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How to Open a Port on Linux

How to Open a Port on Linux
Awais Khan
Technical writer
Linux Network
01.07.2025
Reading time: 7 min

Opening ports in Linux is an important task that allows certain services or applications to exchange data over the network. Ports act as communication gateways, allowing access to authorized services while blocking unauthorized connections. Managing ports is key to secure access, smooth app functionality, and reliable performance. In this guide we'll be using a VPS on Linux.

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Understanding Ports and Their Purpose

Ports are the logical endpoints of network communication, where devices can send and receive information. HTTP uses port 80, HTTPS uses port 443, and SSH uses port 22. An open port means the service that listens for incoming network traffic is associated with it. A closed port, on the other hand, stops communication via that gateway. Maintaining availability and security requires proper management of Linux open ports.

Check Existing Open Ports on Linux

Before opening a port, check the open ports in Linux to see which ones are currently active. You may achieve this using several Linux commands.

netstat

To display open ports, run:

netstat -tuln

The netstat utility provides a real-time view of active network connections, displaying all listening endpoints. The -tuln flags refine the output to show only TCP and UDP ports without resolving hostnames.

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Note: In case netstat isn’t installed, install it via:

sudo apt install net-tools

ss

The ss utility can also be utilized to check ports:

ss -tuln

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Compared to netstat, the ss command is more recent and fast. It shows the ports that are in use as well as socket information.

nmap

For a detailed analysis of Linux open ports, use:

nmap localhost

The nmap utility scans the given host (localhost in this case) for open ports. This is useful for finding ports exposed to public networks.

Image2

Note: You can install nmap on Linux via:

sudo apt install nmap

Opening Ports on Linux

Firewall modification is required to grant access through a chosen endpoint. Linux provides several options for handling these tasks, including iptables, ufw, and firewalld.

Here are the methods to open ports with these utilities.

Method 1: Via iptables

Iptables is a robust and lower level firewall utility that grants fine-grained control over network traffic. To open a port with iptables, take these steps:

  1. Add a Rule to Allow Traffic from a Specific Port 

Enable HTTP access on port 8080 with this command:

sudo iptables -A INPUT -p tcp --dport 8080 -j ACCEPT
  • sudo: Execute the command as superuser.
  • iptables: Refers to the firewall utility.
  • -A INPUT: Inserts a rule in the input chain, controlling incoming traffic.
  • -p tcp: Shows that the rule is for TCP traffic.
  • --dport 8080: Points to port 8080 for the rule.
  • ACCEPT: Specifies that incoming traffic matching the rule is accepted.

This permits incoming TCP on port 8080. However, iptables changes are volatile and will be undone after reboot.

Image5

Note: The iptables can be installed with persistent packages using:

sudo apt install iptables iptables-persistent
  1. Save the Configuration

For making the rule permanent and remain even after a system restart, store iptables rules via:

sudo netfilter-persistent save

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This directive preserves current iptables or nftables rules such that they are preserved during reboots.

  1. Reload Changes

Reload the firewall configuration as needed with:

sudo netfilter-persistent reload

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Method 2: Via UFW

Ufw (Uncomplicated Firewall) is a minimal front-end for managing iptables rules. It allows you to easily open ports with simple commands. This is how you can do it:

  1. Enable Ufw 

First, ensure the ufw firewall is activated:

sudo ufw enable

Executing this command allows UFW to modify firewall settings.

Image6

Note: UFW can be installed with:

sudo apt install ufw
  1. Allow Traffic Via Specific Port 

For instance, to open port 22 for SSH, use:

sudo ufw allow 22/tcp
  • sudo: Grants superuser privileges.
  • ufw allow: Adds a rule to permit traffic.
  • 22/tcp: Sets port 22 for communication while restricting the rule to TCP protocol.

This permits access on port 22, enabling remote SSH connections.

Image9

  1. Verify the Firewall Status 

To ensure the port is accessible and the rule is active, execute:

sudo ufw status

The status command displays all active rules, including the allowed ports.

