[techtalk] Is there a Kill -8, too?

[jenn at simegen.com]

Amanda Knox wrote:
> 
> Just This Girl wrote:
> 
> > Did you try 'kill pid' or 'kill -9 pid'? 'kill -9' should bring down
> > anything.
> 
> Simple question (I hope):
> 
> Why is it '-9' exactly? Are there different kill levels or something? What if
> I typed 'Kill -1'? Just curious, and I doubt I would have the know-how to
> find that exact answer in the man pages ;)

Kill has a variety of purposes. 

Yep, there's a kill -1 (one). Let me open an xterm and type man kill.
(whoops. My 'man kill' has misformatted itself! I'll have to do 
this from memory.)

kill -l lists all the kill options. (that's ELL, not ONE)
Of course, this lists the signals, which isn't terribly explicable to 
even someone like me. Let's see if I can translate:

The 'kill' command sends a signal - a command from the OS - to the 
process named in the command.

The number lists which signal is sent.

Some common ones:

1 (sighup) is 'hang up' - signals the shell it's no longer connected 
to the user. It's used for shell-less programs like daemons as a signal 
to reload their config files.

9 (sigkill) is 'kill' - close down, regardless. It is like signal 15, 
but can't be caught.

15 (sigterm) is 'terminate' - close down, in a controlled fashion. It
signals the program to shut down - and can be caught by the program.
Well written programs will try to catch this and cleanup after themselves.


For more information on signals, try 'man 2 signal' and 'man 7 signal'
or just 'man -k signal', if the first two aren't useful on your system.


(HINT: if you want a command line within X-windows, you DO NOT have
to leave X-windows to get it. I use 'xterm', available in my GUI menu
under 'Xshells'.)



Jenn V.
-- 
  Humans are the only species to feed and house entirely separate species 
     for no reason other than the pleasure of their company. Why?

jenn at simegen.com        Jenn Vesperman        http://www.simegen.com/~jenn/

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