1. 换源，sohu的相当好用。
1.1备份CentOS-Base.repo
cd /etc/yum.repos.d/
cp CentOS-Base.repo CentOS-Base.repo.bak
1.2替换源
用vi打开CentOS-Base.repo，并将内容清空，然后将下面的内容复制进去，并保存。
# 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-$releasever – Base
baseurl=http://mirrors.sohu.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.sohu.com/centos/RPM-GPG-KEY-CentOS-5
#released updates
[updates]
name=CentOS-$releasever – Updates
baseurl=http://mirrors.sohu.com/centos/$releasever/updates/$basearch/
gpgcheck=1