1.使用nmap检测开放端口，可检测远程服务器

[root@localhost ~]# nmap localhost

Starting Nmap 6.40 ( http://nmap.org ) at 2020-06-09 01:40 CST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000023s latency).
Other addresses for localhost (not scanned): 127.0.0.1
Not shown: 998 closed ports
PORT   STATE SERVICE
22/tcp open  ssh
25/tcp open  smtp

Nmap done: 1 IP address (1 host up) scanned in 2.01 seconds

2.使用netstat检测本地端口

[root@localhost ~]# netstat -tunlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      6741/sshd           
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      7053/master         
tcp6       0      0 :::22                   :::*                    LISTEN      6741/sshd           
tcp6       0      0 ::1:25                  :::*                    LISTEN      7053/master         
udp        0      0 0.0.0.0:68              0.0.0.0:*                   

3.使用lsof检测开放端口

[root@localhost ~]# lsof -i:22
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
sshd     6741 root    3u  IPv4  37912      0t0  TCP *:ssh (LISTEN)
sshd     6741 root    4u  IPv6  37914      0t0  TCP *:ssh (LISTEN)
sshd    17129 root    3u  IPv4  48317      0t0  TCP localhost.localdomain:ssh->192.168.100.1:65379 (ESTABLISHED)

4.使用netcat检测端口

[root@localhost ~]# nc -zv localhost 22
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to ::1:22.
Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds.

5.使用Telnet检测端口，只能检测TCP端口。telnet+ip/域名+端口
[root@localhost ~]# telnet localhost 22
Trying ::1...
Connected to localhost.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.4

6.curl检测端口，curl +ip:端口

[root@localhost ~]# curl localhost:22
SSH-2.0-OpenSSH_7.4
Protocol mismatch.