Image8

Method 3: Via Firewalld

Firewalld is a dynamic firewall daemon present on Linux. It is simpler to customize the firewall rules compared to using iptables. Here’s how to enable port access via firewalld:

  1. Add a Permanent Rule for the Desired Port 

To enable HTTPS access on port 443, run:

sudo firewall-cmd --permanent --add-port=443/tcp
  • firewall-cmd: Invokes the firewalld command.
  • --permanent: Ensures the rule stays active after the firewall reloads or the system boots.
  • --add-port=443/tcp: Opens port 443 to accept incoming TCP traffic.

Image12

Note: Install firewalld on Linux via:

sudo apt install firewalld

Once installed, you should activate and run it:

sudo systemctl enable firewalld
sudo systemctl start firewalld
  1. Reload the Firewall 

Finalize the settings to enable the newly defined policy:

sudo firewall-cmd --reload

Image10

Applying firewall modifications makes recent policy updates functional without rebooting.

  1. Verification

Check whether the port is opened successfully:

sudo firewall-cmd --list-all

The --list-all command provides a complete list of rules, helping you determine if port 443 is open.

Image11

Testing the Newly Opened Port

Always check if the newly opened port is available for incoming connections. Here’s how:

Using telnet

Test the port opening via:

telnet localhost port_number

Successful access means the port is open and responsive.

Image13

Using nmap

Analyze the host to verify if the specified endpoint is accessible.:

nmap -p port_number localhost

The -p flag specifies the port to scan.

Image14

Using curl

Check HTTP service availability:

curl localhost:port_number

A successful response confirms the service is running on the opened port.

Image15

Troubleshooting Common Issues

Ports opening may occasionally fail due to configuration errors or conflicting software settings. Follow these tips:

  • Verify Firewall Rules: Run iptables -L or ufw status to assess firewall restrictions and permissions.

  • Check Service Status: Check if the assigned service is active with systemctl status <service-name>.

Opening Specific Ports Based on Protocol

Understanding the protocol used by the service can help configure ports more effectively. For instance, web traffic typically uses TCP (Transmission Control Protocol) for stable communication, while certain gaming services may require UDP (User Datagram Protocol) for faster packet transmission.

Opening a TCP Port

To access port 3306 for MySQL traffic:

sudo ufw allow 3306/tcp

This explicitly permits TCP traffic through port 3306, ensuring stable communication for database queries.

Image16

Opening a UDP Port

To access port 161 for SNMP (Simple Network Management Protocol), run:

sudo ufw allow 161/udp

Image17

UDP provides faster, connectionless communication, ideal for monitoring tools like SNMP.

Managing Port Accessibility

Once a port is opened, controlling its visibility ensures security and prevents unauthorized access.

Restricting Access to Specific IPs

To limit port access to a specific IP address (e.g., 192.168.1.100):

sudo ufw allow from 192.168.1.100 to any port 22

This allows SSH access via port 22 only from the specified IP address, enhancing security.

Image18

Closing Ports

To revoke access to port 80:

sudo ufw deny 80/tcp

This denies incoming traffic on port 80, effectively closing it for HTTP services.

Image19

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Conclusion

Confirming open ports in Linux is a key step for optimizing network functionality and deploying services effectively. With the use of utilities such as iptables, ufw, or firewalld, you can control traffic securely for your apps. You need to test and debug in order to confirm the port is open and working as expected. From web servers to SSH access, to other network services, port management skills ensure smooth operations and better security.

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Linux Network
01.07.2025
Reading time: 7 min

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Using the ps aux Command in Linux

