Loaded plugins: fastestmirror, refresh-packagekit, security

Existing lock /var/run/yum.pid: another copy is running as pid 3037.

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

  The other application is: yum

    Memory :  21 M RSS (318 MB VSZ)

    Started: Wed Jul 25 03:46:51 2018 - 01:04 ago

    State  : Traced/Stopped, pid: 3037

杀死yum进程

rm -f /var/run/yum.pid