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

[root@localhost ~]# yum makecache
Loaded plugins: fastestmirror, refresh-packagekit, security
Existing lock /var/run/yum.pid: another copy is running as pid 2542.
Another app is currently holding the yum lock; waiting for it to exit...
在更换yum源的过程中出现这个报错，可能是系统自动升级正在运行，yum在锁定状态。

[root@localhost ~]# ps -aux | grep yum
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.8/FAQ
root 2542 0.0 0.0 0 0 ? Z 22:18 0:01 [yumBackend.py] <defunct>
root 23606 0.0 0.0 103244 836 pts/1 S+ 23:55 0:00 grep yum
在这时使用kill并不能生效
这是可以强制关闭yum里的进程
[root@localhost ~]# rm -f /var/run/yum.pid
这时继续执行就可以了。