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本文展示了如何在Linux环境中使用for循环脚本来批量创建用户，进行网络段的ping测试以及修改远程主机的root密码。用户输入前缀和密码来创建20个用户，并记录创建结果。同时，通过用户输入的网段进行ping测试，将结果分别写入到UP和DOWN的文件中。最后，利用SSH公钥认证修改远程主机的root密码，并记录修改状态。

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题目：

1.for创建20用户，用户前缀由用户输入，用户初始密码由用户输入。
2.for ping测试指网段的主机，网段由用户输入。
3.使用for实现批量主机root密码的修改，成功或失败都必须记录。

1.for创建20用户，用户前缀由用户输入，用户初始密码由用户输入。

例如：test01,test10
1、编写脚本

[root@localhost day4]# vim add20user.sh
#!/bin/bash
read -p "please input username's prefix:" namepre
read -p "please input initial password:" passwd
count=20
for name in ${namepre}{01..20}
do
	useradd $name &> /dev/null
	if [ $? -eq 0 ];then
		echo $passwd | passwd $name --stdin &> /dev/null
	else
		echo "user $name already exists."
		let count--
	fi
done
echo "created $count users successfully"

2、设置权限

[root@localhost day4]# chmod a+rx add20user.sh

3、运行测试

[root@localhost day4]# ./add20user.sh
please input username's prefix:ccc
please input initial password:ccc
created 20 users successfully

[root@localhost day4]# tail -20 /etc/passwd
ccc01:x:1255:1255::/home/ccc01:/bin/bash
ccc02:x:1256:1256::/home/ccc02:/bin/bash
ccc03:x:1257:1257::/home/ccc03:/bin/bash
ccc04:x:1258:1258::/home/ccc04:/bin/bash
ccc05:x:1259:1259::/home/ccc05:/bin/bash
ccc06:x:1260:1260::/home/ccc06:/bin/bash
ccc07:x:1261:1261::/home/ccc07:/bin/bash
ccc08:x:1262:1262::/home/ccc08:/bin/bash
ccc09:x:1263:1263::/home/ccc09:/bin/bash
ccc10:x:1264:1264::/home/ccc10:/bin/bash
ccc11:x:1265:1265::/home/ccc11:/bin/bash
ccc12:x:1266:1266::/home/ccc12:/bin/bash
ccc13:x:1267:1267::/home/ccc13:/bin/bash
ccc14:x:1268:1268::/home/ccc14:/bin/bash
ccc15:x:1269:1269::/home/ccc15:/bin/bash
ccc16:x:1270:1270::/home/ccc16:/bin/bash
ccc17:x:1271:1271::/home/ccc17:/bin/bash
ccc18:x:1272:1272::/home/ccc18:/bin/bash
ccc19:x:1273:1273::/home/ccc19:/bin/bash
ccc20:x:1274:1274::/home/ccc20:/bin/bash

[root@localhost day4]# ./add20user.sh
please input username's prefix:ccc
please input initial password:ccc
user ccc01 already exists.
user ccc02 already exists.
user ccc03 already exists.
user ccc04 already exists.
user ccc05 already exists.
user ccc06 already exists.
user ccc07 already exists.
user ccc08 already exists.
user ccc09 already exists.
user ccc10 already exists.
user ccc11 already exists.
user ccc12 already exists.
user ccc13 already exists.
user ccc14 already exists.
user ccc15 already exists.
user ccc16 already exists.
user ccc17 already exists.
user ccc18 already exists.
user ccc19 already exists.
user ccc20 already exists.
created 0 users successfully

2.for ping测试指网段的主机，网段由用户输入。

例如用户输入192.168.2 ，则ping 192.168.2.10 — 192.168.2.20
UP： /tmp/host_up.txt
Down: /tmp/host_down.txt

准备工作：
创建相关的文件

[root@localhost day4]# touch /tmp/host_up.txt
[root@localhost day4]# touch /tmp/host_down.txt

1、编写脚本

[root@localhost day4]# vim forPing.sh

#!/bin/bash
read -p "please input network segment:" seg
for ip in ${seg}.{1..10}
do
	if ping -c2 $ip &> /dev/null ;then
		date >> /tmp/host_up.txt
		echo "$ip is up" >> /tmp/host_up.txt
	else
		date >> /tmp/host_down.txt
		echo "$ip is down" >> /tmp/host_down.txt
	fi
done

