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How to Open Ports and List Open Ports in Linux

How to Open Ports and List Open Ports in Linux
Hostman Team
Technical writer
Linux Network
14.02.2025
Reading time: 6 min

When working with networks in Linux, you may need to open or close a network port. Port management is essential for security — the fewer open ports in a system, the fewer potential attack vectors it has. Furthermore, if a port is closed, an attacker cannot gather information about the service running on that specific port.

This guide will explain how to open or close ports as well as how to check open ports in Linux distributions such as Ubuntu/Debian and CentOS/RHEL using firewalls like ufw, firewalld, and iptables. It will also 

We will demonstrate this process on two Linux distributions: Ubuntu 22.04 and CentOS 9, run on Hostman VPS. All commands provided here will work on any Debian-based or RHEL-based distributions.

What is a Network Port?

Ports are used to access specific applications and protocols. For example, a server can host both a web server and a database—ports direct traffic to the appropriate service. Technically, a network port is a non-negative integer ranging from 0 to 65535.

  • Reserved Ports (0-1023): Used by popular protocols and network services like SSH (port 22), FTP (port 21), HTTP (port 80), and HTTPS (port 443).
  • Registered Ports (1024-49151): These ports can be used by specific applications for communication.
  • Dynamic Ports (49151-65535): These are used for temporary connections and can be dynamically assigned to applications.

How to Open Ports in Debian-Based Linux Distributions

On Debian-based systems (Ubuntu, Debian, Linux Mint, etc.), you can use ufw (Uncomplicated Firewall).

ufw comes pre-installed on most popular APT-based distributions. To check if ufw is installed, run:

ufw version

If the version is displayed, ufw is installed. Otherwise, install it with:

apt update && apt -y install ufw

By default, ufw is inactive, meaning all ports are open. You can check its status with:

ufw status

To activate it, use:

ufw enable

You will need to confirm by entering y. Note that enabling ufw may interrupt current SSH connections. By default, ufw blocks all incoming traffic and allows all outgoing traffic.

To check the default policy, use:

cat /etc/default/ufw

Image7

Opening Ports in ufw

To open a port, use the command:

ufw allow <port_number>

For example, to open port 22 for SSH, run:

ufw allow 22

You can list multiple port numbers separated by commas, followed by the protocol (tcp or udp):

ufw allow 80,443,8081,8443/tcp
ufw allow 80,443,8081,8443/udp

Instead of specifying port numbers, you can use the service name as defined in /etc/services.

Image8

For example, to open the Telnet service, which uses port 23 by default:

ufw allow telnet

Note: You cannot specify multiple service names at once; ufw will return an error:

Image1 (1)

To open a port range, use the following syntax:

ufw allow <start_port>:<end_port>/<protocol>

Example:

ufw allow 8000:8080/tcp

Closing Ports in ufw

To close a port using ufw, use the command:

ufw deny <port_number>

For example, to close port 80, run:

ufw deny 80

You can also use the service name instead of the port number. For example, to close port 21 used by the FTP protocol:

ufw deny ftp

Checking Open Ports in ufw

To list all open and closed ports in the Linux system, use:

ufw status

Image18

Another option to view open ports in Linux is:

ufw status verbose

How to Open a Port in RHEL-Based Linux Distributions

Linux RHEL-based distributions (CentOS 7+, RHEL 7+, Fedora 18+, OpenSUSE 15+) use firewalld by default.

Opening Ports in firewalld

To check if firewalld is installed, run:

firewall-offline-cmd -V

If the version is displayed, firewalld is installed. Otherwise, install it manually:

dnf install firewalld

By default, firewalld is disabled. Check its status with:

firewall-cmd --state

To enable firewalld, run:

systemctl start firewalld

To open port 8080 for the TCP protocol, use:

firewall-cmd --zone=public --add-port=8080/tcp --permanent
  • --zone=public: Specifies the zone for the rule.
  • --add-port=8080/tcp: Specifies the port and protocol (TCP or UDP).
  • --permanent: Saves the rule to persist after a system reboot. Without this parameter, the change will only last until the next reboot.

