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How to Copy Files and Directories in Linux

How to Copy Files and Directories in Linux
Emmanuel Oyibo
Technical writer
Linux
07.02.2025
Reading time: 8 min

When you first start working with Linux, one of the essential tasks you’ll encounter is file management. Whether you’re organizing your personal documents, migrating system files, or preparing comprehensive backups, knowing how to duplicate your files accurately is crucial. At the heart of this process is the cp command—a robust utility designed to replicate files and directories effortlessly.

This guide is designed to help you master the cp command. We’ll explore everything from basic file copying to recursive directory replication, along with tips for preserving file metadata and preventing accidental data loss. With detailed examples, real-world scenarios, and best practices, you’ll soon be equipped to use cp like a seasoned Linux professional.

Diving into the cp Command

In Linux, the cp command functions as your primary tool for copying data. Its versatility allows you to handle everything from a single file copy to mirroring complex directory structures with nested subfolders. Unlike graphical file managers, the cp command works entirely from the terminal, giving you precise control over every aspect of the copy process.

How It Works

At its simplest, cp takes a source file (or directory) and duplicates it to a new location. Its flexibility, however, lies in its options—flags that let you modify its behavior to suit your needs. Whether you’re preserving file permissions, ensuring no accidental overwrites occur, or copying entire folder trees, cp has a flag for every scenario.

Basic Command Structure

The cp command follows a simple format. Here’s the canonical syntax:

cp [options] source destination
  • cp: The command to initiate a copy.
  • [options]: Additional parameters (flags) that control the behavior of the copy process.
  • source: The file or directory you wish to duplicate.
  • destination: The target location or filename for the copy.

This straightforward structure makes cp a favorite among system administrators and casual users alike.

Exploring Key Options

The true power of cp is unlocked through its myriad options. Let’s review some of the most useful ones:

  • Recursive Copying (-r or -R): When you need to copy an entire directory—complete with all its subdirectories and files—the recursive flag is indispensable. It tells cp to traverse the directory tree, ensuring nothing is left behind.

  • Interactive Mode (-i): Safety first! The interactive option prompts you before replacing an existing file. This extra step is critical when you’re working with important data, as it minimizes the risk of accidental overwrites.

  • Force Copy (-f): Sometimes you need to override warnings and ensure the file is copied no matter what. The force flag does just that, replacing existing files without a prompt. Use this with caution.

  • Preserve Attributes (-p): File integrity matters, especially when dealing with permissions, timestamps, and ownership information. The preserve flag ensures that the new copy retains all of these attributes, making it perfect for backups or sensitive system files.

  • Verbose Output (-v): For a detailed view of what’s happening during the copy process, the verbose option prints each step to the terminal. This can be particularly helpful when copying large sets of files or debugging complex operations.

Practical Examples: Copying Files

Let’s now dive into some practical examples to see how these options come together in everyday tasks.

Copying a Single File

Imagine you have a file named notes.txt and you want to create a backup copy in the same directory. You can simply run:

cp notes.txt notes_backup.txt

This command creates an exact duplicate named notes_backup.txt. However, if a file by that name already exists and you want to avoid overwriting it without confirmation, you can use:

cp -i notes.txt notes_backup.txt

The -i flag ensures that you’re asked before any overwriting takes place.

Transferring Files Between Folders

If your goal is to move a file from one location to another, specify the destination directory. For instance, to move report.pdf to a directory called archive, use:

cp report.pdf /home/username/archive/

Make sure that the destination directory already exists; cp will not create it for you. If it doesn’t, you can create it with the mkdir command beforehand.

Copying Multiple Files at Once

Sometimes, you might need to duplicate several files simultaneously. To copy file1.txt, file2.txt, and file3.txt into a directory named backup, you would type:

cp file1.txt file2.txt file3.txt /home/username/backup/

This command handles multiple files in one go. If you’re dealing with many files that share a common pattern—say, all log files—you can use a wildcard:

cp *.log /home/username/logs/

This instructs cp to copy every file ending with .log into the logs directory, streamlining the process when working with numerous files.

Mastering Recursive Copying for Directories

Often, the task isn’t limited to a single file but involves entire directories. Copying directories requires a recursive approach to capture every nested file and folder.

