1、编写脚本selinux.sh，实现开启或禁用SELinux功能

#!/bin/bash
if grep SELINUX=disabled /etc/selinux/config &>/dev/null;then
    echo "selinux is stop"
elif grep SELINUX=enforcing /etc/selinux/config &>/dev/null;then                                                                                             
    echo "selinux is start"
fi
read -p "please input (start or stop):" ST
case $ST in
start)
        sed -i s#SELINUX=disabled#SELINUX=enforcing# /etc/selinux/config
        echo selinux is start
        ;;
stop)
        sed -i s#SELINUX=enforcing#SELINUX=disabled# /etc/selinux/config
        echo selinux is stop
        ;;
*)
        echo "please input (start or stop)"
        ;;
esac

2、统计/etc/fstab文件中每个文件系统类型出现的次数

[root@CentOS7 ~]# awk '/^U/{print $3}' /etc/fstab |uniq -c
      3 xfs
      1 swap

3、提取出字符串Yd$C@M05MB%9&Bdh7dq+YVixp3vpw中的所有数字

[root@CentOS7 ~]# echo 'Yd$C@M05MB%9&Bdh7dq+YVixp3vpw' |awk -F '[^[:digit:]]' '{print $7,$10,$14,$22}'
05 9 7 3

4、解决DOS攻击生产案例:根据web日志或者或者网络连接数，监控当某个IP 并发连接数或者短时内PV达到100，即调用防火墙命令封掉对应的IP，监控频 率每隔5分钟。防火墙命令为:iptables -A INPUT -s IP -j REJECT

#!/bin/bash
SLEEPTIME=300
while true ;do
	ss -nt |awk -F ' +|:' '!/^S/{ip[$(NF-2)]++}END{for(i in ip){print i,ip[i]}}' >ss.log
	while read ip num;do
        if [ $num -ge 1 ];then
                iptables -A INPUT -s $ip -j REJECT                                                                                
        fi
	done <ss.log
	sleep $SLEEPTIME
done