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-> (SCO Unix) What is a zombie process?


SCO Unix, Xenix and ODT General FAQ



This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open Desktop or Openserver.

There is lots of Linux, Mac OS X and general Unix info elsewhere on this site: Search this site is the best way to find anything.

Why can't I kill a process with -9?

One of the early things people learn about Unix is that a "kill -9" is invincible- that a process must die if you send it a KILL (-9). However, that's not entirely true:

  • A process can be sleeping in kernel code. Usually that's because of faulty hardware or a badly written driver- or maybe a little of both. A device that isn't set to the interrupt the driver thinks it is can cause this, for example- the driver is waiting for something its never going to get. The process doesn't ignore your signal- it just never gets it (but see Linux TASK_KILLABLE also).

  • A zombie process doesn't react to signals because it's not really a process at all- it's just what's left over after it died. What's supposed to happen is that its parent process was to issue a "wait()" to collect the information about its exit. If the parent doesn't (programming error or just bad programming), you get a zombie. The zombie will go away if its parent dies- it will be "adopted" by init which will do the wait()- so if you see one hanging about, check its parent; if it is init, it will be gone soon, if not the only recourse is to kill the parent..which you may or may not want to do.

  • Finally, a process that is being traced (by a debugger, for example) won't react to the KILL either.

See SCO TA 104438 for more details.




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7 comments



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Thu Nov 17 11:26:26 2005: 1360   anonymous


finally one can say by Zombie process it means the process no longer exits and the cpu should reap these out...



Thu Nov 17 11:27:07 2005: 1361   anonymous


santosh saladi


finally one can say by Zombie process it means the process no longer exits and the cpu should reap these out...






Sat Jul 7 23:01:36 2007: 3054   anonymous


yeah, no shit

and the wind direction has a lot to do with where the air comes from



Fri Jul 23 10:27:00 2010: 8848   mac

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I read about zombie processes.. I just want to ask do they hold resources even after that process has finished its execution???



Fri Jul 23 10:50:40 2010: 8849   TonyLawrence

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No. They are not holding anything but space in the process table.



Tue Nov 15 11:41:56 2011: 10185   Yadvinder

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Hi,
These zombie processes using a lot of space.
And my(HP UNIX SERVER) CPU utilization showing 100% and Idle is 0%
kindly suggest what should I do as ii craeting a lot of problem.
Waiting for your reply..............



Tue Nov 15 11:48:41 2011: 10186   TonyLawrence

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See http://aplawrence.com/Unixart/slow.html for help with slow systems. The zombies are not slowing you down (although the fact that you have them may indicate other issues that could be affecting you).

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This post tagged:

       - Drivers
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       - Shell
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