示例为RHEL6.x RHEL5.X RHEL7.X步骤类似
RedHat系统非官方注册开发者使用官方自带yum源需要激活码，故换源为centos免费源
1.检查是否安装yum包 rpm -qa |grep yum
2.删除自带包 rpm -qa | grep yum | xargs rpm -e --nodeps
3.再检查一下确认卸载干净 rpm -qa |grep yum
4.下载以下更新包 在http://mirrors.163.com/centos/6/os/x86_64/Packages/网站中找以下rpm包
http://mirrors.163.com/centos/8/BaseOS/x86_64/os/Packages/
yum-xxx.el6.centos.noarch.rpm
yum-metadata-parser-xxx.el6.x86_64.rpm
yum-plugin-fastestmirror-xxx.el6.noarch.rpm
yum-updateonboot-xxx.el6.noarch.rpm
yum-utils-xxx.el6.noarch.rpm
python-iniparse-xxx.e16.noarch.rpm
python-urlgrabber-xxx.el6.noarch.rpm
注：xxx是该文件版本
注：python开头的两个rpm包可不下载，网上部分教程写需要但是目前测试发现可以不用下载安装这两个包
python-iniparse iniparse是Python的INI解析器
python-urlgrabber urlgrabber可以大大简化文件的获取。
yum-plugin-fastestmirror yum多个mirror自动选择速度最快的mirror,fastestmirror会自动选择最快的mirror
yum-metadata-parser yum的快速元数据解析器
yum-updateonboot 在系统启动时运行yum update(可能是做boot更新的包)
yum-utils 用于操作存储库和扩展包管理的工具
5.执行安装 rpm -ivh yum-*
注:可能出现类似问题：
①error: Failed dependencies:
python-urlgrabber >= 3.9.1-10 is needed by yum-3.2.29-73.el6.centos.noarch
解决策: rpm -Uvh python-urlgrabber-3.9.1-11.el6.noarch.rpm
更新rpm -Uvh python-urlgrabber版本
再执行： rpm -ivh yum-*
遇到类似问题：①rpm -Uvh 出问题的包名
②rpm -ivh yum-*
② warning: yum-3.4.3-161.el7.centos.noarch.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY
error: Failed dependencies:
rpm >= 0:4.11.3-22 is needed by yum-3.4.3-161.el7.centos.noarch
解决办法： rpm -ivh yum-3.4.3-161.el7.centos.noarch.rpm --nodeps --force
# 参数nodeps：忽略软件包的依赖关系强行安装
# 参数force：忽略软件包及文件的冲突
6. 切换源
①cd /etc/yum.repos.d/
②mv redhat.repo redhat.repo.bak
③mv rhel-source.repo rhel-source.repo.bak
④vi /etc/yum.repos.d/CentOS-Base.repo粘贴CentOS6中的内容
注：④步骤不同版本系统粘贴对应的文件内容
centos5
# CentOS-Base.repo
#
# 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/updates/$basearch/
baseurl=http://vault.centos.org/5.4/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
#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/$basearch/
baseurl=http://vault.centos.org/5.4/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
baseurl=http://vault.centos.org/5.4/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
baseurl=http://vault.centos.org/5.4/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
baseurl=http://vault.centos.org/5.4/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5centos6
# CentOS-Base.repo
#
# 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-6 - Base - 163.com
baseurl=http://mirrors.163.com/centos/6/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=os
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#released updates
[updates]
name=CentOS-6 - Updates - 163.com
baseurl=http://mirrors.163.com/centos/6/updates/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=updates
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional packages that may be useful
[extras]
name=CentOS-6 - Extras - 163.com
baseurl=http://mirrors.163.com/centos/6/extras/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=extras
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-6 - Plus - 163.com
baseurl=http://mirrors.163.com/centos/6/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=centosplus
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users
[contrib]
name=CentOS-6 - Contrib - 163.com
baseurl=http://mirrors.163.com/centos/6/contrib/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
centos7
[base]
name=CentOS-7 - Base
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos/7/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=os
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-7 - Updates
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos/7/updates/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=updates
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-7 - Extras
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos/7/extras/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=extras
gpgcheck=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-7 - Plus
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos/7/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=centosplus
gpgcheck=0
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-77. yum clean all
yum makecache
8、安装tree 或 vim或一些小的插件确认换源成功
yum install tree -y (yum install vim -y) yum install xxx -y
注：xxx是软件包名
9、换源后Red Hat编译和centos编译步骤相同