Installing and Configuring Samba on Ubuntu 22.04

A server administrator often has to work with user accounts — adding, deleting, and configuring access modes. Removing outdated user accounts is one security measure that can significantly reduce the number of vulnerabilities in the system. The Linux utilities deluser and userdel are used for deletion. However, before proceeding directly to deleting a user, we must take certain steps. In this article, we will explore how to delete a user in Ubuntu without compromising the system. At the same time, we will preserve the ability to access the user’s home directory files after deletion. In this article, we will work with the user hostman, which was created beforehand. This article will primarily focus on removing an Ubuntu user via the terminal, but we will also provide instructions for deleting a user account through the graphical interface. Please note that you will need superuser privileges to work with user accounts. The instructions will be suitable for any cloud server running Ubuntu OS. Checking the User Account First, you need to check whether the user is currently logged into the system. This will affect further steps: if the user is currently authorized on the server, you will need to terminate their connection and change the password. Check the list of users authorized in the system using the who utility or its alias w: who If you see that the user hostman is authorized, you need to check which processes are running under this user. This is a necessary step because if background operations are being performed, Ubuntu 22.04 will not allow us to delete the user. Check with the ps utility: sudo ps -u hostman As a result, you might see a response like this:    PID TTY          TIME CMD 1297129 pts/2    00:00:00 bash 1297443 pts/2    00:00:00 htop For testing purposes, we launched the htop utility under the hostman account, which is running in the background. Blocking Access Before stopping the user’s processes, you need to block their access to the system. You can do this by changing their password. User passwords are stored in the system in encrypted form in the /etc/shadow file. This file is readable only by the root user, and in addition to password hashes, it contains their expiration information. There is a special utility that allows you to remove a user’s password in Ubuntu — passwd. To restrict access, we will use the passwd utility with the -l (or --lock) flag, which puts the utility into lock mode: sudo passwd -l hostman As a result, the utility will add an exclamation mark at the beginning of the encrypted password string. That is all that is needed to prevent the user from logging in again since the hashes will no longer match. Killing Processes In Ubuntu, you cannot delete a user via the console if any processes are running under their name. To terminate a process, you can use one of the following commands: kill — deletes a process by its identifier. You can determine the IDs of the hostman user processes with: top -U hostman or ps -u hostman pkill — deletes a process by its name. For example, if the user hostman has launched the top process, you can terminate it with: sudo pkill top killall — deletes all processes, including child processes. Often, a process will launch many so-called subprocesses; stopping them by name or identifier can be complex and time-consuming. We will use the last command to reliably kill all user processes: sudo killall -9 -u hostman The -9 flag means the processes will receive a SIGKILL signal. This means the process will be forcibly terminated, since this signal cannot be ignored or blocked. Essentially, it is equivalent to a “force quit” of a non-responding program in graphical operating systems. After completing the user’s processes, they will no longer be authorized in the system. You can verify this using the who command. Since we locked the login in the previous step, the hostman user will not be able to log in again. Optional — Archiving the Home Directory Quite often, when deleting a Linux user account, you may need to keep its home directory, which might contain important files required either by the user or by the organization you are serving as an administrator. The built-in Ubuntu utilities allow you to remove a user while keeping their home directory. However, this is not recommended for two reasons: Disk Space — the user’s home directory may contain a large amount of data. It is irrational and excessive to store data from all outdated accounts on the main work disk. Over time, you might run out of space for new users. Data Relevance — it is good practice to keep the /home directory containing only the directories corresponding to active user accounts. Keeping this list in order helps with administration. We will use the tar utility to archive the home directory of the hostman user: sudo tar -cvjf /mnt/nobackup/hostman.homedir.tar.gz /home/hostman Let’s go over the arguments and flags: -c — creates the resulting .tar archive file -v — enables verbose mode, showing debugging information and listing archived files -z — creates a compressed .gz archive -f — indicates that the first argument will be used as the archive name The first argument is the final location of the archive. In our example, we