Final answer:
The student's question pertains to Unix signal commands, and involves understanding keyboard shortcuts for SIGINT (Ctrl+C) and SIGTSTP (Ctrl+Z), as well as the difference between kill system call and command, and the meaning of various software error signals such as SIGPIPE, SIGFPE, and SIGSEGV, and the external event signal SIGCHLD.
Step-by-step explanation:
The question revolves around the understanding of Unix signal commands, specifically relating to keyboard shortcuts for process control, as well as some directives used in process management. A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. It is a notification sent to a process in order to notify it to perform some action, such as to terminate or to suspend its execution.
Keyboard Signals
SIGINT, or the signal interrupt, is sent to a process when the interrupt key (usually Ctrl+C) is pressed on the keyboard. It tells the process to terminate immediately. On the other hand, SIGTSTP is a signal to suspend process execution and is usually issued by pressing the suspend key (usually Ctrl+Z). The suspended process can later be resumed with the fg or bg commands.
kill Command
The kill system call is an internal function within the operating system's API used for sending signals to processes from within a program, while the kill system command is a shell command used to send signals to processes from the command-line interface.
Software Errors
Several signals are related to software error conditions, like SIGPIPE, which happens when a process writes to a pipe with no readers; SIGFPE, which refers to a floating-point exception; and SIGSEGV, which is emitted on a segmentation fault when a process tries to access memory that it's not allowed to.
External Events
SIGCHLD is a signal sent to a process when one of its child processes terminates or stops.