错误描述：
[root@test ~]# yum repolist
Loaded plugins: fastestmirror, security
Existing lock /var/run/yum.pid: another copy is running as pid 1696.
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 21 M RSS (861 MB VSZ)
Started: Thu Nov 16 14:40:42 2017 - 03:07 ago
State : Traced/Stopped, pid: 1696
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 21 M RSS (861 MB VSZ)
Started: Thu Nov 16 14:40:42 2017 - 03:09 ago
State : Traced/Stopped, pid: 1696
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 21 M RSS (861 MB VSZ)
Started: Thu Nov 16 14:40:42 2017 - 03:11 ago
State : Traced/Stopped, pid: 1696
####错误关键句： Another app is currently holding the yum lock; waiting for it to exit...
yum运行时提示被锁住了
解决方案：
第一步 解决错误
yum运行时提示被锁住了解决办法
1、当大家用linux的yum时，是不是经常会遇到下面的情况
Loaded plugins: fastestmirror
Existing lock /var/run/yum.pid: another copy is running as pid 3404.
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum
Memory : 41 M RSS (253 MB VSZ)
Started: Wed Apr 11 07:03:37 2012 - 00:25 ago
State : Sleeping, pid: 3404
没关系，两条语句就可以搞定它。
2、[root@centos5 ~]# rm -r /var/run/yum.pid
rm：是否删除 一般文件 “/var/run/yum.pid”? y
[root@centos5 ~]# /sbin/service yum-updatesd restart
停止 yum-updatesd： [确定]
启动 yum-updatesd： [确定]
3、[root@centos5 ~]# yum install gcc*
搞定！！！
第二步 再进行安装yum
[root@test ~]# yum repolist #此命令不仅是安装yum的命令 还可以对yum进行更新
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
* base: mirrors.aliyun.com
* extras: mirrors.aliyun.com
* updates: mirrors.aliyun.com
base | 3.7 kB 00:00
base/primary_db | 4.7 MB 00:20
extras | 3.4 kB 00:00
extras/primary_db | 29 kB 00:00
updates | 3.4 kB 00:00
updates/primary_db | 4.7 MB 00:20
repo id repo name status
base CentOS-6 - Base - mirrors.aliyun.com 6,706
extras CentOS-6 - Extras - mirrors.aliyun.com 46
updates CentOS-6 - Updates - mirrors.aliyun.com 756
repolist: 7,508
第三步 安装、备份与更新yum源
资源网站：http://mirrors.aliyun.com
备份yum源：
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
下载yum源：
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
下载epel源
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo
小结：
yum repolist
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo
yum -y install sl #进行安装需要的软件