place the archive with the user’s home directory on the nobackup disk, which, as the name implies, is not subject to backup. The second argument is the path to the directory from which the archive is created. Stopping Scheduled Jobs Before deleting a user in Ubuntu, it is recommended to stop all cron scheduler tasks launched by that user. You can do this with the crontab command. We will launch it under the hostman user with the -u flag and switch it to delete mode with the -r flag: sudo crontab -r -u hostman Now you can be sure that after deleting the user account, no unknown scripts will be executed for which no one is responsible. Deleting the User Once all the previous steps have been completed, it is time to proceed with the main task: deleting the Ubuntu user. There are two ways to do this: the deluser and userdel utilities. To delete the user account, we will use the deluser utility. Running it without parameters will delete the user account but leave their home directory and other user files intact. You can use the following flags: --remove-home — as the name suggests, deletes the user’s home directory --remove-all-files — deletes all system files belonging to the user, including the home directory --backup — creates an archive of the home directory and mail files and places it in the root directory. To specify a folder for saving the archive, use the --backup-to flag. As you can see from the parameter descriptions above, manually archiving the user’s home directory is not strictly necessary — deluser can do everything for you. In addition, with deluser you can remove a user from a group in Ubuntu or delete the group itself: sudo deluser hostman administrators The command above removes the user hostman from the administrators group. Let’s proceed with the complete deletion of the user and the hostman group without preserving the home directory: sudo deluser --remove-home hostman Deleting the User via Graphical Interface The entire article above is about how to delete a user in the Ubuntu terminal. But if you have a system with a graphical interface, you can delete a user in just a few simple steps. Open the Users section in System Settings. To switch to superuser mode, click the Unlock button. After that, the Delete User button will become active. When you click it, a dialog box will appear, offering to delete the user’s files, specifically those in the home directory. Conclusion Deleting a user in Ubuntu is not difficult; you just need to use the deluser utility with the required parameters. However, in this article, we described several steps that will help you safely delete a user account while preserving the system’s stability.

WordPress is a simple, popular, open-source, and free CMS (content management system) for creating modern websites. Today, WordPress powers nearly half of the websites worldwide. Hostman offers Wordpress cloud hosting with quick load times, robust security, and simplified management.  However, having just a content management system is not enough. Modern websites require an SSL certificate, which provides encryption and allows using a secure HTTPS connection. This short guide will show how to install WordPress on a cloud server, perform initial CMS configuration, and add an SSL certificate to the completed site, enabling users to access the website via HTTPS. The Nginx web server will receive user requests and then proxied to WordPress for processing and generating response content. A few additional components are also needed: a MySQL database, which serves as the primary data storage in WordPress, and PHP, which WordPress is written in. This technology stack is known as LEMP: Linux, Nginx, MySQL, PHP. Step 1. Creating the Server First, you will need a cloud server with Ubuntu 22.04 installed. Go to the Hostman control panel. Select the Cloud servers tab on the left side of the control panel. Click the Create button. You’ll need to configure a range of parameters that ultimately determine the server rental cost. The most important of these parameters are: The operating system distribution and its version (in our case, Ubuntu 22.04). Data center location. Physical configuration. Server information. Once all the data is filled in, click the Order button. Upon completion of the server setup, you can view the IP address of the cloud server in the Dashboard tab, and also copy the command for connecting to the server via SSH along with the root password: Next, open a terminal in your local operating system and connect via SSH with password authentication: ssh root@server_ip Replace server_ip with the IP address of your cloud server. You will then be prompted to enter the password, which you can either type manually or paste from the clipboard. After connecting, the terminal will display information about the operating system. Now you can create a user with sudo priviliges or keep using root. Step 2. Updating the System Before beginning the WordPress installation, it’s important to update the list of repositories available through the APT package manager: sudo apt update -y It’s also a good idea to upgrade already installed packages to their latest versions: sudo apt upgrade -y Now, we can move on to downloading and installing the technology stack components required