Zombies

[Glenn Steen]

On 02/01/07, pete at pwdk.com <pete at pwdk.com> wrote:
> Hi
>
> Happy New Year :-)
>
> I've just been looking at my process list and noticed quite a few
> Zombies, 15 in total, 8 MailScann and 7 sh, the email system seems to be
> working correctly as far as I can tell, so I'm not sure why I'm getting
> these Zombies.

Q: What is a Zombie?
A: A dead-process-placeholder, preventing (child) process ID reuse
before the parent process has either noticed it being dead (by a wait
call), or the parent being terminated itself.

A simple google (just google for "zombie processes") will give you
several excellent explanations to this effect.
A zombie takes no real system resources, nor "interracts" with teh
system in any noticable way, apart from taking up a slot in the
process list...

> Top output :-
>
> 2202 mailnull  20   0     0    0    0 Z    0  0.0   0:00.14 MailScann
> 21103 nobody    23   0     0    0    0 Z    0  0.0   0:00.00 sh
>
>
> Are these normal?
Definitely, you have zobies all the time. If they "stick around", they
_may_ be an indication of a problem, but more likely not.
In this particular case, you can likely deduce that these are MS
"helpers" that run things like AV scanners etc, and they should go
away relatively swiftly (to be replaced with new ones). It depends a
bit on what is happening, and the relative speed of your system etc.
Look at your maillog, if you see SpamAssassin timeouts etc... then you
really do have a problem to work with. But then the zombbies "sticking
around" is just an indicator, not a real problem in and off itself.

> Should I be worried about them?
Not really, no.

> Can anything be done about them?
If you know which parent process (use ps;-), you _could_ kill that ...
but that is _not_ recommended. As said, they should clear up by
themselves (or rather by way of the parent:-).

> Am I loosing emails?
Not due to that, no.
But do check your logs carefully... If the zombies are due to
extremely slow I/O (broken disk, network problem, whatever) you could
be losing mails due to that specific fault;).

>
> I'm running CentOS 4.4 with cPanel, and used the MailScanner Service
> supplied by configserver.com
There are a few on this list who do (I don't), so maybe they'll jump
in with some pertinent advice:)

Cheers
-- 
-- Glenn
email: glenn < dot > steen < at > gmail < dot > com
work: glenn < dot > steen < at > ap1 < dot > se