报错问题展示：[root@NISEC-6601 yum]# yum clean all
bash: yum: 未找到命令...
或者
无法使用YUM源的问题如下：
[root@localhost ~]# yum repolist
已加载插件：product-id, search-disabled-repos, subscription-manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
repolist: 0
[root@localhost ~]#
[root@localhost ~]#
[root@localhost ~]# yum install ntp
已加载插件：product-id, search-disabled-repos, subscription-manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
There are no enabled repos.
Run "yum repolist all" to see the repos you have.
To enable Red Hat Subscription Management repositories:
subscription-manager repos --enable
To enable custom repositories:
yum-config-manager --enable
解决方法：
1.# 清除原有RHEL的YUM及相关软件包
rpm -qa|grep yum|xargs rpm -e --nodeps
rpm -qa|grep python-urlgrabber|xargs rpm -e --nodeps
2.# 软件包下载地址
# https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/
# http://mirrors.163.com/centos/7/os/x86_64/Packages/
下载centos7的相关软件包
http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-4.11.3-45.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm
上传软件包到rhel7.3系统里
安装软件包
注：yum-plugin-fastestmirror和yum两个rpm要一起安装，不能拆开。
rpm -ivh python-iniparse-0.4-9.el7.noarch.rpm
rpm -ivh python-urlgrabber-3.10-10.el7.noarch.rpm
rpm -ivh yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
rpm -ivh yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm yum-3.4.3-168.el7.centos.noarch.rpm
问题1
错误：依赖检测失败：
rpm >= 0:4.11.3-22 被 yum-3.4.3-158.el7.centos.noarch 需要
yum >= 3.0 被 yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch 需要
解决：,升级rpm，上一步已经下载了，直接升级
rpm -Uvh rpm-4.11.3-45.el7.x86_64.rpm --nodeps
下载配置文件
wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
vi CentOS-Base.repo //编辑文件
把文件中所有$releasever改为7，$basearch保持不变
然后将此配置文件上传并复制到/etc/yum.repos.d/路径下，删除redhat.repo文件
[root@localhost etc]# cd yum.repos.d
[root@localhost yum.repos.d]# ls
CentOS-Base.repo redhat.repo
[root@localhost yum.repos.d]# rm redhat.repo
rm：是否删除普通文件 "redhat.repo"？y
[root@localhost yum.repos.d]# ls
CentOS-Base.repo
[root@localhost yum.repos.d]# vi CentOS-Base.repo
[root@localhost yum.repos.d]# yum clean all
1、$releasever
$releasever的值，当前系统的发行版本。是指大版本7
2、$basearch
$basearch的值，系统硬件架构(CPU指令集)
查看命令：arch，结果是x86_64
删除/var/cache/yum/下的x86_64目录
[root@localhost yum.repos.d]# cd /var/cache/yum/
[root@localhost yum]# ls
x86_64
[root@localhost yum]# rm -rf x86_64
[root@localhost yum]# ls
清理yum缓存: yum clean all
将服务器软件包信息缓存至本地，提高搜索安装效率：yum makecache
测试：
能搜索到软件包信息，说明配置完成：
yum search vim
执行yum repolist查看，如果显示出repo仓库列表，并显示软件包数量则OK。（或者使用yum makecache）：
yum repolist
使用yum安装软件包测试：
yum -y install vim