Image12

Alternatively, you can open a port in Linux by specifying a service name instead of a port number. For example, to open the HTTP (port 80) protocol:

firewall-cmd --zone=public --add-service=http --permanent

Reload firewalld to apply the changes:

firewall-cmd --reload

Closing Ports in firewalld

You can close a port using either its number or service name.

To close a port using its number, run:

firewall-cmd --zone=public --remove-port=8080/tcp --permanent

Image4

To close a port using the service name, run:

firewall-cmd --zone=public --remove-service=http --permanent

After opening or closing a port, always reload firewalld to apply the changes:

firewall-cmd --reload

Listing Open Ports in firewalld

To list all open ports in your Linux system, you can use:

firewall-cmd --list-ports

Managing Ports in iptables

Unlike ufw and firewalld, iptables comes pre-installed in many Linux distributions, including Ubuntu, Debian, RHEL, Rocky Linux, and AlmaLinux.

Opening Ports in iptables

To open port 8182 for incoming connections, use:

iptables -A INPUT -p tcp --dport 8182 -j ACCEPT
  • -A INPUT: The -A flag is used to add one or more rules. INPUT specifies the chain to which the rule will be added (in this case, incoming connections).
  • -p tcp: Specifies the protocol. Supported values include tcp, udp, udplite, icmp, esp, ah, and sctp.
  • --dport 8182: Specifies the port to be opened or closed.
  • -j ACCEPT: Defines the action for the port. ACCEPT allows traffic through the port.

To open a port for outgoing connections, use the OUTPUT chain instead:

iptables -A OUTPUT -p tcp --dport 8182 -j ACCEPT

To open a range of ports, use the --match multiport option:

iptables -A INPUT -p tcp --match multiport --dports 1024:2000 -j ACCEPT

Closing Ports in iptables

To close a port, use the -D option and set the action to DROP. For example, to close port 8182 for incoming connections:

iptables -A INPUT -p tcp --dport 8182 -j DROP

To close a range of ports, use the same syntax as for opening a range, but replace ACCEPT with DROP:

iptables -A INPUT -p tcp --match multiport --dports 1024:2000 -j DROP

Saving iptables Rules

By default, iptables rules are only effective until you restart the server. To save the rules permanently, install the iptables-persistent utility.

For APT-based distributions:

apt update && apt -y install iptables-persistent

For DNF-based distributions:

dnf -y install iptables-persistent

To save the current rules, run:

iptables-save

After the next server reboot, the rules will be automatically reloaded.

Viewing Open Ports in iptables

To list all current rules and opened ports on the Linux machine, use:

iptables -L -v -n

To list rules specifically for IPv4, use:

iptables -S

To list rules for IPv6, use:

ip6tables -S

Conclusion

In this guide, we demonstrated how to open and close network ports in Linux and check currently open ports using three different utilities: ufw, firewalld, and iptables. Proper port management reduces the risk of potential network attacks and helps obscure information about the services using those ports.

Linux Network
14.02.2025
Reading time: 6 min

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NATS Installation, Configuration, and Usage Guide

