updates InRelease
Err http://us.archive.ubuntu.com trusty-backports InRelease
Err http://security.ubuntu.com trusty-security InRelease
Err http://us.archive.ubuntu.com trusty Release.gpg
Could not resolve 'us.archive.ubuntu.com'
Err http://us.archive.ubuntu.com trusty-updates Release.gpg
Could not resolve 'us.archive.ubuntu.com'
Err http://security.ubuntu.com trusty-security Release.gpg
Could not resolve 'security.ubuntu.com'
Err http://us.archive.ubuntu.com trusty-backports Release.gpg
Could not resolve 'us.archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty/InRelease
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-updates/InRelease
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-backports/InRelease
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/InRelease
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty/Release.gpg Could not resolve 'us.archive.ubuntu.com'
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-updates/Release.gpg Could not resolve 'us.archive.ubuntu.com'
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-backports/Release.gpg Could not resolve 'us.archive.ubuntu.com'
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/Release.gpg Could not resolve 'security.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.
怀疑是更新源的问题，于是更改更新源：
$ sudo nano /etc/apt/sources.list
添加国内的163源，更新，依旧出错。
添加阿里云的源，更新，仍然出错。
考虑是DNS的问题。
$ sudo vi /etc/resolv.conf
公司的DNS为210.21.196.6，保存。
执行更新：
admin@lnxServer:/etc/apt$ sudo apt-get update
Ign http://us.archive.ubuntu.com trusty InRelease
Hit http://us.archive.ubuntu.com trusty-updates InRelease
Hit http://us.archive.ubuntu.com trusty-backports InRelease
Hit http://us.archive.ubuntu.com trusty Release.gpg
Hit http://us.archive.ubuntu.com trusty-updates/main Sources
Hit http://us.archive.ubuntu.com trusty-updates/restricted Sources
Hit http://us.archive.ubuntu.com trusty-updates/universe Sources
Hit http://us.archive.ubuntu.com trusty-updates/multiverse Sources
Hit http://us.archive.ubuntu.com trusty-updates/main amd64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/restricted amd64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/universe amd64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/multiverse amd64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/main i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/restricted i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/universe i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/multiverse i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/main Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/multiverse Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/universe Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/main Sources
Hit http://us.archive.ubuntu.com trusty-backports/restricted Sources
Hit http://us.archive.ubuntu.com trusty-backports/universe Sources
Hit http://us.archive.ubuntu.com trusty-backports/multiverse Sources
Hit http://us.archive.ubuntu.com trusty-backports/main amd64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/restricted amd64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/universe amd64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/multiverse amd64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/main i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/restricted i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/universe i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/multiverse i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/main Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/multiverse Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/restricted Translation-en
Hit http://security.ubuntu.com trusty-security InRelease
Hit http://security.ubuntu.com trusty-security/main Sources
Hit http://us.archive.ubuntu.com trusty-backports/universe Translation-en
Hit http://security.ubuntu.com trusty-security/restricted Sources
Hit http://us.archive.ubuntu.com trusty Release
Hit http://security.ubuntu.com trusty-security/universe Sources
Hit http://security.ubuntu.com trusty-security/multiverse Sources
Hit http://us.archive.ubuntu.com trusty/main Sources
Hit http://security.ubuntu.com trusty-security/main amd64 Packages
Hit http://us.archive.ubuntu.com trusty/restricted Sources
Hit http://security.ubuntu.com trusty-security/restricted amd64 Packages
Hit http://security.ubuntu.com trusty-security/universe amd64 Packages
Hit http://security.ubuntu.com trusty-security/multiverse amd64 Packages
Hit http://us.archive.ubuntu.com trusty/universe Sources
Hit http://security.ubuntu.com trusty-security/main i386 Packages
Hit http://security.ubuntu.com trusty-security/restricted i386 Packages
Hit http://us.archive.ubuntu.com trusty/multiverse Sources
Hit http://security.ubuntu.com trusty-security/universe i386 Packages
Hit http://security.ubuntu.com trusty-security/multiverse i386 Packages
Hit http://security.ubuntu.com trusty-security/main Translation-en
Get:1 http://security.ubuntu.com trusty-security/multiverse Translation-en [2,570 B]
Hit http://security.ubuntu.com trusty-security/restricted Translation-en
Get:2 http://security.ubuntu.com trusty-security/universe Translation-en [75.8 kB]
Hit http://us.archive.ubuntu.com trusty/main amd64 Packages
Hit http://us.archive.ubuntu.com trusty/restricted amd64 Packages
Hit http://us.archive.ubuntu.com trusty/universe amd64 Packages
Hit http://us.archive.ubuntu.com trusty/multiverse amd64 Packages
Hit http://us.archive.ubuntu.com trusty/main i386 Packages
Hit http://us.archive.ubuntu.com trusty/restricted i386 Packages
Hit http://us.archive.ubuntu.com trusty/universe i386 Packages
Hit http://us.archive.ubuntu.com trusty/multiverse i386 Packages
Hit http://us.archive.ubuntu.com trusty/main Translation-en
Hit http://us.archive.ubuntu.com trusty/multiverse Translation-en
Hit http://us.archive.ubuntu.com trusty/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty/universe Translation-en
Ign http://us.archive.ubuntu.com trusty/main Translation-en_US
Ign http://us.archive.ubuntu.com trusty/multiverse Translation-en_US
Ign http://us.archive.ubuntu.com trusty/restricted Translation-en_US
Ign http://us.archive.ubuntu.com trusty/universe Translation-en_US
Fetched 78.4 kB in 38s (2,053 B/s)
Reading package lists... Done
可以正常更新了。