How to check which ports are open in Linux

How to check open ports on Linux: 1. Use rpm to install the nmap tool, and execute the "nmap 127.0.0.1" command to view the open ports on this machine; 2. Execute the "netstat -anp" command to view the open ports. port.

#The operating environment of this tutorial: linux5.9.8 system, Dell G3 computer.

Linux Check which ports are open

1: The nmap tool detects open ports

nmap is a network scanning and Host detection tool. Installation of nmap is very simple as shown below for rpm installation.

[root@DB-Server Server]# rpm -ivh nmap-4.11-1.1.x86_64.rpm warning: nmap-4.11-1.1.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186 Preparing... ########################################### [100%] 1:nmap ########################################### [100%] [root@DB-Server Server]# rpm -ivh nmap-frontend-4.11-1.1.x86_64.rpm warning: nmap-frontend-4.11-1.1.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186 Preparing... ########################################### [100%] 1:nmap-frontend ########################################### [100%] [root@DB-Server Server]#

Regarding the use of nmap, you can write a long and close-up article, and I will not expand it here. As shown below, nmap 127.0.0.1 checks the open ports of this machine and scans all ports. Of course, other server ports can also be scanned.

[root@DB-Server Server]# nmap 127.0.0.1 Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2016-06-22 15:46 CST Interesting ports on localhost.localdomain (127.0.0.1): Not shown: 1674 closed ports PORT STATE SERVICE 22/tcp open ssh 25/tcp open smtp 111/tcp open rpcbind 631/tcp open ipp 1011/tcp open unknown 3306/tcp open mysql Nmap finished: 1 IP address (1 host up) scanned in 0.089 seconds You have new mail in /var/spool/mail/root [root@DB-Server Server]#

2: The netstat tool detects open ports

can be passed "netstat -anp" to see which ports are open.

(Note: Adding parameter '-n' will convert the application to port display, that is, an address in digital format, such as: nfs->2049, ftp->21, so two terminals can be opened , corresponding to the port number corresponding to the program one by one)

Extension: Check whether the port is open

lsof tool detects open ports

[root@DB-Server Server]# service mysql start Starting MySQL......[ OK ] [root@DB-Server Server]# lsof -i:3306 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME mysqld 7860 mysql 15u IPv6 44714 TCP *:mysql (LISTEN) [root@DB-Server Server]# service mysql stop Shutting down MySQL..[ OK ] [root@DB-Server Server]# lsof -i:3306 [root@DB-Server Server]#

[root@DB-Server Server]# lsof -i TCP| fgrep LISTEN cupsd 3153 root 4u IPv4 9115 TCP localhost.localdomain:ipp (LISTEN) portmap 3761 rpc 4u IPv4 10284 TCP *:sunrpc (LISTEN) rpc.statd 3797 rpcuser 7u IPv4 10489 TCP *:1011 (LISTEN) sshd 4020 root 3u IPv6 12791 TCP *:ssh (LISTEN) sendmail 4042 root 4u IPv4 12876 TCP localhost.localdomain:smtp (LISTEN)

Use telnet to check whether the port is open

Even if the server port is in the listening state, the firewall The port is blocked by iptables, and it is impossible to detect whether the port is open through this method.

netcat tool detects whether the port is open

[root@DB-Server ~]# nc -vv 192.168.42.128 1521 Connection to 192.168.42.128 1521 port [tcp/ncube-lm] succeeded! [root@DB-Server ~]# nc -z 192.168.42.128 1521; echo $? Connection to 192.168.42.128 1521 port [tcp/ncube-lm] succeeded! 0 [root@DB-Server ~]# nc -vv 192.168.42.128 1433 nc: connect to 192.168.42.128 port 1433 (tcp) failed: No route to host

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