Which kill signal is used to stop the terminal session?

The signal used to stop a terminal session is sigtstp. This signal is specifically designated for stopping (pausing) a process in a terminal session, allowing the user to resume it later. When a user presses Ctrl+Z in a Unix-like terminal, it sends the sigtstp signal to the currently foregrounded process. This puts the process into a suspended state, effectively stopping its execution while retaining its current context.

In contrast, the other signals have different purposes. sigterm is a termination signal that requests a process to terminate gracefully. It is often used to allow a process to clean up after itself before exiting. sigkill is more forceful, forcing a process to terminate immediately without cleanup and is not catchable or ignorable. Lastly, sigint is indicative of an interrupt signal, typically sent when the user wants to stop a process running in the foreground, often initiated by pressing Ctrl+C. Unlike sigtstp, which pauses the process, sigint directly requests an immediate termination of its execution.

Thus, sigtstp is the appropriate choice for stopping a terminal session, providing flexibility to pause and later resume processes.