Linux查看监听端口的脚本测试

本文是按照lfree的博客（https://www.cnblogs.com/lfree/p/10368332.html）中的内容，进行学习、测试、总结的。有些知识点也是在阅读这篇博文时，发现不了解这方面的知识，遂网上搜索相关资料总结了一下。

 

 

1：linux 设备里面有个比较特殊的文件:/dev/[tcp|upd]/host/port 只要读取或者写入这个文件，相当于系统会尝试连接:host 这台机器，对应port端口。如果主机以及端口存在，就建立一个socket 连接。将在，/proc/self/fd目录下面，有对应的文件出现。

 

/dev/tcp/${host}/${port} 这个字符串看起来很像一个文件系统中的文件，并且位于 /dev 这个设备文件夹下。但是：这个文件并不存在，而且并不是一个设备文件。这只是 bash 实现的用来实现网络请求的一个接口，其实就像我们自己编写的一个命令行程序，按照指定的格式输入host port参数，就能发起一个socket连接完全一样

 

 

[root@db-server ~]# cat < /dev/tcp/10.20.57.24/23

-bash: connect: connection refused

-bash: /dev/tcp/10.20.57.24/23: connection refused

[root@db-server ~]# cat < /dev/tcp/10.20.57.24/22

ssh-2.0-openssh_4.3

[root@db-server ~]# echo a > /dev/tcp/10.20.57.24/22

[root@db-server ~]# echo $?

0

[root@db-server ~]# echo a > /dev/tcp/10.20.57.24/23

-bash: connect: connection refused

-bash: /dev/tcp/10.20.57.24/23: connection refused

[root@db-server ~]# echo $?

1

[root@db-server ~]# netstat -ntlp

active internet connections (only servers)

proto recv-q send-q local address               foreign address             state       pid/program name   

tcp        0      0 0.0.0.0:42304               0.0.0.0:*                   listen      7497/ora_d009_gsp   

tcp        0      0 0.0.0.0:50336               0.0.0.0:*                   listen      7481/ora_d005_gsp   

tcp        0      0 127.0.0.1:2208              0.0.0.0:*                   listen      2936/hpiod          

tcp        0      0 0.0.0.0:57505               0.0.0.0:*                   listen      7521/ora_d015_gsp   

tcp        0      0 0.0.0.0:769                 0.0.0.0:*                   listen      2707/rpc.statd      

tcp        0      0 0.0.0.0:31298               0.0.0.0:*                   listen      7533/ora_d018_gsp   

tcp        0      0 0.0.0.0:13026               0.0.0.0:*                   listen      7469/ora_d002_gsp   

tcp        0      0 0.0.0.0:40227               0.0.0.0:*                   listen      7485/ora_d006_gsp   

tcp        0      0 0.0.0.0:62788               0.0.0.0:*                   listen      7537/ora_d019_gsp   

tcp        0      0 0.0.0.0:58151               0.0.0.0:*                   listen      7473/ora_d003_gsp   

tcp        0      0 0.0.0.0:18728               0.0.0.0:*                   listen      7505/ora_d011_gsp   

tcp        0      0 0.0.0.0:29705               0.0.0.0:*                   listen      7529/ora_d017_gsp   

tcp        0      0 0.0.0.0:60011               0.0.0.0:*                   listen      7493/ora_d008_gsp   

tcp        0      0 0.0.0.0:19819               0.0.0.0:*                   listen      7461/ora_d000_gsp   

tcp        0      0 0.0.0.0:50605               0.0.0.0:*                   listen      7513/ora_d013_gsp   

tcp        0      0 0.0.0.0:11149               0.0.0.0:*                   listen      7465/ora_d001_gsp   

tcp        0      0 0.0.0.0:25487               0.0.0.0:*                   listen      7501/ora_d010_gsp   

tcp        0      0 0.0.0.0:111                 0.0.0.0:*                   listen      2662/portmap        

tcp        0      0 0.0.0.0:28021               0.0.0.0:*                   listen      7517/ora_d014_gsp   

tcp        0      0 0.0.0.0:46038               0.0.0.0:*                   listen      7525/ora_d016_gsp   

tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   listen      2953/sshd           

tcp        0      0 127.0.0.1:631               0.0.0.0:*                   listen      2964/cupsd          

tcp        0      0 0.0.0.0:22392               0.0.0.0:*                   listen      7489/ora_d007_gsp   

tcp        0      0 127.0.0.1:25                0.0.0.0:*                   listen      2999/sendmail: acce 

tcp        0      0 0.0.0.0:12508               0.0.0.0:*                   listen      7477/ora_d004_gsp   

tcp        0      0 0.0.0.0:26302               0.0.0.0:*                   listen      7509/ora_d012_gsp   

[root@db-server ~]# seq 1 65535 | xargs -i{} echo "echo a > /dev/tcp/10.20.57.24/{} 2>/dev/null 2&>1 ; echo ok=\$?,{}" | bash 2>/dev/null | grep ok=0 | cut -d, -f2

22

111

769

11149

12508

13026

18728

19819

22392

25487

26302

28021

29705

31298

40227

42304

45826

46038

50336

50605

50741

52199

56371

57505

58151

60011

62788

 