NATS is a simple, fast, and lightweight message broker written in the Go programming language. NATS has several data organization features: Key-Value: Data within NATS is stored in "key-value" format, where each key corresponds to a specific value. Subjects: Data within NATS is organized into so-called "Subjects," which are named channels for message transmission. Subjects can be divided into segments with hierarchical structures. Publish/Subscribe (Pub/Sub): Data within NATS is transmitted through a model where "Publishers" send messages to "Subjects," and "Subscribers" can subscribe to these "Subjects" to receive messages. Unlike many other message brokers (such as Apache Kafka or RabbitMQ), NATS has several significant advantages: Simplicity and Performance: Messages are transmitted through a simple and fast Pub/Sub protocol. When a message is sent to a subject, all subscribers immediately receive it. This minimizes delays and other overhead costs. Stateless: Information about the state of messages transmitted through the broker is not stored within it, nor is data about subject subscribers. The absence of complex state synchronization allows NATS to scale easily. No Default Queues: In standard configuration, NATS does not form message queues. This is important in cases where data timeliness is more important than persistence. It also eliminates queue management overhead. Reliable Protocol: Messages within the broker are transmitted using the "at-most-once delivery" method. This means a subscriber either receives a message once or not at all. This increases communication reliability and prevents duplicate responses to forwarded messages. Thus, NATS enables building fast and reliable communication between multiple different services. In this guide, we will thoroughly examine how to install, configure, and correctly use NATS in projects running on Ubuntu 22.04. Downloading NATS Package Updates Before installation, it's recommended to update the list of available repositories in the system: sudo apt update Downloading the Archive Next, you need to manually download the ZIP archive with NATS from its official GitHub repository: wget https://github.com/nats-io/nats-server/releases/download/v2.10.22/nats-server-v2.10.22-linux-amd64.zip After the download is complete, you can check the file list: ls Among them will be the NATS archive: nats-server-v2.10.22-linux-amd64.zip  resize.log  snap Extracting the Archive Next, install the package that performs ZIP archive extraction: sudo apt install unzip -y The -y flag is added so that the installer automatically answers 'yes' to all questions. Now extract the NATS archive using the installed extractor: unzip nats-server-v2.10.22-linux-amd64.zip Check the file list: ls As you can see, a new folder with the archive contents has appeared: nats-server-v2.10.22-linux-amd64  nats-server-v2.10.22-linux-amd64.zip  resize.log  snap We no longer need the archive, so delete it: rm nats-server-v2.10.22-linux-amd64.zip Installing NATS Server Installation Let's look at the contents of the created folder: ls nats-server-v2.10.22-linux-amd64 Inside it is the main directory with the NATS server: LICENSE  nats-server  README.md This is what we need to copy to the system catalog with binary files: sudo mv nats-server-v2.10.22-linux-amd64/nats-server /usr/local/bin/ After copying, you need to set the appropriate access permissions: sudo chmod +x /usr/local/bin/nats-server The folder with NATS contents, like the archive, can now also be deleted: rm nats-server-v2.10.22-linux-amd64 -R Server Verification Let's verify that the NATS server is installed by requesting its version: nats-server -v A similar output should appear in the console terminal: nats-server: v2.10.22 However, this command doesn't start the server; it only returns its version. You can start the server as follows: nats-server [3704] 2024/11/07 02:59:53.908362 [INF] Starting nats-server [3704] 2024/11/07 02:59:53.908623 [INF] Version: 2.10.22 [3704] 2024/11/07 02:59:53.908669 [INF] Git: [240e9a4] [3704] 2024/11/07 02:59:53.908701 [INF] Name: