How to Download Files with cURL

Many cloud applications are built on the popular SSH protocol—it is widely used for managing network infrastructure, transferring files, and executing remote commands. SSH stands for Secure Socket Shell, meaning it provides a shell (command-line interface) around the connection between multiple remote hosts, ensuring that the connection is secure (encrypted and authenticated). SSH connections are available on all popular operating systems, including Linux, Ubuntu, Windows, and Debian. The protocol establishes an encrypted communication channel within an unprotected network by using a pair of public and private keys. Keys: The Foundation of SSH SSH operates on a client-server model. This means the user has an SSH client (a terminal in Linux or a graphical application in Windows), while the server side runs a daemon, which accepts incoming connections from clients. In practice, an SSH channel enables remote terminal management of a server. In other words, after a successful connection, everything entered in the local console is executed directly on the remote server. The SSH protocol uses a pair of keys for encrypting and decrypting information: public key and private key. These keys are mathematically linked. The public key is shared openly, resides on the server, and is used to encrypt data. The private key is confidential, resides on the client, and is used to decrypt data. Of course, keys are not generated manually but with special tools—keygens. These utilities generate new keys using encryption algorithms fundamental to SSH technology. More About How SSH Works Exchange of Public Keys SSH relies on symmetric encryption, meaning two hosts wishing to communicate securely generate a unique session key derived from the public and private data of each host. For example, host A generates a public and private key pair. The public key is sent to host B. Host B does the same, sending its public key to host A. Using the Diffie-Hellman algorithm, host A can create a key by combining its private key with the public key of host B. Likewise, host B can create an identical key by combining its private key with the public key of host A. This results in both hosts independently generating the same symmetric encryption key, which is then used for secure communication. Hence, the term symmetric encryption. Message Verification To verify messages, hosts use a hash function that outputs a fixed-length string based on the following data: The symmetric encryption key The packet number The encrypted message text The result of hashing these elements is called an HMAC (Hash-based Message Authentication Code). The client generates an HMAC and sends it to the server. The server then creates its own HMAC using the same data and compares it to the client's HMAC. If they match, the verification is successful, ensuring that the message is authentic and hasn't been tampered with. Host Authentication Establishing a secure connection is only part of the process. The next step is authenticating the user connecting to the remote host, as the user may not have permission to execute commands. There are several authentication methods: Password Authentication: The user sends an encrypted password to the server. If the password is correct, the server allows the user to execute commands. Certificate-Based Authentication: The user initially provides the server with a password and the public part of a certificate. Once authenticated, the session continues without requiring repeated password entries for subsequent interactions. These methods ensure that only authorized users can access the remote system while maintaining secure communication. Encryption Algorithms A key factor in the robustness of SSH is that decrypting the symmetric key is only possible with the private key, not the public key, even though the symmetric key is derived from both. Achieving this property requires specific encryption algorithms. There are three primary classes of such algorithms: RSA, DSA, and algorithms based on elliptic curves, each with distinct characteristics: RSA: Developed in 1978, RSA is based on integer factorization. Since factoring large semiprime numbers (products of two large primes) is computationally difficult, the security of RSA depends on the size of the chosen factors. The key length ranges from 1024 to 16384 bits. DSA: DSA (Digital Signature Algorithm) is based on discrete logarithms and modular exponentiation. While similar to RSA, it uses a different mathematical approach to link public and private keys. DSA key length is limited to 1024 bits. ECDSA and EdDSA: These algorithms are based on elliptic curves, unlike DSA, which uses modular exponentiation. They assume that no efficient solution exists for the discrete logarithm problem on elliptic curves. Although the keys are shorter, they provide the same level of security. Key Generation Each operating system has its own utilities for quickly generating SSH keys. In Unix-like systems, the command to generate a key pair is: ssh-keygen -t rsa Here, the type of encryption algorithm is specified using the -t flag. Other supported types include: dsa ecdsa ed25519 You can also specify the key length with the -b flag. However, be cautious, as the security of the connection depends on the key length: ssh-keygen -b 2048 -t rsa After entering the command, the terminal will prompt you to specify a file path and name for storing the generated keys. You can accept the default path by pressing Enter, which will create standard file names: id_rsa (private key) and id_rsa.pub (public key). Thus, the public key will be stored in a file with a .pub extension, while the private key will be stored in a file without an extension. Next, the command will prompt you to enter a passphrase. While not mandatory (it is unrelated to the SSH protocol itself), using a passphrase is recommended to prevent unauthorized use of the key by a third-party user on the local Linux system. Note that if a passphrase is used, you must enter it each time you establish the connection. To change the passphrase later, you can use: ssh-keygen -p Or, you can specify all parameters at once with a single command: ssh-keygen -p old_password -N new_password -f path_to_files For Windows, there are two main approaches: Using ssh-keygen from OpenSSH: The OpenSSH client provides the same ssh-keygen command as Linux, following