在使用yum安装时出现类似如下情况：
[root@sjk1 ~]# yum -y install perl-DBD-MySQL
Loaded plugins: fastestmirror, langpacks
Existing lock /var/run/yum.pid: another copy is running as pid 2235.
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 27 M RSS (887 MB VSZ)
Started: Fri Jun 21 14:29:05 2019 - 04:06 ago
State : Traced/Stopped, pid: 2235
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 27 M RSS (887 MB VSZ)
Started: Fri Jun 21 14:29:05 2019 - 04:08 ago
State : Traced/Stopped, pid: 2235
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 27 M RSS (887 MB VSZ)
Started: Fri Jun 21 14:29:05 2019 - 04:10 ago
State : Traced/Stopped, pid: 2235原因：
已经有一个yum进程在运行了，yum处在锁定状态中。
解决方案：
可以通过强制关掉yum进程（因为通过 kill -9 2235 是杀不掉的）
rm -f /var/run/yum.pid 或 rm -f /run/yum.pid[root@sjk1 ~]# find / -name "yum.pid"
/run/yum.pid
[root@sjk1 ~]# rm -f /run/yum.pid