NC253DIPURNIY4HUXYQYC5LLAFA6UZEBKUIWTBLLPSMICFH3E2FMSXB7 [3704] 2024/11/07 02:59:53.908725 [INF] ID: NC253DIPURNIY4HUXYQYC5LLAFA6UZEBKUIWTBLLPSMICFH3E2FMSXB7 [3704] 2024/11/07 02:59:53.909430 [INF] Listening for client connections on 0.0.0.0:4222 [3704] 2024/11/07 02:59:53.909679 [INF] Server is ready In this case, the server starts with binding to the console terminal, not as a background service. Therefore, to return to command input mode, you need to press Ctrl + C. NATS Configuration Creating a Configuration File After the broker server is started, you can create a separate directory for the NATS configuration file: mkdir /etc/nats And then create the configuration file itself: sudo nano /etc/nats/nats-server.conf Its contents will be as follows: cluster { name: "test-nats" } store_dir: "/var/lib/nats" listen: "0.0.0.0:4222" Specifically in this configuration, the most basic parameters are set: name: Server name within the NATS cluster store_dir: Path to the directory where working data will be stored listen: IP address and port that the NATS server will occupy Creating a Separate User For all directories related to NATS, you need to create a separate user: useradd -r -c 'NATS service' nats Now create the directories specified in the configuration file: mkdir /var/log/nats /var/lib/nats For each directory, assign appropriate access permissions to the previously created user: chown nats:nats /var/log/nats /var/lib/nats Creating a Background Service Earlier we started the NATS server with binding to the console terminal. In this case, when exiting the console, the server will stop working. To prevent this, you need to create a file for the systemd service: sudo nano /etc/systemd/system/nats-server.service Its contents will be: [Unit] Description=NATS message broker server After=syslog.target network.target [Service] Type=simple ExecStart=/usr/local/bin/nats-server -c /etc/nats/nats-server.conf User=nats Group=nats LimitNOFILE=65536 ExecReload=/bin/kill -HUP $MAINPID Restart=on-failure [Install] WantedBy=multi-user.target This file contains several key parameters: Description: Short description of the service ExecStart: NATS server startup command with the configuration file explicitly specified User: Name of the user created for NATS Now we need to set up the service to start up at boot:  systemctl enable nats-server --now The --now flag immediately starts the specified service. The corresponding message will appear in the console: Created symlink /etc/systemd/system/multi-user.target.wants/nats-server.service → /etc/systemd/system/nats-server.service. Now check the status of the running service: systemctl status nats-server If the NATS server service started successfully, the corresponding message will be among the console output: ... Active: active (running) ... Connecting to NATS You can connect to the NATS server through the console terminal and thus perform message broker testing. For example, publish messages or subscribe to subjects. Client Installation To manage the NATS server, you need to install the natscli client. You can download it from the official GitHub repository: wget https://github.com/nats-io/natscli/releases/download/v0.1.5/nats-0.1.5-amd64.deb After this, the downloaded archive can be extracted and installed: dpkg -i nats-0.1.5-amd64.deb The archive itself can be deleted as it's no longer needed: rm nats-0.1.5-amd64.deb Sending Messages Now you can send a message to the message broker: nats pub -s 127.0.0.1 "someSubject" "Some message" In this command, we send the message "Some message" to the subject "someSubject" to the message broker running on IP address 127.0.0.1 and located on the standard NATS port - 4222. After this, information about the sent data will appear in the console terminal: 10:59:51 Published 12 bytes to "someSubject" Reading Messages Currently, no one will see this message since there's no agent subscribed to the specified subject. We can simulate a service subscribed to the subject and reading messages using another SSH session. To do this, you need to open another console terminal, connect to the remote machine, and subscribe