新安装的一台服务器，由于在客户那里，自己内网做的yum源没有办法使用了，所以只能使用互联网的yum源来安装或者更新软件了，在使用yum的时候总是提示The requested URL returned error: 404这个错误，经过一番折腾总算解决了。

   首先说下yum源，使用的是163的源。http://mirrors.163.com/.help/CentOS6-Base-163.repo

[base]

name=CentOS-$releasever - Base - 163.com

baseurl=http://mirrors.163.com/centos/$releasever/os/$basearch/

#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os

gpgcheck=1

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

   配置好以后，直接yum clean all，没什么问题，接下来yum makecache的时候报错就出来了。

  

http://mirror.centos.org/centos/%24releasever/os/i386/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404"
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: base. Please verify its path and try again

  网上说是因为DNS的问题，好吧，试了一下，没用啊，DNS改完也不行，ping源地址还是没问题，wget也没问题。再看看报错吧！http://mirror.centos.org/centos/%24releasever/os/i386/repodata/repomd.xml这个地址怎么成这样了呢？%24是神马东东，复制地址，到浏览器，果然是404错误，正常的源地址肯定不是这个，那么看一下配置文件吧，baseurl=http://mirrors.163.com/centos/$releasever/os/$basearch/

   $releaserver这个应该是系统的版本，那么我们看一下这个变量能不能解释吧，

[root@aaa ~]# echo $releasever
[root@aaa ~]#

 好吧，发现问题了吧，这个变量不能解释啊，试试将它换成网站上的6，看能不能行呢。

[base]

name=CentOS-$releasever - Base - 163.com

#baseurl=http://mirrors.163.com/centos/$releasever/os/$basearch/

baseurl=http://mirrors.163.com/centos/6/os/i386/

#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os

gpgcheck=1

gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6

   修改完毕，重新试一下，果然没问题了

[root@aaa yum.repos.d]# yum makecache
base                                                                                                      | 3.7 kB     00:00    
updates                                                                                                   | 3.4 kB     00:00    
updates/filelists_db                                                                                      | 3.2 MB     00:03    
updates/prestodelta                                                                                       | 637 kB     00:00    
updates/primary_db                                                                                        | 3.6 MB     00:01    
updates/other_db                                                                                          | 423 kB     00:00    
Metadata Cache Created

  安装个软件试一下呢？

[root@aaa yum.repos.d]# yum install lrzsz -y
base                                                                                                      | 3.7 kB     00:00    
extras                                                                                                    | 3.5 kB     00:00    
extras/primary_db                                                                                         |  19 kB     00:00    
updates                                                                                                   | 3.4 kB     00:00    
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package lrzsz.i686 0:0.12.20-27.1.el6 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
=================================================================================================================================
 Package                     Arch                       Version                                 Repository                  Size
=================================================================================================================================
Installing:
 lrzsz                       i686                       0.12.20-27.1.el6                        base                        66 k
Transaction Summary
=================================================================================================================================
Install       1 Package(s)
Total download size: 66 k
Installed size: 150 k
Downloading Packages:
lrzsz-0.12.20-27.1.el6.i686.rpm                                                                           |  66 kB     00:00    
warning: rpmts_HdrFromFdno: Header V3 RSA/SHA256 Signature, key ID c105b9de: NOKEY
Retrieving key from http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
Importing GPG key 0xC105B9DE:
 Userid: "CentOS-6 Key (CentOS 6 Official Signing Key) "
 From  : http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : lrzsz-0.12.20-27.1.el6.i686                                                                                   1/1
  Verifying  : lrzsz-0.12.20-27.1.el6.i686                                                                                   1/1
Installed:
  lrzsz.i686 0:0.12.20-27.1.el6                                                                                                 
Complete!

  呵呵~确实没问题了！有些问题还是要注意看报错信息，网上的一些方法可能是他们碰到的，环境不一样，但是报的同一个错误，那么引发问题的原因也可能不一样，所以，关键还是要注意看报错信息，网上的方法可以参考但是不一定是适合你的。