Help! Zombies


 
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# 22  
Old 10-05-2013
Quote:
Originally Posted by alister
In my post, the word "kill" does not refer to the system call nor the utility of the same name; it's merely colloquial English.

Quote:
Originally Posted by Don Cragun
Code:
kill 0 pid_of_zombie

will complete successfully telling you that the zombie hasn't been reaped yet.
That's not necessarily true. From POSIX :: functions :: kill:
Quote:
Existing implementations vary on the result of a kill() with pid indicating an inactive process (a terminated process that has not been waited for by its parent). Some indicate success on such a call (subject to permission checking), while others give an error of [ESRCH]. Since the definition of process lifetime in this volume of POSIX.1-2008 covers inactive processes, the [ESRCH] error as described is inappropriate in this case. In particular, this means that an application cannot have a parent process check for termination of a particular child with kill(). (Usually this is done with the null signal; this can be done reliably with waitpid().
Regards,
Alister
Historic implementations in 1988 (when the first System Interfaces volume of the POSIX standards was approved) behaved both ways. (Notably UNIX System V succeeded, and 4.3BSD returned an ESRCH error.) The standard required the System V behavior, and that was further reinforced when the 2008 edition of the standard clarified that the lifetime of a process does not end until it is reaped.

But, of course, some implementations of UNIX-like systems do not conform to the standards.
# 23  
Old 10-11-2013
Zombie processes which are not cleaned up by unix within a few hours can really only be cleared by a reboot.

The odd few zomboes will be caused by untidy disconnects from clients. If you get large numbers, suspect a hardware or software fault. After replacing a failed hot-pull tape drive it could still be necessary to reboot the computer to clear zombie processes left with incomplete I/O from the original fault. I have seen faulty client/server software which accumulated zombies at an alarming rate.
# 24  
Old 10-13-2013
Hi, methyl.

Your post does not describe zombies (processes which have already exited), but living processes which are permanently stuck in an uninterruptible sleep (as you mentioned, typically due to a driver bug and/or hardware fault).

Regards,
Alister
 
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