(PHP 5, PHP 7)
proc_terminate — Kills a process opened by proc_open
proc_terminate ( resource $process [, int $signal = 15 ] ) : bool
 Signals a process (created using proc_open()) that it should terminate. proc_terminate() returns immediately and does not wait for the process to terminate. 
proc_terminate() allows you terminate the process and continue with other tasks. You may poll the process (to see if it has stopped yet) by using the proc_get_status() function.
process
The proc_open() resource that will be closed.
signal
 This optional parameter is only useful on POSIX operating systems; you may specify a signal to send to the process using the kill(2) system call. The default is SIGTERM. 
Returns the termination status of the process that was run.
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    https://www.php.net/manual/en/function.proc-terminate.php