While /bin holds essential command binaries necessary for system boot and repair, the /usr/bin directory contains non-essential command binaries that are used by both the system and the users.

The primary role of the System Call Interface in the Linux kernel is to provide an interface for user programs to interact with the kernel. System calls are the gateway through which user applications request services from the kernel, such as file operations, process control, and hardware access.

You should check the IFS (Internal Field Separator) built-in variable. It determines how fields are separated when splitting strings. Changing the IFS value can affect string splitting and tokenization in scripts, so it's essential to inspect and modify it when debugging string manipulation issues.

For a system running the Linux kernel, module configuration files are typically stored in the '/etc/modprobe.d/' directory. These files are used to configure the behavior and options of kernel modules, allowing users to customize module settings and behavior.

To disable the debugging mode that was enabled with set -x, you can use the command **set +x**. This command turns off the debugging mode, so the script will no longer display each command before execution. It's a useful way to end debugging when it's no longer needed.

The tool aa-enforce is used to manage and enforce profiles within AppArmor. It allows you to enable and enforce AppArmor profiles for specific applications or processes.

The testparm tool in Samba is used to check the configuration file for errors. It helps you validate your Samba configuration to ensure that it is correctly formatted and free of syntax errors. Running testparm is a useful step in troubleshooting Samba configuration issues.

Ubuntu is a Linux distribution that is commercially backed by Canonical. Canonical provides support and services for Ubuntu, making it a popular choice for both desktop and server environments.

The most suitable Bash construct for taking different actions based on the day of the week is the case statement. You can use case to evaluate the value of the day and define different actions for each day. Options 1, 3, and 4 are not specifically designed for this purpose; they serve different scripting needs.

The chage command in Linux allows you to change the expiration date of a user's password. It provides a range of options to manage password-related settings, including password expiration.