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  2. Windows users are used to creating shortcuts to have fast access to their files and folders. This is is especially useful when these are buried deep in their system. This feature isn't as obvious on most Linux systems as it is on Windows. Create a shortcut on a Unix-like operating system using a symlink. Create Symlink in Linux Terminal way (the link will appear in the folder the terminal points to): ln -s /folderorfile/link/will/point/to /name/of/the/link
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  4. Installing CIFS Utilities Packages To mount a Windows share on a Linux system, first you need to install the CIFS utilities package. Installing CIFS utilities on CentOS and Fedora: sudo dnf install cifs-utils Auto Mounting sudo nano /etc/fstab Add the following line to the file: # <file system> <dir> <type> <options> <dump> <pass> //WIN_SHARE_IP/share_name /mnt/win_share cifs credentials=/etc/win-credentials,file_mode=0755,dir_mode=0755 0 0 Run the following command to mount the share: mount -a Creating Credential File For better security it is recommended to use a credentials file, which contains the share username, password and domain. /etc/win-credentials The credentials file has the following format: username = user password = password domain = domain The file must not be readable by users. To set the correct permissions and ownership run: sudo chown root: /etc/win-credentials sudo chmod 600 /etc/win-credentials Create Symlink in Linux 8. Create a shortcut to your new mounted file share: (Article here) Terminal way (the link will appear in the folder the terminal points to): ln -s /folderorfile/link/will/point/to /name/of/the/link
  5. How to Import and Export Databases Export To Export a database, open up terminal, making sure that you are not logged into MySQL and type, mysqldump -u [username] -p [database name] > [database name].sql The database that you selected in the command will now be exported to your droplet. Import To import a database, first create a new blank database in the MySQL shell to serve as a destination for your data. CREATE DATABASE newdatabase; Then log out of the MySQL shell and type the following on the command line: mysql -u [username] -p newdatabase < [database name].sql With that, your chosen database has been imported into your destination database in MySQL. Create a database user login to mysql mysql -u root -p run the following command mysql> CREATE USER 'newuser'@'localhost' IDENTIFIED BY 'user_password'; Replace newuser with the new user name, and user_password with the user password. Grant Privileges to a MySQL User Account ALL PRIVILEGES – Grants all privileges to a user account. CREATE – The user account is allowed to create databases and tables. DROP - The user account is allowed to drop databases and tables. DELETE - The user account is allowed to delete rows from a specific table. INSERT - The user account is allowed to insert rows into a specific table. SELECT – The user account is allowed to read a database. UPDATE - The user account is allowed to update table rows. To grant specific privileges to a user account, use the following syntax: Grand all privileges to a user account over a specific database: mysql> GRANT ALL PRIVILEGES ON database_name.* TO 'database_user'@'localhost'; Grand all privileges to a user account on all databases: mysql> GRANT ALL PRIVILEGES ON *.* TO 'database_user'@'localhost'; Grand all privileges to a user account over a specific table from a database: mysql> GRANT ALL PRIVILEGES ON database_name.table_name TO 'database_user'@'localhost'; Grant multiple privileges to a user account over a specific database: mysql> GRANT SELECT, INSERT, DELETE ON database_name.* TO database_user@'localhost'; Display MySQL User Account Privileges To find the privilege(s) granted to a specific MySQL user account, use the SHOW GRANTS statement: mysql> SHOW GRANTS FOR 'database_user'@'localhost'; The output will look something like below: +---------------------------------------------------------------------------+ | Grants for database_user@localhost | +---------------------------------------------------------------------------+ | GRANT USAGE ON *.* TO 'database_user'@'localhost' | | GRANT ALL PRIVILEGES ON `database_name`.* TO 'database_user'@'localhost' | +---------------------------------------------------------------------------+ 2 rows in set (0.00 sec) Revoke Privileges from a MySQL User Account The syntax to revoke one or more privileges from a user account is almost identical as when granting privileges. To revoke all privileges from a user account over a specific database, run the following command: mysql> REVOKE ALL PRIVILEGES ON database_name.* FROM 'database_user'@'localhost'; Remove an Existing MySQL User Account To delete a MySQL user account use the DROP USER statement: mysql> DROP USER 'user'@'localhost'
