Another app is currently holding the yum lock; waiting for it to exit...

Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory : 153 M RSS (266 MB VSZ)
    Started: Thu Jul 12 00:03:05 2012 - 06:17 ago
    State  : Sleeping, pid: 4018
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory : 153 M RSS (266 MB VSZ)
    Started: Thu Jul 12 00:03:05 2012 - 06:19 ago
    State  : Sleeping, pid: 4018

解决方法：
rm -rf /var/run/yum.pid 来强行解除锁定，然后你的yum就可以运行了