The command 'wall' is used to broadcast a message to all logged-in users on a system. It displays the message on the terminal of every user who is currently logged in. This is useful for sending important system-wide notifications.

The kernel parameter 'quiet' instructs the kernel to suppress most boot messages during the boot process. This option minimizes the output displayed on the screen, leaving only critical messages visible. The other options provided are not standard kernel parameters for this purpose.

To change the systemd boot target to rescue.target instead of the default target, you use the kernel command line option systemd.unit=rescue.target. This option instructs systemd to start the system directly into the rescue target, which provides a minimal environment useful for maintenance and troubleshooting purposes.

To disable the ctrl-alt-delete key combination in a SysV init system, you need to modify the /etc/inittab file. This file is the main configuration file for SysV init and controls various aspects of the system initialization process, including key bindings. Within this file, the entry 'ca::ctrlaltdel:' responds to the ctrl-alt-delete key combination. By commenting out or removing this entry, you can disable the system's response to ctrl-alt-delete.

During a system boot cycle, after the BIOS completes its tasks such as hardware checks and setup, the bootloader is executed. The bootloader's role is to load the operating system into memory and initiate its startup. It facilitates the transfer of control from the BIOS to the operating system by loading the operating system kernel into memory and starting the OS boot process.