  6. Security Enhanced Linux or SELinux is a security mechanism built into the Linux kernel used by RHEL-based distributions. SELinux adds an additional layer of security to the system by allowing administrators and users to control access to objects based on policy rules. SELinux policy rules specify how processes and users interact with each other as well as how processes and users interact with files. When there is no rule explicitly allowing access to an object, such as for a process opening a file, access is denied. SELinux has three modes of operation: Enforcing: SELinux allows access based on SELinux policy rules. Permissive: SELinux only logs actions that would have been denied if running in enforcing mode. This mode is useful for debugging and creating new policy rules. Disabled: No SELinux policy is loaded, and no messages are logged. By default, in CentOS 8, SELinux is enabled and in enforcing mode. It is highly recommended to keep SELinux in enforcing mode. However, sometimes it may interfere with the functioning of some application, and you need to set it to the permissive mode or disable it completely. In this tutorial, we will explain to disable SELinux on CentOS 8. Prerequisites Only the root user or a user with sudo privileges can change the SELinux mode. Checking the SELinux Mode Use the sestatus command to check the status and the mode in which SELinux is running: sestatus SELinux status: enabled SELinuxfs mount: /sys/fs/selinux SELinux root directory: /etc/selinux Loaded policy name: targeted Current mode: enforcing Mode from config file: enforcing Policy MLS status: enabled Policy deny_unknown status: allowed Memory protection checking: actual (secure) Max kernel policy version: 31 The output above shows that SELinux is enabled and set to enforcing mode. Changing SELinux Mode to Permissive When enabled, SELinux can be either in enforcing or permissive mode. You can temporarily change the mode from targeted to permissive with the following command: sudo setenforce 0 However, this change is valid for the current runtime session only and do not persist between reboots. To permanently set the SELinux mode to permissive, follow the steps below: Open the /etc/selinux/config file and set the SELINUX mod to permissive: /etc/selinux/config # This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=permissive # SELINUXTYPE= can take one of these three values: # targeted - Targeted processes are protected, # minimum - Modification of targeted policy. Only selected processes are protected. # mls - Multi Level Security protection. SELINUXTYPE=targeted Copy Save the file and run the setenforce 0 command to change the SELinux mode for the current session: sudo shutdown -r now Disabling SELinux Instead of disabling SELinux, it is strongly recommended to change the mode to permissive. Disable SELinux only when required for the proper functioning of your application. Perform the steps below to disable SELinux on your CentOS 8 system permanently: Open the /etc/selinux/config file and change the SELINUX value to disabled: /etc/selinux/config # This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=disabled # SELINUXTYPE= can take one of these three values: # targeted - Targeted processes are protected, # minimum - Modification of targeted policy. Only selected processes are protected. # mls - Multi Level Security protection. SELINUXTYPE=targeted Copy Save the file and reboot the system: sudo shutdown -r now When the system is booted, use the sestatus command to verify that SELinux has been disabled: sestatus The output should look like this: SELinux status: disabled Conclusion SELinux is a mechanism to secure a system by implementing mandatory access control (MAC). SELinux is enabled by default on CentOS 8 systems, but it can be disabled by editing the configuration file and rebooting the system. To learn more about the powerful features of SELinux, visit the CentOS SELinux guide.
  7. Introduction The Apache HTTP server is the most widely-used web server in the world. It provides many powerful features including dynamically loadable modules, robust media support, and extensive integration with other popular software. In this guide, you will install an Apache web server with virtual hosts on your CentOS 8 server. Prerequisites You will need the following to complete this guide: A non-root user with sudo privileges configured on your server, set up by following the initial server setup guide for CentOS 8. Ensure that a basic firewall is configured by following Step 4 of the Initial Server Setup with CentOS 8 (recommended) in the above guide. Step 1 — Installing Apache Apache is available within CentOS’s default software repositories, which means you can install it with the dnf package manager. As the non-root sudo user configured in the prerequisites, install the Apache package: sudo dnf install httpd After confirming the installation, dnf will install Apache and all required dependencies. By completing Step 4 of the Initial Server Setup with CentOS 8 guide mentioned in the prerequisites section, you will have already installed firewalld on your server to serve requests over HTTP. If you also plan to configure Apache to serve content over HTTPS, you will also want to open up port 443 by enabling the https service: sudo firewall-cmd --permanent --add-service=https Next, reload the firewall to put these new rules into effect: sudo firewall-cmd --reload After the firewall reloads, you are ready to start the service and check the web server. Step 2 — Checking your Web Server Apache does not automatically start on CentOS once the installation completes, so you will need to start the Apache process manually: sudo systemctl start httpd Verify that the service is running with the following command: sudo systemctl status httpd You will receive an active status when the service is running: Output ● httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disa> Active: active (running) since Thu 2020-04-23 22:25:33 UTC; 11s ago Docs: man:httpd.service(8) Main PID: 14219 (httpd) Status: "Running, listening on: port 80" Tasks: 213 (limit: 5059) Memory: 24.9M CGroup: /system.slice/httpd.service ├─14219 /usr/sbin/httpd -DFOREGROUND ├─14220 /usr/sbin/httpd -DFOREGROUND ├─14221 /usr/sbin/httpd -DFOREGROUND ├─14222 /usr/sbin/httpd -DFOREGROUND └─14223 /usr/sbin/httpd -DFOREGROUND ... As this output indicates, the service has started successfully. However, the best way to test this is to