the same steps. Using PuTTY: PuTTY is a graphical application that allows users to generate public and private keys with the press of a button. Installing the Client and Server Components The primary tool for an SSH connection on Linux platforms (both client and server) is OpenSSH. While it is typically pre-installed on most operating systems, there may be situations (such as with Ubuntu) where manual installation is necessary. The general command for installing SSH, followed by entering the superuser password, is: sudo apt-get install ssh However, in some operating systems, SSH may be divided into separate components for the client and server. For the Client To check whether the SSH client is installed on your local machine, simply run the following command in the terminal: ssh If SSH is supported, the terminal will display a description of the command. If nothing appears, you’ll need to install the client manually: sudo apt-get install openssh-client You will be prompted to enter the superuser password during installation. Once completed, SSH connectivity will be available. For the Server Similarly, the server-side part of the OpenSSH toolkit is required on the remote host. To check if the SSH server is available on your remote host, try connecting locally via SSH: ssh localhost If the SSH daemon is running, you will see a message indicating a successful connection. If not, you’ll need to install the SSH server: sudo apt-get install openssh-server As with the client, the terminal will prompt you to enter the superuser password. After installation, you can check whether SSH is active by running: sudo service ssh status Once connected, you can modify SSH settings as needed by editing the configuration file: ./ssh/sshd_config For example, you might want to change the default port to a custom one. Don’t forget that after making changes to the configuration, you must manually restart the SSH service to apply the updates: sudo service ssh restart Copying an SSH Key to the Server On Hostman, you can easily add SSH keys to your servers using the control panel. Using a Special Copy Command After generating a public SSH key, it can be used as an authorized key on a server. This allows quick connections without the need to repeatedly enter a password. The most common way to copy the key is by using the ssh-copy-id command: ssh-copy-id -i ~/.ssh/id_rsa.pub name@server_address This command assumes you used the default paths and filenames during key generation. If not, simply replace ~/.ssh/id_rsa.pub with your custom path and filename. Replace name with the username on the remote server. Replace server_address with the host address. If the usernames on both the client and server are the same, you can shorten the command: ssh-copy-id -i ~/.ssh/id_rsa.pub server_address If you set a passphrase during the SSH key creation, the terminal will prompt you to enter it. Otherwise, the key will be copied immediately. In some cases, the server may be configured to use a non-standard port (the default is 22). If that’s the case, specify the port using the -p flag: ssh-copy-id -i ~/.ssh/id_rsa.pub -p 8129 name@server_address Semi-Manual Copying There are operating systems where the ssh-copy-id command may not be supported, even though SSH connections to the server are possible. In such cases, the copying process can be done manually using a series of commands: ssh name@server_address 'mkdir -pm 700 ~/.ssh; echo ' $(cat ~/.ssh/id_rsa.pub) ' >> ~/.ssh/authorized_keys; chmod 600 ~/.ssh/authorized_keys' This sequence of commands does the following: Creates a special .ssh directory on the server (if it doesn’t already exist) with the correct permissions (700) for reading and writing. Creates or appends to the authorized_keys file, which stores the public keys of all authorized users. The public key from the local file (id_rsa.pub) will be added to it. Sets appropriate permissions (600) on the authorized_keys file to ensure it can only be read and written by the owner. If the authorized_keys file already exists, it will simply be appended with the new key. Once this is done, future connections to the server can be made using the same SSH command, but now the authentication will use the public key added to authorized_keys: ssh name@server_address Manual Copying Some hosting platforms offer server management through alternative interfaces, such as a web-based control panel. In these cases, there is usually an option to manually add a public key to the server. The web interface might even simulate a terminal for interacting with the server. Regardless of the method, the remote host must contain a file named ~/.ssh/authorized_keys, which lists all authorized public keys. Simply copy the client’s public key (found in ~/.ssh/id_rsa.pub by default) into this file. If the key pair was generated using a graphical application (typically PuTTY on Windows), you should copy the public key directly from the application and add it to the existing content in authorized_keys. Connecting to a Server To connect to a remote server on a Linux operating system, enter the following command in the terminal: ssh name@server_address Alternatively, if the local username is identical to the remote username, you can shorten the command to: ssh server_address The system will then prompt you to enter the password. Type it and press Enter. Note that the terminal will not display the password as you type it. Just like with the ssh-copy-id command, you can explicitly specify the port when connecting to a remote server: ssh client@server_address -p 8129 Once connected, you will have control over the remote machine via the terminal; any command you enter will be executed on the server side. Conclusion Today, SSH is one of the most widely used protocols in development and system administration. Therefore, having a basic understanding of its operation is crucial. This article aimed to provide an overview of SSH connections, briefly explain the encryption algorithms (RSA, DSA, ECDSA, and EdDSA), and demonstrate how public and private key pairs can be used to establish secure connections with a personal server, ensuring that exchanged messages remain inaccessible to third parties. We covered the primary commands for UNIX-like operating systems that allow users to generate key pairs and grant clients SSH access by copying the public key to the server, enabling secure connections.

