用yum安装包有时候会提示

Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory : 128 M RSS (439 MB VSZ)
    Started: Fri Aug 28 08:08:31 2015 - 48:25 ago
    State  : Sleeping, pid: 3462

解决方法：

rm -f /var/run/yum.pid

然后重新执行yum就可以了