How to check listening ports in Linux

We should pay attention to listening ports, to validate and disable the unused ports in infra is a very important thing. In that the way, we can secure the server from the attack surface. So, Will see How to check listening ports in Linux

Known Ports:

993    – IMAPS
1194  – openVPN
1812  – RADIUS
995    – POP3s
2049  – NFS (nfsd, rpc.nfsd, rpc, portmap)
2401  – CVS server
3306  – MySql
3690  – SVN
6000-6063- X11
123    – NTP (Network time protocol used for time syncing uses UDP protocol)
137    – NetBIOS (nmbd)
139    – SMB-Samba (smbd)
143    – IMAP
161    – SNMP (For network monitoring)
389    – LDAP (For centralized administration)
443    – HTTPS (HTTP+SSL for secure web access)
514    – Syslogd (udp port)
636    – ldaps (both ctp and udp)
873    – rsync
989    – FTPS-data
990    – FTPS
20      – FTP Data (For transferring FTP data)
21      – FTP Control (For starting FTP connection)
22      – SSH (For secure remote administration which uses SSL to encrypt the transmission)
23      – Telnet (For insecure remote administration)
25      – SMTP (Mail Transfer Agent for e-mail server such as SEND mail)
53      – DNS (Special service which uses both TCP and UDP)
67      – Bootp
68      – DHCP
69      – TFTP (Trivial file transfer protocol uses udp protocol for connection less transmission of data)
80      –  HTTP/WWW(Apache)
88      – Kerberos
110    – POP3 (Mail delivery Agent)


Issue the below command as root user to check the listening ports.

Will use  netstat command to check open ports.

#netstat -tulpn

t – Will enables listing of tcp ports.
u – Will enables listing of udp ports
n – this will shows the port numbers
l – It will list only listening pockets

/etc/services – by reading this file we can read different types port/protocol combinations and applications.

#less /etc/services

lsof command:

Package for lsof:  lsof-4.87-4.el7.x86_64

To check the package avilability in linux use the below command.

#rpm -qa | grep -i lsof

To list open ports:

#lsof -i

To display all open files:

nmap command:

    Using nmap  command will check the open ports for remote server.

Using below command will check open ports in local machine.

      #nmap -sT  -O localhost

Command to check remote machine open ports:

#nmap -sT -O 192.168.0.105