Ubuntu14出先W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/trusty/main/binary 4/Packages

在Ubuntu14.04 update的时候出现如下错误：

其中W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/main/source/Sources  Hash Sum mismatch 经过修改源解决：

sudo vim /etc/apt/sources.list

继续执行sudo apt-get update 出现

直接将这2个源注释掉，在执行update和upgrade就可

#deb http://extras.ubuntu.com/ubuntu trusty main
#deb-src http://extras.ubuntu.com/ubuntu trusty main