Centos7使用阿里云yum源

### 下载阿里云yum源
```
yum install -y wget

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak 
或
rm -rf /etc/yum.repos.d/*

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

yum clean all

yum makecache

```

### 阿里云repo内容：
```
# 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-$releasever - Base - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/os/$basearch/
        http://mirrors.aliyuncs.com/centos/$releasever/os/$basearch/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
 
#released updates 
[updates]
name=CentOS-$releasever - Updates - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/updates/$basearch/
        http://mirrors.aliyuncs.com/centos/$releasever/updates/$basearch/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
 
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/extras/$basearch/
        http://mirrors.aliyuncs.com/centos/$releasever/extras/$basearch/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
 
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/centosplus/$basearch/
        http://mirrors.aliyuncs.com/centos/$releasever/centosplus/$basearch/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
 
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/contrib/$basearch/
        http://mirrors.aliyuncs.com/centos/$releasever/contrib/$basearch/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

```

### 使用代理请求yum安装
#### 1.在能够上外网的机器上安装nginx，并开放代理服务：
```
server {
        listen 80;
        server_name yum.com;
        location /centos/ {
            proxy_pass http://mirrors.aliyun.com/centos/ ;
        }

location /epel/ {
            proxy_pass http://mirrors.aliyun.com/epel/ ;
        }
        
        location / {
            resolver 8.8.8.8;
            proxy_pass $scheme://$host$request_uri;
        }
    }
```

#### 2.在内网电脑上，可以修改repo文件中的地址，使之请求外网机器的ip
```
[base]
name=CentOS-$releasever - Base - yum.com
failovermethod=priority
baseurl=http://yum.com/centos/$releasever/os/$basearch/
        http://yum.com/centos/$releasever/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
gpgcheck=1
gpgkey=http://yum.com/centos/RPM-GPG-KEY-CentOS-7

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

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

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - yum.com
failovermethod=priority
baseurl=http://yum.com/centos/$releasever/centosplus/$basearch/
        http://yum.com/centos/$releasever/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
gpgcheck=1
enabled=0
gpgkey=http://yum.com/centos/RPM-GPG-KEY-CentOS-7

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - yum.com
failovermethod=priority
baseurl=http://yum.com/centos/$releasever/contrib/$basearch/
        http://yum.com/centos/$releasever/contrib/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://yum.com/centos/RPM-GPG-KEY-CentOS-7
```

### 仅下载不安装
```
yum install --downloadonly --downloaddir=/tmp/ vsftpd

yum reinstall --downloadonly --downloaddir=/tmp/ vsftpd
说明：如果该服务器已经安装了需要下载的软件包，
     那么使用 install下载就不行，可以使用reinstall下载。
     放心（不会真的安装和重新安装，因为后面加了 --downloadonly，表明只是下载。

如果提示没有--downloadonly选项则需要安装yum-plugin-downloadonly软件包；
yum install yum-plugin-downloadonly
```

### 使用cdrom作为yum源
```
mkdir /mnt/cdrom
mount /dev/cdrom /mnt/cdrom
```

```
cd  /etc/yum.repo.d/
rm -rf *.repo
vi /etc/yum.repo.d/cdrom.repo

[cdrom]
name=dreom
baseurl=file:///mnt/cdrom
gpgcheck=0
enabled=1

```

```
yum clean all
yum makecache
```