{"id":146844,"date":"2023-03-14T13:16:29","date_gmt":"2023-03-14T13:16:29","guid":{"rendered":"https:\/\/ded9.com\/?p=146844"},"modified":"2025-11-04T08:32:18","modified_gmt":"2025-11-04T08:32:18","slug":"how-to-show-check-for-open-ports-on-ubuntu-linux","status":"publish","type":"post","link":"https:\/\/ded9.com\/tr\/how-to-show-check-for-open-ports-on-ubuntu-linux\/","title":{"rendered":"How to Show or Check for Open Ports on Ubuntu \/ Linux"},"content":{"rendered":"

Port checking is assigned to the specific program currently in use.<\/p>\n

Of course, this was just one of many reasons to check open ports before running an application.<\/p>\n

For example, you can use the ss command with the -ltmp option to display open ports, including the processes associated with them.<\/p>\n

sudo ss -ltunp<\/code><\/p>\n

\"For<\/p>\n

As you can see, port numbers 53 and 631 are open by default and are used for DNS and the Internet. You can decide whether to allow or block these ports.<\/p>\n

1. Using the Nmap command<\/h2>\n

Network engineers generally use the Nmap Network Mapper tool to diagnose operating systems, scan ports, and perform network mapping.<\/p>\n

Unlike any other tool, nmap can open ports on remote devices without access and does not require root privileges.<\/p>\n

But it requires manual installation through the command:<\/p>\n

sudo apt install nmap<\/code><\/p>\n

To check open ports on localhost:<\/p>\n

nmap localhost<\/code><\/p>\n

\"Using<\/p>\n

By default, Nmap only provides information on TCP ports. To list TCP and UDP ports simultaneously, you must use the -sTU option:<\/p>\n

Sudo nmap -sTU localhost<\/p>\n

\"By<\/p>\n

Similarly, you can also use any hostname you want. For example, let’s go with Google.<\/p>\n

nmap google.com<\/code><\/p>\n

As you can see, Google has closed all unnecessary ports for security reasons.<\/p>\n

2. Check open ports using the lsof command<\/h2>\n

Linux works on the philosophy that “everything is a file,” and users can list all open files using the lsof command.<\/p>\n

Since the lsof tool is required to read data from the proc kernel, you can easily trace network connections, including ports.<\/p>\n

But the lsof command cannot be used without options, so you must use special options to get open ports.<\/p>\n

So, first let me show you the command,d, and then we will explain:<\/p>\n

sudo lsof -i -P -sTCP:LISTEN<\/code><\/p>\n

\"So,<\/p>\n

Now, let’s explain the options used:<\/p>\n

It is used to receive files that are only related to the network.<\/p>\n

P displays the numerical value of the ports.<\/p>\n

sTCP: LISTEN fetches TCP ports in listening (open) mode.<\/p>\n

Similarly, you can also check individual ports. So let’s say I want to check port number 631:<\/p>\n

sudo lsof -P -i:631<\/code><\/p>\n

\"Similarly,<\/p>\n

As you can see, cupsd is used by root on the given port.<\/p>\n