Effective system administration in Linux requires constant awareness of running processes. Whether diagnosing performance bottlenecks, identifying unauthorized tasks, or ensuring critical services remain operational, the ps aux command is an indispensable tool.  This guide provides a comprehensive exploration of ps aux, from foundational concepts to advanced filtering techniques, equipping you to extract actionable insights from process data. And if you’re looking for a reliable, high-performance, and budget-friendly solution for your workflows, Hostman has you covered with Linux VPS Hosting options, including Debian VPS, Ubuntu VPS, and VPS CentOS. Prerequisites To follow the tutorial: Deploy a Linux cloud server instance at Hostman SSH into the server instance Understanding Processes in Linux Before we explore the ps aux command, let's take a moment to understand what processes are in the context of a Linux system. What are Processes? 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I< 2024 0:00 [kworker/0:0H-events_highpri] Similarly, you can sort by memory usage to detect potential leaks: ps aux --sort=-%mem | head -n 10 Example output: USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND mysql 1734280 0.4 36.4 1325172 357284 ? Ssl Jan30 87:39 /usr/sbin/mysqld root 330 0.0 4.4 269016 43900 ? S<s 2024 22:43 /lib/systemd/systemd-journald root 368 0.0 2.7 289316 27100 ? SLsl 2024 8:19 /sbin/multipathd -d -s root 1548462 0.0 2.5 1914688 25488 ? Ssl Jan23 2:08 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock root 1317247 0.0 1.8 1801036 17760 ? Ssl Jan14 22:24 /usr/bin/containerd root 556 0.0 1.2 30104 11956 ? Ss 2024 0:00 /usr/bin/python3 /usr/bin/networkd-dispatcher --run-startup-triggers root 635 0.0 1.1 107224 11092 ? Ssl 2024 0:00 /usr/bin/python3 /usr/share/unattended-upgrades/unattended-upgrade-shutdown --wait-for-signal root 2090997 0.0 0.8 17456 8788 ? Ss 11:26 0:00 sshd: root@pts/0 root 2091033 0.0 0.8 9936 8480 pts/0 Ss 11:26 0:00 bash --rcfile /dev/fd/63 Real-Time Monitoring Combine ps aux with the watch command to refresh output every 2 seconds: watch -n 2 "ps aux --sort=-%cpu" This provides a dynamic view of CPU usage trends. Zombie Process Detection Zombie processes, though largely harmless, clutter the process list. Locate them with: ps aux | grep 'Z' Persistent zombies often indicate issues with parent processes failing to clean up child tasks. Practical Use Cases Now, let’s explore some common use cases of the ps aux command in Linux: Diagnosing High CPU Usage Follow the below steps: Execute this command to list processes by CPU consumption. ps aux --sort=-%cpu Identify the culprit—for example, a malfunctioning script using 95% CPU. 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Hence, it’s essential to consider the context when making an analysis. Common Pitfalls to Avoid Here are some pitfalls to look out for when using ps aux in Linux: Misinterpreting VSZ: High virtual memory usage doesn’t always indicate a problem—it includes swapped-out data. Overlooking Zombies: While mostly benign, recurring zombies warrant investigating parent processes. Terminating Critical Services: Always verify the COMMAND field before using kill to avoid disrupting essential services. Conclusion The ps aux command is a cornerstone of Linux system administration, offering deep insights into process behavior and resource utilization. You can diagnose performance issues, optimize resource allocation, and maintain system stability by mastering its output interpretation, filtering techniques, and real-world applications.  Did you know? Hostman prepared an Object Storage for your project to save all necessary info for your server. Start using now! For further exploration, consult the ps manual (man ps) or integrate process monitoring into automated scripts for proactive system management. Frequently Asked Questions (FAQ) What is the ps aux command in Linux?  It is the most common command to view a snapshot of all running processes on the system. The flags break down as follows: a: Shows processes for all users, not just the current user. u: Displays the process's user/owner and provides detailed resource usage (CPU, RAM). x: Shows processes not attached to a terminal (background daemons). Why do we use the ps command in Linux? We use it to monitor system health and troubleshoot performance. It helps you identify which applications are consuming the most CPU or Memory, find the Process ID (PID) needed to stop a frozen program, and verify if background services are running correctly. How do you use the ps aux command to find zombie processes? Zombie processes (defunct) appear with a Z in the STAT column. 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22 January 2026 · 10 min to read
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How to Create a Text File in Linux Terminal