2、设置权限

[root@localhost day4]# chmod a+rx forPing.sh

3、运行测试

[root@localhost day4]# ./forPing.sh
please input network segment:192.168.210

[root@localhost day4]# cat /tmp/host_up.txt
2023年 01月 06日 星期五 00:03:28 CST
192.168.210.2 is up

[root@localhost day4]# cat  /tmp/host_down.txt
2023年 01月 06日 星期五 00:03:27 CST
192.168.210.1 is down
2023年 01月 06日 星期五 00:03:31 CST
192.168.210.3 is down
2023年 01月 06日 星期五 00:03:34 CST
192.168.210.4 is down
2023年 01月 06日 星期五 00:03:38 CST
192.168.210.5 is down
2023年 01月 06日 星期五 00:03:41 CST
192.168.210.6 is down
2023年 01月 06日 星期五 00:03:44 CST
192.168.210.7 is down
2023年 01月 06日 星期五 00:03:47 CST
192.168.210.8 is down
2023年 01月 06日 星期五 00:03:50 CST
192.168.210.9 is down
2023年 01月 06日 星期五 00:03:53 CST
192.168.210.10 is down

3.使用for实现批量主机root密码的修改，成功或失败都必须记录。

提示：主机IP存放在一个文件中
SSH：实现公钥认证，执行远程中主机命令
实现公钥认证
ssh-keygen 在用于管理的主上生成密钥对
ssh-copy-id -i 192.168.2.3

准备工作：
创建主机IP文件

[root@localhost day4]# vim host_ip.txt
192.168.210.5
192.168.210.6
192.168.210.7

1、编写脚本

[root@localhost day4]# vim chpwd_ssh.sh
#!/bin/bash
host_ip="/root/day4/host_ip.txt"
chpwd_log="/root/day4/chpwd_log.txt"
echo "checking key pair..."
if [ -f /root/.ssh/id_rsa -a -f /root/.ssh/id_rsa.pub ];then
	echo "key pair is ok"
else
	ssh-keygen -q -P "" -f /root/.ssh/id_rsa &> /dev/null && echo "key pair is created successfully"
fi
read -p "please input new password for hosts:" passwd
for line in `cat "$host_ip"`
do
	echo "changing $line's root password..."
	ssh-copy-id root@$line &> /dev/null && ssh root@$line "echo $passwd | passwd root --stdin" &> /dev/null
	if [ $? -eq 0 ];then
		echo "$line change password successfully"
		date >> "$chpwd_log"
		echo "$line change password successfully" >> "$chpwd_log"
	else
		echo "$line change password failed"
		date >> "$chpwd_log"
        echo "$line change password failed" >> "$chpwd_log"
	fi
done

2、设置权限

[root@localhost day4]# chmod a+rx chpwd_ssh.sh

3、运行测试
第一次修改密码（无免密）：

[root@localhost day4]# ./chpwd_ssh.sh
checking key pair...
key pair is ok
please input new password for hosts:test
changing 192.168.210.5's root password...
192.168.210.5 change password failed
changing 192.168.210.6's root password...
192.168.210.6 change password failed
changing 192.168.210.128's root password...
The authenticity of host '192.168.210.128 (192.168.210.128)' can't be established.
ECDSA key fingerprint is SHA256:fUIFDTKDWHnEY9Pdl2go991nL40RiDHB+IXON7mTaPQ.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
root@192.168.210.128's password: 
192.168.210.128 change password successfully

第二次修改密码（免密）：

[root@localhost day4]# ./chpwd_ssh.sh
checking key pair...
key pair is ok
please input new password for hosts:123456
changing 192.168.210.5's root password...
192.168.210.5 change password failed
changing 192.168.210.6's root password...
192.168.210.6 change password failed
changing 192.168.210.128's root password...
192.168.210.128 change password successfully

查看日志：

[root@localhost day4]# cat chpwd_log.txt
2023年 01月 06日 星期五 00:19:40 CST
192.168.210.5 change password failed
2023年 01月 06日 星期五 00:19:46 CST
192.168.210.6 change password failed
2023年 01月 06日 星期五 00:20:45 CST
192.168.210.128 change password successfully
2023年 01月 06日 星期五 00:21:38 CST
192.168.210.5 change password failed
2023年 01月 06日 星期五 00:21:44 CST
192.168.210.6 change password failed
2023年 01月 06日 星期五 00:21:45 CST
192.168.210.128 change password successfully