CentOS 7 的安装：
使用powerISO将centos 7 镜像写入U盘。
使用U盘启动即可安装。
CentOS 7添加第三方yum源：
EPEL源：
键入指令：yum install epel*
查看是否安装成功：yum repolist
一般有类似如下输出：
repo id repo name status
base/7/x86_64 CentOS-7 - Base 8,465
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 7,192
extras/7/x86_64 CentOS-7 - Extras 104
google-chrome google-chrome 3
google64 Google - x86_64 3
updates/7/x86_64 CentOS-7 - Updates 1,668
repolist: 17,435
REMI源：
下载REMI
http://rpms.famillecollet.com/
vim remi.repo 将[remi] 中的 enabled=0 改成 enabled=1 来启用 remi 源
rpmforge源：
下载rpmforge:
在 http://apt.sw.be/redhat/el7/en/x86_64/rpmforge/RPMS/ 下搜索关键字rpmforge （在网页中搜索，快捷键为CTR-F） ，下载对应rpm包。
导入GPG key ： rpm --import http://apt.sw.be/RPM-GPG-KEY.dag.txt
rpmfusion源：
进入 http://rpmfusion.org/Configuration ，下载对应版本的rpm包安装。
其他较为少用的yum源：
Nux's repos: http://li.nux.ro/repos.html (这个源应该为个人或小众人员维护，最好用于个人娱乐。)
rpm --import http://li.nux.ro/download/nux/RPM-GPG-KEY-nux.ro
rpm -Uvh http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-1.el7.nux.noarch.rpm
ATrpms:
http://atrpms.net/
LON-CAPA
安装yum-priorities插件：yum install yum-plugin-priorities.noarch (在centos7中似乎可以不用安装，也可不配置)
当完成上面yum源的安装后，分别对/etc/yum.repos.d/ 下后缀为.repo的文件内容进行更改，
一般系统自带的.repo文件中priority=1，第三方yum源形成的.repo文件priority大于10。
例如：
CentOS-Base.repo(系统自带的.repo文件)
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#
[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
priority=1
#released updates
[updates]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
priority=1
...................
[rpmfusion-free-updates](第三方源形成的.repo文件)
name=RPM Fusion for EL 6 - Free - Updates
#baseurl=http://download1.rpmfusion.org/free/el/updates/6/$basearch/
mirrorlist=http://mirrors.rpmfusion.org/mirrorlist?repo=free-el-updates-released-6&arch=$basearch
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-rpmfusion-free-el-6
priority=14
[rpmfusion-free-updates-debuginfo]
name=RPM Fusion for EL 6 - Free - Updates Debug
#baseurl=http://download1.rpmfusion.org/free/el/updates/6/$basearch/debug/
mirrorlist=http://mirrors.rpmfusion.org/mirrorlist?repo=free-el-updates-released-debug-6&arch=$basearch
enabled=0
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-rpmfusion-free-el-6
priority=14
.............................