In Linux, you can access and edit text files using a text editor that is designed to work with plain text. These files are not specifically coded or formatted. Choose your server now! There are several different ways to create a file in Linux. The Linux Command Line or Terminal is most likely the fastest. This is a crucial skill for any user, but especially for server administrators, who need to create text files, scripts, or configuration files quickly for their jobs. Let's proceed to the guide on four standard techniques for creating a text file on the terminal. And if you’re looking for a reliable, high-performance, and budget-friendly solution for your workflows, Hostman has you covered with Linux VPS Hosting options, including Debian VPS, Ubuntu VPS, and VPS CentOS. File Creation in Linux Can be Frustrating Sometimes Prerequisites for File Creation in Linux Ensure these prerequisites are met before generating files in a Linux environment using the command-line interface: Access to a Functional Linux System: You must either have a Linux-based operating system installed on your computer or secure access to a Linux server via SSH (Secure Shell) protocol. Operational Terminal Interface: Confirm that your terminal application is accessible and fully operational. The terminal serves as your primary gateway to executing commands. Adequate User Permissions: Verify you can create files within the chosen directory. You may need to use sudo (for directories with access restrictions) to escalate privileges. Fundamental Commands Proficiency: You must get familiar with essential commands, such as touch for file creation, echo for printing text, cat for viewing file contents, and text editors like nano, vim, or vi for editing files directly. Text Editing Utilities: Ensure your system includes text editing tools: nano for command line simplicity, vim for advanced configurations, or graphical options like gedit for user-friendly navigation. Directory Management Expertise: Develop familiarity with directory navigation commands like cd for changing the working directory and ls for listing directory contents. This knowledge streamlines your workflow and avoids potential errors. Using the touch Command Generally, we use the touch command to create empty files and change timestamps. It will create an empty file if it doesn't exist already.  To create a text file in the current directory with the touch command: Open your terminal emulator. Type the command: touch filename.txt Start with "touch" command Replace "filename" with the name you picked for the file. If the file with the same name already exists, the access and modification timestamps will be updated without affecting the content of the file. If not, a blank file with the specified name will be generated. Press Enter—if it is successful, there will be no output. Use the ls command to list the directory content and verify file creation. "LS" command is also important of you want to generate text file in Linux Using the echo Command Redirection The echo command is widely used to display text on the terminal. But its capabilities go beyond that; it may also be used to write content to a file or create an empty file. For this, combine the echo command with double redirect symbols (you can also use a single >) and the desired filename. A text file can be created by redirecting the output of the echo command to a file. See how it works: Open your terminal emulator. Type the command: echo “Your text content here” > filename.txt "Echo" command is also important in the process Replace the text in double quotations (do not delete them) with yours to add it to the file.  After you press Enter, your text will be added to the file filename.txt. It will overwrite an existing file, if there is one. Otherwise, it will just create a new one. Press Enter. To verify that the file has been created and contains the desired content, use cat command to display the content.  "Cat" command can help you to display your file you just created Using the cat Command Redirection In Linux, the cat command is mostly used to concatenate and show file contents. It can, however, also be used to generate a text document by redirecting the standard output of cat to a file. Open your terminal emulator. Type the following command: cat > filename.txt This is what you'll see after "cat" command Replace filename.txt with the name for your text file. This command instructs cat to receive input rom the terminal and to redirect it into the filename.txt. Press Enter. The terminal will be waiting for input.  Enter the text you want in the file. Press Enter after each line. Press Ctrl + D when you are done. This signals the end of input to the cat and saves the content.  Run the cat command to check that the file has been created and contains the desired content. This is how you can check how your file in Linux is created Using printf for Advanced File Creation The printf utility is a powerful alternative to echo, offering enhanced formatting options for structuring text. It allows users to create files with precisely formatted content. Open the terminal. Use printf to define the text layout, incorporating formatting elements like newlines (\n) or tabs (\t). Redirect the output to a file using the > operator. Example: printf "First Line\nSecond Line\nIndented\tThird Line\n" >  formatted_file.txt Run the cat command to inspect the file's content and ensure the formatting matches expectations. Append Without Overwriting: To add content to an existing file without overwriting its current data, replace > with the append operator >>: printf "Additional content here.