for running WordPress. Step 3. Installing PHP Let's download and install the PHP interpreter. First, add a specialized repository that provides up-to-date versions of PHP: sudo add-apt-repository ppa:ondrej/php In this guide, we are using PHP version 8.3 in FPM mode (FastCGI Process Manager), along with an additional module to enable PHP’s interaction with MySQL: sudo apt install php8.3-fpm php-mysql -y The -y flag automatically answers “yes” to any prompts during the installation process. To verify that PHP is now installed on the system, you can check its version: php -v The console output should look like this: PHP 8.3.13 (cli) (built: Oct 30 2024 11:27:41) (NTS)Copyright (c) The PHP GroupZend Engine v4.3.13, Copyright (c) Zend Technologies    with Zend OPcache v8.3.13, Copyright (c), by Zend Technologies You can also check the status of the FPM service: sudo systemctl status php8.3-fpm In the console output, you should see a green status indicator: Active: active (running) Step 4. Installing MySQL The MySQL database is an essential component of WordPress, as it stores all site and user information for the CMS. Installation We’ll install the MySQL server package: sudo apt install mysql-server -y To verify the installation, check the database version: mysql --version If successful, the console output will look something like this: mysql  Ver 8.0.39-0ubuntu0.22.04.1 for Linux on x86_64 ((Ubuntu)) Also, ensure that the MySQL server is currently running by checking the database service status: sudo systemctl status mysql The console output should display a green status indicator: Active: active (running) MySQL Security This step is optional in this guide, but it’s worth mentioning. After installing MySQL, you can configure the database’s security settings: mysql_secure_installation This command will prompt a series of questions in the terminal to help you configure the appropriate level of MySQL security. Creating a Database Next, prepare a dedicated database specifically for WordPress. First, log in to MySQL: mysql Then, execute the following SQL command to create a database: CREATE DATABASE wordpress_database; You’ll also need a dedicated user for accessing this database: CREATE USER 'wordpress_user'@'localhost' IDENTIFIED BY 'wordpress_password'; Grant this user the necessary access permissions: GRANT ALL PRIVILEGES ON wordpress_database.* TO 'wordpress_user'@'localhost'; Finally, exit MySQL: quit Step 5. Downloading and Configuring Nginx The Nginx web server will handle incoming HTTP requests from users and proxy them to PHP via the FastCGI interface. Download and Installation We’ll download and install the Nginx web server using APT: sudo apt install nginx -y Next, verify that Nginx is indeed running as a service: systemctl status nginx In the console output, you should see a green status indicator: Active: active (running) You can also check if the web server is functioning correctly by making an HTTP request through a browser. Enter the IP address of the remote server in the address bar, where you are installing Nginx. For example: http://166.1.227.189 If everything is set up correctly, Nginx will display its default welcome page. For good measure, let’s add Nginx to the system’s startup list (though this is typically done automatically during installation): sudo systemctl enable nginx Now, you can proceed to make adjustments to the web server configuration. Configuration In this example, we’ll slightly modify the default Nginx configuration. For this, we need a text editor. We will use nano. sudo apt install nano Now open the configuration file: sudo nano /etc/nginx/sites-enabled/default If you remove all the comments, the basic configuration will look like this: server { listen 80 default_server; listen [::]:80 default_server; root /var/www/html; index index.html index.htm index.nginx-debian.html; server_name _; location / { try_files $uri $uri/ =404; } } To this configuration, we’ll add the ability to proxy requests to PHP through FastCGI: server { listen 80 default_server; listen [::]:80 default_server; root /var/www/html; # added index.php to index files index index.html index.htm index.nginx-debian.html index.php; # specify the domain name to obtain an SSL certificate later server_name mydomain.com www.mydomain.com; location / { # try_files $uri $uri/ =404; # direct root requests to /index.php try_files $uri $uri/ /index.php?$args; } # forward all .php requests to PHP via FastCGI location ~ \.php$ { include snippets/fastcgi-php.conf; fastcgi_pass unix:/run/php/php8.3-fpm.sock; } } Note that the server_name parameter should contain the domain name, with DNS settings including an A record that directs to the configured server with Nginx. Now, let’s check the configuration syntax for errors: sudo nginx -t If everything is correct, you’ll see a confirmation message in the console: nginx: the configuration file /etc/nginx/nginx.conf syntax is oknginx: configuration file /etc/nginx/nginx.conf test is successful Then, reload the Nginx service to apply the new configuration: sudo systemctl reload nginx Step 6. Installing an SSL Certificate To obtain an SSL certificate from Let’s Encrypt, we’ll use a special utility called Certbot. In this guide, Certbot will automate several tasks: Request the SSL