yum配置提示错误：
[root@localhost yum.repos.d]# yum clean all
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory :  21 M RSS ( 35 MB VSZ)
    Started: Sun Oct 27 03:20:16 2013 - 1:13:47 ago
    State  : Sleeping, pid: 11985

解决方法：
[root@localhost yum.repos.d]# rm -rf /var/run/yum.pid 
[root@localhost yum.repos.d]# yum clean all
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
Cleaning repos: rhel-source
Cleaning up Everything
[root@localhost yum.repos.d]#