更新Ubuntu镜像源
1.备份镜像源：/etc/apt/sources.list
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
2.更新镜像源（不更新upgrade特别慢）
cat /etc/apt/sources.list
#
# deb cdrom:[Ubuntu-Server 14.04.4 LTS _Trusty Tahr_ - Release amd64 (20160217.1)]/ trusty main restricted
# deb cdrom:[Ubuntu-Server 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
## Uncomment the following two lines to add software from Ubuntu's
## 'extras' repository.
deb-src http://archive.ubuntu.com/ubuntu bionic main restricted #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ bionic universe
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates universe
deb http://mirrors.aliyun.com/ubuntu/ bionic multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse #Added by software-properties
deb http://archive.canonical.com/ubuntu bionic partner
deb-src http://archive.canonical.com/ubuntu bionic partner
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted multiverse universe #Added by software-properties
deb http://mirrors.aliyun.com/ubuntu/ bionic-security universe
deb http://mirrors.aliyun.com/ubuntu/ bionic-security multiverse
更新Ubuntu系统
1.查看当前版本：
buildfarm@xiaomi-master:~$ lsb_release -a
2.执行更新：
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade #可选
3.重启系统：
sudo reboot
4.升级系统：
do-release-upgrade
Note:升级会从14.04->16.04->18.04,不会一步完成！