[CentOS] RAID level and killing a job

Filipe Brandenburger filbranden at gmail.com
Wed Jan 14 02:00:19 UTC 2009


Hi,

First of all:
On Tue, Jan 13, 2009 at 12:54, Scott R. Ehrlich <scott at mit.edu> wrote:
> ... realize I want to kill it soon after
> (logged in as root).  I issue ps auwx|grep name_of_command, get the PID, and
> issue kill -9 PID.  ps auwx|grep name_of_command is still running.

*NEVER* get used to using kill -9, unless you tried everything else
(kill [same as kill -TERM], kill -HUP, kill -USR1, kill -INT, etc.)
before that. Using kill -9 does not give the chance to the process to
clean up after himself, so it may leave invalid files or even corrupt
data. Of course there will be situations where nothing else works, but
it should *NOT* be used unless as a last resort.

On Tue, Jan 13, 2009 at 13:53, William L. Maltby
<CentOS4Bill at triad.rr.com> wrote:
> IIRC, zombies are processes that have ended but can not be "cleaned up".

Right.

Cleaning up processes (which basically accounts for getting the output
status [and maybe closing some file descriptors although I don't think
so]) is responsability of the parent process (which is the process
that started it, except when that one already died, in which case
processes are "adopted" by init which takes care of cleaning them up).

Zombies indicate a problem with the parent process, not with the
zombie process itself.

> This can happen when a parent has died before the child ends

Wrong. In that case, the child process will be "adopted" by init,
which among other things is responsible for cleaning up these
processes.

> when a
> parent exists but is "sleeping" (for whatever reason: it may be waiting
> on another event, waiting for I/O that never completes, ...).

Right. Another reason is bad programming, if the programmer forked a
child but never included code to reap them when they die.

> IIRC, when the parent has died, then PPID you'll see is "1".

Right, that's when a process is "adopted" by init.

However, init will clean up the "adopted" processes (unless init is
hung or something) so you shouldn't have zombies whose parent is init.

HTH,
Filipe


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