If you are a computer scientist or even a bit familiar with networking, you may have heard of the TCP/IP stack. The TCP/IC stack consists of five different layers, namely the physical layer, the channel layer, the network layer, the transport layer and the application layer. Each TCP/IP layer in the stack has different means of communication, and all communication within the transport layer takes place via port numbers.
The port number is used to uniquely identify the device and IP address. Interprocess communication is common when using computer systems. To facilitate this communication, operating systems keep certain ports open, depending on the object with which the user wants to communicate. This way multiple ports can be opened simultaneously on your system.
When we say that a port is in use, we essentially mean an open port, or a port that listens (ready to accept connections). There are many ways to identify open ports in the operating system. This article presents four possible methods to check if a port is used under Linux.
Pay attention: All methods presented in this article are implemented with Linux Mint 20.
You can use one of the following four methods to determine whether a port is used in Linux Mint 20.
Method 1: Using the lsof command
The lsof command can be used to list all the ports used in your system as follows:
First start up the Linux Mint 20 terminal by clicking on the shortcut. The terminal is shown in the figure below:
Then you have to install the lsof command if you have never used it before. To do so, execute the following command in the terminal:
$ sudo apt get the lsof installation
After successful installation of the inverter, the following output appears in the terminal :
After installation, this command can be used to query all ports used under Linux. To check that your system does not have open ports, execute the following command in the terminal:
The output of this command uses the ports that are in the LISTEN state, as shown in the figure below
Method 2: Use of ss commands
The ss command can be used to set all open TCP and UDP ports in your system as follows:
To query the TCP and UDP ports used, execute the following command in the terminal :
When this command is given, the ports used (TCP and UDP) have the LISTEN status, while all other ports have the UNCONN status.
Method 3: Using the mains state control
The netstat command can also be used to set all open TCP and UDP ports on your system as follows
To query the TCP and UDP ports used, execute the following command in the terminal :
If you try to execute this command without the sudo keyword, you will not be able to open all ports. If you are logged in with the root user account, you can ignore this keyword.
When you execute this command, you will see that all ports used are listening, while all other ports are not listening, as shown in the figure below:
Method 4: Using the nmap command
The nmap command is another utility that allows you to configure the TCP and UDP ports used as follows:
If the nmap utility is not yet installed on your Linux Mint 20 system, you may need to install it manually because it is not installed by default. To do so, execute the following command:
After the successful installation of the nfolder utility on your Linux Mint 20 system, your terminal returns control to you so that you can execute the following command, as shown in the figure below :
After installing this utility, ask for the TCP and UDP ports used in your system by executing the following command in the terminal:
$ sudo nmap -n -PN -sT -sU -up local host
After executing this command, the status of all the ports used is opened, as shown in the output of the figure below:
Conclusion
This article has shown you four different methods to check if a port is used in your Linux system. All these methods have been tested in Linux Mint 20, but you can execute the commands in these methods with small variations on any other Linux distribution. The execution of each command used in these methods takes only a few seconds. So you have time to try one of the four methods to find out which one works best for you.
Related Tags:
check remote open port linux,check if ftp port is open linux,open a port on linux,sudo lsof -i -p -n | grep listen,ubuntu 20.04 netstat,linux check if port is blocked by firewall,how to check port 443 is open linux,check if port is in use mac,how to open a port in linux,docker-pr,linux check if port is open on remote server,1.Generally linux has drivers for everything known to man, but becuase of proprietary interference or hardware is not used anymore, you may still be able to …2.Message of the day if the screen you see when you log into the command line. Usually if s short and mundane, You may want to jazz it up a little bit with …3.After compiling a program that is a replacementment/upgrade version to existing software you might get a library conflict. That happened to me . Had a …,1.Generally linux has drivers for everything known to man, but becuase of proprietary interference or hardware is not used anymore, you may still be able to …,2.Message of the day if the screen you see when you log into the command line. Usually if s short and mundane, You may want to jazz it up a little bit with …,3.After compiling a program that is a replacementment/upgrade version to existing software you might get a library conflict. That happened to me . Had a …,how to close a port in ubuntu,how to open port 4444 kali linux,how to enable port in linux firewall,linux open port iptables,linux how to open a port for listening,how to block port in linux without iptables,check if port is in use linux,how to check which process is using a port in linux,how to check which service is running on which port in linux,check ports in use linux,command to check open ports in linux