to the previously specified subject: nats sub -s 127.0.0.1 "someSubject" A message about successful subscription will appear in the terminal: 11:11:10 Subscribing on someSubject Now repeat sending the message from the first terminal: nats pub -s 127.0.0.1 "someSubject" "Some message" Information about the new message will appear in the second terminal: [#1] Received on "someSubject" Some message Let's send another message from the first terminal: nats pub -s 127.0.0.1 "someSubject" "Some message again" The corresponding notification will appear in the second terminal: [#2] Received on "someSubject" Some message again Note that the console output of received messages has numbering in square brackets. Go Program + NATS Let's create a small program in the Golang programming language using the NATS message broker. Installing Go First, you need to ensure that the Go compiler is installed in the system: go version If the following message appears in the console terminal, then Go is not yet installed: Command 'go' not found, but can be installed with: snap install go # version 1.23.2, or apt install golang-go # version 2:1.18~0ubuntu2 apt install gccgo-go # version 2:1.18~0ubuntu2 See 'snap info go' for additional versions. In this case, you need to download it as an archive from the official website: wget https://go.dev/dl/go1.23.3.linux-amd64.tar.gz -O go.tar.gz And then extracted: sudo tar -xzvf go.tar.gz -C /usr/local As we no longer need the downloaded archive, we can delete it: rm go.tar.gz Next, you need to add the Go compiler to the PATH variable so it can be called from the console terminal: echo export PATH=$HOME/go/bin:/usr/local/go/bin:$PATH >> ~/.profile Then apply the changes: source ~/.profile Verify that Go is installed successfully by requesting its version: go version You will see a similar output: go version go1.23.3 linux/amd64 Creating a Project Let's create a separate folder for the Golang program: mkdir nats_go Then navigate to it: cd nats_go And initialize the Go project: go mod init nats_go Installing the Module After project initialization, you need to install the NATS client from the official GitHub repository. You don't need to download anything manually; it's enough to use the built-in Golang function: go get github.com/nats-io/nats.go/ Writing Code Now you can create a file with the program code: nano nats_go.go Its contents will be: package main import ( "fmt" // module for working with console "os" // module for working with system functions "time" // module for working with time "github.com/nats-io/nats.go" // module for working with NATS server ) func main() { // get NATS server address from environment variable url := os.Getenv("NATS_URL") // if there's no address in environment variable, use default address if url == "" { url = nats.DefaultURL } // connect to NATS server nc, _ := nats.Connect(url) // defer message broker cleanup until main() function completion defer nc.Drain() // send message to subject without subscribers to ensure it disappears nc.Publish("people.philosophers", []byte("Hello, Socrates!")) // subscribe to all sub-subjects in "people" subject sub, _ := nc.SubscribeSync("people.*") // extract message msg, _ := sub.NextMsg(10 * time.Millisecond) // output message status (it's not there because it was sent before subscribing to subjects) fmt.Printf("No message? Answer: %v\n", msg == nil) // send message to "philosophers" sub-subject of "people" subject nc.Publish("people.philosophers", []byte("Hello, Socrates!")) // send message to "physicists" sub-subject of "people" subject nc.Publish("people.physicists", []byte("Hello, Feynman!")) // extract message and output to console msg, _ = sub.NextMsg(10 * time.Millisecond) fmt.Printf("Message: %q in subject %q\n", string(msg.Data), msg.Subject) // extract message and output to console msg, _ = sub.NextMsg(10 * time.Millisecond) fmt.Printf("Message: %q in subject %q\n", string(msg.Data), msg.Subject) // send message to "biologists" sub-subject of "people" subject nc.Publish("people.biologists", []byte("Hello, Darwin!")) // extract message and output to console