复制源文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup打开文件
sudo gedit /etc/apt/sources.list添加镜像源
#Ubuntu 官方源
deb http://archive.ubuntu.com/ubuntu/ gutsy main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ gutsy-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ gutsy-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ gutsy-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ gutsy main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ gutsy-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ gutsy-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ gutsy-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse
#阿里云
deb http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
#网易163
deb http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
#中科大
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-updates main restricted
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic universe
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-updates universe
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic multiverse
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-updates multiverse
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-backports main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-security main restricted
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-security universe
deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-security multiverse
deb http://archive.ubuntu.org.cn/ubuntu-cn/ feisty main restricted universe multiverse更新文件
sudo apt-get update
sudo apt-get dist-upgrade # 涉及核心的升级，通常会对系统功能产生实际的影响，可能在需要的情况下卸载一些已经安装的软件也可能安装一些额外的软件，通常应该谨慎操作，特别是有未完成的工作，但是在允许的情况下应该尽力升级，应为可能涉及一些重大的核心升级，比如安全。
sudo apt-get upgrade # 不会对系统产生重大的影响，可以在任何时候运行。
