利用yum安装时，报错 [Errno 256] No more mirrors to try.

问题：

[root@gg ~]# yum install -y perl-DBD-MySQL  
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Setting up Install Process
wbg                                                                                                           | 4.1 kB     00:00 ...
Not using downloaded repomd.xml because it is older than what we have:
  Current   : Fri Sep 26 20:03:04 2014
  Downloaded: Fri Sep 26 20:02:42 2014
Resolving Dependencies
--> Running transaction check
---> Package perl-DBD-MySQL.x86_64 0:4.013-3.el6 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=====================================================================================================================================
 Package                              Arch                         Version                           Repository                 Size
=====================================================================================================================================
Installing:
 perl-DBD-MySQL                       x86_64                       4.013-3.el6                       wbg                       134 k

Transaction Summary
=====================================================================================================================================
Install       1 Package(s)

Total download size: 134 k
Installed size: 338 k
Downloading Packages:

Error Downloading Packages:
  perl-DBD-MySQL-4.013-3.el6.x86_64: failure: ../Packages/perl-DBD-MySQL-4.013-3.el6.x86_64.rpm from wbg: [Errno 256] No more mirrors to try.

解决方法：

[root@gg yum.repos.d]# yum clean all
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Cleaning repos: wbg
Cleaning up Everything
[root@gg yum.repos.d]# yum makecache
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
wbg                                                                                                           | 4.1 kB     00:00 ...
wbg/group_gz                                                                                                  | 211 kB     00:00 ...
wbg/filelists_db                                                                                              | 3.3 MB     00:00 ...
wbg/primary_db                                                                                                | 3.1 MB     00:00 ...
wbg/other_db                                                                                                  | 1.4 MB     00:00 ...
Metadata Cache Created
[root@gg yum.repos.d]# yum update  
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Setting up Update Process
No Packages marked for Update

再次进行安装：问题已经解决
[root@gg yum.repos.d]# ls
redhat.repo  wbg.repo
[root@gg yum.repos.d]# yum install -y perl-DBD-MySQL  
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package perl-DBD-MySQL.x86_64 0:4.013-3.el6 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=====================================================================================================================================
 Package                              Arch                         Version                           Repository                 Size
=====================================================================================================================================
Installing:
 perl-DBD-MySQL                       x86_64                       4.013-3.el6                       wbg                       134 k

Transaction Summary
=====================================================================================================================================
Install       1 Package(s)

Total download size: 134 k
Installed size: 338 k
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Warning: RPMDB altered outside of yum.
  Installing : perl-DBD-MySQL-4.013-3.el6.x86_64                                                                                 1/1
  Verifying  : perl-DBD-MySQL-4.013-3.el6.x86_64                                                                                 1/1

Installed:
  perl-DBD-MySQL.x86_64 0:4.013-3.el6

Complete!