首先用终端进行root登录：
sudo -i
再切换到/etc/apt/目录下，执行：
cd /etc/apt/
- 第一步，备份官方的默认源
避免自己手贱操作失误，重装系统太费时间
cp /etc/apt/sources.list /etc/apt/sources.list.bak #此命令是备份该官方源文件
Ubuntu 14.04.4官方默认更新源sources.list
# deb cdrom:[Ubuntu 14.04.4 LTS _Trusty Tahr_ - Release amd64 (20160217.1)]/ trusty main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ trusty main restricted
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://cn.archive.ubuntu.com/ubuntu/ trusty universe
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty universe
deb http://cn.archive.ubuntu.com/ubuntu/ trusty-updates universe
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://cn.archive.ubuntu.com/ubuntu/ trusty multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://cn.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu trusty-security main restricted
deb-src http://security.ubuntu.com/ubuntu trusty-security main restricted
deb http://security.ubuntu.com/ubuntu trusty-security universe
deb-src http://security.ubuntu.com/ubuntu trusty-security universe
deb http://security.ubuntu.com/ubuntu trusty-security multiverse
deb-src http://security.ubuntu.com/ubuntu trusty-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu trusty partner
# deb-src http://archive.canonical.com/ubuntu trusty partner
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu trusty main
deb-src http://extras.ubuntu.com/ubuntu trusty mainUbuntu 16.04官方默认更新源sources.list
#deb cdrom:[Ubuntu 16.04.1 LTS _Xenial Xerus_ - Release amd64 (20160719)]/ xenial main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ xenial main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://cn.archive.ubuntu.com/ubuntu/ xenial universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial universe
deb http://cn.archive.ubuntu.com/ubuntu/ xenial-updates universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates universe- 第二步，修改官方源为第三方源
sudo vim /etc/apt/sources.list
附赠网上多数人推荐的第三方源：
- 中科大源：
deb http://mirrors.ustc.edu.cn/ubuntu/ precise-updates main restricted
deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-updates main restricted
deb http://mirrors.ustc.edu.cn/ubuntu/ precise universe
deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise universe
deb http://mirrors.ustc.edu.cn/ubuntu/ precise-updates universe
deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-updates universe
deb http://mirrors.ustc.edu.cn/ubuntu/ precise multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ precise-updates multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-updates multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu precise-security main restricted
deb-src http://security.ubuntu.com/ubuntu precise-security main restricted
deb http://security.ubuntu.com/ubuntu precise-security universe
deb-src http://security.ubuntu.com/ubuntu precise-security universe
deb http://security.ubuntu.com/ubuntu precise-security multiverse
deb-src http://security.ubuntu.com/ubuntu precise-security multiverse- 搜狐源
deb http://mirrors.sohu.com/ubuntu/ precise-updates main restricted
deb-src http://mirrors.sohu.com/ubuntu/ precise-updates main restricted
deb http://mirrors.sohu.com/ubuntu/ precise universe
deb-src http://mirrors.sohu.com/ubuntu/ precise universe
deb http://mirrors.sohu.com/ubuntu/ precise-updates universe
deb-src http://mirrors.sohu.com/ubuntu/ precise-updates universe
deb http://mirrors.sohu.com/ubuntu/ precise multiverse
deb-src http://mirrors.sohu.com/ubuntu/ precise multiverse
deb http://mirrors.sohu.com/ubuntu/ precise-updates multiverse
deb-src http://mirrors.sohu.com/ubuntu/ precise-updates multiverse
deb http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse- 网易源
deb http://mirrors.163.com/ubuntu/ precise-updates main restricted
deb-src http://mirrors.163.com/ubuntu/ precise-updates main restricted
deb http://mirrors.163.com/ubuntu/ precise universe
deb-src http://mirrors.163.com/ubuntu/ precise universe
deb http://mirrors.163.com/ubuntu/ precise-updates universe
deb-src http://mirrors.163.com/ubuntu/ precise-updates universe
deb http://mirrors.163.com/ubuntu/ precise multiverse
deb-src http://mirrors.163.com/ubuntu/ precise multiverse
deb http://mirrors.163.com/ubuntu/ precise-updates multiverse
deb-src http://mirrors.163.com/ubuntu/ precise-updates multiverse
deb http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse阿里云源
# deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricted
deb-src http://archive.ubuntu.com/ubuntu xenial main restricted #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial universe
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe
deb http://mirrors.aliyun.com/ubuntu/ xenial multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse #Added by software-properties
deb http://archive.canonical.com/ubuntu xenial partner
deb-src http://archive.canonical.com/ubuntu xenial partner
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe
deb http://mirrors.aliyun.com/ubuntu/ xenial-security multiverse大家，有时候，需要把http改成https
然后，大家可以像我这样，来做好备份，有时候，会因为网络问题，需要用到不同的源，好切换！
/etc/apt/sources.list #（比如，这是官方的源）
/etc/apt/sources.list.qinghua #（比如，这是清华的源）
/etc/apt/sources.list.zhongkeda #（比如，这是中科大的源）
/etc/apt/sources.list.sohu #（比如，这是搜狐的源）
/etc/apt/sources.list.wangyi #（比如，这是网易的源）
/etc/apt/sources.list.aliyun #（比如，这是阿里云的源）
然后，需要用到哪个了，在比如，我需要用到清华源，则，
mv sources.list.qinghua sources.list
然后，把官方的源，暂时改为
mv sources.list sources.list.bak
保存后之后回到命令行下执行命令：
apt-get update && apt-get upgrade && apt-get dist-upgrade
apt-get clean #删除以下载的包
reboot #重新启动
这样应该就没问题了
备注：
apt-get常用命令:
update – 取回更新的软件包列表信息
upgrade – 进行一次升级
install – 安装新的软件包(注：软件包名称是 libc6 而非 libc6.deb)
remove – 卸载软件包
purge – 卸载并清除软件包的配置
autoremove – 卸载所有自动安装且不再使用的软件包
dist-upgrade – 发布版升级，见 apt-get(8)
dselect-upgrade – 根据 dselect 的选择来进行升级
build-dep – 为源码包配置所需的编译依赖关系
clean – 删除所有已下载的包文件
autoclean – 删除已下载的旧包文件
check – 核对以确认系统的依赖关系的完整性
source – 下载源码包文件
download – 下载指定的二进制包到当前目录
changelog – 下载指定软件包，并显示其changelog