certificate. Create an additional Nginx configuration file. Edit the existing Nginx configuration file (which currently describes the HTTP server setup). Restart Nginx to apply the changes. Obtaining the Certificate Like other packages, install Certbot via APT: sudo apt install certbotsudo apt install python3-certbot-nginx The first command installs Certbot, and the second adds a Python module for Certbot’s integration with Nginx. Alternatively, you can install python3-certbot-nginx directly, which will automatically include Certbot as a dependency: sudo apt install python3-certbot-nginx -y Now, let’s initiate the process to obtain and install the SSL certificate: sudo certbot --nginx First, Certbot will prompt you to register with Let’s Encrypt. You’ll need to provide an email address, agree to the Terms of Service, and optionally opt-in for email updates (you may decline this if desired). Then, enter the list of domain names, separated by commas or spaces, for which the certificate should be issued. Specify the exact domain names that are listed in the Nginx configuration file under the server_name directive: mydomain.com www.mydomain.com After the certificate is issued, Certbot will automatically configure it by adding the necessary SSL settings to the Nginx configuration file: listen 443 ssl; # managed by Certbot # RSA certificate ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot # Redirect non-https traffic to https if ($scheme != "https") { return 301 https://$host$request_uri; } # managed by Certbot So, the complete Nginx configuration file will look as follows: server { listen 80 default_server; listen [::]:80 default_server; listen 443 ssl; # managed by Certbot # RSA certificate ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot root /var/www/html; index index.html index.htm index.nginx-debian.html index.php; server_name domain.com www.domain.com; # Redirect non-https traffic to https if ($scheme != "https") { return 301 https://$host$request_uri; } # managed by Certbot location / { # try_files $uri $uri/ =404; # direct root requests to /index.php try_files $uri $uri/ /index.php?$args; } # forward all .php requests to PHP via FastCGI location ~ \.php$ { include snippets/fastcgi-php.conf; fastcgi_pass unix:/run/php/php8.3-fpm.sock; } } Automatic Certificate Renewal Let’s Encrypt certificates expire every 90 days, so they need to be renewed regularly. Instead of manually renewing them, you can set up an automated task. For this purpose, we’ll use Crontab, a scheduling tool in Unix-based systems that uses a specific syntax to define when commands should run. Install Crontab: sudo apt install cron And enable it: sudo systemctl enable cron Now open the Crontab file: crontab -e Add the following line to schedule the Certbot renewal command: 0 12 * * * /usr/bin/certbot renew --quiet In this configuration: The command runs at noon (12:00) every day. Certbot will check the certificate’s expiration status and renew it if necessary. The --quiet flag ensures that Certbot runs silently without generating output. Step 7. Downloading WordPress In this guide, we’ll use WordPress version 6.5.3, which can be downloaded from the official website: wget https://wordpress.org/wordpress-6.5.3.tar.gz Once downloaded, unpack the WordPress archive: tar -xvf wordpress-*.tar.gz After unpacking, you can delete the archive file: rm wordpress-*.tar.gz This will create a wordpress folder containing the WordPress files. Most core files are organized in the wp-content, wp-includes, and wp-admin directories. The main entry point for WordPress is index.php. Moving WordPress Files to the Web Server Directory You need to copy all files from the wordpress folder to the web server’s root directory (/var/www/html/) so that Nginx can serve the PHP-generated content based on user HTTP requests. Clear the existing web server directory (as it currently contains only the default Nginx welcome page, which we no longer need): rm /var/www/html/* Copy WordPress files to the web server directory: cp -R wordpress/* /var/www/html/ The -R flag enables recursive copying of files and folders. Set ownership and permissions. Ensure that Nginx can access and modify these files by setting the www-data user and group ownership, as well as appropriate permissions, for the WordPress directory: sudo chown -R www-data:www-data /var/www/html/sudo chmod -R 755 /var/www/html/ This allows Nginx to read, write, and modify WordPress files as needed, avoiding permission errors during the WordPress installation process. Step 8. Configuring WordPress WordPress configuration is managed through an intuitive web-based admin panel. No programming knowledge is necessary, though familiarity with languages like JavaScript, PHP, HTML, and CSS can be helpful for creating or customizing themes and plugins. Accessing the Admin Panel Open a web browser and go to the website using the domain specified in the Nginx configuration, such as: https://mydomain.com If all components were correctly set up, you should be redirected to WordPress’s initial configuration page: https://mydomain.com/wp-admin/setup-config.php Select Language: Choose your preferred language and click Continue. Database Configuration: WordPress will prompt you to enter database details. Click Let’s