Linux port open, prohibit, view

1. Add\Disable ports

Modify the configuration file command:
vim /etc/sysconfig/iptables
Add:
iptables -A INPUT -p tcp –dport$port -j ACCEPT 禁止: iptables -A INPUT -p tcp –dport$port -j DROP

Start the service:
/etc/init.d/iptables restart

2. View open ports

netstat -nupl (UDP type port)
netstat -ntpl (TCP type port)

a means all
n means do not query dns
t means tcp protocol
u means udp protocol
p means query occupied programs
l means query listening programs

netstat -ntpl | grep 3306 //This means to find the process in the listening state with port number 3306

[root@home ~]# netstat -ntpl | grep 3306
tcp        0      0 0.0.0.0:3306                0.0.0.0:*                   LISTEN      25302/mysqld   

[root@home ~]# netstat -nupl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name   
udp        0      0 172.18.1.143:123            0.0.0.0:*                               1526/ntpd           
udp        0      0 127.0.0.1:123               0.0.0.0:*                               1526/ntpd           
udp        0      0 0.0.0.0:123                 0.0.0.0:*                               1526/ntpd     

[root@home ~]# netstat -ntpl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name   
tcp        0      0 0.0.0.0:6369                0.0.0.0:*                   LISTEN      3284/beam.smp       
tcp        0      0 0.0.0.0:18083               0.0.0.0:*                   LISTEN      3284/beam.smp       
tcp        0      0 127.0.0.1:8743              0.0.0.0:*                   LISTEN      26488/java          
tcp        0      0 127.0.0.1:25                0.0.0.0:*                   LISTEN      19651/sendmail      
tcp        0      0 0.0.0.0:443                 0.0.0.0:*                   LISTEN      24538/nginx