Yum（全称为 Yellow dog Updater, Modified）是一个在fedora和RedHat以及centos中的shell前端软件包管理器。基于rpm包管理，能够从指定的服务器自动下载RPM包并且安装，可以自动处理依赖性关系，并且一次安装所有依赖的软件包，无须繁琐地一次次下载、安装。
相对于rpm来说，使用yum安装软件不必考虑依赖关系，大大简化了软件的安装过程，并且它的功能强大，易用性非常好。这些优点使其成为了linux领域中最主流的软件包管理器。
其使用形式以及主要选项如下：
yum [options] [command] [package ...]
command is one of:
* install package1 [package2] [...]
* update [package1] [package2] [...]
* update-to [package1] [package2] [...]
* check-update
* upgrade [package1] [package2] [...]
* upgrade-to [package1] [package2] [...]
* distribution-synchronization [package1] [package2] [...]
* remove | erase package1 [package2] [...]
* list [...]
* info [...]
* provides | whatprovides feature1 [feature2] [...]
* clean [ packages | metadata | expire-cache | rpmdb | plugins | all ]
* makecache
* groupinstall group1 [group2] [...]
* groupupdate group1 [group2] [...]
* grouplist [hidden] [groupwildcard] [...]
* groupremove group1 [group2] [...]
* groupinfo group1 [...]
* search string1 [string2] [...]
* shell [filename]
* resolvedep dep1 [dep2] [...]
* localinstall rpmfile1 [rpmfile2] [...]
(maintained for legacy reasons only - use install)
* localupdate rpmfile1 [rpmfile2] [...]
(maintained for legacy reasons only - use update)
* reinstall package1 [package2] [...]
* downgrade package1 [package2] [...]
* deplist package1 [package2] [...]
* repolist [all|enabled|disabled]
* version [ all | installed | available | group-* | nogroups* | grouplist | groupinfo ]
* history [info|list|packages-list|packages-info|summary|addon-info|redo|undo|rollback|new|sync|stats]
* load-transaction [txfile]
* check
* help [command]
1 安装
yum install 全部安装；
yum install package安装指定的安装包；
2 更新和升级
yum update 全部更新；
yum update package 更新指定程序包；
yum check-update 检查可更新的程序；
yum upgrade package1 升级指定程序包； Yum downgrade package 降级程序包；
3 查找和显示
yum info package 显示安装包信息；
yum list 显示所有已经安装和可以安装的程序包；
yum list package 显示指定程序包安装情况；
string查找安装包;
4 删除程序
yum remove package 删除程序包；
yum deplist package 查看程序依赖情况；
5 清除缓存
yum clean packages 清除缓存目录下的软件包；
yum clean headers 清除缓存目录下的 headers；
yum clean oldheaders 清除缓存目录下旧的 head；ers
yum clean, yum clean all (= yum clean packages; yum clean oldheaders)；
