yum的安装与配置
（1）yum的安装
检查yum是否已经安装：
[root@localhost~]# rpm -qa|grep yum
如果没有任何显示，表示系统中还没有安装yum工具，yum安装包在centos系统光盘中可以找到，执行如下指令进行安装：
[root@localhost~]# rpm -ivh yum-*.noarch.rpm
安装yum需要python-elementtree、python-sqlite、urlgrabber、yumconf等软件包的支持，这些软件包在Centos Linux系统安装光盘均可找到，如果在安装yum过程中出现软件包之间的依赖性，只需按照依赖提示寻找相应软件包安装即可，直到yum包安装成功。
下面是某个环境的安装示例：
[root@localhost~]# rpm -ivh yum-2.4.3-1.c4.noarch.rpm
warning:yum-2.4.3-1.c4.noarch.rpm: V3 DSA signature:NOKEY, key ID 443e1821
error:Failed dependencies:
python-elementtree is needed by yum-2.4.3-1.c4.noarch
python-sqlite is needed by yum-2.4.3-1.c4.noarch
urlgrabber is needed by yum-2.4.3-1.c4.noarch
yumconf is needed by yum-2.4.3-1.c4.noarch
[root@localhost~]# rpm -ivh python-elementtree-1.2.6-4.2.1.i386.rpm
warning:python-elementtree-1.2.6-4.2.1.i386.rpm: V3 DSAsignature: NOKEY, key ID 443e1821
Preparing... ########################################### [100%]
1:python-elementtree ###########################################[100%]
http://www.uplook.cn/?a=index&m=index&c=iframe&url=mailto%3Aroot%40localhost ~]#rpm -ivh sqlite-3.3.3-1.2.i386.rpm
warning:sqlite-3.3.3-1.2.i386.rpm: V3 DSA signature:NOKEY, key ID 443e1821
Preparing... ########################################### [100%]
1:sqlite ########################################### [100%]
[root@localhost~]# rpm -ivh python-sqlite-1.1.7-1.2.i386.rpm
warning:python-sqlite-1.1.7-1.2.i386.rpm: V3 DSAsignature: NOKEY, key ID 443e1821
Preparing... ########################################### [100%]
1:python-sqlite ########################################### [100%]
[root@localhost~]# rpm -ivh python-urlgrabber-2.9.8-2.noarch.rpm
warning:python-urlgrabber-2.9.8-2.noarch.rpm: V3 DSAsignature: NOKEY, key ID 443e1821
Preparing... ########################################### [100%]
1:python-urlgrabber ########################################### [100%]
http://www.uplook.cn/?a=index&m=index&c=iframe&url=mailto%3Aroot%40localhost ~]#rpm -ivh centos-yumconf-4-4.5.noarch.rpm
warning:centos-yumconf-4-4.5.noarch.rpm: V3 DSA signature: NOKEY, key ID 443e1821
Preparing... ########################################### [100%]
1:centos-yumconf ########################################### [100%]
[root@localhost~]# rpm -ivh yum-2.4.3-1.c4.noarch.rpm
warning:yum-2.4.3-1.c4.noarch.rpm: V3 DSA signature:NOKEY, key ID 443e1821
Preparing... ########################################### [100%]
1:yum ########################################### [100%]