request a page from Apache. You can access the default Apache landing page to confirm that the software is running properly through your IP address. If you do not know your server’s IP address, you can get it a few different ways from the command line. Type q to return to the command prompt and then type: hostname -I This command will display all of the host’s network addresses, so you will get back a few IP addresses separated by spaces. You can try each in your web browser to determine whether they work. Alternatively, you can use curl to request your IP from icanhazip.com, which will give you your public IPv4 address as read from another location on the internet: curl -4 icanhazip.com When you have your server’s IP address, enter it into your browser’s address bar: http://your_server_ip You’ll see the default CentOS 8 Apache web page: This page indicates that Apache is working correctly. It also includes some basic information about important Apache files and directory locations. Step 3 — Managing the Apache Process Now that the service is installed and running, you can now use different systemctl commands to manage the service. To stop your web server, type: sudo systemctl stop httpd To start the web server when it is stopped, type: sudo systemctl start httpd To stop and then start the service again, type: sudo systemctl restart httpd If you are simply making configuration changes, Apache can often reload without dropping connections. To do this, use this command: sudo systemctl reload httpd By default, Apache is configured to start automatically when the server boots. If this is not what you want, disable this behavior by typing: sudo systemctl disable httpd To re-enable the service to start up at boot, type: sudo systemctl enable httpd Apache will now start automatically when the server boots again. The default configuration for Apache will allow your server to host a single website. If you plan on hosting multiple domains on your server, you will need to configure virtual hosts on your Apache web server. Step 4 — Setting Up Virtual Hosts (Recommended) When using the Apache web server, you can use virtual hosts (if you are more familiar with Nginx, these are similar to server blocks) to encapsulate configuration details and host more than one domain from a single server. In this step, you will set up a domain called example.com, but you should replace this with your own domain name. If you are setting up a domain name with DigitalOcean, please refer to our Networking Documentation. Apache on CentOS 8 has one virtual host enabled by default that is configured to serve documents from the /var/www/html directory. While this works well for a single site, it can become unwieldy if you are hosting multiple sites. Instead of modifying /var/www/html, you will create a directory structure within /var/www for the example.com site, leaving /var/www/html in place as the default directory to be served if a client request doesn’t match any other sites. Create the html directory for example.com as follows, using the -p flag to create any necessary parent directories: sudo mkdir -p /var/www/example.com/html Create an additional directory to store log files for the site: sudo mkdir -p /var/www/example.com/log Next, assign ownership of the html directory with the $USER environmental variable: sudo chown -R $USER:$USER /var/www/example.com/html Make sure that your web root has the default permissions set: sudo chmod -R 755 /var/www Next, create a sample index.html page using vi or your favorite editor: sudo vi /var/www/example.com/html/index.html Press i to switch to INSERT mode and add the following sample HTML to the file: /var/www/example.com/html/index.html <html> <head> <title>Welcome to Example.com!</title> </head> <body> <h1>Success! The example.com virtual host is working!</h1> </body> </html> Copy Save and close the file by pressing ESC, typing :wq, and pressing ENTER. With your site directory and sample index file in place, you are almost ready to create the virtual host files. Virtual host files specify the configuration of your separate sites and tell the Apache web server how to respond to various domain requests. Before you create your virtual hosts, you will need to create a sites-available directory to store them in. You will also create the sites-enabled directory that tells Apache that a virtual host is ready to serve to visitors. The sites-enabled directory will hold symbolic links to virtual hosts that we want to publish. Create both directories with the following command: sudo mkdir /etc/httpd/sites-available /etc/httpd/sites-enabled Next, you will tell Apache to look for virtual hosts in the sites-enabled directory. To accomplish this, edit Apache’s main configuration file using vi or your favorite text editor and add a line declaring an optional directory for additional configuration files: sudo vi /etc/httpd/conf/httpd.conf Press capital G to navigate towards the end of the file. Then press i to switch to INSERT mode and add the following line to the very end of the file: /etc/httpd/conf/httpd.conf ... # Supplemental configuration # # Load config files in the "/etc/httpd/conf.d" directory, if any. IncludeOptional conf.d/*.conf IncludeOptional sites-enabled/*.conf Save and close the file when you are done adding that line. Now that you have your virtual host directories in place, you will create your virtual host file. Start by creating a new file in the sites-available directory: sudo vi /etc/httpd/sites-available/example.com.conf Add in the following configuration block, and change the example.com domain to your domain name: /etc/httpd/sites-available/example.com.conf <VirtualHost *:80> ServerName