问题：
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 39 M RSS (649 MB VSZ)
Started: Tue Jun 12 03:30:59 2018 - 03:06 ago
State : Traced/Stopped, pid: 95530
解决办法：
rm -rf /var/run/yum.pid