What is the signal command to hang up or shut down a process?

The command that is used to hang up or shut down a process is "sighup." This signal, represented by SIGHUP (Signal Hang Up), is typically sent to a process when its controlling terminal is closed or when a user logs out. In the context of managing processes, receiving a SIGHUP often instructs the process to terminate or reinitialize itself. For many daemons and background services, SIGHUP can be used to tell them to reload their configurations without having to completely restart the service.

In contrast, other signals serve different purposes. For example, SIGINT is used to interrupt a process, usually from a terminal (like when a user presses Ctrl+C), but it does not specifically signify a hang-up. SIGTSTP is similar to SIGINT but is intended to stop a process temporarily, effectively putting it in the background. Meanwhile, SIGKILL is a much stronger signal that immediately terminates a process without giving it a chance to clean up or save its state. Therefore, SIGHUP is the correct and most appropriate signal to indicate hanging up or shutting down a process in this context.