Exploring the Linux landscape often means dealing with several file formats, especially compressed ones like .tar.gz. This format is popular because it combines multiple documents and folders into one compressed archive. Whether you're obtaining software packages, organizing project backups, or overseeing data storage, mastering this format usage is essential.  Throughout this guide, we will examine various strategies for unpacking .gz archives in Linux. From the versatile tar command to the more straightforward gzip and gunzip commands, we'll cover everything. We'll also dive into combining commands like unzip and tar, and using graphical interfaces for those who prefer a more visual approach. Why Choose .tar.gz? Listed below are few key reasons why you might opt to utilize this format: Space Efficiency: The combination of tar and gzip allows for the streamlined compression of large data amounts, enhancing disk space usage. Simplified Data Management: Merging several documents and directories into a single archive enhances data management and organizes storage. Easy Distribution: This widely-adopted format ensures seamless transfers between systems without any compatibility hurdles. Preservation of Metadata: The tar utility maintains file permissions and timestamps, making it perfect for backups and migrating systems. Creating a .tar.gz File Before jumping into extraction, it's helpful to know how to create an archive. This makes it easier to combine and compress many documents into one neat, smaller package. Here is the standard syntax for creation: tar -czf archive-name.tar.gz file1 file2 directory1 Where: c: Creates an entirely new archive. z: Perform compression. f: Assigns a specific name to the archive. For instance, to compress report1, report2, and the directory projects into a file called backup, apply: tar -czf backup.tar.gz report1.txt report2.txt projects For verification, list the directory items via: ls Examining .tar.gz Content To examine the items without extracting them, use a command that lists every compressed item. This is particularly handy for verifying items before unpacking. To list .gz content: tar -ztvf archive-name.tar.gz For instance, to list the items of backup: tar -ztvf backup.tar.gz Extracting .tar.gz in Linux Linux offers a variety of extraction methods for these archives, each bringing its own advantages. Here are comprehensive instructions for utilizing various commands and tools. Method 1: Via tar Utility The tar command is a powerful and flexible utility designed to manage compressed documents, offering functions to create, extract, and display the items of archives. This command is your ultimate tool for handling .gz resources efficiently. Basic Extraction To unpack .gz items directly into the current directory, apply: tar -xvzf archive-name.tar.gz Where: x: Unpacks the archive's items. v: Verbose mode actively displays each file being unpacked. z: Decompresses the data. f: Gives the archive a unique name. For unpacking the backup, apply: tar -xvzf backup.tar.gz Extracting to a Specific Directory For placing the unpacked files in a different location, use the -C option to indicate your chosen directory. This is handy when you need to ensure your retrieved file are neatly arranged in a designated location. To unpack the items into a chosen directory, apply: tar -xvzf archive-name.tar.gz -C /path/to/destination For instance, to unpack the backup into the Documents folder, utilize: tar -xvzf backup.tar.gz -C /home/user/Documents Extracting Specific Content For retrieving certain items from the archive, simply provide their names. This enables you to pinpoint and retrieve just the necessary data.  