如果主机不能连外网，则我们可以为yum源配置一个能连外网的代理服务器，这样我们就可以继续使用yum命令安装软件。
注意： 设置 `http_proxy` 环境变量，并不能达到让yum能连外网。yum连外网有自已的设置方法。
全局设置
假设我们想要为 `/etc/yum.repos.d/` 下的所有仓库设置代理，则可以修改 `/etc/yum.conf` 文件，在该文件尾部添加如下一行：
proxy=http://ip:port
特定仓库
比如 `CentOS-Base.repo`中有三个仓库：base、updates和extras。我们只想给base仓库设置代理，则只需要在对应的仓库后面添加一行，如下：
[base] name=CentOS-$releasever - Base #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 proxy=http://ip:port #released updates [updates] name=CentOS-$releasever - Updates #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 #additional packages that may be useful [extras] name=CentOS-$releasever - Extras #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
特定仓库不走代理
假设我们在`/etc/yum.conf`中设置了全局代理，但是又想某个仓库不走代理，此时，我们只需要在特定的仓库后面添加一行 `proxy=_none_` 即可。比如 `CentOS-Base.repo`中有三个仓库，我们希望base仓库不走代理，则设置如下：
[base] name=CentOS-$releasever - Base #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 proxy=_none_ #released updates [updates] name=CentOS-$releasever - Updates #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7 #additional packages that may be useful [extras] name=CentOS-$releasever - Extras #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
参考链接：
https://pshizhsysu.gitbook.io/linux/yum/wei-yum-yuan-pei-zhi-dai-li
标签：basearch,http,CentOS,centos,配置,代理,mirrorlist,releasever,yum From： https://www.cnblogs.com/neozheng/p/18412151