msg, _ = sub.NextMsg(10 * time.Millisecond) fmt.Printf("Message: %q in subject %q\n", string(msg.Data), msg.Subject) } Now you can run the created program: go run . The program's output will appear in the console terminal: No message? Answer: true Message: "Hello, Socrates!" in subject "people.philosophers" Message: "Hello, Feynman!" in subject "people.physicists" Message: "Hello, Darwin!" in subject "people.biologists" Python Program + NATS As another example, let's consider using the NATS message broker in the Python programming language. First, you need to ensure that the Python interpreter is installed in the system by requesting its version: python --version The corresponding message will appear in the console: Python 3.10.12 Note that this guide uses Python version 3.10.12. Installing PIP To download the NATS client for Python, you first need to install the PIP package manager: apt install python3-pip -y The -y flag helps automatically answer positively to all questions during installation. Installing the Client Now you can install the NATS client for Python: pip install nats-py Creating a Project For the Python program, let's create a separate directory: mkdir nats_python And navigate to it: cd nats_python Writing Code Let's create a file with the program code: nano nats_python.py Its contents will be: import os import asyncio # import NATS client import nats from nats.errors import TimeoutError # get environment variable containing NATS server address servers = os.environ.get("NATS_URL", "nats://localhost:4222").split(",") async def main(): # connect to NATS server nc = await nats.connect(servers=servers) # send message to subject without subscribers to ensure it disappears await nc.publish("people.philosophers", "Hello, Socrates!".encode()) # subscribe to all sub-subjects in "people" subject sub = await nc.subscribe("people.*") try: # extract message msg = await sub.next_msg(timeout=0.1) except TimeoutError: pass # send message to "philosophers" sub-subject of "people" subject await nc.publish("people.philosophers", "Hello, Socrates!".encode()) # send message to "physicists" sub-subject of "people" subject await nc.publish("people.physicists", "Hello, Feynman!".encode()) # extract message and output to console msg = await sub.next_msg(timeout=0.1) print(f"{msg.data.decode('utf-8')} in subject {msg.subject}") # extract message and output to console msg = await sub.next_msg(timeout=0.1) print(f"{msg.data.decode('utf-8')} in subject {msg.subject}") # send message to "biologists" sub-subject of "people" subject await nc.publish("people.biologists", "Hello, Darwin!".encode()) # extract message and output to console msg = await sub.next_msg(timeout=0.1) print(f"{msg.data.decode('utf-8')} in subject {msg.subject}") # unsubscribe from subjects await sub.unsubscribe() # clean up message broker await nc.drain() if __name__ == '__main__': asyncio.run(main()) Now you can run the created script: python nats_python.py The result of its operation will be the following output in the console terminal: Hello, Socrates! in subject people.philosophers Hello, Feynman! in subject people.physicists Hello, Darwin! in subject people.biologists As you can notice, the logic of this Python program doesn't differ from the logic of the Go program. The difference is only in the syntactic constructions of the specific programming language. Conclusion This guide examined the use of the NATS message broker in sequential stages: Downloading and installing NATS from the official GitHub repository Minimal NATS server configuration Managing the NATS server through the console terminal client Using NATS in a Golang program Using NATS in a Python program We downloaded all NATS clients used in this guide (for terminal, Go, and Python) from the official NATS repository on GitHub, which hosts modules and libraries for all programming languages supported by NATS. You can find more detailed information about configuring and using NATS in the official documentation. There are also many examples of using NATS in different programming languages.
24 June 2025 · 13 min to read
Linux