Here’s the format: tar -xvzf archive-name.tar.gz file1 file2 For example, to retrieve report1 and report2 from backup, apply: tar -xvzf backup.tar.gz report1.txt report2.txt Extracting Contents with a Specific Extension For retrieving items with a particular extension, the --wildcards option proves to be quite useful. This option lets you filter and retrieve data based on their names or extensions. Here's the syntax: tar -xvzf archive-name.tar.gz --wildcards '*.txt' For instance, to retrieve all .txt docs from backup: tar -xvzf backup.tar.gz --wildcards '*.txt' Method 2: Via gzip Utility The gzip is a tool primarily used for compressing data, but it can also decompress them with the -d option. This method is straightforward and effective for handling .gz resources. To unzip a .gz file, apply the subsequent command: gzip -d archive-name.tar.gz For instance, to unpack backup, apply: gzip -d backup.tar.gz After decompressing, retrieve the items via: tar -xf archive-name.tar For instance: tar -xf backup.tar Method 3: Via gunzip Utility The gunzip is a specifically designed tool for decompressing .gz documents, functioning as an alias for gzip -d. This command is simple to use and directly addresses the need to decompress .gz files. To decompress, apply: gunzip archive-name.tar.gz For example: gunzip backup.tar.gz After decompressing, unpack the items through: tar -xf archive-name.tar For example: tar -xf backup.tar Method 4: Via GUI For users who favor a GUI, various Linux desktop environments include file managers equipped with extraction tools. This method is user-friendly and ideal for beginners. Extracting Contents to the Current Directory Find the .gz file within your file manager. Right-click on it and choose "Extract." Extracting Contents to a Specific Directory Spot the .gz file within your file explorer. Right-click on it and select "Extract to…". Choose the destination directory. Handling Large Archives with Parallel Decompression When handling massive archives, pigz (Parallel Implementation of gzip) can significantly enhance decompression speed by using several CPU cores. Here's how to use it: Install pigz on Linux via: sudo apt install pigz To uncompress a .gz file via pigz, apply: pigz -d archive-name.tar.gz After decompression, retrieve the resulting .tar doc with: tar -xf archive-name.tar Utilizing Compression with Encryption For added security, you can encrypt your .gz doc. GPG (GNU Privacy Guard) can be used to encrypt documents, ensuring that sensitive information remains protected during storage and transfer. Encrypting an Archive For encryption, use GPG with the following command: gpg -c archive-name.tar.gz Decrypting an Archive To decrypt an encrypted archive, apply: gpg -d archive-name.tar.gz.gpg > archive-name.tar.gz Tips for Content Extraction in Linux Backup Important Docs: Always create backups before unpacking multiple docs to avoid data loss. Check Permissions: Ensure you possess the required permissions to retrieve documents in the designated directory. Utilize Wildcards Carefully: Be cautious when using wildcards to avoid unintentional extraction. Troubleshooting Frequent Issues with Extraction Here are a few common extraction difficulties and the ways to address them: Corrupted Archives In case an archive is corrupted, try using the --ignore-zeros option to retrieve it: tar -xvzf archive-name.tar.gz --ignore-zeros Insufficient Permissions Confirm that you have the proper permissions to access and modify files. Utilize sudo if required: sudo tar -xvzf archive-name.tar.gz -C /path/to/destination Disk Space Issues Check that you have enough disk space to unzip the documents. Verify disk usage with: df -h Conclusion Unpacking .tar.gz documents in Linux is a simple task, with multiple methods to cater to different user preferences. Whether you're using the tar, gzip, gunzip commands, or a GUI, Linux equips you with efficient tools to handle compressed data seamlessly. This guide empowers you with the know-how to confidently retrieve .gz docs. Whether it's handling software packages, arranging backups, or managing data storage, mastering the creation and extraction of such files keeps your workflow streamlined and efficient.  By mastering the creation and extraction of these files, you streamline your workflow and enhance your overall efficiency, making data management a breeze.

