[plug] zombie state

[Alan Graham]

A zombie isn't an application locked up.  It's a child process that has
finished, whose parent hasn't cleaned it up properly.

Unix processes start other processes by executing a 'fork'.  The 'fork'
copies the process, so that there are two identical processes except for
the process id.  The copy is termed the child process, the original is
the parent.  Typically, the code after the fork looks at the PID to see
if this is the parent or the child  If it's the parent, it 'wait's for
the child to end.  If it doesn't 'wait', when the child ends it
zombies.  The idea is that eventually the parent will execute a 'wait',
which will allow the zombies to end.  

It sounds like the virus scanner is forking a child process to handle
each incoming mail.  Once each child ends, it zombies.  The parent
process continues to monitor port 25 while the child is examining the
mail to ensure that each mail coming in is handled in a timely fashion,
no matter how long each preceding mail is taking to be scanned.  The
parent should be cleaning up its own child processes periodically.

Zombies don't normally cause problems.  They should have released their
resources before they ended, so it's just an entry on the process
table.  Are they causing a problem?

HTH

Alan

On Fri, 2004-07-23 at 17:45, Jon Miller wrote:
> On a Debian server  an application will go into a zombie state and lock-up.  Is there a reason for this? or better still is there a way to unlock it automatically? The application is a virus scanning software that receives mail on port 25, scans the mail and sends it to another server on another servers port 25.
> 
> 
> Thanks
> 
> Jon L. Miller, MCNE, CNS, ASE
> Director/Sr Systems Consultant
> MMT Networks Pty Ltd
> http://www.mmtnetworks.com.au
> 
> "I don't know the key to success, but the key to failure
>  is trying to please everybody." -Bill Cosby
> 
> ______________________________________________________________________
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-- 
Alan Graham <alan.graham at infonetsystems.com.au>
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