如上测试所示，上面脚本不会记录环回地址（127.0.0.1）的listen端口。而且脚本执行的效率较低，等待时间过长。

 

 

2：使用nc命令测试，测试结果发现，这个命令的速度完全秒杀上面脚本。但是也是不能定位环回地址（127.0.0.1）的listen端口。需要指定ip地址127.0.0.1才能定位定位环回地址（127.0.0.1）的listen

 

root@db-server ~]# echo a | nc -w 1 -n -v  10.20.57.24 1-65535 2>/dev/null | grep "succeeded"

connection to 10.20.57.24 22 port [tcp/*] succeeded!

connection to 10.20.57.24 111 port [tcp/*] succeeded!

connection to 10.20.57.24 769 port [tcp/*] succeeded!

connection to 10.20.57.24 11149 port [tcp/*] succeeded!

connection to 10.20.57.24 12508 port [tcp/*] succeeded!

connection to 10.20.57.24 13026 port [tcp/*] succeeded!

connection to 10.20.57.24 18728 port [tcp/*] succeeded!

connection to 10.20.57.24 19819 port [tcp/*] succeeded!

connection to 10.20.57.24 22392 port [tcp/*] succeeded!

connection to 10.20.57.24 25487 port [tcp/*] succeeded!

connection to 10.20.57.24 26302 port [tcp/*] succeeded!

connection to 10.20.57.24 28021 port [tcp/*] succeeded!

connection to 10.20.57.24 29705 port [tcp/*] succeeded!

connection to 10.20.57.24 31298 port [tcp/*] succeeded!

connection to 10.20.57.24 40227 port [tcp/*] succeeded!

connection to 10.20.57.24 42304 port [tcp/*] succeeded!

connection to 10.20.57.24 46038 port [tcp/*] succeeded!

connection to 10.20.57.24 50111 port [tcp/*] succeeded!

connection to 10.20.57.24 50336 port [tcp/*] succeeded!

connection to 10.20.57.24 50605 port [tcp/*] succeeded!

connection to 10.20.57.24 57505 port [tcp/*] succeeded!

connection to 10.20.57.24 58151 port [tcp/*] succeeded!

connection to 10.20.57.24 60011 port [tcp/*] succeeded!

connection to 10.20.57.24 62788 port [tcp/*] succeeded!

[root@db-server ~]# echo a | nc -w 1 -n -v  127.0.0.1 1-65535 2>/dev/null | grep "succeeded"

connection to 127.0.0.1 22 port [tcp/*] succeeded!

connection to 127.0.0.1 25 port [tcp/*] succeeded!

connection to 127.0.0.1 111 port [tcp/*] succeeded!

connection to 127.0.0.1 631 port [tcp/*] succeeded!

connection to 127.0.0.1 769 port [tcp/*] succeeded!

connection to 127.0.0.1 2208 port [tcp/*] succeeded!

connection to 127.0.0.1 11149 port [tcp/*] succeeded!

connection to 127.0.0.1 12508 port [tcp/*] succeeded!

connection to 127.0.0.1 13026 port [tcp/*] succeeded!

connection to 127.0.0.1 18728 port [tcp/*] succeeded!

connection to 127.0.0.1 19819 port [tcp/*] succeeded!

connection to 127.0.0.1 22392 port [tcp/*] succeeded!

connection to 127.0.0.1 25487 port [tcp/*] succeeded!

connection to 127.0.0.1 26302 port [tcp/*] succeeded!

connection to 127.0.0.1 28021 port [tcp/*] succeeded!

connection to 127.0.0.1 29705 port [tcp/*] succeeded!

connection to 127.0.0.1 31298 port [tcp/*] succeeded!

connection to 127.0.0.1 40227 port [tcp/*] succeeded!

connection to 127.0.0.1 42304 port [tcp/*] succeeded!

connection to 127.0.0.1 46038 port [tcp/*] succeeded!

connection to 127.0.0.1 50336 port [tcp/*] succeeded!

connection to 127.0.0.1 50605 port [tcp/*] succeeded!

connection to 127.0.0.1 57505 port [tcp/*] succeeded!

connection to 127.0.0.1 58151 port [tcp/*] succeeded!

connection to 127.0.0.1 60011 port [tcp/*] succeeded!

connection to 127.0.0.1 62788 port [tcp/*] succeeded!

[root@db-server ~]# 

 

 

这些命令其实是查看服务器处于 listening状态的端口。跟服务器开放的端口是两回事情。如下所示，使用nmap扫描，发现服务器只开放了这些端口。

 

 

# nmap 10.20.57.24

starting nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2019-02-15 17:01 cst

interesting ports on 10.20.57.24:

not shown: 1674 filtered ports

port     state  service

22/tcp   open   ssh

631/tcp  closed ipp

1521/tcp open   oracle

3306/tcp closed mysql

5901/tcp closed vnc-1

5902/tcp closed vnc-2

 

对比测试如下：

 

 

 

 

 

 

 

 

 

参考资料：

 

https://www.jianshu.com/p/80d6b5a61372

http://www.cnblogs.com/chengmo/archive/2010/10/22/1858302.html