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