Listing and Deleting Iptables Firewall Rules

The iptables application is a firewall essential for securely working with network resources on the Linux platform. While there is extensive material dedicated to configuring iptables, we will focus on a few specific tasks: how to view rule lists, delete unnecessary rules, flush chains, and clear the packet count and byte size counters.  We do not recommend modifying the SSH connection on port 22 unless you are absolutely sure of your actions, as you might accidentally block remote access to your test host. In this guide, we will use a Hostman cloud server running Ubuntu. The setup process will be similar on CentOS and Debian. Before proceeding, make sure you have a user with sudo privileges. Viewing Rules In iptables, you can view the rules set by default or by a previous administrator. Execute the command: sudo iptables -S The result will be displayed like this: -P INPUT DROP -P FORWARD DROP -P OUTPUT ACCEPT -N ICMP -N TCP -N UDP -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A INPUT -i lo -j ACCEPT -A INPUT -m conntrack --ctstate INVALID -j DROP -A INPUT -p udp -m conntrack --ctstate NEW -j UDP -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j TCP -A INPUT -p icmp -m conntrack --ctstate NEW -j ICMP -A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable -A INPUT -p tcp -j REJECT --reject-with tcp-reset -A INPUT -j REJECT --reject-with icmp-proto-unreachable -A TCP -p tcp -m tcp --dport 22 -j ACCEPT Viewing a Specific Chain This function is used when you want to exclude a specific chain (e.g., INPUT, OUTPUT, TCP, etc.) from the general output. Specify the chain name after the -S option. Example: sudo iptables -S TCP The result: -N TCP -A TCP -p tcp -m tcp --dport 22 -j ACCEPT View Rules as a Table This method is convenient for comparing different rules. The tabular format is built into the utility and is activated using the -L option. Enter: sudo iptables -L You can also limit the output to a specific chain: sudo iptables -L INPUT Sample output: Chain INPUT (policy DROP) target prot opt source destination ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere DROP all -- anywhere anywhere ctstate INVALID UDP udp -- anywhere anywhere ctstate NEW TCP tcp -- anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN ctstate NEW ICMP icmp -- anywhere anywhere ctstate NEW REJECT udp -- anywhere anywhere reject-with icmp-port-unreachable REJECT tcp -- anywhere anywhere reject-with tcp-reset REJECT all -- anywhere anywhere reject-with icmp-proto-unreachable Explanation: target – action taken when a packet matches the rule (e.g., ACCEPT, DROP, redirect to another chain). prot – protocol used (UDP, TCP, ALL). opt – IP options, if any. source – source IP/subnet (e.g., "anywhere" = from anywhere). destination – destination IP/subnet. The last column (without a header) contains additional rule parameters like port numbers or connection states. Viewing Packet and Byte Counters You can also display the packet and total byte count per rule. This is useful for estimating traffic by rule. Available with -L and -v: sudo iptables -L INPUT -v Sample output: Chain INPUT (policy DROP 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 284K 42M ACCEPT all -- any any anywhere anywhere ctstate RELATED,ESTABLISHED 0 0 ACCEPT all -- lo any anywhere anywhere 0 0 DROP all -- any any anywhere anywhere ctstate INVALID 396 63275 UDP udp -- any any anywhere anywhere ctstate NEW 17067 1005K TCP tcp -- any any anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN ctstate NEW 2410 154K ICMP icmp -- any any anywhere anywhere ctstate NEW 396 63275 REJECT udp -- any any anywhere anywhere reject-with icmp-port-unreachable 2916 179K REJECT all -- any any anywhere anywhere reject-with icmp-proto-unreachable 0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:ssh ctstate NEW,ESTABLISHED Compare this to previous output and you’ll see two new columns: pkts and bytes. Resetting Packet and Byte Counters You can reset these counters using the -Z option. This happens automatically on reboot, but can also be done manually to test for new traffic: sudo iptables -Z To reset a specific chain: sudo iptables -Z OUTPUT To reset a specific rule in a chain by number: sudo iptables -Z OUTPUT 2 Deleting Rules Deleting by Specification Use -D followed by the full rule specification. View existing rules first. For example, to remove the rule that drops invalid outgoing traffic: sudo iptables -D OUTPUT -m conntrack --ctstate INVALID -j DROP No need to use -A when deleting. Deleting by Rule Number Use --line-numbers to get rule numbers: sudo iptables -L --line-numbers Sample output: Chain INPUT (policy DROP) num target prot opt source destination 1 ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED 2 ACCEPT all -- anywhere anywhere 3 DROP all -- anywhere anywhere ctstate INVALID ... Then delete by number: sudo iptables -D INPUT 3 Flushing Chains Be cautious when flushing chains; you could block your SSH connection. Flush a Single Chain sudo iptables -F INPUT Flush All Chains sudo iptables -F This command allows all traffic (inbound, outbound, forwarded), essentially disabling the firewall. If you run it on a production system, you’ll need to reconfigure the firewall from scratch. Always back up your current rules: iptables-save > iptables_backup.txt Restore them later with: iptables-restore < iptables_backup.txt Before flushing, set the default policy to ACCEPT to avoid losing SSH access: sudo iptables -P INPUT ACCEPT sudo iptables -P FORWARD ACCEPT sudo iptables -P OUTPUT ACCEPT Then flush everything: sudo iptables -t nat -F sudo iptables -t mangle -F sudo iptables -F sudo iptables -X This allows all traffic. If you list rules after this, only the default chains (INPUT, FORWARD, OUTPUT) will be present. Conclusion This tutorial provides practical guidance on how to view, reset, and delete iptables firewall rules and perform similar actions on specific chains. Keep in mind that any changes will be lost upon server reboot unless saved.
23 June 2025 · 6 min to read
Linux

