安装软件时总是找不到软件包。。。听说要更新软件源。。
找了N个软件源，执行更新命令都出好多错。。。
这个终于没错了。。
使用ctrl+alt+T打开终端窗口，执行以下操作：
一、首先备份源列表：（好习惯）
sudo cp /etc/apt/sources.list /etc/apt/sources.list.old
二、打开源文件
sudo gedit /etc/apt/sources.list
三、将sources.list中的内容替换成下面的内容（全部覆盖）：
deb http://old-releases.ubuntu.com/ubuntu/ natty main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ natty main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
四、更新
sudo apt-get update
END.
-----------------------------------------------
之后由于安装 hotspot 时出问题了，又找到了一个可用的163的源：
# deb cdrom:[Ubuntu 14.04 LTS _Trusty Tahr_ - Release i386 (20140417)]/ trusty main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://mirrors.163.com/ubuntu/ trusty main restricted
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted
deb-src http://mirrors.163.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://mirrors.163.com/ubuntu/ trusty universe
deb-src http://mirrors.163.com/ubuntu/ trusty universe
deb http://mirrors.163.com/ubuntu/ trusty-updates universe
deb-src http://mirrors.163.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://mirrors.163.com/ubuntu/ trusty multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates multiverse
deb-src http://mirrors.163.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://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted
deb http://mirrors.163.com/ubuntu/ trusty-security universe
deb-src http://mirrors.163.com/ubuntu/ trusty-security universe
deb http://mirrors.163.com/ubuntu/ trusty-security multiverse
deb-src http://mirrors.163.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 main