1、查看当前所有已经使用的端口情况

命令：netstat -nultp

[root@VM-0-10-centos conf]# netstat -nultp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      21774/nginx: master 
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1123/sshd           
tcp6       0      0 :::45023                :::*                    LISTEN      4072/java           
tcp6       0      0 127.0.0.1:8005          :::*                    LISTEN      4072/java           
tcp6       0      0 :::8009                 :::*                    LISTEN      4072/java           
tcp6       0      0 :::36361                :::*                    LISTEN      4072/java           
tcp6       0      0 :::9999                 :::*                    LISTEN      4072/java           
tcp6       0      0 :::8080                 :::*                    LISTEN      4072/java           
udp        0      0 0.0.0.0:68              0.0.0.0:*                           907/dhclient        
udp        0      0 172.17.0.10:123         0.0.0.0:*                           639/ntpd            
udp        0      0 127.0.0.1:123           0.0.0.0:*                           639/ntpd            
udp6       0      0 fe80::5054:ff:fe29::123 :::*                                639/ntpd            
udp6       0      0 ::1:123                 :::*                                639/ntpd        

2、查看具体端口是否被占用

命令：netstat  -anp  |grep   端口号

[root@VM-0-10-centos conf]# netstat -anp | grep 9999
tcp6       0      0 :::9999                 :::*                    LISTEN      4072/java 

主要看监控状态为LISTEN表示已经被占用。

3、lsof -i:port命令

[root@VM-0-10-centos bin]# lsof -i:9999
COMMAND   PID USER   FD   TYPE   DEVICE SIZE/OFF NODE NAME
java    18396 root   22u  IPv6 46964003      0t0  TCP *:distinct (LISTEN)