[root@ldap-server ~]# cat /etc/redhat-release 
CentOS release 6.7 (Final)
[root@ldap-server ~]# uname -r
2.6.32-573.el6.x86_64
[root@ldap-server ~]# uname -m
x86_64

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
mv /etc/yum.repos.d/epel.repo /etc/yum.repos.d/epel.repo.backup
mv /etc/yum.repos.d/epel-testing.repo /etc/yum.repos.d/epel-testing.repo.backup
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo

[root@ldap-server ~]# sed -i.bak ‘s#keepcache=0#keepcache=1#g‘ /etc/yum.conf
[root@ldap-server ~]# grep keepcache /etc/yum.conf 
keepcache=1

[root@ldap-server ~]# sed -i.bak ‘s#SELINUX=enforcing#SELINUX=disabled#g‘ /etc/selinux/config 
[root@ldap-server ~]# grep SELINUX=disabled /etc/selinux/config
SELINUX=disabled
[root@ldap-server ~]# setenforce 0
[root@ldap-server ~]# getenforce 0
Disabled

[root@ldap-server ~]#  /etc/init.d/iptables stop

[root@ldap-server ~]# crontab -l
#time sync by junxun at 2017-07-23
*/5 * * * * /usr/sbin/ntpdate pool.ntp.org >/dev/null 2>&1