1 $ sudo  apt-get update

报了一堆错误：

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

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

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

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

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

解决方案： 修改DNS

sudo vi  /etc/resolvconf/resolv.conf.d/base

在里面插入：

nameserver 8.8.8.8
nameserver 8.8.4.4

修改好保存!wq，
然后执行

$ sudo resolvconf -u

再看 /etc/resolv.conf，最下面就多了2行：

$ cat /etc/resolv.conf

　显示

# 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 8.8.8.8

nameserver 8.8.4.4

此时执行

$ sudo  apt-get update

可以运行，然后就可以使用sudo apt-get install **指令了。