Recursively Duplicating a Directory

Suppose you want to duplicate a website’s content located in /var/www/html to create a backup. The command would be:

cp -r /var/www/html /backup/html_backup

Here, the -r flag tells cp to copy everything within /var/www/html—subdirectories, hidden files, and all.

Combining Recursive and Preserve Options

When backing up directories, it’s often crucial to maintain file permissions, timestamps, and other metadata. In such cases, combine the recursive flag with the preserve flag:

cp -rp /var/www/html /backup/html_backup

This command ensures that every file in /var/www/html is copied to /backup/html_backup with all its original attributes intact. It’s an ideal solution for sensitive data or system configurations.

Tips, Tricks, and Advanced Techniques

Now that you understand the basics, let’s explore some advanced strategies and best practices for using the cp command effectively.

Combine Options for Enhanced Safety

It’s common to use multiple options together to tailor the behavior of cp. For instance, to safely copy a directory while preserving file attributes and prompting for overwrites, you can use:

cp -rpi /data/source_directory /data/destination_directory

This powerful combination ensures a thorough and secure copy process.

Handling File Names with Special Characters

File names in Linux may include spaces or special characters. To ensure these names are handled correctly, enclose them in quotes. For example:

cp "My Important Document.txt" "My Important Document Copy.txt"

This prevents the shell from misinterpreting spaces as delimiters between different arguments.

Avoiding Unintentional Overwrites

For batch operations or automated scripts, you might want to ensure that existing files are never overwritten. The -n option (short for no-clobber) achieves this:

cp -n *.conf /backup/configs/

This command copies configuration files only if a file with the same name doesn’t already exist in the destination, adding an extra layer of safety.

Use Verbose Mode for Debugging

When dealing with a large volume of files or troubleshooting a copy operation, the verbose flag (-v) can be immensely helpful:

cp -rv /source/folder /destination/folder

Verbose mode prints every file as it is processed, giving you a clear view of the ongoing operation and making it easier to identify any issues.

Real-World Applications and Scenarios

The cp command isn’t just for occasional use—it’s a vital tool in many professional settings. Here are a few real-world scenarios where mastering cp can make a significant difference:

System Administration and Backups

System administrators often use cp to create backups before making critical changes to system configurations. For instance:

cp -rp /etc /backup/etc_backup

This command creates a comprehensive backup of the /etc directory, preserving all system settings and permissions. In the event of an error or system failure, such backups are indispensable.

Data Migration and Server Transfers

When moving data between servers or different parts of a network, cp helps ensure that all files are transferred accurately. Combining cp with other tools like rsync can create robust solutions for data migration.

Development and Testing

Developers frequently duplicate directories to create test environments or sandbox copies of their projects. Whether you’re testing a new feature or debugging an issue, copying the entire project directory with preserved attributes can save you time and prevent potential errors.

Best Practices for Using cp Effectively

To wrap up, here are some key recommendations to keep in mind when using the cp command:

  • Double-check Destination Paths: Always verify that the target directory exists to avoid errors during the copy process.
  • Use Interactive Mode for Critical Files: When working with important data, the -i flag can prevent unintentional overwrites by asking for confirmation.
  • Quote File Names with Spaces: Ensure that any file names containing spaces or special characters are enclosed in quotes.
  • Plan Your Backup Strategy: Regularly back up essential directories using recursive and preserve options to maintain data integrity.
  • Combine Options Thoughtfully: Mix and match flags such as -r, -p, and -v to tailor cp to your specific needs, ensuring safety and clarity in your file operations.

Final Thoughts

The Linux cp command is a cornerstone of effective file management. Its simplicity belies the powerful functionality hidden within its many options. By mastering cp, you not only streamline your workflow but also protect your data through careful handling of file attributes, recursive copying, and thoughtful automation.

Whether you’re a novice stepping into the Linux world or an experienced user looking to refine your skills, the techniques and examples provided in this guide will serve as a reliable reference for your file duplication tasks. Remember to consult the manual page (man cp) for additional details and advanced options.

Embrace the versatility of the cp command, and soon you’ll find that managing files and directories on Linux becomes second nature.

Linux
07.02.2025
Reading time: 8 min

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Linux

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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