\n" >> formatted_file.txt Using a Text Editor You can also create new files in linux text editors. There is always at least one integrated command-line text editor in your Linux distribution. But you can choose and install a different one according to your preferences, for example, Vim, Nano, or Emacs. Each of them has its own features and advantages. Vim vim, which stands for "Vi IMproved," is a very flexible and adaptable text editor. It is well-known for its modal editing, which allows for distinct modes for various functions like text entry, navigation, and editing. It allows split windows, multiple buffers, syntax highlighting, and a large selection of plugins for extra features. To create a text file using vim, follow the steps below: Open vim, with the desired filename as an argument. "Vim" command is one of the key steps in file creation Press i to switch to Insert mode. Start typing and editing the filename.txt.  To save and exit, press Esc to ensure that command mode is running. Type: wq (write and quit) and press Enter. Simple command to finish your work Nano nano is ideal for short adjustments and straightforward text files because it is lightweight and requires little setup. It provides support for basic text manipulation functions, search and replace, and syntax highlighting. To create a text file using nano, follow the steps below:  Run nano with the desired filename as an argument. It will open a new buffer for editing the file filename.txt. Nano is useful in you want to fix something in your text file Start typing and editing the filename.txt.  To save and exit, press Ctrl + O to write the file, confirm the filename, and then press Ctrl + X to exit Nano. Click "yes" to exit Emacs emacs is a powerful and flexible text editor that supports syntax highlighting, multiple buffers, split windows, and integration with external tools and programming languages. To create a text file using emacs, follow the steps below:  Open emacs, with the desired filename as an argument. Start typing and editing the filename.txt.  "Emacs" is more flexible text editor To save and exit, press Ctrl + X, followed by Ctrl + S to save the file, and then Ctrl + X, followed by Ctrl + C to exit Emacs. Note: If a message states that "VIM command not found", "nano command not found" or "emacs command not found" in Linux, it typically means that the vim, nano or emacs text editor is not installed on the system, or it's not included in the PATH environment variable, which is a list of directories where the operating system looks for executable files. Don't forget to install necessary command in Linux To resolve this, install the text editor first using the command:  apt-get install vim apt-get install nano  apt-get install emacs Gedit An intuitive text editor that supports working with plain text and has syntax highlighting for programming languages. A straightforward graphical interface makes it usable for various tasks, from quick edits to complex document preparation. Open the Gedit Application: Launch Gedit either through the applications menu or by executing the following command in the terminal: gedit example.txt Gedit will create a new file if the specified one does not exist. Input Your Text: Type or paste your desired content into the editor. Save the File: Save your work with Ctrl + S or select File > Save. If creating a new file, specify a filename and a location. Verify: Return to the terminal and confirm the file exists with the ls command or review its content with cat. Linux File Creation Recommendations Ensure you have sufficient permissions to create files in the target directory. If they are insufficient, consider working in a directory where you have full rights (or elevate privileges with sudo). Check if a file with the identical name is already present before using the > operator, as the command will overwrite existing content. To prevent data loss, opt for the append operator >>. Familiarize yourself with the printf, echo, and text editors like vim or nano. These tools will help you reduce errors when working with files in Linux, as well as boost productivity. Use printf for creating files requiring structured content, such as configuration files or scripts with precise formatting needs. Choose your server now! Conclusion Now you have acquainted yourself with the fundamental skill of creating a file in Linux using the terminal! Using the Linux command line, several fast and efficient methods exist to create and manage text files. Apply several techniques to meet a different requirement using the touch, echo, cat, printf commands, or text editors like vim, nano, gedit, or emacs. Users can select the method that sufficiently meets their requirements, such as creating empty files, appending text, or significantly modifying material. In summary, any of these methods enable Linux users to easily and quickly handle text files straight from the command line. Frequently Asked Questions (FAQ) How do I create an empty text file in Linux?  The standard command is touch. Simply run: touch filename.txt This creates a blank file immediately. How do I create a file and add content at the same time?  You can use the echo command with the redirection operator (>). echo "Hello World" > filename.txt This creates the file and puts "Hello World" inside it. How do I create and open a file for editing?  Use a terminal text editor like nano or vi. When you run: nano filename.txt Linux will open a blank editor screen. Once you type your text and save (Ctrl+O in nano), the file is created on your disk. What is the fastest way to create a file?  The redirection symbol alone is the quickest method for creating an empty file:> filename.txt This tells the shell to redirect "nothing" into a new file, creating it instantly. How do I create a large file for testing?  Use the fallocate command. For example, to create a 1GB file instantly:fallocate -l 1G bigfile.img How do I view the content of a text file?  Use the cat command to print the text to your terminal: cat filename.txtFor longer files, use less filename.txt to scroll through pages.
21 January 2026 · 10 min to read

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