Re: [vox-tech] Zombie Processes

[Chris Lupo <lupo@ece.ucMAPSdavis.edu>]

On Fri, 26 Jan 2001 jdnewmil@dcn.davis.ca.us wrote:

> On Fri, 26 Jan 2001, Jan Wynholds wrote:
> 
> > Hey all:
> > 
> > Just had an eeeeenteresting thing happen to me at work
> > yesterday.  Here is a brief rendition of the
> > occurances (oh, this is on a RHL 6.2):
> > 
> > 1. A win98 program that interfaces a pgsql db crashed.
> > 2. The TCP handler for the db records 'freaked out'
> > and tried to kill the instance that was handling the
> > rec's (from the win98 box).
> > 3. The kill failed, and left a bunch of <defunct>
> > (zombie) processes languishing.
> 
> Zombie processes are dead and gone... you are only seeing the record that
> they existed, kept around so their parent process can read their exit
> status.  This is a bug in the parent process, in that it did not extract
> the exit status of the child process.
> 

This is true that zombie processes have their memory freed and will not be
scheduled for execution.  But, it is not necessarily a bug in the parent
process.  There may be something preventing the parent process from
emitting a wait signal (resource contention or something).  It could also
be that the parent process has already terminated or been killed, in which
case the zombie child is inherited by the init process, and will go away
soon. If the parent is still living, it's possible that whatever is
keeping it from emitting the wait signal has the parent deadlocked, in
which case the zombie children will remain in the process table until the
parent is itself killed.

-- Chris