yum命令格式：
yum install softwarename 安装
yum repolist 列出设定yum源的信息
yum remove softwarename 卸载
yum list softwarename 查看软件源中是否有此软件
yum list all 列出所有软件名称
yum list installd 列出已经安装的软件名称
yum list available 列出可以用yum安装的软件名称
yum clean all 清空yum缓存
yum search softwarename 根据软件信息搜索软件名字
yum whatprovides filename 在yum源中查找包含filename文件的软件包
yum update 更新软件
yum history 查看系统软件改变历史
yum reinstall softwarename 重新安装
yum info softwarename 查看软件信息
yum groups list 查看软件组信息
yum groups info softwaregroup 查看软件组内包含的软件
yum groups install softwaregroup 安装组件
dhcp安装不了的解决途径：
mkdir /iso 建立个目录
mv /home/kiosk/Desktop/*.iso /iso 防止误删除
mkdir /source7.0 /source7.2 挂载点
mount /iso/rhel-server-7.0-x86_64-dvd.iso /source7.0 分别挂载
mount /iso/rhel-server-7.2-x86_64-dvd.iso /source7.2
此处的7.0与7.2使我们真机和虚拟机的版本，例如我重新安装系统之后版本为7.1，所以镜像就得挂载相对应的。
cd /etc/yum.repos.d/ 切换路径
mkdir /repobackup 建立目录
mv * /repobackup 备份
vim yum.repo
[source7.2]
name=source7.2
baseurl=file:///source7.2
gpgcheck=0
yum clean all
详细操作：
[root@foundation21 ~]# mkdir /iso
[root@foundation21 ~]# mv /home/kiosk/Desktop/*.iso /iso
[root@foundation21 ~]# mkdir /source7.0 /source7.2
[root@foundation21 ~]# mount /iso/rhel-server-7.0-x86_64-dvd.iso /source7.0
mount: /dev/loop0 is write-protected, mounting read-only
[root@foundation21 ~]# mount /iso/rhel-server-7.2-x86_64-dvd.iso /source7.2
mount: /dev/loop1 is write-protected, mounting read-only
[root@foundation21 ~]# cd /etc/yum.repos.d/
[root@foundation21 yum.repos.d]# mkdir /repobackup
[root@foundation21 yum.repos.d]# mv * /repobackup
[root@foundation21 yum.repos.d]# vim yum.repo
[root@foundation21 yum.repos.d]# yum clean all
Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-
: manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Cleaning repos: source7.2
Cleaning up everything
[root@foundation21 yum.repos.d]# cd
[root@foundation21 ~]# yum install dhcp 安装dhcp
Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-
: manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
source7.2 | 4.1 kB 00:00
(1/2): source7.2/group_gz | 136 kB 00:00
(2/2): source7.2/primary_db | 3.6 MB 00:00
Resolving Dependencies
--> Running transaction check
---> Package dhcp.x86_64 12:4.2.5-42.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
dhcp x86_64 12:4.2.5-42.el7 source7.2 511 k
Transaction Summary
================================================================================
Install 1 Package
Total download size: 511 k
Installed size: 1.4 M
Is this ok [y/d/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : 12:dhcp-4.2.5-42.el7.x86_64 1/1
source7.2/productid | 1.6 kB 00:00
Verifying : 12:dhcp-4.2.5-42.el7.x86_64 1/1
Installed:
dhcp.x86_64 12:4.2.5-42.el7
Complete!
共享yum源：
1，上个实验在本地yum源配置完成之后安装apache点击打开链接,链接里面有阿帕奇的详细解释：
yum install httpd
systemctl start httpd
systemctl enable httpd
systemctl stop firewalld
systemctl disable firewalld
mkdir /var/www/html/source7.0 /var/www/html/source7.2
2,挂载镜像有两种方式：
临时挂载：
执行完如下命令后会挂载成功，但是在系统重启之后就需要重新挂载！
mount /iso/rhel-server-7.0-x86_64-dvd.iso /var/www/html/source7.0
mount /iso/rhel-server-7.2-x86_64-dvd.iso /var/www/html/source7.2
永久性挂载：
编辑如下文件可以实现开机永久性挂载。
vim /etc/rc.d/rc.local
写入：
mount /iso/rhel-server-7.0-x86_64-dvd.iso /var/www/html/source7.0
mount /iso/rhel-server-7.2-x86_64-dvd.iso /var/www/html/source7.2
:wq退出保存
chmod +x /etc/rc.d/rc.local 赋予执行权限
3,访问测试（在虚拟机）
在浏览器中输入地址，依次测试连接
http://ip/source7.0
http://172.25.254.78/source7.0，78为主机IP。
http://172.25.254.78/source7.2
***在虚拟机里面输入不需要输入http直接172.25.254.78即可测试。
4,配置虚拟机yum
rm -fr /etc/yum.repos.d/*
vim /etc/yum.repos.d/yum.repo
[source7.0]
name=source7.0
baseurl=http://172.25.254.78/source7.0
gpgcheck=0
配置文件完成后可以在虚拟机输入yum install dhcp进行下载
[root@foundation21 ~]# df 重启之后可以看到已经挂载完成
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 307974224 17399728 290574496 6% /
devtmpfs 1868044 0 1868044 0% /dev
tmpfs 1881152 88 1881064 1% /dev/shm
tmpfs 1881152 8868 1872284 1% /run
tmpfs 1881152 0 1881152 0% /sys/fs/cgroup
/dev/sda1 505580 149472 356108 30% /boot
/dev/loop0 3654720 3654720 0 100% /var/www/html/source7.0
/dev/loop1 3947824 3947824 0 100% /var/www/html/source7.2
tmpfs 376232 12 376220 1% /run/user/1000
yum命令仅仅是对软件进行管理，rpm命令才是真正安装软件的，yum的好处是可以解决软件依赖性。