go! and provide the following information: Database Name: wordpress_database (from the previous setup) Database Username: wordpress_user Database Password: wordpress_password Database Host: localhost Table Prefix: wp_ (or leave as default) Click Submit. If the credentials are correct, WordPress will confirm access to the database. Run Installation: Click Run the installation. WordPress will then guide you to enter site and admin details: Site Title Admin Username Admin Password Admin Email Option to discourage search engine indexing (recommended for development/testing sites) Install WordPress: Click Install WordPress. After installation, you’ll be prompted to log in with the admin username and password you created. Accessing the Dashboard Once logged in, you'll see the WordPress Dashboard, which contains customizable widgets. The main menu on the left allows access to core WordPress functions, including: Posts and Pages for content creation Comments for moderating discussions Media for managing images and files Themes and Plugins for design and functionality Users for managing site members and roles Your WordPress site is now fully configured, and you can begin customizing and adding content as needed. Conclusion This guide showed how to install WordPress along with all its dependencies and how to connect a domain and add a SSL certificate from Let’s Encrypt to an already functioning website, enabling secure HTTPS connections with the remote server. The key dependencies required for WordPress to function include: PHP: The scripting language WordPress is written in. MySQL: The database system used by WordPress to store content and user data. Nginx (or Apache in other implementations): The web server that processes user requests initially. For more detailed information on managing site content through the WordPress admin panel, as well as creating custom themes and plugins, refer to the official WordPress documentation. Frequently Asked Questions How do I install WordPress on Ubuntu? First set up Nginx, PHP, and MySQL. Then either download WordPress manually or use a deployment script. How do I enable HTTPS with Let’s Encrypt? Use Certbot to generate a certificate, then automate renewal with a simple cron job. Is Nginx better than Apache for WordPress? For performance and memory efficiency, yes. Nginx handles high traffic with fewer resources.

SSH is a network protocol that provides a secure connection between a client and a server. All communication is encrypted, preventing theft of data transmitted over the network and other remote network attacks. Let’s say you have ordered a cloud server from Hostman. You will need SSH installed and configured to connect to and administer the server. The guide below will describe how to install SSH on Ubuntu 22.04 and configure it. Prerequisites Before proceeding with the installation and configuration of the Secure Shell service, ensure the following requirements are met: Linux Command Line Skills for Configuration Having a solid grasp of basic Linux commands like sudo, apt, nano, and systemctl is essential when setting up the service. These commands will be frequently used during the installation and configuration process. It's crucial to be comfortable working within the command line environment to manage the service effectively. Root or Sudo Access for Setup To install and configure the server, administrative (root) privileges are required. Users must either have sudo access or be logged in as root. Without these privileges, the setup process cannot proceed. Internet Connection for Package Download A stable internet connection is necessary to install the OpenSSH server and any additional related packages. Without a functional connection, the system cannot retrieve the required software components. Configuring Firewall for Access If a firewall, like ufw, is enabled on the system, it may block remote access by default. It is essential to configure your firewall to allow incoming connections. Use ufw or another firewall tool to ensure port 22 is open and accessible. Access to the System (Local or Remote) You need physical access to your machine to configure the service locally, or it must be remotely accessible via its IP address. Ensure the system is properly connected to the network to establish a connection. Don't forget, that you can deploy your cloud server fast and cheap by choosing our VPS Server Hosting Step 1: Prepare Ubuntu The first thing you need to do before you start installing SSH on Ubuntu is to update all apt packages to the latest versions. To do this, use the following command: sudo apt update && sudo apt upgrade Step 2: Install SSH on Ubuntu OpenSSH is not pre-installed on the system, so let's install it manually. To do this, type in the terminal: sudo apt install openssh-server The installation of all the necessary components will begin. Answer "Yes" to all the system prompts.  