Re: [aclug-L] two minor questions

[Bob Deep <bobd@xxxxxxxxxxxx>]

Jesse Kaufman wrote:
> 
> any ideas why my computer hangs on shutting down the gpm stuff when i
> reboot?  i've let it sit for a 1/2 an hour, and it never got through...
> 
> also, how do i completely kill a process... when i do a kill (via
> windowmaker), it kills the vis, but when i do a ps, it still shows
> netscape-communicator (for example), or soffice.bin (all too many times)
> as running... sometimes it's not listed in ps, but when i run ps ax, it
> shows up with a 'STAT' of S, and many times, lists the TTY as ?, but i
> try typing kill <pid>, and every time, it's still there... is there some
> sort of kill command that is even more explicite and definate than kill
> <pid>?

First a bit of background on what kill does...  Kill really is
mis-named, I think it should be called "signal" or something because it
simply sends a signal to a process.  What's a signal?  Glad you asked. 
Signals are a way to communicate with a running process, and infact,
signals are how the kernel controls a process (for the most part).  Lets
say you issue a "sleep" command and tell the kernel you want to sleep
for 10 seconds... What this does is simply tell the kernel to send you a
signal (in this case a wake up signal) in 10 seconds, then your process
goes to sleep (changes from computeable to wait for signal state).  In
10 seconds you get passed a signal which causes you to become
computeable again.

The kernel uses various signals to handle things like disk I/O, math
errors, or memory access violations.  There are a few signals that you
can use to communicate between processes if you want.. They are very
flexable and can help in reducing the CPU loads involved in polling for
a specific event... You can just set up to receive a signal when that
event takes place, and go to sleep.  See the output of "kill -l" for a
list of the sytem defined signals...

On a sun box you can use "kill -9 <pid>" to send signal -9 (SIGKILL) to
the process, if that fails to do it, you are left with having to
reboot.  I beleive that plain kill sends signal -15 (SIGTERM) which is
the "do it nice" shutdown signal where SIGKILL is the "just die and
forget about cleaning up" signal.

Some processes simply cannot die... But they are special situations....
Like when a child looses it's parent so it has no way of returning a
return value but for some reason, the kernel still thinks it needs to
wait for the pid to be harvested...  Zombies I beleive is the term... 
In this case, the process just sits there forever or until a boot... 
The good thing is that they won't ever become computable and once they
get swapped they won't get moved back into memory so they just end up
taking up swap space and a process slot (for the most part).

The processes you describe, if they are in the "S" state, means they are
swapped to disk and cannot easily become computable..  You should be
able to kill these processes with signal -9 but it may take a while for
them to get swapped in... A Signal causes the process to become
computable, and in order to die, it must run a bit of code..

-= Bob =-
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