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

[root@localhost ~]# yum -y install mariadb-server mariadb mariadb-devel
Loaded plugins: fastestmirror, langpacks
Existing lock /var/run/yum.pid: another copy is running as pid 4142.
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory : 129 M RSS (541 MB VSZ)
    Started: Wed Jul 20 21:34:31 2016 - 13:59 ago
    State  : Sleeping, pid: 4142
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory : 129 M RSS (541 MB VSZ)
    Started: Wed Jul 20 21:34:31 2016 - 14:01 ago
    State  : Sleeping, pid: 4142
^C

Exiting on user cancel.
[root@localhost ~]# rm -rf /run/yum.pid

小技巧：

　　通过以下命令找到yum.pid的具体路径，然后rm -rf掉。

find / -name yum.pid