How to Check Listening Ports in Linux

To Check Listening Ports in Linux

After configuring the network, checking the ports which are still listening  on the network interface is one of the important things in network management and security. This article will help you to check Listening ports in Linux. Following examples help you to find listen port after network configuration.

 

Checking Listening Ports

Use nmap command with following option to view listening ports for TCP.

[root@node2 Desktop]# nmap -sT -O localhost
Starting Nmap 6.40 ( http://nmap.org ) at 2017-02-25 01:49 IST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.0019s latency).
Other addresses for localhost (not scanned): 127.0.0.1
Not shown: 995 closed ports
PORT    STATE SERVICE
22/tcp  open  ssh
25/tcp  open  smtp
80/tcp  open  http
111/tcp open  rpcbind
631/tcp open  ipp
Device type: general purpose
Running: Linux 3.X
OS CPE: cpe:/o:linux:linux_kernel:3
OS details: Linux 3.7 - 3.9
Network Distance: 0 hops

Use ss command to display all listen tcp and udp port.

[root@node2 Desktop]# ss -lntu
Netid  State      Recv-Q Send-Q               Local Address:Port                 Peer Address:Port 
tcp    UNCONN     0      0                                *:45113                           *:*     
tcp    UNCONN     0      0                                *:111                             *:*     
tcp    UNCONN     0      0                                *:123                             *:*     
.
.
.
tcp    LISTEN     0      128                             :::80                             :::*     
tcp    LISTEN     0      128                             :::22                             :::*     
tcp    LISTEN     0      128                            ::1:631                            :::*


Use netstat command to list all open ports or currently running ports including TCP and UDP in Linux.

[root@node2 Desktop]# netstat -lntu
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:36393           0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN    
.
.
.
udp6       0      0 :::683                  :::*                               
udp6       0      0 ::1:323                 :::*                               
udp6       0      0 :::54192                :::*


To view a list of different applications and port/protocol combination in single configuration file.

[root@node2 Desktop]# cat /etc/services | less


To view particular listening port in configuration file, run the following command

[root@node2 Desktop]# cat /etc/services | grep 80
http            80/tcp          www www-http    # WorldWideWeb HTTP
http            80/udp          www www-http    # HyperText Transfer Protocol
http            80/sctp                         # HyperText Transfer Protocol
socks           1080/tcp                        # socks proxy server
.
.
.
nimbusdb        48004/tcp               # NimbusDB Connector
nimbusdbctrl    48005/tcp               # NimbusDB Control
3gpp-cbsp       48049/tcp               # 3GPP Cell Broadcast Service Protocol


Filter the particular listen port details by its service name using netstat.

[root@node2 Desktop]# netstat -anp | grep httpd
tcp6       0      0 :::80                   :::*                    LISTEN      13560/httpd         
unix  3      [ ]         STREAM     CONNECTED     69292    13560/httpd   

Filter the particular listen port details by its port name using lsof.

[root@node2 Desktop]# lsof -i | grep 22
rpc.statd  2350 rpcuser    7u  IPv4  22736      0t0  UDP *:43289 
rpc.statd  2350 rpcuser    8u  IPv4  22740      0t0  TCP *:36393 (LISTEN)
rpc.statd  2350 rpcuser    9u  IPv6  22744      0t0  UDP *:54192 
rpc.statd  2350 rpcuser   11u  IPv6  22748      0t0  TCP *:35835 (LISTEN)
master     2404    root   13u  IPv4  22844      0t0  TCP localhost:smtp (LISTEN)
master     2404    root   14u  IPv6  22845      0t0  TCP localhost:smtp (LISTEN)

 

Also filter the listening port details by ss commands.

[root@node2 Desktop]# ss -lnt | grep 80
LISTEN     0      128                      :::80                      :::*

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Tags: Linux
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