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Full Discussion: Help! Zombies
Top Forums UNIX for Dummies Questions & Answers Help! Zombies Post 302860177 by Don Cragun on Saturday 5th of October 2013 01:04:25 AM
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.
 

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KILLPG(3)						     Linux Programmer's Manual							 KILLPG(3)

NAME
killpg - send signal to a process group SYNOPSIS
#include <signal.h> int killpg(int pgrp, int sig); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): killpg(): _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE DESCRIPTION
killpg() sends the signal sig to the process group pgrp. See signal(7) for a list of signals. If pgrp is 0, killpg() sends the signal to the calling process's process group. (POSIX says: if pgrp is less than or equal to 1, the behavior is undefined.) For the permissions required to send a signal to another process, see kill(2). RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
EINVAL sig is not a valid signal number. EPERM The process does not have permission to send the signal to any of the target processes. For the required permissions, see kill(2). ESRCH No process can be found in the process group specified by pgrp. ESRCH The process group was given as 0 but the sending process does not have a process group. CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (killpg() first appeared in 4BSD). NOTES
There are various differences between the permission checking in BSD-type systems and System V-type systems. See the POSIX rationale for kill(). A difference not mentioned by POSIX concerns the return value EPERM: BSD documents that no signal is sent and EPERM returned when the permission check failed for at least one target process, while POSIX documents EPERM only when the permission check failed for all tar- get processes. C library/kernel differences On Linux, killpg() is implemented as a library function that makes the call kill(-pgrp, sig). SEE ALSO
getpgrp(2), kill(2), signal(2), capabilities(7), credentials(7) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 KILLPG(3)
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