其实，解决这个问题十分简单，只要设置妥当DNS服务器即可，如电信网络的设置如下所示。
$ sudo vi /etc/resolv.conf
再次执行sudo apt-get update命令，结果一切正常
Hit http://archive.ubuntu.com precise-proposed/restricted TranslationIndex
Hit http://archive.ubuntu.com precise-proposed/universe TranslationIndex
Hit http://archive.ubuntu.com precise/main Translation-en
Hit http://archive.ubuntu.com precise/multiverse Translation-en
Hit http://archive.ubuntu.com precise/restricted Translation-en
Hit http://archive.ubuntu.com precise/universe Translation-en
Hit http://archive.ubuntu.com precise-updates/main Translation-en
Hit http://archive.ubuntu.com precise-updates/multiverse Translation-en
Hit http://archive.ubuntu.com precise-updates/restricted Translation-en
Hit http://archive.ubuntu.com precise-updates/universe Translation-en
Hit http://archive.ubuntu.com precise-security/main Translation-en
Hit http://archive.ubuntu.com precise-security/multiverse Translation-en
Hit http://archive.ubuntu.com precise-security/restricted Translation-en
Hit http://archive.ubuntu.com precise-security/universe Translation-en
Hit http://archive.ubuntu.com precise-backports/main Translation-en
Hit http://archive.ubuntu.com precise-backports/multiverse Translation-en
Hit http://archive.ubuntu.com precise-backports/restricted Translation-en
Hit http://archive.ubuntu.com precise-backports/universe Translation-en
Hit http://archive.ubuntu.com precise-proposed/main Translation-en
Hit http://archive.ubuntu.com precise-proposed/multiverse Translation-en
Hit http://archive.ubuntu.com precise-proposed/restricted Translation-en
Hit http://archive.ubuntu.com precise-proposed/universe Translation-en
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