In Linux, the "ln" command is used to create symbolic links between files. A symbolic link is a reference to another file or directory, allowing you to access the linked content from a different location in the file system.

On CentOS, you can use the 'rpm -q' command to check if a specific package is installed. This command queries the RPM database to determine if the package is installed on the system.

In the given example, $2 represents the second argument passed to the script, which is "arg2". It's important to note that in shell scripting, arguments are accessed using positional parameters like $1, $2, $3, and so on.

To diagnose the issue of a user not being able to execute certain commands with sudo, you would primarily look at the /etc/sudoers file. This file contains the configuration for sudo privileges, and it's the first place to check for any restrictions or misconfigurations that might be affecting the user's access.

The correct option is /lib/modules. Kernel modules (device drivers and other kernel extensions) that are loaded during the boot process are typically defined in the /lib/modules directory. This directory contains subdirectories for different kernel versions and modules specific to those versions.

Journaling in file systems primarily helps ensure file system consistency. It records changes to the file system in a journal, which can be used to recover the file system in case of a crash or unexpected system shutdown, preventing data corruption.

In a situation where you want to deny a user from running specific commands as root, you would modify their entry in the sudoers file. This file contains rules and permissions for granting or denying superuser privileges to users and groups.

For enhanced security, Linux passwords are not stored in plain text but are hashed before storing. Hashing is a one-way process that converts the password into a fixed-length string of characters. This makes it difficult for attackers to reverse the process and obtain the original password.

The correct command to monitor real-time network interface statistics in Linux is iptraf. It provides detailed information about network traffic, including traffic per interface, protocols, and ports. ifconfig and netstat are used for network configuration and monitoring, but they don't offer real-time statistics. nmap is a network scanning tool.

In package management, a "Source Package" is a collection of patches, configuration files, and scripts that adapt a software source code to a particular distribution. Source packages are used to build binary packages specific to a particular Linux distribution.