OpenVPN is a widely-used tool in Linux for setting up VPN connections with SSL/TLS-based tunnels. It provides a secure and reliable way to establish encrypted communication over the internet or private networks, ensuring data privacy and integrity.

The correct command to add a new user in Linux is useradd. This command creates a new user account and associated files. It is used to specify user details like the home directory and shell.

The file that defines the rules for the sudo command in Linux is /etc/sudoers. This file specifies who is allowed to run what commands with administrative privileges and how. It's a crucial part of managing user access and privileges in a Linux system.

The primary difference between ext4 and ext3 file systems is that Ext4 supports larger file sizes and filesystems. Ext4 extends the maximum file size from 16 terabytes to 1 exabyte and supports filesystems up to 1 exabyte, whereas Ext3 has limitations in this regard. This makes Ext4 more suitable for modern storage needs.

To temporarily disable a service in Linux without stopping it, you can use the systemctl mask command. This command creates a symbolic link to /dev/null, preventing the service from being started automatically, but it doesn't stop the currently running service. It's a useful way to prevent a service from starting at boot.

To ensure that a specific service always restarts after failure in Linux, you would primarily use Systemd. Systemd is a modern init system that provides a feature-rich service management system and includes options for service restarts and recovery after failure.

The /boot directory is crucial for the system booting process in Linux. It contains essential files such as the kernel, initial RAM disk (initrd), and bootloader configurations. These files are necessary for the system to start up.

To provide each user with their own private space for files and data, you would use the /home directory structure in Linux. User home directories are typically located within /home, and this separation ensures user privacy and data security.

The /media directory in Linux is often used for mounting temporary file storage systems, like USB drives. When you plug in a USB drive, it's commonly mounted under the /media directory for easy access.

LXC (Linux Containers) provides a similar containerization service as Docker, but it is more focused on providing a full system environment. This means it can run multiple Linux distributions and even non-Linux operating systems with their own kernel, making it more flexible for certain use cases.