ubuntu sudo apt-get update 失敗 解決方法

sudo apt-get update

報了一堆錯誤：

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  

錯誤顯示了源有問題，好像是被牆了。

查找解決辦法，修改/etc/apt/source.list文件。將源改爲163的或者阿里的：

deb http://mirrors.163.com/ubuntu/ vivid main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-backports main restricted universe multiverse

可是source.list文件是隻讀的，修改不了。

要使用sudo gedit /etc/apt/source.list修改，可是gedit 指令沒有裝，使用sudo apt-get install gedit又安裝不了。

解決辦法：（修改DNS）

修改dns:

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

在裏面插入：
nameserver 8.8.8.8
nameserver 8.8.4.4

修改好保存!wq，

而後執行

sudo resolvconf -u

再看/etc/resolv.conf，最下面就多了2行：

cat /etc/resolv.conf

　顯示

# 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

此時執行

sudo apt-get update

能夠運行，而後就可使用sudo apt-get install **指令了。