yum提醒another app is currently holding the yum lock;waiting for it to exit

yum提示another app is currently holding the yum lock;waiting for it to exit

可能是系统自动升级正在运行，yum在锁定状态中。
可以通过强制关掉yum进程：
#rm -f /var/run/yum.pid
然后就可以使用yum了。