There are no enabled repos. Run “yum repolist all“ to see the repos you have.解决办法

原因 ：是因为没有repo 文件 ，进入到 /etc/yum.repos.d/ 目录下，只有 redhat.repo 文件 ，且文件内容为空，下载对应版本repo文件, 放入/etc/yum.repos.d/里，下载地址：http://mirrors.163.com/.help/centos.html

[root@master yum.repos.d]# more redhat.repo 
#
# Certificate-Based Repositories
# Managed by (rhsm) subscription-manager
#
# *** This file is auto-generated.  Changes made here will be over-written. ***
# *** Use "subscription-manager repo-override --help" if you wish to make changes. ***
#
# If this file is empty and this system is subscribed consider
# a "yum repolist" to refresh available repos
#

[root@master yum.repos.d]# more CentOS7-Base-163.repo 
# 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-7 - Base - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=os
baseurl=http://mirrors.163.com/centos/7/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#released updates
[updates]
name=CentOS-7 - Updates - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=updates
baseurl=http://mirrors.163.com/centos/7/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#additional packages that may be useful
[extras]
name=CentOS-7 - Extras - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=7&arch=$basearch&repo=extras
baseurl=http://mirrors.163.com/centos/7/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-7 - Plus - 163.com
baseurl=http://mirrors.163.com/centos/7/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

再次执行 ，报了  [Errno 14] HTTP Error 404 - Not Found 错误。

[root@master yum.repos.d]#  yum install -y yum-utils device-mapper-persistent-data     lvm2 bash-completion
Loaded plugins: product-id, search-disabled-repos
http://mirrors.163.com/centos/7Server/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

将 CentOS7-Base-163.repo  文件中的 $releasever 用 7 替代（我的系统是redhat 7）。再次执行正常