How to Mount an SMB Share in Linux

The Server Message Block (SMB) protocol facilitates network file sharing, allowing applications to read and write to files and request services from server programs. This protocol is pivotal for seamless communication between different devices in a network, particularly in mixed OS environments like Windows and Linux. Mounting an SMB share in Linux enables users to access files on a Windows server or another SMB-enabled device directly from their Linux system. This tutorial will guide you through the process of mounting an SMB share on Linux, ensuring smooth file sharing and network communication. Prerequisites for Mounting SMB Shares Before mounting an SMB share, ensure the following prerequisites are met: A Linux system, such as a Hostman cheap cloud server, with root or sudo privileges. The cifs-utils package installed on your Linux system. Access credentials (username and password) for the SMB share. Network connectivity between your Linux system and the SMB server. Installing Necessary Packages The cifs-utils package is essential for mounting SMB shares on Linux. Additionally, the psmisc package provides the fuser command, which helps manage and monitor file usage. Update Package List and Upgrade System First, update your package list and upgrade your system: sudo apt update Install cifs-utils and psmisc Install the necessary packages: sudo apt install cifs-utils psmisc Verify Installation Verify the installation of cifs-utils and availability of the fuser command: mount -t cifsfuser Finding SMB Share Details Identify the SMB share details, including the server name or IP address and the share name. You might need to consult your network administrator or check the server configuration. Example: Server: smbserver.example.com Share: sharedfolder Mounting SMB Shares Using the mount Command To mount the SMB share, use the mount command with the -t cifs option, specifying the SMB protocol. Create a directory to serve as the mount point: sudo mkdir /mnt/smb_share Mount the SMB share using the following command: sudo mount -t cifs -o username=your_username,password=your_password //192.0.2.17/SharedFiles /mnt/smb_share Replace your_username and your_password with your actual username and password. Ensure /mnt/smb_share is an existing directory. Verifying the Mount To confirm that the SMB share is successfully mounted, use the mount command: mount -t cifs Navigate to the mount point and list the files: cd /mnt/smb_sharels Creating a Credentials File To avoid entering credentials each time, create a credentials file. This file should be hidden and secured. Use a text editor to create the file: nano ~/.smbcredentials Add the following content, replacing with your actual credentials: username=your_usernamepassword=your_password Set appropriate permissions for the file: sudo chown your_username: ~/.smbcredentialssudo chmod 600 ~/.smbcredentials Mount Using the Credentials File Mount the SMB share using the credentials file: sudo mount -t cifs -o credentials=~/.smbcredentials //192.168.2.12/SharedFiles /mnt/smb_share Automating SMB Share Mounts To automate the mounting process, add an entry to the /etc/fstab file. This will ensure the SMB share is mounted at boot. 1. Open /etc/fstab for editing: sudo nano /etc/fstab 2. Add the following line: //smbserver.example.com/sharedfolder /mnt/smbshare cifs username=johndoe,password=securepassword,iocharset=utf8,sec=ntlm 0 0 3. Save and close the file. 4. Test the fstab entry: sudo mount -a Ensure no errors are displayed. Troubleshooting Common Issues Permission Denied Check your credentials and permissions on the SMB server. No Such File or Directory Ensure the server IP, share path, and mount point are correct. Mount Error 13 = Permission Denied Double-check your username and password. Mount Error 112 = Host is Down Verify network connectivity and server availability. Unmounting an SMB Share To unmount the SMB share, use the umount command followed by the mount point: sudo umount /mnt/smb_share Conclusion Mounting an SMB share in Linux is a straightforward process that enhances file sharing capabilities across different operating systems. By following this tutorial, you can efficiently set up and troubleshoot SMB share mounts, facilitating seamless network communication and file access. Don't forget to check how to configure server image on Lunix! Frequently Asked Questions What is Samba in Linux and how does it relate to SMB? Samba is an open-source implementation of the SMB/CIFS protocol in Linux. It allows Linux systems to share files and printers with Windows devices over a network. What is the command to mount a Windows share in Linux? Use mount -t cifs //server/share /mnt/share -o username=your_user. How can I auto-mount an SMB share on boot in Linux? Add the mount configuration to /etc/fstab using proper credentials. Do I need root access to mount an SMB share? For traditional mounting, yes. But user-space tools like gio mount can be used without root.
16 June 2025 · 4 min to read

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