Re: kill zombies

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houghi wrote:
> Lew Pitcher wrote:
>
>>The /proper/ answer to "how can one eliminate a zombie" is to arrange for the
>>zombie's parent process to reap the zombie's termination status. Sometimes, this
>>can be done through a signal to the parent process, but most often it requires
>>that you kill the parent process.
>>
>>There's absolutely no need to reboot, just to get rid of zombies.
>
>
> The parent process is not available anymore in most instances and is
> already killed.

/Not/ if they are zombies.

A zombie is, by definition, a terminated process that hasn't had it's
termination status reaped yet.

There are two ways that a process can get into this situation:
1) the process's living parent hasn't performed a wait() (or family) call to
accept terminations, or
2) the process's parent is dead, and init hasn't yet reaped the zombie process's
termination

Situation #2 happens on occasion, but the interval between an orphan process
terminating and init reaping it's status is extremely small and seldom seen in a
ps listing. The only time it really becomes evident is when your inittab is
misconfigured, and init isn't yet in a state to start reaping process status
values from orphaned processes.

Situation #1 is the most common reason for a zombie process to show up in a ps
listing. Situation #1 also implies that the zombie process's parent process is
still "living" (otherwise the 'zombie' becomes an orphan, and it's termination
status gets reaped by init).

> The only thing you really can do is do a renice on them.

Nonsense. Renice only works on living processes. These zombie processes are
*dead* in all but name, and are never scheduled for execution. Thus, renice does
/nothing/ for them.



- --
Lew Pitcher
IT Specialist, Enterprise Data Systems,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed are my own, not my employers')
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