www.example.com ServerAlias example.com DocumentRoot /var/www/example.com/html ErrorLog /var/www/example.com/log/error.log CustomLog /var/www/example.com/log/requests.log combined </VirtualHost> Copy This will tell Apache where to find the root directly that holds the publicly accessible web documents. It also tells Apache where to store error and request logs for this particular site. Save and close the file when you are finished. Now that you have created the virtual host files, you will enable them so that Apache knows to serve them to visitors. To do this, create a symbolic link for each virtual host in the sites-enabled directory: sudo ln -s /etc/httpd/sites-available/example.com.conf /etc/httpd/sites-enabled/example.com.conf Your virtual host is now configured and ready to serve content. Before restarting the Apache service, let’s make sure that SELinux has the correct policies in place for your virtual hosts. Step 5 — Adjusting SELinux Permissions for Virtual Hosts (Recommended) SELinux is a Linux kernel security module that brings heightened security for Linux systems. CentOS 8 comes equipped with SELinux configured to work with the default Apache configuration. Since you changed the default configuration by setting up a custom log directory in the virtual hosts configuration file, you will receive an error if you attempt to start the Apache service. To resolve this, you need to update the SELinux policies to allow Apache to write to the necessary files. There are different ways to set policies based on your environment’s needs as SELinux allows you to customize your security level. This step will cover two methods of adjusting Apache policies: universally and on a specific directory. Adjusting policies on directories is more secure, and is therefore the recommended approach. Adjusting Apache Policies Universally Setting the Apache policy universally will tell SELinux to treat all Apache processes identically by using the httpd_unified Boolean. While this approach is more convenient, it will not give you the same level of control as an approach that focuses on a file or directory policy. Run the following command to set a universal Apache policy: sudo setsebool -P httpd_unified 1 The setsebool command changes SELinux Boolean values. The -P flag will update the boot-time value, making this change persist across reboots. httpd_unified is the Boolean that will tell SELinux to treat all Apache processes as the same type, so you enabled it with a value of 1. Adjusting Apache Policies on a Directory Individually setting SELinux permissions for the /var/www/example.com/log directory will give you more control over your Apache policies, but may also require more maintenance. Since this option is not universally setting policies, you will need to manually set the context type for any new log directories specified in your virtual host configurations. First, check the context type that SELinux gave the /var/www/example.com/log directory: sudo ls -dlZ /var/www/example.com/log/ This command lists and prints the SELinux context of the directory. You will receive output similar to the following: Output drwxr-xr-x. 2 root root unconfined_u:object_r:httpd_sys_content_t:s0 6 Apr 23 23:51 /var/www/example.com/log/ The current context is httpd_sys_content_t, which tells SELinux that the Apache process can only read files created in this directory. In this tutorial, you will change the context type of the /var/www/example.com/log directory to httpd_log_t. This type will allow Apache to generate and append to web application log files: sudo semanage fcontext -a -t httpd_log_t "/var/www/example.com/log(/.*)?" Next, use the restorecon command to apply these changes and have them persist across reboots: sudo restorecon -R -v /var/www/example.com/log The -R flag runs this command recursively, meaning it will update any existing files to use the new context. The -v flag will print the context changes the command made. You will receive the following output confirming the changes: Output Relabeled /var/www/example.com/log from unconfined_u:object_r:httpd_sys_content_t:s0 to unconfined_u:object_r:httpd_log_t:s0 You can list the contexts once more to see the changes: sudo ls -dlZ /var/www/example.com/log/ The output reflects the updated context type: Output drwxr-xr-x. 2 root root unconfined_u:object_r:httpd_log_t:s0 6 Apr 23 23:51 /var/www/example.com/log/ Now that the /var/www/example.com/log directory is using the httpd_log_t type, you are ready to test your virtual host configuration. Step 6 — Testing the Virtual Host (Recommended) Once the SELinux context has been updated with either method, Apache will be able to write to the /var/www/example.com/log directory. You can now successfully restart the Apache service: sudo systemctl restart httpd List the contents of the /var/www/example.com/log directory to see if Apache created the log files: ls -lZ /var/www/example.com/log You’ll receive confirmation that Apache was able to create the error.log and requests.log files specified in the virtual host configuration: Output -rw-r--r--. 1 root root system_u:object_r:httpd_log_t:s0 0 Apr 24 00:06 error.log -rw-r--r--. 1 root root system_u:object_r:httpd_log_t:s0 0 Apr 24 00:06 requests.log Now that you have your virtual host set up and SELinux permissions updated, Apache will now serve your domain name. You can test this by navigating to http://example.com, where you should see something like this: This confirms that your virtual host is successfully configured and serving content. Repeat Steps 4 and 5 to create new virtual hosts with SELinux permissions for additional domains.
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