A systems administrator identifies multiple processes in a zombie state. Which of the following signals would be best for the administrator to send to the PPID?

A zombie process (defunct process) occurs when a child process terminates, but its parent process has not yet executed the wait() system call to read its exit status. Because zombie processes are already dead, signals cannot be delivered directly to them. To clear zombie processes, the administrator must address the parent process (PPID). Sending SIGTERM (Signal 15) requests a graceful termination of the parent process. Once the parent terminates, any remaining zombie processes become orphans and are immediately inherited by init or systemd (PID 1). PID 1 periodically executes wait(), which cleans up and removes all inherited zombie processes from the kernel process table.

B. SIGHUP (Signal 1) notifies a process of terminal disconnect or requests daemon configuration reloading, which does not guarantee process termination or orphan reaping.
C. SIGQUIT (Signal 3) instructs a process to quit and produce a core dump, which is unneeded and less suitable than standard termination via SIGTERM.
D. SIGSTOP (Signal 19) pauses process execution without terminating the parent, preventing the parent process from executing wait() to clean up zombie entries.

Bovet, D. P., & Cesati, M. "Understanding the Linux Kernel," 3rd Edition. O'Reilly Media, Chapter 3: Processes.

IEEE Std 1003.1-2017 (POSIX.1). "Signal Concepts and Process Lifecycle." The Open Group Base Specifications Issue 7.