SELinux (Security-Enhanced Linux) is a Linux kernel security module that provides a mechanism for enforcing mandatory access control (MAC) policies. MAC is a type of access control that restricts the actions that can be performed by processes and users on a system. SELinux was developed by the United States National Security Agency (NSA) and was … Read more
To gracefully restart an Nginx web server after making changes to a configuration file, you can use the following command: nginx -s reload This command sends a SIGHUP signal to the Nginx master process, which causes the master process to reload its configuration file and pass the new configuration to its worker processes. The -s … Read more
In bash shell, you can check if a variable is empty or not using the following syntax: if [ -z “$VARIABLE_NAME” ]; then echo “Variable is empty” else echo “Variable is not empty” fi The -z operator checks if the length of the string stored in the $VARIABLE_NAME is zero, indicating that the variable is … Read more
In OpenBSD, FreeBSD, and NetBSD, you can list the rules in a PF firewall using the following command: pfctl -sr This command will display a list of the rules in the firewall, including both the filter and the nat rules. The output of this command provides information about the direction of the rule (in/out), the … Read more
In CentOS/RHEL version 5 and 6, you can update your system using the following command: yum update This command will update all installed packages to the latest version available in the configured repositories. You can run this command regularly to keep your system up-to-date with the latest security patches and bug fixes. Note: Before you … Read more
The specific time at which cron entries in cron.daily, cron.weekly, and cron.monthly run depends on the configuration of the system’s cron daemon. By default, most systems run the scripts in cron.daily at 6:25 AM every day, the scripts in cron.weekly at 6:30 AM every week (typically on Sundays), and the scripts in cron.monthly at 6:35 … Read more
Installing OpenBSD using PXE (Preboot Execution Environment) involves the following steps: Setting up a PXE server: You need to set up a PXE server that will host the OpenBSD installation files and provide them to the client system during the boot process. The PXE server can be a standalone system or a virtual machine. Configuring … Read more
A console-based network load monitor on Debian and Ubuntu can be achieved using the vnstat tool. vnstat is a network traffic monitor that keeps a record of network traffic data and provides real-time statistics on the command line. Here’s how to install and use vnstat: Install vnstat: sudo apt-get update sudo apt-get install vnstat Configure … Read more
You can install the ipset administration tool on CentOS and RHEL by using the package manager yum. Here’s how to install ipset: Update the package index: sudo yum update Install the ipset package: sudo yum install ipset After the installation is complete, you can use the ipset command to manage IP sets and IPTables. For … Read more
The “If-Modified-Since” header is used in an HTTP request to ask the server to return the requested resource only if it has been modified since the specified date and time. This allows the client to avoid downloading a resource that hasn’t changed. You can use the curl command with the -z or –time-cond option to … Read more