In Linux, permissions are extremely valuable in dealing with access to folders as well as files. It makes sure proper authority over which one can deal with them. Effectively handling these privileges is fundamental for enhancing system file management and security. These privileges give groups or users the ability for reading, executing, or modifying, directories and their content. These rules safeguard data and restrict access, particularly in environments with more than one user. Each folder or file comes with particular rights that represent what users can accomplish. This article will demonstrate the basis of permissions, point out access, understanding, and changing privileges for them, and manage folders and their content. Basis of Permissions For beginners, the directories or file privileges can be challenging. It involves the concepts of types and groups as below:  Types  In Linux, each folder or file holds three kinds of permissions, each serving a particular purpose: Read (r): It indicates the permission to view the file’s content or enlist the items inside the folder. Write (w): It allows modifications to the particular file or addition and deletion of files inside the directory. Execute (x): It permits the file execution as the program or getting the folder content. Groups They are classified into three groups, each serving a particular role: User (Owner): It indicates the user who has the ownership rights of the folder or file. Group: It indicates a bunch of users having shared access rights. Others: It includes those who are not owners or participants of the desired group. Permission Formats Privileges are visualized in two formats: symbolic and octal. The symbolic employs symbols to mean rights, r indicates reading, w refers to writing, and x is utilized for the execution purpose. In contrast, the octal utilizes numbers, where 4 means reading, 2 stands for writing, and 1 signifies execution. Linux Display Permissions  Linux offers several methods to examine privileges. Individuals can employ a terminal for detailed information or go through the file manager's properties option for a graphical visualization. Using GUI This approach is the most straightforward for evaluating rights of permissions. It permits individuals to display them through the file manager's properties. To employ this method, hit the right-click on the desired folder and click Properties: Next, navigate to Permissions for viewing the permissions given to the particular directory and its content: In the figure, readers can see and adjust privileges for directories and their content, defining what the group is permitted to do, such as modifying, accessing, or deleting them. Additionally, it provides security context info and offers the choice to implement these privileges to all enclosed files: Through the ls Command You can employ the ls command along with -l, followed by the specified folder or file, to analyze its stats, including privileges: ls -l <file_or_directory_name> It retrieves thorough entries, including file privileges and a variety of properties. For instance, the below one retrieves the privilege attributes of the Downloads: ls -l Downloads In the output, the starting part indicates the permissions for all files or folders. For instance, -rw-rw-r-- describes the file as having reading and writing rights for the group as well as the owner. Also, reading-only privileges for others. drwxrwxr-x demonstrates the particular folder possessing the privileges of reading, writing, and executing for the group and owner. Also, reading and executing privileges for others. The next section describes the number of hard links to a particular file or folder. The next section shows (e.g., linuxuser) the owner. The next part shows the group which is corresponding with the directory or file. The fifth part describes the file's size in bytes. Next you see the most recent modification date and time, and finally the seventh section shows the file or folder’s name. Through the namei Utility In Linux, namei is an effective utility that shows the individual sections of a file or folder path along with their rights: namei -l /path/to/file Now, employ the namei -l to visualize comprehensive details about the Downloads folder: namei -l Downloads In this outcome, f: Downloads relates to the last entry in the folder, e.g. Downloads. The d signifies that it is a directory. The rwxr-xr-x means that the linuxuser has the right to read, write, and execute. However, both the linuxuser owner and the group have the capacity to read and execute privileges. It confirms that the linuxuser group as well as a user have the owners' rights of the particular folder. Through the stat Command This utility retrieves comprehensive info about the particular folder and its content, e.g. files: stat fileName  Let’s employ it to retrieve the comprehensive statistics of the Downloads: stat Downloads It retrieves the size of the file, rights, and a lot more: Modifying Permissions Editing file and folder rights are effective for system privacy purposes. Linux provides two main methods to revise privileges: symbolic and absolute mode. Symbolic Mode In this mode, individuals adjust permissions by adding (+), deleting (-), or setting (=) specific rights for the owner, group, or others. For making these modifications, the chmod is utilized.  Let's check out the permissions for the hostmanData file: ls -l hostmanData For adding execution access for the file’s owner, utilize the chmod utility as below: chmod u+x hostmanData Next, verify the updated privileges by running: ls -l hostmanData Absolute Mode In this method, rights are given through octal synonyms. There, every digit is related to reading, writing, and executing access for the user, group, and others. For instance, the code line allows full privileges to the owner and gives reading and executing access to the group and others: chmod 755 hostmanData Modifying Owner Rights The chown utility permits individuals to alter the folder's ownership and content. It allocates the new group or owner to maintain access control. Modifying Ownership We can alter the owner status of a particular directory or file via the chown. For instance, to alter the privileges of the hostmanData file to anees, employ the below code line: sudo chown anees hostmanData Next, confirm the changes via the following code line: ls -l hostmanData Modifying Group Ownership For updating the owner of a group of files, you can employ the below syntax: sudo chown :users hostmanData The above line updates the group of the hostmanData from linuxuser to users: Other Permissions  Linux permits individuals the appropriate way to handle advanced or complex operations via the below utilities: setuid: It allowed the file to execute with the authority of the owner compared to the user when implemented to the particular executable file. setgid: It permits the specific file for execution with the particular authority of the group that corresponds with the given file. Sticky Bit: It makes sure that the file’s owner has the capacity for renaming or deleting particular files inside a particular folder. Final Words In Linux, permissions are significantly important for handling access to particular folders or files. It plays an essential impact in system management or security. In this article, we covered the basis of permissions, their authority and modification, and editing ownership. We also demonstrated special rights to deal with complicated tasks. With a solid comprehension of these concepts, users can effectively secure Linux and manage access with ease.