After the installation is complete, go to the next step to start the service. Step 3: Start SSH Now you need to enable the service you just installed using the command below: sudo systemctl enable --now ssh On successful startup, you will see the following system message. The --now key helps you launch the service and simultaneously set it to start when the system boots. To verify that the service is enabled and running successfully, type: sudo systemctl status ssh The output should contain the Active: active (running) line, which indicates that the service is successfully running. If you want to disable the service, execute:  sudo systemctl disable ssh It disables the service and prevents it from starting at boot. Step 4: Configure the firewall Before connecting to the server via SSH, check the firewall to ensure it is configured correctly. In our case, we have the UFW installed, so we will use the following command: sudo ufw status In the output, you should see that SSH traffic is allowed. If you don't have it listed, you need to allow incoming SSH connections. This command will help with this: sudo ufw allow ssh Step 5: Connect to the server Once you complete all the previous steps, you can log into the server using the SSH protocol. To do this, you will need the server's IP address or domain name and the name of a user created on the server. In the terminal line, enter the command: ssh username@IP_address Or:  ssh username@domain Important: To successfully connect to a remote server, SSH must be installed and configured on the remote server and the user's computer from which you make the connection.  - Step 6 (optional): Create Key Pair for Secure Authentication For enhanced security, consider configuring a key pair instead of relying on password authentication. To generate one, use the following command: ssh-keygen Step 7: Configure SSH Having completed the previous five steps, you can already connect to the server remotely. However, you can further increase the connection's security by changing the default connection port to another or changing the password authentication to key authentication. These and other changes require editing the SSH configuration file. The main OpenSSH server settings are stored in the main configuration file sshd_config (location: /etc/ssh). Before you start editing, you should create a backup of this file:  sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.initial If you get any errors after editing the configuration file, you can restore the original file without problems. After creating the backup, you can proceed to edit the configuration file. To do this, open it using the nano editor: sudo nano /etc/ssh/sshd_config In the file, change the port to a more secure one. It is best to set values from the dynamic range of ports (49152 - 65535) and use different numbers for additional security. For example, let's change the port value to 49532. To do this, we uncomment the corresponding line in the file and change the port as shown in the screenshot below. In addition to this setting, we recommend changing the password authentication mode to a more secure key authentication mode. To do this, uncomment the corresponding line and make sure the value is "Yes", as shown in the screenshot. Now, let's prohibit logging on to the server as a superuser by changing the corresponding line as shown in the picture below. There are other settings you can configure to increase the server security:  UseDNS checks if the hostname matches its IP address. The value "Yes" enables this parameter. PermitEmptyPasswords prohibits using empty passwords for authentication if the value is "No." MaxAuthTries limits the number of unsuccessful attempts to connect to the server within one communication session.  AllowUsers and AllowGroups are responsible for the list of users and groups allowed to access the server: # AllowUsers User1, User2, User3# AllowGroups Group1, Group2, Group3 Login GraceTime sets the time provided for successful authorization. We recommend reducing the value of this parameter by four times. ClientAliveInterval limits the time of user inactivity. After exceeding the specified limit, the user is disconnected. After making all the changes in the main configuration file, save them and close the editor.  Restart the service to make the changes take effect: sudo systemctl restart ssh If you have changed the port in the configuration file, you should connect using the new port:  ssh -p port_number username@IP_address Or: ssh -p port_number_port_username@domain Troubleshooting Connection Issues Ensure the service is running with: sudo systemctl status ssh Restart it if necessary: sudo systemctl restart ssh Check firewall settings to allow traffic on port 22: sudo ufw allow 22 Confirm the system is reachable by running: ping <server-ip-address> Disabling the Service If you need to disable remote access for any reason, follow these steps: Stop the Service To temporarily stop accepting connections: sudo systemctl stop ssh Prevent Automatic Startup To disable it from starting on reboot: sudo systemctl disable ssh Confirm Inactive Status Verify that the service is no longer running: sudo systemctl status ssh Uninstall the Server If the service is no longer needed, remove it and its associated configuration files: sudo apt remove openssh-server Conclusion This article presents a step-by-step guide on installing and configuring SSH in Ubuntu 22.04 and describes how to edit the main configuration file to improve security. We hope this guide helps you to set up a secure remote connection to your Ubuntu server.To see more about SSH keys click here.