今天没事搞了两个虚机玩玩，但是安装软件的时候出现错误，如下：
yum提示Another app is currently holding the yum lock; waiting for it to exit...
# yum -y install vixie-cron Loaded plugins: fastestmirror, refresh-packagekit, security Existing lock /var/run/yum.pid: another copy is running as pid 25960. Another app is currently holding the yum lock; waiting for it to exit...
yum在锁定状态中。
已经有一个yum进程在运行了，目前使用kill杀了进程：
# kill -s 9 *****
# ps aux|grep yum
root 16744 0.0 0.0 1032 900 pts/1 S+ 09:19 0:00 grep yum
root 55960 0.0 0.0 0 0 ? Z Sep19 0:01 [yumBackend.py] <defunct>
kill不了，那怎么办呢？
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。