linux系统使用yum命令时，遇到出现以下错误：
Loaded plugins: fastestmirror
Existing lock /var/run/yum.pid: another copy is running as pid 3404.
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 41 M RSS (253 MB VSZ)
Started: Wed Apr 11 07:03:37 2012 - 00:25 ago
State : Sleeping, pid: 3404
使用以下命令可以解决问题：
rm -rf /var/run/yum.pid