很多人选择CentOS源于他的开源、免费、可升级。我选择他最看重最后一点---可升级。开源不用说，linux嘛；免费，哈我是一个提倡盗版者；可升级这点可就是CentOS的绝对优势了，你可以像使用正版红帽一样！I love Red Hat,So I love CentOS.
闲话少叙，奔主题。使用yum安装软件，升级系统是非常方便的。但如果网速不行，或在学校（就像首师大）访问国外网成问题的，升级起来慢死。这样，最好更改yum镜像站点为中国站点地址，这里推荐。中国科技大学的镜像站点。（瞧人家多NB，人家那也是大学，再看...）。
修改/etc/yum.repos.d/CentOS-Base.repo
如下：
# CentOS-Base.repo
#
# This file uses a new mirrorlist system developed by Lance Davis for CentOS.
# 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-$releasever - Base
#mirrorlist=
baseurl=
gpgcheck=1
gpgkey=
#released updates
[updates]
name=CentOS-$releasever - Updates
#mirrorlist=
baseurl=
gpgcheck=1
gpgkey=
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
#mirrorlist=
baseurl=
gpgcheck=1
gpgkey=
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=
baseurl=
gpgcheck=1
gpgkey=
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#mirrorlist=
baseurl=
gpgcheck=1
enabled=0
gpgkey=
简单的说就是把mirrorlist注释掉，将baseurl改成ustc.edu.cn的镜像地址。
我实验没问题，有问题希望交流。
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