This system is not registered with an entitlement server. You can use subscription-manager to register.

错误信息

[root@bogon apache-tomcat-7.0.70]# yum install gcc-c++
Loaded plugins: 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 <repo>
 To enable custom repositories:
     yum-config-manager --enable <repo>

解决方法

1、查看redhat 7.0系统本身所安装的那些yum软件包

[root@bogon apache-tomcat-7.0.70]# rpm -qa | grep yum
yum-rhn-plugin-2.0.1-10.el7.noarch
yum-metadata-parser-1.1.4-10.el7.x86_64
yum-3.4.3-158.el7.noarch

2、卸载这些软件包

[root@bogon apache-tomcat-7.0.70]# rpm -e yum-rhn-plugin-2.0.1-10.el7.noarch --nodeps
[root@bogon apache-tomcat-7.0.70]# rpm -e yum-metadata-parser-1.1.4-10.el7.x86_64 --nodeps
[root@bogon apache-tomcat-7.0.70]# rpm -e yum-3.4.3-158.el7.noarch --nodeps

3、保证本机电脑能上网

[root@bogon apache-tomcat-7.0.70]# ping www.baidu.com
PING www.a.shifen.com (61.135.169.121) 56(84) bytes of data.
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=1 ttl=57 time=5.17 ms
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=2 ttl=57 time=4.52 ms
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=3 ttl=57 time=5.69 ms
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=4 ttl=57 time=3.33 ms
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=5 ttl=57 time=5.57 ms
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=6 ttl=57 time=5.18 ms

4、找到自己所需要的版本下载

wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-chardet-2.2.1-1.el7_1.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-158.el7.centos.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-45.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-updateonboot-1.1.31-45.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-45.el7.noarch.rpm

5、安装软件包

rpm -ivh python-*

rpm -ivh yum-*

6、新建repo 配置文件（如果是其他版本，则将下面的7改为你当前的版本数字）

vim /etc/yum.repos.d/CentOS-Base.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

7、清除缓存

yum clean all

8、测试是否正常

yum -y install lftp

参考网址：

https://www.linuxidc.com/Linux/2017-04/142444.htm

http://qingfengjushi1.iteye.com/blog/2282986（这个链接地址里面有已经下载好的rpm）

https://www.cnblogs.com/horizonli/p/5507112.html