Recently we had written two articles in the same kind of topic.
Those articles helps you to check whether the given ports are open or not in the remote servers.
If you want to **[check whether a port is open on the remote Linux system][1]** then navigate to this article.
If you want to **[check whether a port is open on multiple remote Linux system][2]** then navigate to this article.
If you would like to **[check multiple ports status on multiple remote Linux system][2]** then navigate to this article.
But this article helps you to check the list of open ports on the local system.
There are few utilities are available in Linux for this purpose.
However, I’m including top four Linux commands to check this.
It can be done using the following four commands. These are very famous and widely used by Linux admins.
* **`netstat:`** netstat (“network statistics”) is a command-line tool that displays network connections related information (both incoming and outgoing) such as routing tables, masquerade connections, multicast memberships and a number of network interface
* **`nmap:`** Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks.
* **`ss:`** ss is used to dump socket statistics. It allows showing information similar to netstat. It can display more TCP and state information than other tools.
* **`lsof:`** lsof stands for List Open File. It is used to print all the open files which is opened by process.
### How To Check The List Of Open Ports In Linux Using netstat Command?
netstat stands for Network Statistics, is a command-line tool that displays network connections related information (both incoming and outgoing) such as routing tables, masquerade connections, multicast memberships and a number of network interface.
It lists out all the tcp, udp socket connections and the unix socket connections.
It is used for diagnosing network problems in the network and to determine the amount of traffic on the network as a performance measurement.
```
# netstat -tplugn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 2038/master
tcp 0 0 127.0.0.1:199 0.0.0.0:* LISTEN 1396/snmpd
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 1398/httpd
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1388/sshd
tcp6 0 0 :::25 :::* LISTEN 2038/master
tcp6 0 0 :::22 :::* LISTEN 1388/sshd
udp 0 0 0.0.0.0:39136 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:56130 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:40105 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:11584 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:30105 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:50656 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:1632 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:28265 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:40764 0.0.0.0:* 1396/snmpd
udp 0 0 10.90.56.21:123 0.0.0.0:* 895/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:* 895/ntpd
udp 0 0 0.0.0.0:123 0.0.0.0:* 895/ntpd
udp 0 0 0.0.0.0:53390 0.0.0.0:* 1396/snmpd
udp 0 0 0.0.0.0:161 0.0.0.0:* 1396/snmpd
udp6 0 0 :::123 :::* 895/ntpd
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 224.0.0.1
eth0 1 224.0.0.1
lo 1 ff02::1
lo 1 ff01::1
eth0 1 ff02::1
eth0 1 ff01::1
```
If you would like to check any particular port status then use the following format.
```
# # netstat -tplugn | grep :22
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1388/sshd
tcp6 0 0 :::22 :::* LISTEN 1388/sshd
```
### How To Check The List Of Open Ports In Linux Using ss Command?
ss is used to dump socket statistics. It allows showing information similar to netstat. It can display more TCP and state information than other tools.
```
# ss -lntu
Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port
udp UNCONN 0 0 *:39136 *:*
udp UNCONN 0 0 *:56130 *:*
udp UNCONN 0 0 *:40105 *:*
udp UNCONN 0 0 *:11584 *:*
udp UNCONN 0 0 *:30105 *:*
udp UNCONN 0 0 *:50656 *:*
udp UNCONN 0 0 *:1632 *:*
udp UNCONN 0 0 *:28265 *:*
udp UNCONN 0 0 *:40764 *:*
udp UNCONN 0 0 10.90.56.21:123 *:*
udp UNCONN 0 0 127.0.0.1:123 *:*
udp UNCONN 0 0 *:123 *:*
udp UNCONN 0 0 *:53390 *:*
udp UNCONN 0 0 *:161 *:*
udp UNCONN 0 0 :::123 :::*
tcp LISTEN 0 100 *:25 *:*
tcp LISTEN 0 128 127.0.0.1:199 *:*
tcp LISTEN 0 128 *:80 *:*
tcp LISTEN 0 128 *:22 *:*
tcp LISTEN 0 100 :::25 :::*
tcp LISTEN 0 128 :::22 :::*
```
If you would like to check any particular port status then use the following format.
```
# # ss -lntu | grep ':25'
tcp LISTEN 0 100 *:25 *:*
tcp LISTEN 0 100 :::25 :::*
```
### How To Check The List Of Open Ports In Linux Using nmap Command?
Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks, although it works fine against single hosts.
Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics.
While Nmap is commonly used for security audits, many systems and network administrators find it useful for routine tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime.
```
# nmap -sTU -O localhost
Starting Nmap 6.40 ( http://nmap.org ) at 2019-03-20 09:57 CDT
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00028s latency).
Other addresses for localhost (not scanned): 127.0.0.1
Not shown: 1994 closed ports
PORT STATE SERVICE
22/tcp open ssh
25/tcp open smtp
80/tcp open http
199/tcp open smux
123/udp open ntp
161/udp open snmp
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
OS detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1.93 seconds
```
If you would like to check any particular port status then use the following format.
```
# nmap -sTU -O localhost | grep 123
123/udp open ntp
```
### How To Check The List Of Open Ports In Linux Using lsof Command?
It shows you the list of open files on the system and the processes that opened them. Also shows you other informations related to the files.
```
# lsof -i
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
