The signal number (from ps -f) or name (from kill -l). The default is TERM (signal number 15). With a signal number of 9, the kill is unconditional. If nothing else works to kill a process, kill -9 almost always kills it, but does not allow the process any time to clean up.
Consider all subsequent strings to be arguments, not options.
With no argument, list the signal names. (Used by itself.) The argument can be a signal name or a number representing either the signal number or the exit status of a process terminated by a signal. If it is a name, the correspoding number is returned; otherwise, the corresponding name is returned.
Specify the signal number to send.
Specify signal. May be a signal name or number.