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：

Copyproxy=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：

Copy[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：

Copy[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