[root@centos7 ~]#vim deny_dos.sh
[root@centos7 ~]#cat deny_dos.sh
#!/bin/bash
#
#*************************************************************
#Author:                 chen
#QQ:                     2088346053
#Date:                   2021-12-31
#FileName:               deny_dos.sh
#Description:            The test script
#Copyright (C):          2021 All rights reserved
#*************************************************************
LINK=100
while true;do
    ss -nt | awk -F"[[:space:]]+|:" '/^ESTAB/{print $(NF-2)}'|sort |uniq -
c|while read count ip;do
        if [ $count -gt $LINK ];then
            iptables -A INPUT -s $ip -j REJECT
        fi
    done
done
[root@centos7 ~]#chmod +x /root/deny_dos.sh
[root@centos7 ~]#crontab -e
[root@centos7 ~]#crontab -l
*/5 * * * * /root/deny_dos.sh