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Full Discussion: Zambie process
Top Forums UNIX for Dummies Questions & Answers Zambie process Post 302099188 by tayyabq8 on Sunday 10th of December 2006 10:22:02 AM
Old 12-10-2006
I think you were unable to find definition of Zombie process because of spelling mistake, its Zombie not Zambie.

Zombie Process:
Quote:
On Unix operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. In the term's colorful metaphor, the child process has died but has not yet been reaped.

When a process ends, all of the memory and resources associated with it are deallocated so they can be used by other processes. However, the process's entry in the process table remains. The parent is sent a SIGCHLD signal indicating that a child has died; the handler for this signal will typically execute the wait system call, which reads the exit status and removes the zombie. The zombie's process ID and entry in the process table can then be reused. However, if a parent ignores the SIGCHLD, the zombie will be left in the process table. In some situations this may be desirable, for example if the parent creates another child process it ensures that it will not be allocated the same process ID.

A zombie process is not the same as an orphan process. Orphan processes don't become zombie processes; instead, they are adopted by init (process ID 1), which waits on its children.

The term zombie process derives from the common definition of zombie-an undead person.

Zombies can be identified in the output from the Unix ps command by the presence of a "Z" in the STAT column. Zombies that exist for more than a short period of time typically indicate a bug in the parent program. As with other leaks, the presence of a few zombies isn't worrisome in itself, but may indicate a problem that would grow serious under heavier loads.

To remove zombies from a system, the SIGCHLD signal can be sent to the parent manually, using the kill command. If the parent process still refuses to reap the zombie, the next step would be to remove the parent process. When a process loses its parent, init becomes its new parent. Init periodically executes the wait system call to reap any zombies with init as parent.

Retrieved from "http://en.wikipedia.org/wiki/Zombie_process"
 

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preap(1)							   User Commands							  preap(1)

NAME
preap - force a defunct process to be reaped by its parent SYNOPSIS
preap [-F] pid... DESCRIPTION
A defunct (or zombie) process is one whose exit status has yet to be reaped by its parent. The exit status is reaped via the wait(3C), waitid(2), or waitpid(3C) system call. In the normal course of system operation, zombies may occur, but are typically short-lived. This may happen if a parent exits without having reaped the exit status of some or all of its children. In that case, those children are reparented to PID 1. See init(1M), which periodically reaps such processes. An irresponsible parent process may not exit for a very long time and thus leave zombies on the system. Since the operating system destroys nearly all components of a process before it becomes defunct, such defunct processes do not normally impact system operation. However, they do consume a small amount of system memory. preap forces the parent of the process specified by pid to waitid(3C) for pid, if pid represents a defunct process. preap will attempt to prevent the administrator from unwisely reaping a child process which might soon be reaped by the parent, if: o The process is a child of init(1M). o The parent process is stopped and might wait on the child when it is again allowed to run. o The process has been defunct for less than one minute. OPTIONS
The following option is supported: -F Forces the parent to reap the child, overriding safety checks. OPERANDS
The following operand is supported: pid Process ID list. EXIT STATUS
The following exit values are returned by preap, which prints the exit status of each target process reaped: 0 Successfully operation. non-zero Failure, such as no such process, permission denied, or invalid option. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWesu (32-bit) | +-----------------------------+-----------------------------+ | |SUNWesxu (64-bit) | +-----------------------------+-----------------------------+ SEE ALSO
proc(1), init(1M), waitid(2), wait(3C), waitpid(3C), proc(4), attributes(5) WARNINGS
preap should be applied sparingly and only in situations in which the administrator or developer has confirmed that defunct processes will not be reaped by the parent process. Otherwise, applying preap may damage the parent process in unpredictable ways. SunOS 5.10 26 Mar 2001 preap(1)
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