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Ubuntu 13.04.

Recently zombies have started appearing.

My processes are:

PROCESS       CPU         INFORMATION          

chrome            65%     Surf the web
calculator        10%     Calculate operations
<zombieunknown>    0%     <unknown>
<deadprocess>      0%     <defunct>

So how are they coming up? This was recorded on boot, when just Chrome and calculator were running.

Thanks in advance.

Kevin Bowen
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horIzoN
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    OP maybe wanting to know why the zombies are appearing, not what zombies are. –  Jul 27 '13 at 12:41
  • @vasa1 - That's exactly right. – horIzoN Jul 27 '13 at 13:00
  • The explanation of what they are explains why they happen, at least in as much detail as can be known without any knowledge of what the parent process is. – qqx Jul 27 '13 at 13:24

1 Answers1

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In the UNIX world, developers sometimes use the term to refer to a program process that has died but hasn't yet given its process table entry back to the system.

When a process finishes execution, it will have an exit status to report to its parent process. Because of this last little bit of information, the process will remain in the operating system’s process table as a zombie process, indicating that it is not to be scheduled for further execution, but that it cannot be completely removed (and its process ID cannot be reused) until it has been determined that the exit status is no longer needed.

When a child exits, the parent process will receive a SIGCHLD signal to indicate that one of its children has finished executing; the parent process will typically call the wait() system call at this point. That call will provide the parent with the child’s exit status, and will cause the child to be reaped, or removed from the process table.

The idea behind keeping a zombie process is to keep the appropriate data structures about the termination of the process in case the parent ever gets interested via a wait.

You cannot kill zombies, as they are already dead. But if you have too many zombies then kill parent process or restart service.

You can kill zombie process using PID obtained from any one of the above command. 

kill -9 <PID_Number>

Source:Mel Kham

Mitch
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  • this reminds me of thunderbird. Sometimes it is not ending as program properly and stays a zombie, without given PID. When I want to start thunderbird new, there is then message-box, that I should log out or reboot the machine. – dschinn1001 Jul 27 '13 at 13:37