1.查看RHEL是否安装了yum：
rpm -qa |grep yum
2 删除redhat自带的yum包：
rpm -qa|grep yum|xargs rpm -e --nodeps（不检查依赖，直接删除rpm包）
rpm -qa |grep yum
3.下载新的yum包。使用Centos7的yum包：
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-161.el7.centos.noarch.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-50.el7.noarch.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-9.el7.noarch.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-chardet-2.2.1-1.el7_1.noarch.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
rpm -ivh python-urlgrabber-3.10-9.el7.noarch.rpm
rpm -ivh python-chardet-2.2.1-1.el7_1.noarch.rpm
rpm -ivh python-kitchen-1.1.1-5.el7.noarch.rpm
rpm -ivh yum-metadata-parser-1.1.4-10.el7.x86_64.rpm yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm yum-utils-1.1.31-50.el7.noarch.rpm yum-3.4.3-161.el7.centos.noarch.rpm
4.更换yum源。使用阿里云的源
cd /etc/yum.repos.d
mv redhat.repo redhat.repo.bak
CentOS 7wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo修改CentOS-Base.repo文件中的$releasever全部替换为版本号 7
mv CentOS-Base.repo redhat.repo
运行yum makecache生成缓存
yum clean all
yum makecache
yum update