YUM是RHEL系统中提供的一个安装，卸载和搜索软件包的工具。它能做的不仅仅是安装、卸载软件包，它能做的还有更多，下面我们将在本文中为你展示。
YUM可以自动安装软件包的依赖包，例如当你使用yum安装httpd时，它还会自动安装https apache server以及它依赖的软件包。通过rpm软件包安装时就没有这么方便咯（译注：就是不会自动处理软件包依赖问题咯！），你必须下载所有它依赖的软件包，然后依序安装它们。
yum工具从远端服务器上的软件仓库（通常由OS提供商提供）获取软件包的信息。一个软件仓库是能在特定架构上运行的一系列rpm软件包的集合。例如，对于32位和64位系统各有一个软件仓库，还有针对RHEL5以及RHEL6的软件仓库。你也可以建立一个本地仓库，配置你的yum让其从你的本地仓库里搜索安装软件包。在接下来的例子中，我将向你展示除了安装和卸载软件，yum还可以做的其它事情。为方便理解，我将在我的Amazon EC2 RHEL 6.4服务器上使用httpd软件包为例。
从软件仓库里搜索软件包 # yum search httpd Loaded plugins: amazon-id, rhui-lb, security ==================== N/S Matched: httpd ========== httpd.x86_64 : Apache HTTP Server httpd-devel.i686 : Development interfaces for the Apache HTTP server httpd-devel.x86_64 : Development interfaces for the Apache HTTP server httpd-manual.noarch : Documentation for the Apache HTTP server httpd-tools.x86_64 : Tools for use with the Apache HTTP Server mod_dav_svn.x86_64 : Apache httpd module for Subversion server mod_dnssd.x86_64 : An Apache HTTPD module which adds Zeroconf support想获得详细的输出信息，可以使用下面的命令：
# yum provides httpd Loaded plugins: amazon-id, rhui-lb, security httpd-2.2.15-26.el6.x86_64 : Apache HTTP Server Repo : rhui-REGION-rhel-server-releases Matched from:yum provides httpd在软件仓库里搜索含有httpd的软件包。
提供所有软件组列表 # yum grouplist以上命令将为你显示已经安装的以及可用的软件组。你可以使用软件组安装选项来安装其中一个软件组。例如，我们将安装一个PHP Support的软件组。这个软件组内包含需要的PHP软件包。
# yum groupinstall PHP Support Loaded plugins: amazon-id, downloadonly, rhui-lb, security Setting up Group Process Warning: Group Support does not exist. Resolving Dependencies -> Running transaction check --> Package php.x86_64 0:5.3.3-23.el6_4 will be installed -> Processing Dependency: php-common(x86-64) = 5.3.3-23.el6_4 for package: php-5.3.3-23.el6_4.x86_64 -> Processing Dependency: php-cli(x86-64) = 5.3.3-23.el6_4 for package: php-5.3.3-23.el6_4.x86_64 --> Package php-gd.x86_64 0:5.3.3-23.el6_4 will be installed -> Processing Dependency: libXpm.so.4()(64bit) for package: php-gd-5.3.3-23.el6_4.x86_64 --> Package php-pdo.x86_64 0:5.3.3-23.el6_4 will be installed --> Package php-pear.noarch 1:1.9.4-4.el6 will be installed --> Package php-xml.x86_64 0:5.3.3-23.el6_4 will be installed -> Running transaction check --> Package libXpm.x86_64 0:3.5.10-2.el6 will be installed --> Package php-cli.x86_64 0:5.3.3-23.el6_4 will be installed --> Package php-common.x86_64 0:5.3.3-23.el6_4 will be installed -> Finished Dependency Resolution Dependencies Resolved ================================================== Package Arch Version Repository Size ================================================== Installing: php x86_64 5.3.3-23.el6_4 rhui-REGION-rhel-server-releases 1.1 M php-gd x86_64 5.3.3-23.el6_4 rhui-REGION-rhel-server-releases 106 k php-pdo x86_64 5.3.3-23.el6_4 rhui-REGION-rhel-server-releases 75 k php-pear noarch 1:1.9.4-4.el6 rhui-REGION-rhel-server-releases 393 k php-xml x86_64 5.3.3-23.el6_4 rhui-REGION-rhel-server-releases 103 k Installing for dependencies: libXpm x86_64 3.5.10-2.el6 rhui-REGION-rhel-server-releases 51 k php-cli x86_64 5.3.3-23.el6_4 rhui-REGION-rhel-server-releases 2.2 M php-common x86_64 5.3.3-23.el6_4 rhui-REGION-rhel-server-releases 524 k Transaction Summary ================================================== Install 8 Package(s) Total download size: 4.5 M Installed size: 16 M Is this ok [y/N]: y Downloading Packages: (1/8): libXpm-3.5.10-2.el6.x86_64.rpm | 51 kB 00:00 (2/8): php-5.3.3-23.el6_4.x86_64.rpm | 1.1 MB 00:00 (3/8): php-cli-5.3.3-23.el6_4.x86_64.rpm | 2.2 MB 00:00 (4/8): php-common-5.3.3-23.el6_4.x86_64.rpm | 524 kB 00:00 (5/8): php-gd-5.3.3-23.el6_4.x86_64.rpm | 106 kB 00:00 (6/8): php-pdo-5.3.3-23.el6_4.x86_64.rpm | 75 kB 00:00 (7/8): php-pear-1.9.4-4.el6.noarch.rpm | 393 kB 00:00 (8/8): php-xml-5.3.3-23.el6_4.x86_64.rpm | 103 kB 00:00 ----------------------------------------------- Total 2.9 MB/s | 4.5 MB 00:01 Running rpm_check_debug Running Transaction Test Transaction Test Succeeded Running Transaction Installing : php-common-5.3.3-23.el6_4.x86_64 1/8 Installing : php-cli-5.3.3-23.el6_4.x86_64 2/8 Installing : libXpm-3.5.10-2.el6.x86_64 3/8 Installing : php-gd-5.3.3-23.el6_4.x86_64 4/8 Installing : 1:php-pear-1.9.4-4.el6.noarch 5/8 Installing : php-5.3.3-23.el6_4.x86_64 6/8 Installing : php-xml-5.3.3-23.el6_4.x86_64 7/8 Installing : php-pdo-5.3.3-23.el6_4.x86_64 8/8 Verifying : 1:php-pear-1.9.4-4.el6.noarch 1/8 Verifying : php-xml-5.3.3-23.el6_4.x86_64 2/8 Verifying : php-common-5.3.3-23.el6_4.x86_64 3/8 Verifying : libXpm-3.5.10-2.el6.x86_64 4/8 Verifying : php-cli-5.3.3-23.el6_4.x86_64 5/8 Verifying : php-5.3.3-23.el6_4.x86_64 6/8 Verifying : php-pdo-5.3.3-23.el6_4.x86_64 7/8 Verifying : php-gd-5.3.3-23.el6_4.x86_64 8/8 Installed: php.x86_64 0:5.3.3-23.el6_4 php-gd.x86_64 0:5.3.3-23.el6_4 php-pdo.x86_64 0:5.3.3-23.el6_4 php-pear.noarch 1:1.9.4-4.el6 php-xml.x86_64 0:5.3.3-23.el6_4 Dependency Installed: libXpm.x86_64 0:3.5.10-2.el6 php-cli.x86_64 0:5.3.3-23.el6_4 php-common.x86_64 0:5.3.3-23.el6_4 Complete! 使用YUM安装软件包